GB2303740A

GB2303740A - Integrated microwave balun coupler for a dipole antenna

Info

Publication number: GB2303740A
Application number: GB9124435A
Authority: GB
Inventors: Olivier Forgeot
Original assignee: Dassault Electronique SA
Current assignee: Thales SA
Priority date: 1990-12-14
Filing date: 1991-11-18
Publication date: 1997-02-26
Anticipated expiration: 2011-11-18
Also published as: ITTO910926A1; ITTO910926A0; GB9124435D0; FR2736212B1; FR2736212A1; GB2303740B; IT1265701B1

Description

2303740 Inte9Tated microwave freglAencv balun counler. in particular for

diRgle antenna The invention relates to antennas or radiating devices.

It is important to make a correct electrical coupling between the antenna and the circuit which works in conjunction with it. This particularly applies to antennas of the dipole type.

As a general rule, a link is provided, preferably by coaxial cables, to a matching assembly of the de-sym metrising balun type. Most often, the latter must also match the impedance of the feed line to that of the antenna.

It is a particular object of the invention to provide such an assembly which is simple and economic to manufacture.

It is another object of the invention to provide an assembly which easily processes two polarizations, in particular the right and left circular polarizations.

It is another object of the invention to provide an assembly which has small lateral dimensions, which is advantageous for certain applications.

The microwave frequency coupling device proposed, in particular for an antenna of the dipole type, is of the type comprising two inputs respectively connected to two active points of the dipole, and a de-symmetrising matching assembly in front of one output.

According to the invention, there is provided a microwave frequency coupling device, comprising two inputs respectively connected to active points of a dipole antenna; a de-symmetrising matching assembly in front of an output; and a dielectric Lubstrii-Ele having..on a first side a metallisation connectdd to,,.,:bne 6f the inputs and which widens as it becomes more distapt-therefrom and, on a second side, a narrow metallisaticm to the other input and in the same direction. as 'tfie'widened metallisation, wherein the widened metallisation extends as an earth plane over the substrate, while the narrow metallisation forms with this earth plane a transmission line to said output.

Advantageously, another dielectric substrate is provided on the side of the first one where the narrow metallisation is located and comprising, opposite the first earth plane, another earth plane electrically connected to the first one. This forms a structure of the type called "tri-plate".

In the case of a device comprising at least two pairs of inputs connected to at least two differently oriented dipoles, and at least two outputs, this device comprises a pair of dielectric substrates at least partly superimposed; the upper substrate extends towards one of the pairs of inputs with, on the outside at the top, a metal- lisation which is connected to an input of this pair and which widens on becoming more distant from the latter, and on the inside a narrow metallisation connected to the other input of the same pair and having the same direction as the widened metallisation; the lower substrate extends towards the other pair of inputs, with, on the outside at the bottom, a metallisation which is connected to an input of this other pair and which widens on becoming more distant from the latter, and on the inside a narrow metallisation connected to the other input of this other pair and having the same direction as the widened metallisation; the widened metallisations then extending as earth planes above and below the two substrates, in their superimposed sections; and finally, the narrow metallisations form with these earth planes transmission lines to the said outputs. 30 In order to process circular polarisation, the narrow metallisations cross over, in the superimposed sections of the two substrates, in order to form a 0/90 degree coupler. Other objects and'advantages of the invention will be evident on examinDig the following detailed description taken together with th& appended drawings, in which:

- Figure 1 is a basic general diagram of a radiating dipole of the "bow tie" type taken by way of example; - Figure 2 shows an embodiment of an antenna with two crossed dipoles for processing two polarizations; Figures 3 and 4 show the use of a radiating device in combination with an electric coupling device; - Figures 5A to 5D show an advantageous embodiment of such an electric coupling; - Figures 6A to 6D show another advantageous embodiment of such an electric coupling; - Figure 7 shows a variant embodiment of the electrical output; - Figures 8A and 8B show two variants of the invention, while Figures BC to 8H are cross-sectional views allowing a better understanding of these variants; and Figures 9A and 9B show another variant.

