EP1425822B1 - Decade band tapered slot antenna, and methods of making and configuring same - Google Patents
Decade band tapered slot antenna, and methods of making and configuring same Download PDFInfo
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- EP1425822B1 EP1425822B1 EP02757580A EP02757580A EP1425822B1 EP 1425822 B1 EP1425822 B1 EP 1425822B1 EP 02757580 A EP02757580 A EP 02757580A EP 02757580 A EP02757580 A EP 02757580A EP 1425822 B1 EP1425822 B1 EP 1425822B1
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- balun
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/08—Radiating ends of two-conductor microwave transmission lines, e.g. of coaxial lines, of microstrip lines
- H01Q13/085—Slot-line radiating ends
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
- H01Q9/04—Resonant antennas
- H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
- H01Q9/045—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means
- H01Q9/0457—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means electromagnetically coupled to the feed line
Definitions
- This invention relates in general to tapered slot antennas and, more particularly, to a method and apparatus for obtaining wide band performance in a tapered slot antenna.
- antenna technology has experienced an increase in the use of antennas that utilize an array of antenna elements, one example of which is a phased array antenna.
- Antennas of this type have many applications in commercial and defense markets, such as communications and radar systems. In many of these applications, broadband performance is desirable. Some of these antennas are designed so that they can be switched between two or more discrete frequency bands. Thus, at any given time, the antenna is operating in only one of these multiple bands. However, in order to achieve true broadband operation, the antenna needs to be capable of satisfactory operation in a single wide frequency band, without the need to switch between two or more discrete frequency bands.
- a tapered slot antenna element One type of antenna element that has been found to work well in an array antenna is often referred to as a tapered slot antenna element.
- the spacing between antenna elements in an array antenna is typically determined by the frequency at which the antenna operates, and a tapered slot antenna element fits comfortably within the space available for an antenna element in many array antennas.
- European Patent application EP 0, 343, 322 describes an antenna having a strip conductor, and a ground plane separate from and lying parallel to the strip conductor.
- the ground plane has a slot which extends transverse to the strip conductor.
- United States patent US 6, 008, 770 describes a tapered slot antenna which provides a tapered pattern composed by utilising a Fermi-Dirac distribution function.
- Existing tapered slot antenna elements typically have a bandwidth of about 3:1 to 4:1, although some have a bandwidth that approaches 6:1. While these existing tapered slot antenna elements have been generally adequate for their intended purposes, they have not been satisfactory in all respects. In this regard, there are applications in which it is desirable for a tapered slot antenna element to provide broadband performance involving a bandwidth in the neighbourhood of 10:1, or even larger. Existing designs and design techniques have not been able to provide a tapered slot antenna element which approaches this desired level of broadband performance.
- An aspect of the present invention provides an antenna element as set out in claim 1.
- FIGURE 1 is a diagrammatic fragmentary front view of an apparatus 10 which includes an antenna element 12 and part of a radome 13.
- the apparatus 10 is configured for use in a not-illustrated phased array antenna system.
- the antenna system includes a plurality of the antenna elements 12 arranged in a two-dimensional array of rows and columns, and includes a radome which extends over all the antenna elements, a portion of this radome being shown at 13 in FIGURE 1.
- FIGURE 2 is a diagrammatic fragmentary rear view of the apparatus 10, and FIGURE 3 is a diagrammatic sectional view taken along the section line 3-3 in FIGURE 1.
- the antenna element 12 includes two adjacent and parallel layers 17 and 18 of a dielectric material.
- the dielectric layers each have a dielectric constant (Er) of approximately 3.0.
- the dielectric layers 17 and 18 are bonded to each other by a thin layer 19 of bond film, which is of a type well known in the art.
- the dielectric layers 17 and 18 are each approximately 20 mils thick.
- the bond film 19 is approximately 2-3 mils thick.
- FIGURE 4 is a diagrammatic fragmentary sectional front view of the apparatus 10, taken along a central plane which extends between the dielectric layers 17 and 18, with the bond film 19 omitted for clarity.
- the dielectric layer 17 has on the front side thereof a first ground plane 26 (FIGURE 1)
- the dielectric layer 18 has on the rear side thereof a second ground plane 27 (FIGURE 2)
- the dielectric layer 18 has on the front side thereof a third ground plane defined by three separate portions 28A, 28B and 28C (FIGURE 4), which are sometimes referred to collectively herein as a ground plane 28.
- the ground planes 26 and 27 are each electro-deposited metal layers with a thin gold plating on the outer side thereof to resist corrosion.
- the ground planes 26 and 27 each have an overall thickness which is approximately 1-2 mils.
- the ground plane 28 is an electro-deposited metal layer which is approximately 0.5-1 mils thick.
- the ground plane 26 has a recess etched through it, and this recess includes a balun portion 36 and a slot portion 37.
- the balun portion 36 of the recess is approximately rectangular, except that it has corners which are slightly rounded. It has a length dimension 38, and a width dimension 39.
- the length dimension 38 is one-quarter of a wavelength of interest.
- the embodiment of FIGUREs 1-4 is optimized for use in a frequency range of approximately 1.8 GHz to 18 GHz, and the length dimension 38 is approximately one-quarter of the wavelength of a center frequency of about 10 GHz.
- the width dimension 39 in the disclosed embodiment is in the range of approximately one-quarter of this wavelength to approximately three-eighths of this wavelength. That is, the width dimension 39 is at least as large as the length dimension 38, but is kept somewhat short of one-half wavelength in order to avoid potentially undesirable operational characteristics.
- the width dimension 39 should be as large as possible within these stated constraints.
- the size of the array must progressively decrease, because the space available for each antenna element is approximately one-half of the wavelength of the highest frequency of operation.
- the maximum amount of space available for the width dimension 39 of the balun portion 36 also progressively decreases.
- the width dimension 39 is about 5% longer than the length dimension 38, but is not 50% to 70% longer, due to space limitations imposed by the operational frequency range of the antenna system.
- the slot portion 37 of the recess in ground plane 26 has a narrow end which communicates with the balun portion 36 along one of the linear sides of the balun portion 36, at a location spaced from each end of that linear side.
- the opposite end of the slot portion 37 is significantly wider than the narrow end.
- FIGURE 5 is a graph showing the shape of one edge of the slot portion 37, where the horizontal axis represents the centerline of the slot, from the end at the balun portion 36 to the end at the radome 13.
- the vertical axis in FIGURE 5 represents the half-width of the slot, or in other words, the distance from the edge of the slot to the centerline.
- the edges of the slot portion 37 are mirror images of each other with respect to the centerline of the slot, and therefore only one of these edges is depicted in the graph of
- the edges of the slot portion 37 do not follow a pure first-order exponential curve. Instead, the slot edges have a shape which has been carefully configured to minimize reflections and reduce return loss in a manner facilitating a wide bandwidth in excess of 10:1.
- the technique used to configure the shape of the slot edge is described in detail later. For the moment, it is sufficient to note certain characteristics of the specific shape shown in FIGURE 5 for the slot portion 37. More specifically, it can be seen that the narrowest part 41 of the slot portion 37 is not precisely at the end of the slot portion which opens into the balun portion 36, but instead is spaced a small distance from this end. This narrow part 41 provides a region of increased capacitance.
- each edge of the slot portion 37 is somewhat “wavy" in the section from the balun portion 36 to the discontinuity 42, which is not a random meandering, but instead is a carefully configured shape that reduces reflections and return loss in order to increase bandwidth and improve performance.
- the curve shown in FIGURE 5 might be described as approximately a first-order exponential curve that has at least one higher-order characteristics superimposed on the first-order characteristic, and in fact the particular curve of FIGURE 5 has a number of higher-order characteristics superimposed on the first-order characteristic.
- the specific curve shown in FIGURE 5 can be expressed in the form of the following equation, where the coefficients for the equation are set forth in Table 1.
- the ground plane 27 has therethrough a recess which includes a balun portion 43 and a slot portion 44
- the ground plane 28 has therethrough a recess which includes a balun portion 46 and a slot portion 47.
- the slot portions 37, 44 and 47 all have the same size and shape, in particular the shape described above in association with FIGURE 5. Further, the slot portions 37, 44 and 47 are all precisely aligned with each other. In a similar manner, the balun portions 36, 43 and 46 all have the same size and shape, and are precisely aligned with each other.
- the dielectric layers 17 and 18 each have therethrough an approximately rectangular opening, which has the same size and shape as the balun portions 36, 43 and 46, and which is aligned with the balun portions 36, 43 and 46.
- these aligned openings of approximately rectangular shape in the three groundplanes and the two dielectric layers define a balun hole 49 of approximately rectangular shape, which extends completely through the antenna element 12.
- FIGURE 6 is diagrammatic fragmentary perspective view showing a portion of the rear side of the antenna element 12 in an enlarged scale.
- the balun opening 49 through the antenna element 12 is plated with an electrically conductive material, such that a strip 51 of this conductive material extends along the edges of the balun hole.
- the ends of the strip 51 are spaced so as to define a slot 52 aligned with the narrow ends of the slot portions 37, 44 and 47.
- the strip 51 extends between and is electrically coupled to the ground planes 26 and 27, and is also in electrical contact with the ground plane 28A.
- the antenna element 12 also has its opposite side edges plated with an electrically conductive material, such that respective strips 53 and 54 of this conductive material extend the full length of the dielectric elements 17-18, and also extend between and are electrically coupled to each of the ground planes 26 and 27.
- the strip 53 is also in electrical contact with the ground plane 28A along its entire length, and the strip 54 is in electrical contact with each of the ground planes 28B and 28C.
- the dielectric layers 17 and 18 have respective wedge-shaped openings 57 and 58 therethrough, which are identical size and shape and are aligned with each other.
- the openings 57 and 58 begin at the outer ends of the dielectric elements 17 and 18, and decrease progressively in width in a direction toward the balun hole 49.
- the tapering sides of the openings 57 and 58 are spaced inwardly from the tapering edges of the slot portions 37, 44 and 47. In a direction along the centerline of the slot portions 37, 44 and 47, the inner ends of the openings 57 and 58 are approximately aligned with the discontinuity 42 (FIGURE 5).
- the discontinuity 42 compensates to some extent for an impedance discontinuity caused within the dielectric material by the start of the openings 57 and 58 at their left ends.
- the layer 19 of bond film (FIGURE 3) has a wedge-shaped opening through it which is identical in size and shape to the openings 57 and 58, and which is aligned with the openings 57 and 58.
- the ground plane 28 (FIGURE 4) has, in addition to the recess which includes the balun portion 46 and the slot portion 47, a further recess 66 which is an elongate channel that extends from an inner end of the dielectric layer 18 around the balun portion 46, and opens into the narrow end of the slot portion 47.
- the channel 66 communicates along one side with the balun portion 46, but it would alternatively be possible for a portion of the groundplane 28A to extend between them.
- An elongate conductive strip 67 extends through the channel 66, such that one end is disposed at the inner end of the dielectric layer 18 located at the left side of FIGURE 1, and the other end extends across the narrow end of the slot portion 47 and is shorted directly to the ground plane 28A.
- the conductive strip 67 and the ground plane 28A are discussed herein as if they are physically separate parts, because they serve different operational functions in the antenna element 12. However, as a practical matter, the ground plane 28A and the conductive strip 67 are just different integral portions of the same conductive layer.
- an approximately semicircular cutout 71 is provided through the ground plane 26 and the dielectric layer 17, in order to expose an end portion of the conductive strip 67, and an end portion of each of the portions 28A and 28C of the ground plane 28.
- This permits a contact of a not-illustrated connector arrangement to respectively engage the strip 67 and the ground plane portions 28A and 28C, in order to electrically couple the conductive strip 67 of the antenna element 12 to antenna system circuitry which is known in the art and therefore not shown in the drawings.
- the not-illustrated antenna system circuitry is electrically coupled to the arrangement of interconnected ground planes through direct engagement of a metal chassis of the antenna system with one or more of the outer ground planes 26-27 and the conductive strips 53-54.
- the conductive strip 67 serves as a conductive element of the type which is commonly referred in the art as a stripline, and carries signals that are being transmitted from or received by the antenna element 12.
- the direct connection between the ground plane 28A and an end of the stripline 67 represents an electrical termination of that end of the stripline 67. Since the stripline 67 terminates directly into the groundplane 28, reactances are minimized where the stripline 67 extends across the slot portion 47, in comparison to pre-existing devices where the stripline is coupled by a via to a groundplane on the opposite side of a dielectric layer, or where the stripline terminates into some form of standalone termination structure designed to produce a standing wave resonance.
- a plurality of vias extend through both of the dielectric layers 17 and 18 at a number of different locations, so as to electrically couple all three of the ground planes 26-28.
- Three of these vias are identified with reference numerals 76, 77 and 78.
- the vias facilitate precise control over impedance characteristics within the slot portions 37, 44 and 47 and along the stripline 67, and also help to reduce or eliminate the extent to which electromagnetic fields can form parallel plate and waveguide modes within the dielectric material.
- One of the illustrated vias is identified by reference numeral 79, and is slightly larger in diameter than the rest of the vias.
