US3534369A - Multiband tv-fm antenna - Google Patents

Description

Oct. 13, 1970 N. J. REA

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Oct. 13, 1970 N. J. REA

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NORMAN J- P54 A TTOENEYS United States Patent US. Cl. 343-7925 9 Claims ABSTRACT OF THE DISCLOSURE A multiband TV-FM periodic antenna is provided in which the front element has an extending hairpin-like section, capacitatively coupled thereto. In operation, the eX- tending section is unconnected at low band frequencies but effectively connected at the high band frequencies.

This application relates to a multiband antenna of the backward wave type and more particularly relates to an antenna for VHF television and FM radio reception. Specifically, this invention relates to a periodic multidipole antenna which is effective for all VHF television and FM radio reception.

This invention also relates to an interlaced VHF-UHF television and FM radio antenna.

It has been common to provide multiband antennas by providing plural antennas mounted on the same mast, essentially in cascade. For example, a mast could carry a first antenna section designed for the low-band channels 2-6; a second antenna designed for the high-band channels 7-13; and a third antenna designed for FM band. Such antennas require many elements, are inherently inefficient and are expensive.

Problems have existed in devising a multiband interlaced antenna effective for the VHF-TV and FM bands. It has been found experimentally, that a periodic antenna for all TV and PM will encounter problems of high side lobes, poor impedance matching characteristics, and reduced gain for certain of the frequencies. These problems become accentuated when the antenna is used for color TV reception.

In explaining the problems encountered in the operation of my antenna, the following considerations are helpful, but in general are only reasonable approximations of the true performance, particularly as applied to periodic antennas.

When an antenna is used only for the low and high bands of VHF, the frequency ranges to be covered are 54-88 mc. (channels 26) and 174-216 (channels 7-13) and 88-108 (FM). It will be apparent that antenna dipole elemets cut as half-wave elements (total length) at 88 me. will act as a full-wave element at 174 me.

Consider now the performance at the low end of the high band (channel 7, 174 me.) when the low band is extended to include FM to 108 mc. Antenna dipole elements cut as half-wave elements (total length) at 108 mc. will act as having a length between a half and a full wave, at 174 mc. and adjacent frequencies, and not as a resonant element. Therefore, in the low end of the high band (174 mc.), substantial problems of high side lobes, impedance mismatch and changing phase centers occur. This produces incorrect and distorted colors, ghosts, and in general, poor reception when what is required for high quality FM and color reception is just the opposite.

In the periodic antenna, if the first element is poorly matched to the incoming signal at selected frequencies, such as 174 mc., severe pattern breakup occurs. The aforementioned multiple side lobes and varying phase centers result along with undesirable harmonics, reducing the ice gain, causing ghosts and generally increasing the distortion.

In my invention, I have provided a means for increasing the total effective dipole lengths of one or more of the antenna elements which present undersirable harmonics so as to neutralize the undesired effects and eliminating pattern breakup.

An object of my invention is to provide a multiband interlaced antenna for FM and TV.

A further object of my invention is to provide a multiband parasitic director.

Another object of my invention is to provide an antenna element operative at a first range of frequencies, and being relatively inert at a second higher range of frequencies.

A further object of my invention is to provide an improved periodic antenna for multiband use.

Still another object of the invention is to provide an improved parasitic array of director elements.

A still further object of this invention is to provide a multiband TV and FM antenna in which the component elements function in all bands.

Yet another object of this invention is to provide a multiband, trimodal antenna for the VHF, UHF TV bands, and the FM band.

Briefly, in my invention, I provide an array of spaced parallel dipoles, of the general periodic type, each having a length of predetermined ratio to the preceding dipole, the longest dipole being proportioned to resonate at channel 2. The array tapers with shorter dipoles for various channels including channel 13 and for FM radio band reception. In an aspect of the invention, the active elements are equally spaced one from the other.

The front active element has an associated extension element, parallel thereto, which is substantially uncoupled or unconnected at the low band, but becomes coupled at the high band to increase the effective length. That is, the extensions are capacitatively coupled, the impedance of such coupling being an effective short circlit at the high band. The total dipole length is increased by an amount so that the front element becomes relatively inert and does not cause pattern breakup and the related effects mentioned before.