The drawings are substantially of definite character and define geometric characteristics. Consequently they should be considered as an integral part of the description and not only will they be able to allow a better understanding of the latter they will also contribute to the definition of the invention as necessary.

Figure 1 shows the basic diagram of a known antenna of the so-called "bow tie" type. The latter is composed of two sectors 11A and 11B of generally triangular shape, placed head-to-tail with their points facing each other. The two sectors are symmetrical with respect to a plane PS1 perpendicular to their own plane (assuming that these sectors are flat). on this occasion the sectors shown here are also symmetrical with respect to another plane PS2 perpendicular to the first one with respect to the axis of symmetry AS of the two sectors 11A and 11B.

Such an antenna was the subject of theoretical proposals according to which the sectors 11A and 11B were in air:

- "Triangular dipole antennas", Antenna Engin eering Handbook, R.C. JOHNSON & H. JASIK, Mac Graw Hill Book Company, page 25-12, "Experimentally Determined Radiation Charac teristics of Conical and Triangular Antennas", G.H.BROWN & O.M. WOODWARD Jr, R.C.A. Review, Vol. 3, N4, December 1952.

In practice, Applicant prefers disposing these two sectors on a substrate 10, which is for example made of glass-teflon material such as 11DUROID11 sold by the ROGERS company of the United States.

As shown in Figure 2 there are disposed, on the upper f lat surface of a substrate 10, not only the two opposite sectors 11A and 11B but also two other sectors 12A and 12B having a plane of symmetry PS2 perpendicular to the plane of symmetry PS1 (Figure 1) of the sectors 11A and 11B.

It will be possible for other aspects of this embodiment to become apparent in our British Patent Applica tion No. (corresponding to French Patent Applica tion No. 9015723).

The present invention applies not only to "bow tie" antennas and other dipoles, but also to an extended range of wide band bi-polarisation antennas, particularly those known as "log-periodic" dipoles, spiral antennas and sinuous antennas (see in particular the already quoted Antenna Engineering Handbook, pages 14-54).

The devices which have just been described can be installed in modules, provided with their electric coupling circuits. The mechanical diagram of such a module is shown in Figure 4 in simplified form, while an electrical circuit diagram is given in Figure 3.

The two pairs of dipoles such as 11A and 11B, which can be placed under a radome 20, are placed at the top of a module 21, delimited by a metal body. The rear section of the substrate 10 faces an electromagnetic absorber 22, placed in the upper housing of the casing 21. Instead of an electromagnetic absorber, it is possible to use an electro- magnetic reflector, or even a combination of the two, over different sections of the frequency band.

Four coaxial cables are provided (one for each conductive sector). The screens of the coaxial cables are connected to each other and to the metal casing 21. The cores of the coaxial cables are respectively connected to the live points of one of the conductive sectors. This defines coaxial cables 31A,,31B, and 32A,32B for the conductive sectors 11A,11B and 12A,12B respectively.

Advantageously, in an intermediate housing of the casing 21, the coaxial cables form a loop, after which they join two de- symmetrising baluns 41 and 42.

The balun 41 receives the coaxial cables 31A and 31B, while the balun 42 receives the coaxial cables 32A and 32B.

By means of the loops which can be seen in Figure 4, it is ensured that the electric lengths of the coaxial cables from the live point of the dipole in question to the balun are the same in order to align the propagation times of the signals. Furthermore, it is necessary to take account of the fact that the cables associated with the two opposite sectors 11A and 11B will have to be joined together again on the same balun 41. As represented by the axis line 30, this results in a rotation of the cables, with a crossover, to allow the junction which has just been described. The intermediate loops allow for compensation for possible differences in length due to this crossover.