- the via 79 is disposed closely adjacent the point at which one end of the stripline 67 terminates directly into the ground plane portion 28A, and serves to ensure that this end of the stripline 67 is directly and reliably terminated to not only the center groundplane 28, but also the two outer groundplanes 26-27. It will be noted that a respective row of the vias extends adjacent each edge of the slot portions 37, 44 and 47, with approximately uniform spacing from each via to the edge of the slot portions, and with approximately uniform spacing between adjacent vias. Behind each of these rows, along most of the length thereof, is a further row of vias.
- FIGURE 7 is a diagrammatic fragmentary perspective view of the outer end portion of the apparatus 10, in an enlarged scale.
- the radome 13 includes a dielectric layer 91 which is fixedly coupled to an outer end of the antenna element 12 by a bond film 92, a second dielectric layer 93 which is fixedly coupled to the dielectric layer 91 by a bond film 94, and a third dielectric layer 97 which is fixedly coupled to the dielectric layer 93 by a bond film 98.
- the bond films 92, 94 and 98 are materials of a type known in the art.
- the dielectric layer 97 is relatively thin, and serves primarily as a protective outer cover.
- the dielectric layers 91, 93 and 97 have respective thickness of 120 mils, 60 mils and 2 mils, and have respective dielectric constants (Er) of 1.08, 1.3 and 3.6.
- the dielectric layers 91, 93 and 97 could have respective thicknesses of 60 mils, 120 mils and 2 mils, and respective dielectric constants of 1.3, 1.08 and 3.6.
- the dielectric layers 91 and 93 are transmissive to radiation which is being transmitted from or received by the antenna element 12. Further, the dielectric layers 91 and 93 effect a degree of refraction of this radiation, as discussed in more detail below.
- the dielectric layers 91 and 93 can also effect a small degree of impedance matching between the adjacent wide end of the slot portions located on one side thereof, and the free space located on the other side thereof.
- the stripline 67 and the not-illustrated antenna system circuitry to which it is coupled are matched, so as to provide a substantial uniform impedance of approximately 50 ohms from the circuitry through the stripline 67 to the slotline.
- Free space beyond the right end of the apparatus 10 has an impedance of approximately 377 ohms, for a two-dimensional square unit cell representing uniform spacing in both directions of the two-dimensional array of antenna elements 12 within the phased array antenna system.
- the slotline effects an impedance transformation from a value of approximately 50 ohms at the left end, which is matched to the impedance of the stripline 67, to a value of approximately 360-370 ohms at the right end, which closely approaches the impedance of free space.
- groundplanes 26-28 provides more conductive material along the edges of the slotline than in pre-existing arrangements that have only one or two groundplanes, which in turn provides increased capacitance within the slotline.
- the increased capacitance permits the narrow end of the slotline to be slightly wider than in pre-existing devices, while still achieving an impedance of 50 ohms which is matched to the impedance of the stripline 67.
- fabrication of the ground planes 26-28 is easier, due to the fact that tolerances involved in the etching techniques for the groundplanes are fixed.
- the wedge-shaped openings 57 and 58 within the dielectric layers 17 and 18, and the congruent wedge-shaped opening within the bond film layer 19, help facilitate this impedance transformation, by reducing the amount of dielectric and bond film material disposed within the slotline at the right end thereof.
- the impedance within the slotline will more closely approach the impedance of the free space located beyond the right end of the apparatus 10 than would be the case if the openings 57 and 58 were omitted and the right end of the slotline was completely filled with dielectric material. This is due to the fact that air has a somewhat higher impedance than the dielectric material, and the provision of the openings 57 and 58 substitutes air for what would otherwise be dielectric material.
- the balun hole 49 is designed so that the width dimension 39 (FIGURE 1) is as large as possible in the region where the slotline opens into the balun hole 49, up to about three-eighths of a wavelength of interest. This is intended to provide the largest possible impedance discontinuity between the balun hole 49 and the narrow end of the slotline. This large discontinuity is facilitated by the fact that the slotline opens into the balun hole 49 through a side of the balun hole 49 which is approximately linear, and at a location spaced from both ends of this linear side.
- the balun hole has an impedance of approximately 300 ohms, which represents a relatively large discontinuity in relation to the 50 ohm impedance of the adjacent end of the slotline.
- impedance approximately 300 ohms
- the large impedance discontinuity between the balun hole 49 and the left end of the slotline will cause the majority of this electromagnetic energy to travel rightwardly rather than leftwardly along the slotline, and to be transmitted into free space.
- the balun hole 49 has a length dimension which is approximately one-quarter wavelength (as discussed above), and this creates an open circuit standing wave which also tends to cause electromagnetic energy to travel rightwardly within the slotline.
- the inner edge of the balun hole 49 is plated with a conductive strip 51, except at the slotline.
- the strip 51 helps to keep electromagnetic fields present within the balun hole 49 from entering the dielectric material of layers 17 and 18, which helps to increase system bandwidth. Consequently, the strip 51 helps establish the standing wave or resonant condition with respect to electromagnetic energy within the balun hole 49, which in turn helps to direct electromagnetic energy rightwardly within the slotline.
- the balun hole 49 is a tuned inductive hole, which can operate over a 10:1 bandwidth without electrical or structural adjustment.
- the balun hole 49 does not have any dielectric material within it.
- the balun hole 49 is filled with air, rather than dielectric material.
- the wavelength of electromagnetic radiation is longer in air than it would be in dielectric material. Consequently, to the extent the balun hole 49 is made as wide as possible in order to maximize the impedance discontinuity between the balun hole and the adjacent end of the slotline, a given width will be further below one-half wavelength when the balun hole is filled with air than would be the case if the balun hole was filled with dielectric material.
- FIGURE 8 is a highly diagrammatic view of the apparatus 10, including both the antenna element 12 and the radome 13.
- Arrow 111 represents electromagnetic radiation which is traveling outwardly through the slotline. As this radiation passes through the interface between the antenna element 12 and the dielectric layer 91, it is refracted to a degree, so that it travels in a slightly different direction, as indicated diagrammatically in FIGURE 8 by the arrow 112. Similarly, as this radiation passes through the interface between dielectric layer 91 and dielectric 93, it experiences a further degree of refraction which further increases its angle, as indicated diagrammatically by arrow 113.
- this radiation passes through the interface between dielectric layer 93 and free space, it is refracted a little further, so that it travels at a slightly greater angle, as indicated diagrammatically by arrow 114.
- This refraction within the radome 13 permits the apparatus 10 to operate more effectively over a wider scan angle, which in the disclosed embodiment approaches about 50° to 60°. In a sense, the refraction causes a portion of the radiation transmitted at each edge of the scan angle to have a higher effective power level than would be the case without such refraction.
- the provision of the wedge-shaped openings 57 and 58 in the dielectric layer of the antenna element 12 permit the use of lower dielectric constants for the dielectric layers 91 and 93 of the radome 13 than would otherwise be the case. This in turn reduces the extent to which electromagnetic energy is diverted into transverse surface waves within the dielectric layers, for example as indicated diagrammatically by a broken line arrow 117, which in turn reduces or avoids an effect that is sometimes referred to as scan blindness.
- reference numeral 121 diagrammatically represents radiation which is approaching the antenna element 12 at an angle to the centerline of the slot portions in the antenna element 12. As this radiation passes through the radome 13 and enters the antenna element 12, the radiation is progressively refracted, as indicated diagrammatically by arrows 122, 123 and 124, until the radiation is traveling through the slot portion of the antenna element 12 approximately parallel to the centerline.
- FIGURE 9 is a graph showing return loss as a function of frequency for the embodiment of FIGUREs 1-8, for what is known in the art as E-plane scan. Since return loss is a standard way of expressing the amount of reflection, it is desirable that return loss be as low as possible. It will be noted that the apparatus 10 provides a return loss which is continuously below -10dB for a scan width of 60° across a bandwidth from approximately 1.8 GHz to approximately 17.5 GHz. Persons skilled in the art will recognize that, expressed according to another industry standard, the embodiment of FIGUREs 1-8 provides a bandwidth of at least 10:1 for -9.5dB (VSWR less than 2).
- FIGURE 10 is a graph similar to FIGURE 9, but showing return loss for what is commonly known in the art as H-plane scan.
- FIGURE 10 shows that the apparatus 10 provides a return loss of -10dB across a scan width of 45° to 50° from a frequency of about 3.5 GHz to a frequency in excess of 18 GHz.
- Advantageous performance characteristics are due in part to the shape determined for the edges of the slot portions 37, 44 and 47, which collectively serve as the slotline of the antenna element 12. An explanation will now be provided of how the shape for the edges of the slot portions is determined.
- the apparatus 10 is conceptually broken into three functional sections for purposes of carrying out an analysis which determines an optimum shape for the edges of the slot portions. More specifically, one functional section is referred to as the balun, and corresponds roughly to the balun hole 49 and the conductive stripline 67. The next functional section is referred to as the slot, and corresponds roughly to the part of the slot portion which extends from the balun hole 49 to the discontinuity 42 at the left end of the wedge-shaped openings 57 and 58.
- the third functional section 203 is referred to as the end piece, and corresponds roughly to the part of the apparatus 10 located to the right of the discontinuity 42, in particular from the left end of the wedge-shaped openings 57-58 to the right side of the outer dielectric layer 97.
- FIGURE 11 is a diagram showing three blocks 201-203, which respectively represent the three functional sections discussed above, namely the balun, slot and end piece sections.
- blocks 201-203 represent the apparatus 10 of FIGURE 1, as indicated diagrammatically by a broken line in FIGURE 11.
- Each of the blocks 201-203 is depicted as a two-port element, including one port with two terminals on the left side, and another port with two terminals on the right side. Adjacent ports of the adjacent blocks are coupled to each other.
- the end piece 203 has the port on the right side coupled to a further block 208, which diagrammatically represents the impedance of the free space disposed beyond the right end of the apparatus 10 in FIGURE 1.
- two-port blocks such as those depicted at 201-203 can each be represented by what is commonly referred to as an [ABCD] matrix.
- the left port has a voltage V X and current I X and the right port has a voltage V Y and current I Y .
- the balun and end piece (which correspond to blocks 201 and 203) are designed so as to achieve appropriate design goals.
- the balun hole 49 (FIGURE 1) has various aspects, such as shape, size and the absence of dielectric material, which are intended to achieve the design goal of a large impedance discontinuity between the balun hole and slotline, which in turn supports a wide bandwidth for the antenna element 12.
- Possible design configurations for both the balun and end piece can be rigorously analyzed with an existing software program to determine expected operational characteristics.
- One suitable software program for this task is available under the tradename High Frequency Structure Simulator (HFSS), and can be commercially obtained from Ansoft Corporation of Pittsburgh, Pennsylvania.
- HFSS High Frequency Structure Simulator
- the apparatus 10 is designed for use across a frequency range of interest.
- the operational characteristics of the balun section will be different at different frequencies, and the operational characteristics of the end piece section will be different at different frequencies. Accordingly, several predetermined frequencies are selected, which are spread throughout the frequency range of interest. Then, a respective different [ABCD] matrix is determined for the balun section 201 for each selected frequency, and a respective different [ABCD] matrix is determined for the end piece section 203 for each such frequency.
- Appropriate techniques for determining an [ABCD] matrix from a physical design are known in the art.
- parameters representing the physical design can be provided to a known software program, which can then calculate a form of transfer function known in the art as an [S] matrix.
- the HFSS computer program mentioned above is suitable for this task. Thereafter, the [S] matrix can be converted into a corresponding [ABCD] matrix, using known mathematical techniques.
- FIGURE 12 is a diagrammatic view of a model which is a transmission line 241, made up of a plurality of N contiguous rectangular segments SEG1, SEG2, SEG3,... SEGN.
- N 40 contiguous rectangular segments
- the centerline of the slot is indicated diagrammatically at 243, and the outer ends of the N segments collectively represent the edges of the slot.
- the segments all have same length in a direction parallel to the centerline 243, but have a variety of different widths in a direction transverse to the centerline 243.
- the segments in FIGURE 12 do not necessarily represent the precise slot shape shown in FIGURE 5, but instead can be considered representative of one of a number of different shapes that are evaluated to determine which shape should serve as the optimum shape shown in
- the common length value for all of the segments SEG1 through SEGN and also the N respective width values are varied selectively and independently, and the performance of the apparatus 10 is evaluated for each such configuration of the segmented transmission line, in a manner explained in more detail below. It should be noted that the number N of segments is not varied. Consequently, to the extent that the common length value for the segments is varied, the overall length of the segmented transmission line, and thus the overall length of the slot it represents, will vary. Thus, part of what is optimized is the length of the slot itself.
- Nelder-Mead Various existing techniques are known for effecting the independent variation of a number of parameters in a selective manner so as to optimize a specified characteristic.
- One such technique is commonly known in the art as the Nelder-Mead technique.
- There are commercially available software programs which implement the Nelder-Mead technique one example of which is the program MATLAB® available from The MathWorks of Natick, Massachusetts. Programs of this type provide generic Nelder-Mead capability, and can be provided with input data for a specific application which cause the program to apply the generic principles to that specific application. Since Nelder-Mead techniques are known in the art, they are not described in detail here. Instead, to facilitate an understanding of the present invention, a brief overview is provided.
- a program which implements Nelder-Mead techniques is capable of varying multiple parameters in an intelligent manner according to Nelder-Mead principles, while evaluating a characteristic which is to be optimized.
- configurations of parameters which tend to improve the specified characteristic are favored over configurations which do not improve the characteristic, and the favored configurations are used to predict other new configurations that may possibly provide even greater improvement in the specified characteristic.
- an initial slot shape is selected, for example where the edges of the slot simply follow a first-order exponential curve.
- a segmented transmission line model of the type shown in FIGURE 12 is used to model this initial slot shape, using N segments where N is roughly 40 to 60.
- the respective widths of the segments and also the common length of the segments are then independently varied using Nelder-Mead techniques in order to come up with a plurality of different configurations of the segmented transmission line, which each represent a different slot shape. For each such configuration, performance of that configuration is evaluated.
- FIGURE 13 is a diagrammatic view, in an enlarged scale, of the end portions of four of the transmission line segments shown in the upper right portion of FIGURE 12.
- the solid lines in FIGURE 13 correspond directly to the segments which are shown in FIGURE 12.
- the broken lines in FIGURE 13 show how the overall number of line segments is tripled from N to 3N.
- two points 261 and 262 are identified through interpolation at uniformly spaced locations along a straight line extending between two points 263 and 264, which are at respective corners of two of the N segments shown in FIGURE 12.
- Each of the points 261-264 then becomes a corner of a respective new segment having a length which is one-third the length of each of the N segments shown in FIGURE 12.
- the Nelder-Mead techniques are not used to independently vary the widths of all 3N segments, but only the widths of the N segments shown in FIGURE 12. The other two-thirds of the segments have widths that are directly dependent on the original N widths, rather than widths determined through completely independent variation.
- a theoretical transmission line has a length l, which corresponds to the uniform dimension of each of the 3N segments in a direction parallel to the centerline 243 (FIGURE 12) of the slot.
- the theoretical transmission line in FIGURE 14 has an impedance Z SEG and, in the case of each of the 3N segments shown in FIGURE 13, this impedance depends on one or more different factors. First, it depends on the width of the segment in a direction transverse to the centerline 243. Further, and with reference to the apparatus 10 shown in FIGURE 1, it depends on whether there is material within the slot and, if so, the characteristics of that material.
- the embodiment of FIGURE 1 has portions of the dielectric layers 17 and 18 which are disposed within the slot, and the dielectric layers have impedance characteristics that vary with frequency, even for a given width.
- the impedance characteristic would vary with width but not frequency, because the impedance of air does not vary with frequency.
- the theoretical transmission line can be modeled as a two-port element of the type discussed earlier, and its characteristics can thus can be represented by an [ABCD] matrix.
- the value of the wavelength ⁇ can vary not only as a function of frequency, but also as function of the type of material present within the slot.
- the wavelength will be one value if there is dielectric material within the slot (as is the case in the embodiment of FIGURE 1), but will be a different value if the slot contains air rather than dielectric material.
- an [ABCD] matrix can be determined in the following manner for the entire apparatus of FIGURE 1, identified by the subscript "APP", including the antenna element 12 and the radome portion 13.
- [ A B C D ] APP [ A B C D ] B x [ A B C D ] S x [ A B C D ] EP
- V IN I FS ( A Z FS + B )
- I IN I FS ( C Z FS + D )
- A, B, C and D are from [ A B C D ] APP
- the antenna element 12 of FIGURE 1 is coupled to a not-illustrated antenna system, for example through a cable.
- the antenna system supplies electrical signals to and from the input port at the left side of FIGURE 11.
- Z 0 represents the characteristic impedance of the not-illustrated cable and other circuitry of the antenna system. It is customary in the art to design this circuitry and cable so that the impedances are all matched, to thereby provide a line of effectively constant impedance with no reflection. In the disclosed embodiment, this characteristic impedance Z 0 has a value of 50 ohms.
- a first criteria involves a determination of the maximum value of return loss RL calculated for a given slot shape.
- the slot shape having the lowest maximum value of RL could be selected as the optimum design.
- all evaluated slot shapes with a maximum value of return loss RL lower than a specified value (such as -10dB) could be identified, and the shapes in this group could then be comparatively evaluated using other criteria.
- a second criteria would be to determine the maximum value, for each slot shape, of the absolute value of the calculated reflection R.
- the slot design with the lowest such maximum value could be selected as the optimum design.
- all evaluated slot shapes for which this calculated maximum value is less than a specified value could be selected, and the slot shapes in this group could then be comparatively evaluated using other criteria.
- FIGURE 15 is a flowchart, which summaries the optimization technique discussed above. More specifically, in block 301, the designs of the balun and end piece are each optimized and finalized. Then, transfer functions are determined for each of the balun and end piece at each of a plurality of predetermined frequencies spread across a frequency range of interest. As discussed above, each of these transfer functions can be represented in the form of an [ABCD] matrix.
- an initial slot shape is selected in order to "seed" the optimization routine.
- the initial slot shape is selected to be a pure first-order exponential curve, but it would alternatively be possible to use some other initial slot shape.
- the selected slot shape is modeled as a segmented transmission line, in the manner discussed above in association with FIGUREs 12 and 13. Then, at block 306, the lowest of the predetermined frequencies in the range is selected.
- each such transfer function can be in the form of an [ABCD] matrix, as discussed above.
- These various transfer functions for the different segments are then combined to obtain a single transfer function for the entire segmented transmission line.
- this is also an [ABCD] matrix, as discussed above.
- the transfer functions for the balun section, slot section and end piece section are used to calculate and save a reflection value and a return loss value, in a manner discussed previously. Then, at block 311, a determination is made of whether the currently selected frequency is the highest frequency in the range. If not, the next highest of the predetermined frequencies is selected at block 312, and control returns to block 307 to analyze the performance of the current slot design at this newly-selected frequency.
- an evaluation is made of whether the optimum shape has been found. This determination involves use of performance criteria of the type discussed above. Further, it depends on the extent to which the Nelder-Mead techniques discussed above have reached a point where a variety of different slot shapes have been evaluated and it appears that the optimum shape is likely to be a shape that has already been evaluated, rather than a shape that has yet been evaluated. In general, a number of slot shapes will be evaluated before a decision is made at block 316 that the optimum slot shape has been identified.
- the blocks 316 and 317 basically represent a particular application for the known Nelder-Mead techniques that were discussed earlier. In contrast, if at some point it is determined at block 316 that an optimum slot shape has been determined, the evaluation process is finished, and ends at block 318.
- FIGURE 16 is a diagrammatic front view of an antenna element 412 which is alternative embodiment of the antenna element 12 of FIGURE 1.
- the antenna element 412 of FIGURE 16 would normally be used with a radome of the type shown at 13 in FIGURE 1, but the radome is omitted from FIGURE 16.
- the antenna element 412 of FIGURE 16 is substantially identical to the antenna element 12 of FIGURE 1, except for the differences which are discussed below.
- the two dielectric layers and the bond film of the antenna element 412 each extend outwardly beyond the ends of the three ground planes, one of the dielectric layers being visible at 417, and one of the ground planes being visible at 426.
- the upper and lower side edges of the antenna element 412 each have plating which extends from the left end of the antenna element to the right ends of the ground planes. This edge plating does not extend the rest of the way to the right end of the antenna element 412.
- the dielectric layers each have a wedge-shaped opening therein, one of which is visible at 457. It will be noted that the left end of each wedge-shaped opening is located rightwardly of the right ends of the ground planes, including the ground plane 426. In other words, the wedge-shaped openings in the dielectric layers are not disposed within the slotline defined by the slots in the ground planes. Consequently, the edges of the slot portions in the antenna element 412 do not have a discontinuity comparable to that shown at 42 in FIGURE 1, because the discontinuity 42 is due to the fact that the wedge-shaped opening 57 in FIGURE 1 is disposed within the slotline.
- the edges of the slot portions of the ground planes do not follow a first-order exponential curve, but instead have higher-order effects which give them a somewhat wavy shape, in a manner similar to that described above in association with the embodiment of FIGURE 1.
- the procedure used to determine the shape of the slot edges for the embodiment of FIGURE 16 is similar to the procedure described above for the embodiment of FIGURE 1, and is therefore not described again in detail here. Further, the operation of the embodiment of FIGURE 16 is similar to the operation of the embodiment of FIGURE 1, and is therefore not explained again in detail here.
- FIGURE 17 is a diagrammatic perspective view of an antenna element 512 which is a further alternative embodiment of the antenna element 12 of FIGURE 1.
- the antenna element 512 includes a body 514 which is made from a single metal plate.
- a recess is provided through the metal plate, and includes a balun portion 536 in the shape of a rectangular hole, and an elongate slot portion 537 which communicates at its narrow end with the balun portion 536.
- the balun portion 536 and the slot portion 537 have sizes and shapes that are comparable to those discussed above in association with the embodiment of FIGURE 1.
- the edges of the slot portion 537 do not follow merely a first-order exponential curve, but instead include higher-order effects which give the edges a somewhat wavy shape.
- the shape of the edges is determined by a procedure similar to that discussed above in association with the embodiment of FIGURE 1, and this procedure is not described again in detail here.
- the antenna element 512 includes a coaxial stripline 561, which has an electrically conductive exterior sheath that is fixedly secured to the front of the plate 514 by a conductive epoxy adhesive of a known type.
- FIGURE 18 is a diagrammatic sectional view of the coaxial stripline 561, taken along the section line 18-18 in FIGURE 17.
- the coaxial stripline 561 includes two adjacent dielectric layers 563 and 564, with a conductive stripline 567 disposed between them.
- the stripline 567 has a width which is substantially less than the width of the dielectric layers 563 and 564, so that the dielectric layers 563 and 564 serve as a layer of insulating material which extends coaxially around the stripline 567.
- a sheath 569 of an electrically conductive material extends completely around the dielectric layers 563 and 564. As mentioned above, the sheath 569 is physically and electrically coupled to the metal plate 514 in FIGURE 17 by a conductive epoxy adhesive of a known type, which is not separately shown in the drawings.
- FIGURE 19 is a diagrammatic fragmentary sectional top view of the coaxial stripline 561, taken along a plane defined by the top surface of the stripline 567, and showing an end portion of the coaxial stripline 561 which is located in the region of the narrow end of the slot portion 537 (FIGURE 17).
- the conductive sheath 569 has an annular gap 572 which extends completely around the coaxial stripline 561. The gap 572 is aligned with the slot portion 537, and permits current within the stripline 567 to generate electromagnetic fields that can escape the sheath 569 and extend into the slot portion 537.
- the stripline 567 begins expanding progressively in width, which serves as a transition to an approximately rectangular end portion 573, three sides of which electrically engage the sheath 569.
- a via at 574 extends through the conductive stripline between opposite sides of the sheath 569, and is electrically coupled to the end portion 573 of the stripline 567.
- the end of the stripline 567 is shorted directly to a ground plane defined by the metal plate 514 (FIGURE 17), in order to effect electrical termination of the stripline 567.
- One technique for fabricating the coaxial stripline 561 is as follows.
- the dielectric material 564 is fabricated, and then a layer of metal is deposited on top of it.
- the metal layer is then photolithographically etched in a known manner, in order to remove selected portions of it, such that the remaining portions define the stripline 567 with its end portion 573.
- the dielectric layer 563 is formed over the dielectric layer 564 and the stripline 567.
- a cylindrical hole is created through the dielectric layers and the metal layer, at a location where the via 574 is to be formed.
- this arrangement is immersed in an electroless plating tank, in order to form the sheath 569 over the entire exterior thereof, and in order to form the via 574 within the cylindrical hole.
- the annular mask prevents conductive material from being plated within the region of the gap 572. After the plating is completed, the mask is removed in order to expose the gap 572. The resulting assembly is then secured to the metal plate 514, using a conductive epoxy adhesive, as discussed above.
- the operation of the antenna element 512 of FIGUREs 17-19 is generally similar to that of the antenna element 12 of FIGURE 1. Therefore, a separate detailed discussion of the operation of the antenna element 512 is believed to be unnecessary, and is omitted here.
- the present invention provides a number of technical advantages.
- One such technical advantage results from the absence of dielectric material in the balun hole, such that the hole contains air. Since air has a lower dielectric constant than dielectric material, air has a higher impedance than a dielectric material, and the wavelength of a given frequency is longer in air than in a dielectric material. Consequently, for a given physical width of the balun hole, the effective electrical width is smaller for air than for a dielectric material. This in turn means that the effective electrical width is farther below 8/2 for air than for a dielectric material, which reduces undesirable effects.
- the inner edge of the balun hole is conductive, for example due to the provision of plating, because it helps to increase the bandwidth of the balun hole by containing electrical fields to the hole.
- the conductive edge of the hole prevents electric fields from extending into the dielectric material around the hole.