The baluns 41 and 42 each have two coaxial inputs and each have one output, which is for example coaxial. A variant (Figure 7) consists in an output on a. microstrip line which is applied to a printed circuit, on a substrate 80, the microstrip line 81A is opposite to an earth plane 81B, the complete assembly being under a metal screen 85.

The known baluns are for example the patterns known as "Minerva" or "Marchand" which are described for example in:

6 - - "Transmission Line Conversion Transformer", N. MARCHAND, Electronics, vol 17, pp 142-145, December 1944, - 11100:1 Bandwidth Balun Transformer", J.W. DUNCAN & V.P. MINERVA, Proceedings of the I.R.E., pp 156- 164, February 1960, - "Design and performance of microstrip balun for Archimedes Spiral antennas", D.E. BAKER, J.R. NORTIER, C.A. VAN DER NEUT, Transaction of the SA Institute of electrical Engineers, December 1987.

In the case of four dipoles, it is firstly possible to use the outputs of the baluns 41 and 42, possibly through interface stages 71 and 72, in order to supply on connectors 91 and 92 channels A and B respectively which correspond to two crossed linear polarizations, like the horizontal and vertical polarizations.

As a variant, as shown in Figure 3, the two channels are applied to subdividers (reverse 3 dB couplers) 71 and 72. One of the outputs of the latter is applied to a 0/90 degree phase shifter, 73 and 74 respectively. The output of each phase shifter goes to a 3dB coupler, 75 and 76, situated on the other channel, and also receiving the other output of the coupler 71 or 72 of the same channel.

Those skilled in the art know that the coupling thus carried out allows the obtaining on the two output connectors of signals having right circular polarisation and left circular polarisation respectively.

Because of the small surface dimensions of the two pairs of basic dipoles, the module according to the invention can be produced with small lateral dimensions, the depth being a little greater, as can be seen in Figure 4.

For certain applications, it is desirable to have a large number of modules of this type in a volume which is as small as possible and for which the manufacturing is as simple as possible.

Two variant embodiments which are particularly advantageous in this respect will now be described.

Figures 5A to 5D relate to a variant embodiment in which interest is taken in only one of the channels, for example the horizontal polarisation defined by the sectors 11A and 11B.

The two coaxial cables 31A and 31B have cores which end respectively at two metallised surfaces of another substrate 41S. This substrate 41S can also be made of DUROID. On one side, the substrate 41S carries a relatively narrow metallisation 41A, which retains the same transverse dimension over its entire length (or widens very slightly), in order to end at the core of a coaxial connector 91 disposed at the other end.

The lower surface of the substrate 41S is provided with a metallisation 41B which, on the side of the core of the coaxial cable 31B, has practically the same width as the metallisation 41A. On the other hand, this metallisation 41B rapidly widens in order, on arrival, to be connected to the 91 much wider earth of the coaxial connector.

Those skilled in the art know that this produces the de-symmetrising according to the principle of a balun.

The advantage of the above embodiment is that it allows, with very few parts, the direct passage from the coaxial cables connecting the dipoles to the substrate 41S to a coaxial connector which directly supplies the output.

The assembly can be housed in a metal cavity 5, provided for example with mode absorbers 51A, 51B, 51C and 51D.

This is suitable for the case of transverse rectilinear polarizations.

Reference is now made to Figures 6A to 6D which show an even more advantageous variant, in particular for circular polarisation.

In these Figures 6 are found two substrates 41S and 42S, for example made of DUROID. The latter are superimposed at the level of a zone 49 which is for example of generally rectangular shape.

Out of this zone, they have practically the 4 structure already described with reference to Figure 5.

In brief, accepting that the substrate 41S is at a lower level than the substrate 42S:

- the substrate 41S carries on the bottom the metallisation 41B which widens greatly, and on the top the metallisation 41A which widens slightly or not at all.

- the substrate 42S carries on the top the metallisation 42B which widens greatly, and on the bottom the metallisation 42A which slightly widens.

Between the two substrates there is provided an insert of very small thickness made of a material similar to that of the substrate, such as DUROID.