- balun hole has a generally rectangular shape, because it helps to create an abrupt impedance discontinuity between the balun hole and the associated end of the slotline. With an abrupt discontinuity in impedance, electric fields in the region of the narrow end of the slot see the balun hole as approximately an open circuit across a frequency range of interest, which gives the balun hole a relatively wide bandwidth.
- dielectric material is omitted within the rectangular balun hole, and the edge of the balun hole is conductive, because the bandwidth of the balun hole is further enhanced. The resulting balun hole is effectively a tuned conductive hole.
- balun hole is approximately rectangular, contains no dielectric material, has conductive edges, is associated with two or more ground planes, and is associated with a stripline termination into a ground plane, the standalone bandwidth of the balun hole can approach about 8:1.
- balun hole is used with a slot having a shape that has been optimized using techniques according to the invention.
- the balun hole is inductive and the slot is capacitive.
- the optimization technique is used to achieve conjugate matching of the balun hole and slot, they cooperate to provide good performance even at low frequencies, in a manner somewhat analogous to resonance in a tuned RLC circuit.
- they can provide a decade (10:1) bandwidth capable of a ⁇ 60° E-plane and ⁇ 50° H-plane scan volume.
- ground planes can also provide another advantage, by helping to minimize reactances at the stripline to slotline transition. Further, providing three or more ground planes increases the amount of conductive material present along the edges of the slot, thereby increasing capacitance, which in turn allows the narrow end of the slot be wider. Where the narrow end of the slot is wider, it is easier to fabricate the slot while still achieving a low impedance of approximately 50 ohms for the narrow end of the slot. This is because the tolerances for etching are basically fixed, and etching the narrow end of the slot is progressively increased.
- stripline terminated directly into one of the ground planes, because this effectively provides an actual physical short circuit to a ground plane, in comparison to pre-existing techniques that essentially seek to emulate or approximate a physical short circuit by creating a standing wave resonance.
- the disclosed antenna elements provide a stripline to slotline transition with a transformer ratio that is close to unity, and with minimal stray reactances.
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Abstract
Description
- This invention relates in general to tapered slot antennas and, more particularly, to a method and apparatus for obtaining wide band performance in a tapered slot antenna.
- During recent decades, antenna technology has experienced an increase in the use of antennas that utilize an array of antenna elements, one example of which is a phased array antenna. Antennas of this type have many applications in commercial and defense markets, such as communications and radar systems. In many of these applications, broadband performance is desirable. Some of these antennas are designed so that they can be switched between two or more discrete frequency bands. Thus, at any given time, the antenna is operating in only one of these multiple bands. However, in order to achieve true broadband operation, the antenna needs to be capable of satisfactory operation in a single wide frequency band, without the need to switch between two or more discrete frequency bands.
- One type of antenna element that has been found to work well in an array antenna is often referred to as a tapered slot antenna element. The spacing between antenna elements in an array antenna is typically determined by the frequency at which the antenna operates, and a tapered slot antenna element fits comfortably within the space available for an antenna element in many array antennas.
- European
Patent application EP 0, 343, 322 describes an antenna having a strip conductor, and a ground plane separate from and lying parallel to the strip conductor. The ground plane has a slot which extends transverse to the strip conductor. - United States patent US 6, 008, 770 describes a tapered slot antenna which provides a tapered pattern composed by utilising a Fermi-Dirac distribution function.
- Tan-huat Chio et al in "Large wideband dual-polarized array of Vivaldi; antennas with radome," Microwave conference 1999, Asia Pacific Singapore 30 November - 3 December 1999, pages 92-95 (XP010374119), ISBN: 0-7803-5761-2, describes a tapered slot antenna having two ground planes, with a dielectric in between, on which a stripline feed is provided.
- Existing tapered slot antenna elements typically have a bandwidth of about 3:1 to 4:1, although some have a bandwidth that approaches 6:1. While these existing tapered slot antenna elements have been generally adequate for their intended purposes, they have not been satisfactory in all respects. In this regard, there are applications in which it is desirable for a tapered slot antenna element to provide broadband performance involving a bandwidth in the neighbourhood of 10:1, or even larger. Existing designs and design techniques have not been able to provide a tapered slot antenna element which approaches this desired level of broadband performance.
- From the foregoing, it may be appreciated that a need has arisen for a method and apparatus that contribute, in a tapered slot antenna element, to broadband performance exhibiting a substantially greater bandwidth than is available in pre-existing tapered slot antenna elements.
- An aspect of the present invention provides an antenna element as set out in claim 1.
- According to a complimentary aspect of the invention there is provided a method, as set out in
claim 25. - A better understanding of the present invention will be realized from the detailed description which follows, taken in conjunction with the accompanying drawings, in which:
- FIGURE 1 is a diagrammatic fragmentary front view of an apparatus embodying aspects of the present invention, including an antenna element and part of a radome;
- FIGURE 2 is a diagrammatic fragmentary rear view of the
apparatus 10; - FIGURE 3 is a diagrammatic sectional view taken along the section line 3-3 in FIGURE 1;
- FIGURE 4 is a diagrammatic fragmentary sectional front view of the apparatus in FIGURE 1, taken along a center plane thereof;
- FIGURE 5 is a graph showing the shape of one edge of a slot portion which is part of the antenna element of FIGURE 1;
- FIGURE 6 is a diagrammatic fragmentary perspective view of showing a portion of the rear side of the
antenna element 12 in an enlarged scale; - FIGURE 7 is a diagrammatic fragmentary perspective view showing in an enlarged scale an outer end portion of the apparatus of FIGURE 1;
- FIGURE 8 is a highly diagrammatic view of the apparatus of FIGURE 1, showing a refraction characteristic effected by certain dielectric layers in the radome thereof;
- FIGURE 9 is a graph showing return loss in E-plane scan as a function of frequency for the apparatus of FIGURE 1;
- FIGURE 10 is a graph showing return loss in H-plane scan as a function of frequency for the apparatus of FIGURE 1;
- FIGURE 11 is a block diagram showing functional sections of the apparatus of FIGURE 1;
- FIGURE 12 is a diagrammatic view of a segmented transmission line which serves as a model for analyzing a slotline present in the apparatus of FIGURE 1;
- FIGURE 13 is a diagrammatic view, in an enlarged scale, of the end portions of four of the transmission line segments of FIGURE 12, and also shows in broken lines how the number of segments can be tripled through interpolation;
- FIGURE 14 is a diagrammatic view of one of the transmission line segments of FIGURE 12, represented in theoretical form;
- FIGURE 15 is a flowchart which summarizes an optimization technique used in designing the apparatus of FIGURE 1;
- FIGURE 16 is a diagrammatic front view of an antenna element which is an alternative embodiment of the antenna element of FIGURE 1;
- FIGURE 17 is a diagrammatic perspective view of an antenna element which is still another alternative embodiment of the antenna element of FIGURE 1;
- FIGURE 18 is a diagrammatic sectional view taken along the section line 18-18 in FIGURE 17; and
- FIGURE 19 is a diagrammatic fragmentary sectional top view of a coaxial stripline which is a component of the antenna element of FIGURE 17.
- FIGURE 1 is a diagrammatic fragmentary front view of an
apparatus 10 which includes anantenna element 12 and part of aradome 13. In the disclosed embodiment, theapparatus 10 is configured for use in a not-illustrated phased array antenna system. The antenna system includes a plurality of theantenna elements 12 arranged in a two-dimensional array of rows and columns, and includes a radome which extends over all the antenna elements, a portion of this radome being shown at 13 in FIGURE 1. - FIGURE 2 is a diagrammatic fragmentary rear view of the
apparatus 10, and FIGURE 3 is a diagrammatic sectional view taken along the section line 3-3 in FIGURE 1. As best seen in FIGURE 3, theantenna element 12 includes two adjacent andparallel layers dielectric layers thin layer 19 of bond film, which is of a type well known in the art. Thedielectric layers bond film 19 is approximately 2-3 mils thick. - FIGURE 4 is a diagrammatic fragmentary sectional front view of the
apparatus 10, taken along a central plane which extends between thedielectric layers bond film 19 omitted for clarity. Thedielectric layer 17 has on the front side thereof a first ground plane 26 (FIGURE 1), thedielectric layer 18 has on the rear side thereof a second ground plane 27 (FIGURE 2), and thedielectric layer 18 has on the front side thereof a third ground plane defined by threeseparate portions - The
ground planes ground planes - The
ground plane 26 has a recess etched through it, and this recess includes abalun portion 36 and aslot portion 37. Thebalun portion 36 of the recess is approximately rectangular, except that it has corners which are slightly rounded. It has alength dimension 38, and awidth dimension 39. In the disclosed embodiment, thelength dimension 38 is one-quarter of a wavelength of interest. The embodiment of FIGUREs 1-4 is optimized for use in a frequency range of approximately 1.8 GHz to 18 GHz, and thelength dimension 38 is approximately one-quarter of the wavelength of a center frequency of about 10 GHz. Thewidth dimension 39 in the disclosed embodiment is in the range of approximately one-quarter of this wavelength to approximately three-eighths of this wavelength. That is, thewidth dimension 39 is at least as large as thelength dimension 38, but is kept somewhat short of one-half wavelength in order to avoid potentially undesirable operational characteristics. - In general, it is desirable that the
width dimension 39 should be as large as possible within these stated constraints. As a practical matter, however, when the frequency of operation of a phased array antenna system progressively increases, the size of the array must progressively decrease, because the space available for each antenna element is approximately one-half of the wavelength of the highest frequency of operation. Thus, as the space available for eachantenna element 12 progressively decreases, the maximum amount of space available for thewidth dimension 39 of thebalun portion 36 also progressively decreases. Thus, in FIGURE 1, thewidth dimension 39 is about 5% longer than thelength dimension 38, but is not 50% to 70% longer, due to space limitations imposed by the operational frequency range of the antenna system. - Turning to the
slot portion 37 of the recess inground plane 26, theslot portion 37 has a narrow end which communicates with thebalun portion 36 along one of the linear sides of thebalun portion 36, at a location spaced from each end of that linear side. The opposite end of theslot portion 37 is significantly wider than the narrow end. The shapes of the edges of theslot portion 37 will be discussed in more detail with reference to FIGURE 5. - More specifically, FIGURE 5 is a graph showing the shape of one edge of the
slot portion 37, where the horizontal axis represents the centerline of the slot, from the end at thebalun portion 36 to the end at theradome 13. The vertical axis in FIGURE 5 represents the half-width of the slot, or in other words, the distance from the edge of the slot to the centerline. The edges of theslot portion 37 are mirror images of each other with respect to the centerline of the slot, and therefore only one of these edges is depicted in the graph of - It will be noted from FIGURE 5 that the edges of the
slot portion 37 do not follow a pure first-order exponential curve. Instead, the slot edges have a shape which has been carefully configured to minimize reflections and reduce return loss in a manner facilitating a wide bandwidth in excess of 10:1. The technique used to configure the shape of the slot edge is described in detail later. For the moment, it is sufficient to note certain characteristics of the specific shape shown in FIGURE 5 for theslot portion 37. More specifically, it can be seen that the narrowest part 41 of theslot portion 37 is not precisely at the end of the slot portion which opens into thebalun portion 36, but instead is spaced a small distance from this end. This narrow part 41 provides a region of increased capacitance. Also, toward the opposite end of theslot portion 37, there is asignificant discontinuity 42, which is discussed later. Further, each edge of theslot portion 37 is somewhat "wavy" in the section from thebalun portion 36 to thediscontinuity 42, which is not a random meandering, but instead is a carefully configured shape that reduces reflections and return loss in order to increase bandwidth and improve performance. - Roughly speaking, the curve shown in FIGURE 5 might be described as approximately a first-order exponential curve that has at least one higher-order characteristics superimposed on the first-order characteristic, and in fact the particular curve of FIGURE 5 has a number of higher-order characteristics superimposed on the first-order characteristic. In this regard, using well-known curve-fitting techniques, the specific curve shown in FIGURE 5 can be expressed in the form of the following equation, where the coefficients for the equation are set forth in Table 1.