At the level of the superimposition section 49, the widened metallisations 41B to 42B spread completely in order to define earth planes situated above and below the sandwich thus constituted by the two substrates 41S and 42S and by the very thin intermediate layer (not shown).

The metallisations 41A and 42A can themselves be directly connected to the connectors 91 and 92 for the case in which it would be desired to make this assembly operate in rectilinear polarisation.

The whole advantage of this assembly is in the case of circular polarisation:

- in this case it then suffices to make the metallisations 41A and 42A, at right angles to the superimposition section 49, follow paths which cross over with very adjacent portions.

This provides a coupling between the two channels, with the 0/90 degree phase shift function. outputs with right and left circular polarisation are thus obtained directly on the connectors 91 and 92.

In the above, the same section of the balun performs the de-symmetrising and the impedance, matching. Two variants will now be described where these functions are separated.

In Figures 8A and 8B, the de-symmetrising zone (41, 42) is preceded by an impedance matching zone (36, 36), by the joint tapering of the two conductive lines which are opposite each other (35A, 35B for example) on either side of the substrate here referenced S.

Figure 8A retains the link by coaxial cables between two sectors 11A,11B and cables 31A and 31B (not visible), and between two sectors 12A,12B and cables 32A and 32B (not visible).

In Figure 8B, the link is this time provided by two-wire lines. The sectors 11A and 11B (not visible) are connected to lines 33A and 33B (see cross-section of Figure 8C). The sectors 12A (rotated through 90 degrees) and 12B (not visible) are connected to lines 34A and 34B (not visible).

The rest is the same f or both Figures. The lines 35A and 35B widen together between the start (Fig. 8D) and the end (Fig. 8E) of the impedance matching zone.

The de-symmetrising is carried out in the zone of different widening (Figures 8F and 8G). If so.desired, a crossed coupling is carried out in the zone 49 (Fig. 8H) in order to gain access to elliptical or circular polariza tions.

The output is effected on connectors, as in Figures 4, 5 and 6, or on a line to an electronic circuit as in Figure 7.

The present invention described embodiments.

is not limited to the When considering polarisation, it is appropriate to process the potential difference between the two sectors or opposite dipoles. With the embodiments having more than two dipoles it is possible to consider sums or differences, and more generally any linear combination of the potentials of the conductive sectors.

Figures 9A and 9B respectively show an antenna with 35 3 dipoles and a combined coupling of their output signals, this combined coupling being carried out on a circuit with several layers and interconnections by slits and/or metallised holes. The transmission lines at the left can be of the coaxial type or of the two- wire type. It is thus possible to obtain any desired polarisation mode. 5 The processing of the collected signals can be carried out in parallel on different channels, or by multiplexing of a same processing channel. Finally, the radiating elements according to the invention, with their coupler, appropriately screened, have not only small lateral dimensions, but also a low lateral radiation considering their size and the frequencies in question. They therefore lend themselves particularly well to the construction of arrayed antennas.

The invention can be applied in numerous fields: telecommunications, particularly at microwave frequencies, and other microwave frequency applications including wide band measurements for example measurements on the radiation of other aerials.

Claims

C L A I M S

1. A microwave frequency coupling device, comprising two inputs respectively connected to active points of a dipole antenna; a desymmetrising matching assembly in front of an output; and a dielectric substrate having on a f irst side a metallisation connected to one of the inputs and which widens as it becomes more distant therefrom and, on a second side, a narrow metallisation connected to the other input and in the same direction as the widened metallisation, wherein the widened metallisation extends as an earth plane over the substrate, while the narrow metallisation forms with this earth plane a transmission line to said output.

2. A device according to Claim 1, wherein there is a further dielectric substrate provided on said second side of the first-mentioned metallisation and comprising, opposite the first earth plane, a second earth plane electrically connected to the first earth plane.