TABLE 1 - COEFFICIENTS i a i 0 15.56616 1 3.540443 2 -0.2724377 3 8.41E-03 4 -1.46E-04 5 1.63E-06 6 -1.25E-08 7 6.95E-11 8 -2.88E-13 9 9.09E-16 10 -2.23E-18 11 4.27E-21 12 -6.46E-24 13 7.73E-27 14 -7.30E-30 15 5.41E-33 16 -3.11E-36 17 1.35E-39 18 -4.32E-43 19 9.54E-47 20 -1.30E-50 21 8.21E-55 - Referring again to FIGUREs 2 and 4, the
ground plane 27 has therethrough a recess which includes abalun portion 43 and aslot portion 44, and the ground plane 28 has therethrough a recess which includes abalun portion 46 and aslot portion 47. Theslot portions slot portions balun portions balun portions balun portions balun hole 49 of approximately rectangular shape, which extends completely through theantenna element 12. - FIGURE 6 is diagrammatic fragmentary perspective view showing a portion of the rear side of the
antenna element 12 in an enlarged scale. Thebalun opening 49 through theantenna element 12 is plated with an electrically conductive material, such that astrip 51 of this conductive material extends along the edges of the balun hole. The ends of thestrip 51 are spaced so as to define aslot 52 aligned with the narrow ends of theslot portions strip 51 extends between and is electrically coupled to the ground planes 26 and 27, and is also in electrical contact with theground plane 28A. - The
antenna element 12 also has its opposite side edges plated with an electrically conductive material, such thatrespective strips strip 53 is also in electrical contact with theground plane 28A along its entire length, and thestrip 54 is in electrical contact with each of the ground planes 28B and 28C. - The dielectric layers 17 and 18 have respective wedge-shaped
openings openings dielectric elements balun hole 49. The tapering sides of theopenings slot portions slot portions openings discontinuity 42 compensates to some extent for an impedance discontinuity caused within the dielectric material by the start of theopenings layer 19 of bond film (FIGURE 3) has a wedge-shaped opening through it which is identical in size and shape to theopenings openings - The ground plane 28 (FIGURE 4) has, in addition to the recess which includes the
balun portion 46 and theslot portion 47, afurther recess 66 which is an elongate channel that extends from an inner end of thedielectric layer 18 around thebalun portion 46, and opens into the narrow end of theslot portion 47. Thechannel 66 communicates along one side with thebalun portion 46, but it would alternatively be possible for a portion of thegroundplane 28A to extend between them. - An elongate
conductive strip 67 extends through thechannel 66, such that one end is disposed at the inner end of thedielectric layer 18 located at the left side of FIGURE 1, and the other end extends across the narrow end of theslot portion 47 and is shorted directly to theground plane 28A. Theconductive strip 67 and theground plane 28A are discussed herein as if they are physically separate parts, because they serve different operational functions in theantenna element 12. However, as a practical matter, theground plane 28A and theconductive strip 67 are just different integral portions of the same conductive layer. - With reference to FIGURE 1, an approximately semicircular cutout 71 is provided through the
ground plane 26 and thedielectric layer 17, in order to expose an end portion of theconductive strip 67, and an end portion of each of theportions strip 67 and theground plane portions conductive strip 67 of theantenna element 12 to antenna system circuitry which is known in the art and therefore not shown in the drawings. In the case of theantenna element 12 shown in FIGURE 1, the not-illustrated antenna system circuitry is electrically coupled to the arrangement of interconnected ground planes through direct engagement of a metal chassis of the antenna system with one or more of the outer ground planes 26-27 and the conductive strips 53-54. - The
conductive strip 67 serves as a conductive element of the type which is commonly referred in the art as a stripline, and carries signals that are being transmitted from or received by theantenna element 12. The direct connection between theground plane 28A and an end of thestripline 67 represents an electrical termination of that end of thestripline 67. Since thestripline 67 terminates directly into the groundplane 28, reactances are minimized where thestripline 67 extends across theslot portion 47, in comparison to pre-existing devices where the stripline is coupled by a via to a groundplane on the opposite side of a dielectric layer, or where the stripline terminates into some form of standalone termination structure designed to produce a standing wave resonance. - A plurality of vias extend through both of the
dielectric layers reference numerals slot portions stripline 67, and also help to reduce or eliminate the extent to which electromagnetic fields can form parallel plate and waveguide modes within the dielectric material. One of the illustrated vias is identified byreference numeral 79, and is slightly larger in diameter than the rest of the vias. The via 79 is disposed closely adjacent the point at which one end of thestripline 67 terminates directly into theground plane portion 28A, and serves to ensure that this end of thestripline 67 is directly and reliably terminated to not only the center groundplane 28, but also the two outer groundplanes 26-27. It will be noted that a respective row of the vias extends adjacent each edge of theslot portions - FIGURE 7 is a diagrammatic fragmentary perspective view of the outer end portion of the
apparatus 10, in an enlarged scale. As best seen in FIGURE 7, theradome 13 includes adielectric layer 91 which is fixedly coupled to an outer end of theantenna element 12 by abond film 92, asecond dielectric layer 93 which is fixedly coupled to thedielectric layer 91 by abond film 94, and athird dielectric layer 97 which is fixedly coupled to thedielectric layer 93 by abond film 98. Thebond films dielectric layer 97 is relatively thin, and serves primarily as a protective outer cover. - In the embodiment of FIGURE 7, the
dielectric layers dielectric layers antenna element 12. Further, thedielectric layers - In this regard, and with reference to FIGURE 4, when an electrical signal is applied to the left end of the
stripline 67, the signal travels through the stripline to its opposite end, where the stripline extends transversely across theslot portion 47. Here, the electrical signal generates an electromagnetic field around the stripline, which tends to try to travel in opposite directions within the "slotline" defined by theslot portions stripline 67 to an impedance of approximately 340 to 350 ohms at the wide outer end. Thestripline 67 and the not-illustrated antenna system circuitry to which it is coupled are matched, so as to provide a substantial uniform impedance of approximately 50 ohms from the circuitry through thestripline 67 to the slotline. Free space beyond the right end of theapparatus 10 has an impedance of approximately 377 ohms, for a two-dimensional square unit cell representing uniform spacing in both directions of the two-dimensional array ofantenna elements 12 within the phased array antenna system. The slotline effects an impedance transformation from a value of approximately 50 ohms at the left end, which is matched to the impedance of thestripline 67, to a value of approximately 360-370 ohms at the right end, which closely approaches the impedance of free space. - The use of three groundplanes 26-28 provides more conductive material along the edges of the slotline than in pre-existing arrangements that have only one or two groundplanes, which in turn provides increased capacitance within the slotline. The increased capacitance permits the narrow end of the slotline to be slightly wider than in pre-existing devices, while still achieving an impedance of 50 ohms which is matched to the impedance of the
stripline 67. To the extent that the narrower end of the slotline can be wider, fabrication of the ground planes 26-28 is easier, due to the fact that tolerances involved in the etching techniques for the groundplanes are fixed. - The wedge-shaped
openings dielectric layers bond film layer 19, help facilitate this impedance transformation, by reducing the amount of dielectric and bond film material disposed within the slotline at the right end thereof. Thus, at the right end of theantenna element 12, the impedance within the slotline will more closely approach the impedance of the free space located beyond the right end of theapparatus 10 than would be the case if theopenings openings - As mentioned above, the
balun hole 49 is designed so that the width dimension 39 (FIGURE 1) is as large as possible in the region where the slotline opens into thebalun hole 49, up to about three-eighths of a wavelength of interest. This is intended to provide the largest possible impedance discontinuity between thebalun hole 49 and the narrow end of the slotline. This large discontinuity is facilitated by the fact that the slotline opens into thebalun hole 49 through a side of thebalun hole 49 which is approximately linear, and at a location spaced from both ends of this linear side. - In the disclosed embodiment, the balun hole has an impedance of approximately 300 ohms, which represents a relatively large discontinuity in relation to the 50 ohm impedance of the adjacent end of the slotline. As noted above, electromagnetic fields generated by the
stripline 67 where it crosses the slotline will tend to want to travel in both directions along the slotline. However, the large impedance discontinuity between thebalun hole 49 and the left end of the slotline will cause the majority of this electromagnetic energy to travel rightwardly rather than leftwardly along the slotline, and to be transmitted into free space. To the extent that a small portion of the electromagnetic energy travels leftwardly, thebalun hole 49 has a length dimension which is approximately one-quarter wavelength (as discussed above), and this creates an open circuit standing wave which also tends to cause electromagnetic energy to travel rightwardly within the slotline. - As discussed earlier in association with FIGURE 6, the inner edge of the
balun hole 49 is plated with aconductive strip 51, except at the slotline. Thestrip 51 helps to keep electromagnetic fields present within thebalun hole 49 from entering the dielectric material oflayers strip 51 helps establish the standing wave or resonant condition with respect to electromagnetic energy within thebalun hole 49, which in turn helps to direct electromagnetic energy rightwardly within the slotline. In a sense, thebalun hole 49 is a tuned inductive hole, which can operate over a 10:1 bandwidth without electrical or structural adjustment. - In the disclosed embodiment, the
balun hole 49 does not have any dielectric material within it. Thus, thebalun hole 49 is filled with air, rather than dielectric material. For a given frequency, the wavelength of electromagnetic radiation is longer in air than it would be in dielectric material. Consequently, to the extent thebalun hole 49 is made as wide as possible in order to maximize the impedance discontinuity between the balun hole and the adjacent end of the slotline, a given width will be further below one-half wavelength when the balun hole is filled with air than would be the case if the balun hole was filled with dielectric material. - When electromagnetic radiation reaches the right end of the
antenna element 12, it passes through theradome 13 and is emitted into free space. As mentioned above, thedielectric layers radome 13 impart a degree of refraction to this electromagnetic radiation. This refraction occurs with respect to wavefronts transmitted or received by the antenna system that are oriented at an angle with respect to the antenna system boresight, which is parallel to the centerlines of the slot portions of the antenna elements. Wavefronts which are perpendicular to the antenna system boresight, and thus perpendicular to the centerlines of the slot portions in the antenna elements, are not subject to refraction, or in other words can be viewed as undergoing refraction of 0°. The following discussion of refraction assumes that the wavefronts involved are oriented at an angle to the antenna system boresight and the centerlines of the clot portions of the antenna elements. - In this regard, FIGURE 8 is a highly diagrammatic view of the
apparatus 10, including both theantenna element 12 and theradome 13.Arrow 111 represents electromagnetic radiation which is traveling outwardly through the slotline. As this radiation passes through the interface between theantenna element 12 and thedielectric layer 91, it is refracted to a degree, so that it travels in a slightly different direction, as indicated diagrammatically in FIGURE 8 by thearrow 112. Similarly, as this radiation passes through the interface betweendielectric layer 91 and dielectric 93, it experiences a further degree of refraction which further increases its angle, as indicated diagrammatically byarrow 113. Then, as this radiation passes through the interface betweendielectric layer 93 and free space, it is refracted a little further, so that it travels at a slightly greater angle, as indicated diagrammatically byarrow 114. This refraction within theradome 13 permits theapparatus 10 to operate more effectively over a wider scan angle, which in the disclosed embodiment approaches about 50° to 60°. In a sense, the refraction causes a portion of the radiation transmitted at each edge of the scan angle to have a higher effective power level than would be the case without such refraction. - The provision of the wedge-shaped
openings antenna element 12 permit the use of lower dielectric constants for thedielectric layers radome 13 than would otherwise be the case. This in turn reduces the extent to which electromagnetic energy is diverted into transverse surface waves within the dielectric layers, for example as indicated diagrammatically by abroken line arrow 117, which in turn reduces or avoids an effect that is sometimes referred to as scan blindness. - Although the foregoing discussion of refraction was presented in the context of transmitted radiation, persons skilled in the art will recognize that received radiation is also subject to refraction. In FIGURE 8, for example, reference numeral 121 diagrammatically represents radiation which is approaching the
antenna element 12 at an angle to the centerline of the slot portions in theantenna element 12. As this radiation passes through theradome 13 and enters theantenna element 12, the radiation is progressively refracted, as indicated diagrammatically byarrows antenna element 12 approximately parallel to the centerline. - FIGURE 9 is a graph showing return loss as a function of frequency for the embodiment of FIGUREs 1-8, for what is known in the art as E-plane scan. Since return loss is a standard way of expressing the amount of reflection, it is desirable that return loss be as low as possible. It will be noted that the
apparatus 10 provides a return loss which is continuously below -10dB for a scan width of 60° across a bandwidth from approximately 1.8 GHz to approximately 17.5 GHz. Persons skilled in the art will recognize that, expressed according to another industry standard, the embodiment of FIGUREs 1-8 provides a bandwidth of at least 10:1 for -9.5dB (VSWR less than 2). - FIGURE 10 is a graph similar to FIGURE 9, but showing return loss for what is commonly known in the art as H-plane scan. FIGURE 10 shows that the
apparatus 10 provides a return loss of -10dB across a scan width of 45° to 50° from a frequency of about 3.5 GHz to a frequency in excess of 18 GHz. - Although the foregoing discussion has been presented primarily in the context of signals that are being transmitted by the
apparatus 10 of FIGURE 1, theapparatus 10 is equally suitable for use in receiving electromagnetic signals. Persons skilled in the art will understand from the foregoing discussion of signal transmission how theapparatus 10 would function for purposes of signal reception. - Advantageous performance characteristics, such as those reflected by FIGUREs 9 and 10, are due in part to the shape determined for the edges of the
slot portions antenna element 12. An explanation will now be provided of how the shape for the edges of the slot portions is determined. - In this regard, and with reference to FIGUREs 1 and 4, the
apparatus 10 is conceptually broken into three functional sections for purposes of carrying out an analysis which determines an optimum shape for the edges of the slot portions. More specifically, one functional section is referred to as the balun, and corresponds roughly to thebalun hole 49 and theconductive stripline 67. The next functional section is referred to as the slot, and corresponds roughly to the part of the slot portion which extends from thebalun hole 49 to thediscontinuity 42 at the left end of the wedge-shapedopenings functional section 203 is referred to as the end piece, and corresponds roughly to the part of theapparatus 10 located to the right of thediscontinuity 42, in particular from the left end of the wedge-shaped openings 57-58 to the right side of theouter dielectric layer 97. - FIGURE 11 is a diagram showing three blocks 201-203, which respectively represent the three functional sections discussed above, namely the balun, slot and end piece sections. Collectively, blocks 201-203 represent the
apparatus 10 of FIGURE 1, as indicated diagrammatically by a broken line in FIGURE 11. Each of the blocks 201-203 is depicted as a two-port element, including one port with two terminals on the left side, and another port with two terminals on the right side. Adjacent ports of the adjacent blocks are coupled to each other. Theend piece 203 has the port on the right side coupled to afurther block 208, which diagrammatically represents the impedance of the free space disposed beyond the right end of theapparatus 10 in FIGURE 1. - As is known in the art, two-port blocks such as those depicted at 201-203 can each be represented by what is commonly referred to as an [ABCD] matrix. For example, focusing on the
block 202 in FIGURE 11, which represents the slot, the left port has a voltage VX and current IX and the right port has a voltage VY and current IY. The relationship between these ports can be expressed by the following equation, where the subscript "S" identifies the slot section: - Similarly, and still referring to FIGURE 11, the overall transfer function for the
apparatus 10 can be represented by a single [ABCD] matrix, as follows:
where
and where the subscripts "APP", "B", "S" and "EP" respectively refer to theapparatus 10, thebalun section 201, theslot section 202, and theend piece section 203. - Before attempting to determine an optimum shape for the edges of the slot, the balun and end piece (which correspond to
blocks 201 and 203) are designed so as to achieve appropriate design goals. For example, as discussed above, the balun hole 49 (FIGURE 1) has various aspects, such as shape, size and the absence of dielectric material, which are intended to achieve the design goal of a large impedance discontinuity between the balun hole and slotline, which in turn supports a wide bandwidth for theantenna element 12. Possible design configurations for both the balun and end piece can be rigorously analyzed with an existing software program to determine expected operational characteristics. One suitable software program for this task is available under the tradename High Frequency Structure Simulator (HFSS), and can be commercially obtained from Ansoft Corporation of Pittsburgh, Pennsylvania. - Once the physical design of the balun section and the end piece section have been completed, several appropriate [ABCD] matrixes are determined for each. In this regard, the
apparatus 10 is designed for use across a frequency range of interest. The operational characteristics of the balun section will be different at different frequencies, and the operational characteristics of the end piece section will be different at different frequencies. Accordingly, several predetermined frequencies are selected, which are spread throughout the frequency range of interest. Then, a respective different [ABCD] matrix is determined for thebalun section 201 for each selected frequency, and a respective different [ABCD] matrix is determined for theend piece section 203 for each such frequency. - Appropriate techniques for determining an [ABCD] matrix from a physical design are known in the art. As one example, parameters representing the physical design can be provided to a known software program, which can then calculate a form of transfer function known in the art as an [S] matrix. The HFSS computer program mentioned above is suitable for this task. Thereafter, the [S] matrix can be converted into a corresponding [ABCD] matrix, using known mathematical techniques.
- Turning to the
slot section 202 of FIGURE 11, one aspect of the present invention is the provision of a technique where the portion of the slotline corresponding to theblock 202 is represented by a model which is a transmission line having the same size and shape as the slot, the transmission line being in the form of a number of contiguous transmission line segments. For example, FIGURE 12 is a diagrammatic view of a model which is atransmission line 241, made up of a plurality of N contiguous rectangular segments SEG1, SEG2, SEG3,... SEGN. In FIGURE 12 there are 40 segments, and thus N = 40. The centerline of the slot is indicated diagrammatically at 243, and the outer ends of the N segments collectively represent the edges of the slot. The segments all have same length in a direction parallel to thecenterline 243, but have a variety of different widths in a direction transverse to thecenterline 243. The segments in FIGURE 12 do not necessarily represent the precise slot shape shown in FIGURE 5, but instead can be considered representative of one of a number of different shapes that are evaluated to determine which shape should serve as the optimum shape shown in - In order to determine an optimum shape for the edges of the slot, the common length value for all of the segments SEG1 through SEGN and also the N respective width values are varied selectively and independently, and the performance of the
apparatus 10 is evaluated for each such configuration of the segmented transmission line, in a manner explained in more detail below. It should be noted that the number N of segments is not varied. Consequently, to the extent that the common length value for the segments is varied, the overall length of the segmented transmission line, and thus the overall length of the slot it represents, will vary. Thus, part of what is optimized is the length of the slot itself. - Since the common length and the respective widths of the N segments are varied independently, the optimization process becomes progressively more complex and time consuming if the value of N is increased. As a result, competing considerations are involved in the selection of the value of N. In particular, it is desirable on one hand to have a relatively large value of N so that the ends of the segments provide good resolution in the definition of the slot edges. On the other hand, it is desirable to have a relatively small value of N in order to reduce the computational complexity involved in evaluating different configurations of the segmented transmission line model. For an antenna element of the type disclosed at 12 in the embodiment of FIGUREs 1-8, it has been found that a value of N in the range of approximately 40 to 60 provides a good balance between these two competing considerations.
- Various existing techniques are known for effecting the independent variation of a number of parameters in a selective manner so as to optimize a specified characteristic. One such technique is commonly known in the art as the Nelder-Mead technique. There are commercially available software programs which implement the Nelder-Mead technique, one example of which is the program MATLAB® available from The MathWorks of Natick, Massachusetts. Programs of this type provide generic Nelder-Mead capability, and can be provided with input data for a specific application which cause the program to apply the generic principles to that specific application. Since Nelder-Mead techniques are known in the art, they are not described in detail here. Instead, to facilitate an understanding of the present invention, a brief overview is provided.
- In particular, a program which implements Nelder-Mead techniques is capable of varying multiple parameters in an intelligent manner according to Nelder-Mead principles, while evaluating a characteristic which is to be optimized. Generally speaking, configurations of parameters which tend to improve the specified characteristic are favored over configurations which do not improve the characteristic, and the favored configurations are used to predict other new configurations that may possibly provide even greater improvement in the specified characteristic.
- In the context of the present invention, an initial slot shape is selected, for example where the edges of the slot simply follow a first-order exponential curve. Then, a segmented transmission line model of the type shown in FIGURE 12 is used to model this initial slot shape, using N segments where N is roughly 40 to 60. The respective widths of the segments and also the common length of the segments are then independently varied using Nelder-Mead techniques in order to come up with a plurality of different configurations of the segmented transmission line, which each represent a different slot shape. For each such configuration, performance of that configuration is evaluated.
- In this regard, in order to evaluate performance, the number of segments in the model is tripled through interpolation. For example, FIGURE 13 is a diagrammatic view, in an enlarged scale, of the end portions of four of the transmission line segments shown in the upper right portion of FIGURE 12. The solid lines in FIGURE 13 correspond directly to the segments which are shown in FIGURE 12. The broken lines in FIGURE 13 show how the overall number of line segments is tripled from N to 3N. For example, two
points points - For a given configuration of 3N segments, for example as represented by broken lines in FIGURE 13, the performance of the system is evaluated in the following manner. Each of the 3N segments is treated as a separate transmission line. With reference to FIGURE 14, a theoretical transmission line has a length ℓ, which corresponds to the uniform dimension of each of the 3N segments in a direction parallel to the centerline 243 (FIGURE 12) of the slot. Further, the theoretical transmission line in FIGURE 14 has an impedance ZSEG and, in the case of each of the 3N segments shown in FIGURE 13, this impedance depends on one or more different factors. First, it depends on the width of the segment in a direction transverse to the
centerline 243. Further, and with reference to theapparatus 10 shown in FIGURE 1, it depends on whether there is material within the slot and, if so, the characteristics of that material. - For example, the embodiment of FIGURE 1 has portions of the
dielectric layers dielectric layers - As evident from FIGURE 14, the theoretical transmission line can be modeled as a two-port element of the type discussed earlier, and its characteristics can thus can be represented by an [ABCD] matrix. In the case of one of the 3N rectangular segments shown in FIGURE 14, the [ABCD] matrix for a particular lossless ideal segment would be defined as follows:
where - In these equations, it should be noted that the value of the wavelength λ can vary not only as a function of frequency, but also as function of the type of material present within the slot. For example, for a given frequency, the wavelength will be one value if there is dielectric material within the slot (as is the case in the embodiment of FIGURE 1), but will be a different value if the slot contains air rather than dielectric material.
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-
-
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-
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- As mentioned above, the
antenna element 12 of FIGURE 1 is coupled to a not-illustrated antenna system, for example through a cable. The antenna system supplies electrical signals to and from the input port at the left side of FIGURE 11. Assume that Z0 represents the characteristic impedance of the not-illustrated cable and other circuitry of the antenna system. It is customary in the art to design this circuitry and cable so that the impedances are all matched, to thereby provide a line of effectively constant impedance with no reflection. In the disclosed embodiment, this characteristic impedance Z0 has a value of 50 ohms. -
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- The performance evaluation procedure discussed above is specific to a particular frequency. For a given slot shape, this evaluation needs to be carried out separately for each of a number of different frequencies spread across a frequency range of interest. This will result in a number of different values of return loss RL calculated for that particular slot shape at respective different frequencies, and these values of return loss RL can then be presented in the form of graph similar to FIGUREs 9 and 10.
- Further, the foregoing discussion has focused on how to evaluate one proposed slot shape. In order to come up with an optimum shape, a number of different slot shapes need to be evaluated in a similar manner, and the results of these evaluations are then compared in order to determine which slot shape provides the optimum performance. Various different criteria can be used to make this evaluation, and these criteria may be used either separately or in combination. Some examples of such criteria will now be discussed, but it should be recognized that the present invention is not limited to these particular criteria.
- A first criteria involves a determination of the maximum value of return loss RL calculated for a given slot shape. The slot shape having the lowest maximum value of RL could be selected as the optimum design. Alternatively, all evaluated slot shapes with a maximum value of return loss RL lower than a specified value (such as -10dB) could be identified, and the shapes in this group could then be comparatively evaluated using other criteria.
- A second criteria would be to determine the maximum value, for each slot shape, of the absolute value of the calculated reflection R. The slot design with the lowest such maximum value could be selected as the optimum design. Alternatively, all evaluated slot shapes for which this calculated maximum value is less than a specified value could be selected, and the slot shapes in this group could then be comparatively evaluated using other criteria.
- The two criteria discussed above tend to focus on any single point maximum for the reflection R or the return loss RL. Other criteria could take more of an averaging approach to performance, across the frequency range of interest. For example, a third criteria would be to sum the absolute values of reflection R calculated at various frequencies for a given slot design, as follows:
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- FIGURE 15 is a flowchart, which summaries the optimization technique discussed above. More specifically, in
block 301, the designs of the balun and end piece are each optimized and finalized. Then, transfer functions are determined for each of the balun and end piece at each of a plurality of predetermined frequencies spread across a frequency range of interest. As discussed above, each of these transfer functions can be represented in the form of an [ABCD] matrix. - Next, at
block 302, an initial slot shape is selected in order to "seed" the optimization routine. In the disclosed embodiment, the initial slot shape is selected to be a pure first-order exponential curve, but it would alternatively be possible to use some other initial slot shape. Next, atblock 303, the selected slot shape is modeled as a segmented transmission line, in the manner discussed above in association with FIGUREs 12 and 13. Then, atblock 306, the lowest of the predetermined frequencies in the range is selected. - Next, at
block 307, a respective transfer function is determined at the selected frequency for each of the segments of the segmented transmission line. In the disclosed embodiment, each such transfer function can be in the form of an [ABCD] matrix, as discussed above. These various transfer functions for the different segments are then combined to obtain a single transfer function for the entire segmented transmission line. In the disclosed embodiment, this is also an [ABCD] matrix, as discussed above. - Control then proceeds from
block 307 to block 308. For the current slot shape and the selected frequency, the transfer functions for the balun section, slot section and end piece section are used to calculate and save a reflection value and a return loss value, in a manner discussed previously. Then, atblock 311, a determination is made of whether the currently selected frequency is the highest frequency in the range. If not, the next highest of the predetermined frequencies is selected atblock 312, and control returns to block 307 to analyze the performance of the current slot design at this newly-selected frequency. - In contrast, if it is determined at
block 311 that the current slot shape has been evaluated for all predetermined frequencies in the range, control proceeds to block 313, where all of the reflection values and return loss values for the current slot shape are used to evaluate the performance of the system for that slot shape. These evaluations are then saved. - Next, at
block 316, an evaluation is made of whether the optimum shape has been found. This determination involves use of performance criteria of the type discussed above. Further, it depends on the extent to which the Nelder-Mead techniques discussed above have reached a point where a variety of different slot shapes have been evaluated and it appears that the optimum shape is likely to be a shape that has already been evaluated, rather than a shape that has yet been evaluated. In general, a number of slot shapes will be evaluated before a decision is made atblock 316 that the optimum slot shape has been identified. - When a determination is made in
block 316 that an optimum slot shape has not yet been located, control proceeds to block 317, where a new and different slot shape is selected for evaluation, through variation of the widths of the N segments and/or the common length of the N segments. Theblocks block 316 that an optimum slot shape has been determined, the evaluation process is finished, and ends atblock 318. - FIGURE 16 is a diagrammatic front view of an
antenna element 412 which is alternative embodiment of theantenna element 12 of FIGURE 1. Theantenna element 412 of FIGURE 16 would normally be used with a radome of the type shown at 13 in FIGURE 1, but the radome is omitted from FIGURE 16. Theantenna element 412 of FIGURE 16 is substantially identical to theantenna element 12 of FIGURE 1, except for the differences which are discussed below. - More specifically, the two dielectric layers and the bond film of the
antenna element 412 each extend outwardly beyond the ends of the three ground planes, one of the dielectric layers being visible at 417, and one of the ground planes being visible at 426. The upper and lower side edges of theantenna element 412 each have plating which extends from the left end of the antenna element to the right ends of the ground planes. This edge plating does not extend the rest of the way to the right end of theantenna element 412. - The dielectric layers each have a wedge-shaped opening therein, one of which is visible at 457. It will be noted that the left end of each wedge-shaped opening is located rightwardly of the right ends of the ground planes, including the
ground plane 426. In other words, the wedge-shaped openings in the dielectric layers are not disposed within the slotline defined by the slots in the ground planes. Consequently, the edges of the slot portions in theantenna element 412 do not have a discontinuity comparable to that shown at 42 in FIGURE 1, because thediscontinuity 42 is due to the fact that the wedge-shapedopening 57 in FIGURE 1 is disposed within the slotline. - Although it is not readily visible in FIGURE 16, the edges of the slot portions of the ground planes do not follow a first-order exponential curve, but instead have higher-order effects which give them a somewhat wavy shape, in a manner similar to that described above in association with the embodiment of FIGURE 1. The procedure used to determine the shape of the slot edges for the embodiment of FIGURE 16 is similar to the procedure described above for the embodiment of FIGURE 1, and is therefore not described again in detail here. Further, the operation of the embodiment of FIGURE 16 is similar to the operation of the embodiment of FIGURE 1, and is therefore not explained again in detail here.