3. A device according to Claim 2, comprising at least two pairs of inputs connected to at least two differently oriented dipoles, and at least two outputs, wherein said first-mentioned and further dielectric substrates are at least partly superimposed; wherein the upper substrate extends towards one of the pairs of said inputs with, on the outside at the top, a metallisation connected to an input of said one of the pairs, and which widens on becoming more distant therefrom, and on the inside a narrow metallisation connected to the other input of said one of the pairs, and having the same direction as the widened metallisation; wherein the lower substrate extends towards the other pair of said inputs, with, on the outside at the bottom, a metallisation connected to an input of said other pair of said inputs, and which widens on becoming more distant therefrom, and on the inside a narrow metallisation - 12 connected to the other input of said other pair of said inputs, and having the same direction as the widened metallisation; and wherein the widened metallisations then extends as earth planes above and below the first-mentioned and further substrates, in their superimposed sections, while the narrow metallisations form with these earth planes transmission lines to the said outputs.

4. A device according to Claim 3, wherein in the superimposed sections of the two substrates, the narrow metallisations cross over in order to form a 0/90 degree coupler. 5. A device according to any one of claims 1 to 4, wherein it is enclosed in a conductive cavity. 15 6. A device according to Claim 5, wherein said conductive cavity comprises mode absorbing means. 7. A device according to any one of claims 1 to 6, wherein the inputs are connected to the dipoles by the cores of coaxial cables whose screens are interconnected. 20 8. A device according to any one of Claims 1 to 6, wherein the inputs are connected to the dipoles by twowire lines. 9. A microwave frequency coupling device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

1 Al.'.

.1 ing: - 11 Amendments to the claims have been filed as follows 1. A microwave frequency coupling device, compris- first and second inputs respectively connected to active points of a dipole antenna; an output; between the inputs and output a de-symmetrising matching assembly comprising a -die-lectric substrate having opposed first and second sides with, on its first side, a first metallisation which has first and second ends and is connected at said first end to said first input and widens along a direction towards said second end and, on its second side, a narrow second metallisation connected to the second input and extending in the same direction as the first metallisation, wherein the first metallisation extends as a first ground plane over the substrate while the second metallisation forms with said first ground plane a transmission line to said output; and 20 a second dielectric substrate provided on said second side of the first dielectric substrate and comprising, a second ground plane electrically connected to the first ground plane. 2. A device according to Claim 1, wherein the second ground plane is opposite the first ground plane.

3. A device according to Claim 1 or 2, comprising at least two pairs of said inputs connected to at least two dif ferently oriented dipoles, and at least two said outputs, wherein said first-mentioned and further dielectric substra- tes are at least partly superimposed; wherein an upper of the substrates extends towards one of the pairs of said inputs with, on the outside at the top, a said first metallisation connected to an input of said one of the pairs, and with on the inside a said second metallisation connected to the other input of said one of the pairs; wherein the lower of the substrates extends towards the i other pair of said inputs, with, on the outside at the bottom, another said first metallisation connected to an input of said other pair of said inputs, and on the inside another said second metallisation connected to the other input of said other pair of said inputs; and wherein the said first metallisations then extend as ground planes above and below the first-mentioned and further substrates, in their superimposed sections, while the said second metallisations form With these ground planes 10 transmission lines to the said outputs.

4. A device according to Claim 3, wherein in the superimposed sections of the two substrates, the said second metallisations cross over in order to form a 0/90 degree coupler.

is

5.

wherein it

6. conductive

7.

A device according to any one of claims 1 to 4, is enclosed in a conductive cavity.

A device 'according to Claim 5, wherein said cavity comprises mode absorbing means.

A device according to any one of claims 1 to 6, wherein the inputs are connected to the dipoles by the cores of coaxial cables whose screens are interconnected.

8. A device according to any one of Claims 1 to 6, wherein the inputs are connected to the dipoles by two-wire lines.

9. A microwave frequency coupling device substan tially as hereinbefore described with reference to, and as illustrated in, Figures 3 to 7 and 8B of the accompanying drawings.