- FIGURE 17 is a diagrammatic perspective view of an
antenna element 512 which is a further alternative embodiment of theantenna element 12 of FIGURE 1. Theantenna element 512 includes abody 514 which is made from a single metal plate. A recess is provided through the metal plate, and includes abalun portion 536 in the shape of a rectangular hole, and anelongate slot portion 537 which communicates at its narrow end with thebalun portion 536. In general, thebalun portion 536 and theslot portion 537 have sizes and shapes that are comparable to those discussed above in association with the embodiment of FIGURE 1. In this regard, the edges of theslot portion 537 do not follow merely a first-order exponential curve, but instead include higher-order effects which give the edges a somewhat wavy shape. The shape of the edges is determined by a procedure similar to that discussed above in association with the embodiment of FIGURE 1, and this procedure is not described again in detail here. - One significant difference is that the
slot portion 537 contains air rather than a dielectric material. The effects of having air in the slot portion, rather than a dielectric material, have already been discussed above in detail. Theantenna element 512 includes acoaxial stripline 561, which has an electrically conductive exterior sheath that is fixedly secured to the front of theplate 514 by a conductive epoxy adhesive of a known type. - FIGURE 18 is a diagrammatic sectional view of the
coaxial stripline 561, taken along the section line 18-18 in FIGURE 17. As shown in FIGURE 18, thecoaxial stripline 561 includes two adjacentdielectric layers conductive stripline 567 disposed between them. Along most of its length, thestripline 567 has a width which is substantially less than the width of thedielectric layers dielectric layers stripline 567. - A
sheath 569 of an electrically conductive material extends completely around thedielectric layers sheath 569 is physically and electrically coupled to themetal plate 514 in FIGURE 17 by a conductive epoxy adhesive of a known type, which is not separately shown in the drawings. - FIGURE 19 is a diagrammatic fragmentary sectional top view of the
coaxial stripline 561, taken along a plane defined by the top surface of thestripline 567, and showing an end portion of thecoaxial stripline 561 which is located in the region of the narrow end of the slot portion 537 (FIGURE 17). With reference to FIGUREs 17 and 19, theconductive sheath 569 has anannular gap 572 which extends completely around thecoaxial stripline 561. Thegap 572 is aligned with theslot portion 537, and permits current within thestripline 567 to generate electromagnetic fields that can escape thesheath 569 and extend into theslot portion 537. - Approximately halfway across the
gap 572, thestripline 567 begins expanding progressively in width, which serves as a transition to an approximatelyrectangular end portion 573, three sides of which electrically engage thesheath 569. A via at 574 extends through the conductive stripline between opposite sides of thesheath 569, and is electrically coupled to theend portion 573 of thestripline 567. Thus, in effect, the end of thestripline 567 is shorted directly to a ground plane defined by the metal plate 514 (FIGURE 17), in order to effect electrical termination of thestripline 567. - One technique for fabricating the
coaxial stripline 561 is as follows. Thedielectric material 564 is fabricated, and then a layer of metal is deposited on top of it. The metal layer is then photolithographically etched in a known manner, in order to remove selected portions of it, such that the remaining portions define thestripline 567 with itsend portion 573. Then, thedielectric layer 563 is formed over thedielectric layer 564 and thestripline 567. Next, a cylindrical hole is created through the dielectric layers and the metal layer, at a location where the via 574 is to be formed. Then, this arrangement is immersed in an electroless plating tank, in order to form thesheath 569 over the entire exterior thereof, and in order to form the via 574 within the cylindrical hole. The annular mask prevents conductive material from being plated within the region of thegap 572. After the plating is completed, the mask is removed in order to expose thegap 572. The resulting assembly is then secured to themetal plate 514, using a conductive epoxy adhesive, as discussed above. - The operation of the
antenna element 512 of FIGUREs 17-19 is generally similar to that of theantenna element 12 of FIGURE 1. Therefore, a separate detailed discussion of the operation of theantenna element 512 is believed to be unnecessary, and is omitted here. - The present invention provides a number of technical advantages. One such technical advantage results from the absence of dielectric material in the balun hole, such that the hole contains air. Since air has a lower dielectric constant than dielectric material, air has a higher impedance than a dielectric material, and the wavelength of a given frequency is longer in air than in a dielectric material. Consequently, for a given physical width of the balun hole, the effective electrical width is smaller for air than for a dielectric material. This in turn means that the effective electrical width is farther below 8/2 for air than for a dielectric material, which reduces undesirable effects. A further advantage results where the inner edge of the balun hole is conductive, for example due to the provision of plating, because it helps to increase the bandwidth of the balun hole by containing electrical fields to the hole. In the case of an antenna element with layers of a dielectric material, the conductive edge of the hole prevents electric fields from extending into the dielectric material around the hole.
- Still another advantage is realized where the balun hole has a generally rectangular shape, because it helps to create an abrupt impedance discontinuity between the balun hole and the associated end of the slotline. With an abrupt discontinuity in impedance, electric fields in the region of the narrow end of the slot see the balun hole as approximately an open circuit across a frequency range of interest, which gives the balun hole a relatively wide bandwidth. A related advantage is realized where dielectric material is omitted within the rectangular balun hole, and the edge of the balun hole is conductive, because the bandwidth of the balun hole is further enhanced. The resulting balun hole is effectively a tuned conductive hole.
- Still another advantage results from the provision of more than two ground planes, and the termination of the stripline directly into one of these ground planes, because this facilitates a relatively wide bandwidth for the balun hole. Where the balun hole is approximately rectangular, contains no dielectric material, has conductive edges, is associated with two or more ground planes, and is associated with a stripline termination into a ground plane, the standalone bandwidth of the balun hole can approach about 8:1.
- Still another advantage involving increased bandwidth results where such a balun hole is used with a slot having a shape that has been optimized using techniques according to the invention. At low frequencies, the balun hole is inductive and the slot is capacitive. But where the optimization technique is used to achieve conjugate matching of the balun hole and slot, they cooperate to provide good performance even at low frequencies, in a manner somewhat analogous to resonance in a tuned RLC circuit. In particular, they can provide a decade (10:1) bandwidth capable of a ±60° E-plane and ±50° H-plane scan volume.
- The provision of three or more ground planes can also provide another advantage, by helping to minimize reactances at the stripline to slotline transition. Further, providing three or more ground planes increases the amount of conductive material present along the edges of the slot, thereby increasing capacitance, which in turn allows the narrow end of the slot be wider. Where the narrow end of the slot is wider, it is easier to fabricate the slot while still achieving a low impedance of approximately 50 ohms for the narrow end of the slot. This is because the tolerances for etching are basically fixed, and etching the narrow end of the slot is progressively increased.
- Still another advantage results where the stripline terminated directly into one of the ground planes, because this effectively provides an actual physical short circuit to a ground plane, in comparison to pre-existing techniques that essentially seek to emulate or approximate a physical short circuit by creating a standing wave resonance. The disclosed antenna elements provide a stripline to slotline transition with a transformer ratio that is close to unity, and with minimal stray reactances.
Claims (34)
- An antenna element (12) having a dielectric layer (18), an electrically conductive layer (28), and an elongate conductive element (67), wherein :the dielectric layer (18) has a hole (49) therethrough;the electrically conductive layer (28) is disposed adjacent one surface of said dielectric layer (18), said conductive layer (28) having a recess etched therein which includes a balun portion (46) and a tapered slot portion (37), said slot portion (47) having a narrow end communicating with said balun portion (46), and said balun portion (46) being aligned with said hole (49) through said dielectric layer (18); andthe elongate conductive element (67) being directly connected to and in the same plane as said conductive layer (28), said conductive layer (28) extending generally transversely with respect to said slot portion (47) in the region of said narrow end thereof , wherein said hole (49) through said dielectric layer (18) has substantially the same size and shape as said balun portion (46) of said recess in said conductive layer (28), the element including a further conductive layer (27) which has therein a further recess, said further recess including a further balun portion (43) and including a further slot portion (44) which communicates at one end with said further balun portion (43), said slot portions (44, 47) of said recesses being of similar size and shape and being substantially aligned with each other, and said further balun portion (43) having substantially the same size and shape as, and being aligned with, said hole (49) through said dielectric layer (18).
- An antenna element (12) according to Claim 1, including a conductive strip (51) which extends along an edge of said hole (49) in said dielectric layer (18), except in the region of said slot portions (44, 47), and which is in electrical contact with each of said conductive layers (27, 28).
- An antenna element (12) according to Claim 1,
including two further conductive layers (26, 27), said conductive layers (26, 27) all being substantially parallel to each other;
including a further dielectric layer (17), said dielectric layers (17, 18) being substantially parallel to each other and to said conductive layers (26, 27, 28), and each said dielectric layer (17, 18) being disposed between a respective pair of said conductive layers (26/28, 27/28);
wherein said further dielectric layer (17) has therethrough a hole (49), said holes (49) through said dielectric layers (17, 18) being of substantially the same size and shape, and being aligned with each other; and
wherein said further conductive layers (26, 27) each have therein a further recess, each said further recess including a further balun portion (36, 43) and including a further slot portion (37, 44) which communicates at one end with said further balun portion (36, 43) thereof, said slot portions (37, 43, 47) in each of said conductive layers (26, 27, 28) being of similar size and shape and being substantially aligned with each other, and said balun portions (36, 43, 46) in each of said conductive layers (26, 27, 28) being of similar size and shape and being aligned with each other and with said holes (49) through said dielectric layers (17, 18). - An antenna element (12) according to Claim 3, including a conductive strip (51) which extends along edges of said holes (49) in said dielectric layers (17, 18), except in the region of said slot portions (37, 44, 47) of said conductive layers (26, 27, 28), and which is in electrical contact with each of said conductive layers (26, 27, 28).
- An antenna element (12) according to Claim 1, wherein said slot portion (47) has edges on opposite sides thereof which each follow a predetermined curve other than a first-order exponential curve.
- An antenna element (12) according to Claim 5, wherein said predetermined curve for each said edge is configured to facilitate minimization of return loss for electromagnetic signals induced within said slot portion (47) through said elongate conductive element (67).
- An antenna element (12) according to Claim 1,
wherein said balun portion (46) has a shape which facilitates a large and abrupt discontinuity in impedance between said slot portion (47) and said balun portion (46), said shape of said balun portion (46) including said balun portion (46) having an approximately straight side, said one end of said slot portion (47) communicating with said balun portion (46) at a location between the ends of said straight side of said balun portion (46). - An antenna element (12) according to Claim 7, wherein said balun portion (46) has a shape which is approximately rectangular.
- An antenna element (12) according to Claim 8,
wherein said balun portion (46) has in a first direction generally parallel to said one end of said slot portion (47) a dimension which is approximately one-quarter of a selected wavelength, and has in a second direction substantially perpendicular to said first direction a second dimension which is at least one-quarter of said selected wavelength and which is less than one-half of said selected wavelength. - An antenna element (12) according to Claim 7,
wherein said slot portion (47) has edges on opposite sides thereof which each follow a predetermined curve other than a first-order exponential curve. - An antenna element according to Claim 10,
wherein said predetermined curve for each said edge is configured to facilitate minimization of return loss for electromagnetic signals induced within said slot portion (47) through said elongate conductive element (67). - An antenna element (12) according to Claim 1,
wherein the dielectric layer (18) is a first dielectric layer (18) of a pair of first and second dielectric layers (17, 18) which extend approximately parallel to each other;
wherein the conductive layer (28) is a first conductive layer (28) of a set of first, second, and third conductive layers (28, 27, 26) which extend approximately parallel to each other and to said first and second dielectric layers (17, 18), said first dielectric layer (18) being located between said first and second conductive layers (28, 27), and said second dielectric layer (17) being located between said first and third dielectric layers (28, 26), said first, second, and third conductive layers (28, 27, 26) each having therein a recess which includes a balun portion (36, 43, 46) and a slot portion (37, 44, 47) communicating at one end with the balun portion (36, 43, 46) thereof, said slot portions (37, 44, 47) in each of said first, second, and third conductive layers u(28, 27, 26) being of similar size and shape and being substantially aligned with each other, and said balun portions (36, 43, 46) in each of said first, second, and third conductive layers (28, 27, 26) being of similar size and shape and being aligned with each other;
a plurality of conductive vias (76, 77, 78) which extend through openings in said first and second dielectric layers (17, 18) to electrically couple said first, second, and third conductive layers u(28, 27, 26) to each other. - An antenna element (12) according to Claim 12,
wherein said elongate conductive element (67) is provided between said first and second dielectric layers (17, 18), and has an end portion which extends across said slot portion (47) of said first conductive layer (28) and is directly electrically connected to said first conductive layer (28) at said one end of said slot portion (47) therein. - An antenna element (12) according to Claim 13,
wherein said first conductive layer (28) has an elongate further recess therein which communicates at one end with said slot portion (47), and wherein said elongate conductive element (67) extends through said further recess. - An antenna element (12) according to Claim 5,
wherein said predetermined curve for each said edge is configured as a function of characteristics of said balun portion (46) and said slot portion (47) to facilitate minimization of return loss for electromagnetic signals induced within said slot portion (47) by said conductive element (67). - An antenna element (12) according to Claim 5,
including further structure disposed adjacent an end of said slot portion (47) remote from said one end thereof; and
wherein said predetermined curve is configured as a function of characteristics of said balun portion (46), said slot portion (47), and said further structure to facilitate minimization of return loss for electromagnetic signals induced within said slot portion (47) by said conductive element (67). - An antenna element (12) according to Claim 5,
wherein said predetermined curve includes first and second exponential characteristics involving respective different exponential powers. - An antenna element (12) according to Claim 5,
wherein said predetermined curve includes a plurality of exponential characteristics involving respective different exponential powers. - An antenna element (12) according to Claim 5,
wherein said conductive layer (28) includes two electrically conductive layers (28, 27) disposed on opposite sides of said dielectric layer (18), said conductive layers (28, 27) having respective recesses therein which are aligned with each other and which each include a balun hole (49) that is part of said balun portion (46, 43) and a slot that is part of said slot portion (47, 44); and
wherein said conductive layers (28, 27) include a plurality of vias (76, 77, 78) which each extend between said conductive layers (28, 27) through said dielectric layer (18), said vias (76, 77, 78) being disposed near each edge of each said slot portion (47, 44) at spaced locations therealong. - An antenna element (12) of Claim 1, wherein said slot portion (47) has a width which is narrowest in a first section of said slot portion (47) located near said one end thereof, said slot portion (47) having second and third sections which are disposed on opposite sides of said first section and which each have a width larger than the width of said first section.
- An antenna element (12) according to Claim 1, further comprising:a refracting layer (91) extending approximately perpendicular to a centerline of said slot portion (47) at a location beyond said further end of said slot portion (47), said refracting layer (91) being made of a material which is transmissive to and effects refraction of electromagnetic signals in a selected frequency range that travel in one of two opposite directions along said slot portion (47).
- An antenna element (12) according to Claim 21, including a further layer (93) which extends approximately perpendicular to said centerline of said slot portion (47) and which is disposed adjacent said refracting layer (91) on a side thereof remote from said slot portion (47), said further layer (93) being made of a material which is transmissive to and effects refraction of the electromagnetic signals in said selected frequency range which are traveling in one of said two opposite directions along said slot portion (47).
- An antenna element (12) according to Claim 22, wherein said refracting and further layers (91, 93) are respective portions of a radome (13).
- An antenna element (12) according to Claim 21, wherein said refracting and further layers (91, 93) have dielectric constants which are different.
- A method, comprising the steps of:creating a hole (49) through a dielectric layer (18);fabricating an electrically conductive layer (28) adjacent one surface of said dielectric layer (18), said conductive layer (28) haying a recess etched therein which includes a balun portion (46) and a slot tapered portion (47), said slot portion (47) having a narrow end communicating with said balun portion (46), and said balun portion (46) being aligned with said hole (49) through said dielectric layer (18); andforming an elongate conductive element (67) in direct contact with and in the same plane as said conductive layer (28) said elongate conductive element (67) extending generally transversely with respect to said slot portion (47) in the region of said narrow end wherein said creating step is carried out so that said hole (49) through said dielectric layer (18) has substantially the same size and shape as said balun portion (46) of said recess in said conductive layer (28), the method including the step of fabricating a further conductive layer (27) which has therein a further recess, said further recess including a further balun portion (43) and including a further slot portion (44) which communicates at one end with said further balun portion (43), said slot portions (44, 47) of said recesses being of similar size and shape and being substantially aligned with each other, and said further balun portion (43) having substantially the same size and shape as, and being aligned with, said hole (49) through said dielectric layer (18).
- A method according to Claim 25, including the step of fabricating a conductive strip (51) which extends along an edge of said hole (49) in said dielectric layer (18), except in the region of said slot portions (44, 47), and which is in electrical contact with each of said conductive layers (28, 27).
- A method according to Claim 25, wherein said balun portion (46) is formed with a shape which facilitates a large and abrupt discontinuity in impedance between said slot portion (47) and said balun portion (46), said shape of said balun portion (46) including said balun portion (46) having an approximately straight side, said one end of said slot portion (47) communicating with said balun portion (46) at a location between the ends of said straight side of said balun portion (46).
- A method according to Claim 27, wherein creating step is carried out in a manner so that said balun portion (46) has a shape which is approximately rectangular.
- A method according to Claim 28, wherein said creating step is carried out so that said balun portion (46) has in a first direction generally parallel to said one end of said slot portion (47) a dimension which is approximately one-quarter of a selected wavelength, and has in a second direction substantially perpendicular to said first direction a second dimension which is at least one-quarter of said selected wavelength and which is less than one-half of said selected wavelength.
- A method according to Claim 25, further comprising:providing the dielectric layer (18) as first and second dielectric layers (18, 17) which extend approximately parallel to each other;fabricating the conductive layer (28) as first, second, and third conductive layers (28, 27, 26) which extend approximately parallel to each other and to said first and second dielectric layers (18, 17), said first dielectric layer (18) being located between said first and second conductive layers (28, 27), and said second dielectric layer (17) being located between said first and third dielectric layers;forming in each of said first, second, and third conductive layers (28, 27, 26) a respective recess which includes a balun portion (46, 43, 36) and a slot portion (47, 44, 37) communicating at one end with the balun portion (46, 43, 36) thereof, said slot portions (47, 44, 37) in each of said first, second, and third conductive layers (28, 27, 26) being of similar size and shape and being substantially aligned with each other, and said balun portions (46, 43, 36) in each of said first, second, and third conductive layers (28, 27, 26) being of similar size and shape and being aligned with each other;forming a plurality of conductive vias (76, 77, 78) which extend through openings in said first and second dielectric layers (18, 17) to electrically couple said first, second, and third conductive layers (28, 27, 26) to each other.
- A method according to Claim 30, wherein said fabricating step is carried out in a manner so that said elongate conductive element (67) is disposed between said first and second dielectric layers (18, 17), and has an end portion which extends across said slot portion (47) of said first conductive layer (28) and is directly electrically connected to said first conductive layer (28) at said one end of said slot portion (47) therein.
- A method according to Claim 25, wherein said slot portion (47) is formed with a width which is narrowest in a first section of said slot portion (47) located near said one end thereof, said slot portion (47) having second and third sections which are disposed on opposite sides of said first section and which each have a width larger than the width of said first section.
- A method according to Claim 25, further comprising: forming a refracting layer (91) which extends approximately perpendicular to a centerline of said slot portion (47) at a location beyond said further end of said slot portion (47), said refracting layer (91) being made of a material which is transmissive to and effects refraction of electromagnetic signals in a selected frequency range that travel in one of two opposite directions along said slot portion (47).
- A method according to Claim 33, including the step of forming a further layer (93) which extends approximately perpendicular to said centerline of said slot portion (47) and which is disposed adjacent said refracting layer (91) on a side thereof remote from said slot portion (47), said further layer (93) being made of a material which is transmissive to and effects refraction of the electromagnetic signals in said selected frequency range which are traveling in one of said two opposite directions along said slot portion (47).
Applications Claiming Priority (9)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US31741001P | 2001-09-04 | 2001-09-04 | |
US317410P | 2001-09-04 | ||
US10/023,229 US6867742B1 (en) | 2001-09-04 | 2001-12-14 | Balun and groundplanes for decade band tapered slot antenna, and method of making same |
US23229 | 2001-12-14 | ||
US23800 | 2001-12-14 | ||
US22753 | 2001-12-14 | ||
US10/023,800 US6850203B1 (en) | 2001-09-04 | 2001-12-14 | Decade band tapered slot antenna, and method of making same |
US10/022,753 US6963312B2 (en) | 2001-09-04 | 2001-12-14 | Slot for decade band tapered slot antenna, and method of making and configuring same |
PCT/US2002/028108 WO2003021715A2 (en) | 2001-09-04 | 2002-09-04 | Decade band tapered slot antenna, and methods of making and configuring same |
Publications (2)
Publication Number | Publication Date |
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EP1425822A2 EP1425822A2 (en) | 2004-06-09 |
EP1425822B1 true EP1425822B1 (en) | 2006-10-04 |
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Application Number | Title | Priority Date | Filing Date |
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EP02757580A Expired - Lifetime EP1425822B1 (en) | 2001-09-04 | 2002-09-04 | Decade band tapered slot antenna, and methods of making and configuring same |
Country Status (7)
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EP (1) | EP1425822B1 (en) |
AT (1) | ATE341842T1 (en) |
AU (1) | AU2002323588A1 (en) |
DE (1) | DE60215204T2 (en) |
ES (1) | ES2274073T3 (en) |
IL (2) | IL160680A0 (en) |
WO (1) | WO2003021715A2 (en) |
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US8564491B2 (en) * | 2008-04-05 | 2013-10-22 | Sheng Peng | Wideband high gain antenna |
WO2010129967A1 (en) * | 2009-04-06 | 2010-11-11 | Sheng Peng | Wideband high gain 3g or 4g antenna |
US9577330B2 (en) * | 2014-12-30 | 2017-02-21 | Google Inc. | Modified Vivaldi antenna with dipole excitation mode |
EP4014279A4 (en) * | 2019-08-14 | 2023-08-16 | Compass Technology Group LLC | Flat lens antenna |
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Publication number | Priority date | Publication date | Assignee | Title |
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US4853704A (en) * | 1988-05-23 | 1989-08-01 | Ball Corporation | Notch antenna with microstrip feed |
US6008770A (en) * | 1996-06-24 | 1999-12-28 | Ricoh Company, Ltd. | Planar antenna and antenna array |
-
2002
- 2002-09-04 ES ES02757580T patent/ES2274073T3/en not_active Expired - Lifetime
- 2002-09-04 EP EP02757580A patent/EP1425822B1/en not_active Expired - Lifetime
- 2002-09-04 DE DE60215204T patent/DE60215204T2/en not_active Expired - Lifetime
- 2002-09-04 AT AT02757580T patent/ATE341842T1/en not_active IP Right Cessation
- 2002-09-04 WO PCT/US2002/028108 patent/WO2003021715A2/en active IP Right Grant
- 2002-09-04 AU AU2002323588A patent/AU2002323588A1/en not_active Abandoned
- 2002-09-04 IL IL16068002A patent/IL160680A0/en unknown
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2004
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DE60215204T2 (en) | 2007-01-18 |
AU2002323588A1 (en) | 2003-03-18 |
EP1425822A2 (en) | 2004-06-09 |
IL160680A (en) | 2009-12-24 |
WO2003021715A2 (en) | 2003-03-13 |
ATE341842T1 (en) | 2006-10-15 |
IL160680A0 (en) | 2004-08-31 |
WO2003021715A3 (en) | 2003-08-28 |
DE60215204D1 (en) | 2006-11-16 |
ES2274073T3 (en) | 2007-05-16 |
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