I further provide a parasitic director array of elements which are variably spaced apart, the outer ones being further spaced apart than the inner ones. It is known that in the operation of log periodic dipoles, slow traveling waves are present. Slow waves are waves whose apparent or phase velocity is less than that of free space. In my director array, the velocity of the wave is gradually slowed as it reaches the active elements and less energy is lost.

The parasitic array comprises elements of equal length; however, each element has a unique associated parallel extension, which allows the elements to operate effectively in the low and high bands.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will best be understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of one embodiment of the antenna array of this invention;

FIG. 2 is a top diagrammatic view of the antenna of FIG. 1;

FIG. 3 is a front view, partly in section of the first driven antenna element of the array;

FIG. 4 is a side sectional view along 4-4 of FIG. 3;

FIG. 4A is a perspective view showing further detail of a supporting insulator and takeoff terminals;

FIG. is a side sectional view of the bimodal parasitic director element;

FIG. 6 is a schematic diagram of the bimodal director element;

FIGS. 6A, 6B and 6C are diagrams of the current distribution in the bimodal director element for low and high band;

FIG. 7 is a diagram of an embodiment of my invention having a multidirector system;

FIG. 8 is a top view of a multi-element parasitic section;

FIG. 9 is a top view of another embodiment of my invention for use also in UHF;

FIG. 10 is a schematic diagram of another embodiment for use also in UHF illustrating the current distribution.

THE ACTIVE ARRAY Referring now to FIG. 1, there is shown a mast 10 supporting a conductive cross arm 11 on which the active array 100 and the parasitic elements 40, 40' are mounted. The active array comprises dipole elements 20, 30, 30', 32, 32, 34, 34', 36, 36 and feed wires 12, 13. As shown in more detail in FIGS. 2 and 3, the dipole 20, 20 comprises dipole rods 21 and 21A, and identical extension elements 22 and 22A. Extension 22 comprises an elongated thin rod bent back upon itself to form generally a hairpin (FIG. 3). The extension is attached to the dipole element by a pair of triangularly-shaped insulators 50 (see FIG. 4) which have grooves 51 to accommodate the dipole element 21 and the rod ends 22 in a resilient fit.

Rod 22 extends approximately 6 inches (Dimension W) beyond the end of the dipole in one preferred embodiment (FIG. 3). At for example, 174 mc., the total effective length of each active arm is /2 wavelength and the total antenna length is 1 wavelength. The various dimensions of the driven element for the preferred embodiments (assembly 1) are shown in the drawing, FIGS. 2 and 3, as dimensions X, Y and Z, and are listed below. Since other embodiments may also be used, typical dimensions are also included (assemblies 2 and 3).

There is also shown an end grounding strap 14, FIG. 2, which is common to all of the antennas, which grounds the driven dipoles and provides direct connection to the cross arm to bleed noise and static charges.

Referring now to FIG. 2, it will be seen that the elements 20, 30, 32, 34, 36 increase in length, each one bearing a predetermined ratio to the preceding one. It will also be observed that each of the dipole elements 20, 30, 32, 34, 36 is equally spaced from the next successive element.

The operation of my invention may be briefly described here. The theory by which my antenna operates has not been firmly established; however, it is my belief that by providing a dipole structure, the length of each successive dipole varying periodically and yet providing equally spaced dipoles, I have provided a structure in which undesired side lobes from successive elements tend to cancel each other out. It was also discovered that a spacing of 12%. between successive parallel, dipole elements provided an interference radiation relationship which substantially cancelled the side lobe levels inherent in the individual dipole patterns at the high band frequencies. This eliminates the V requirement or the parasitic stubs used in other devices.

MECHANICAL CONSTRUCTION The mechanical constructionis illustrated in more detail in FIGS. 3, 4 and 4A. The cross arm 11 is square 4 shaped and supports a series of arcuate-shaped insulators 60 which support the dipole elements as well as providing the electrical connections between successive pairs of dipole elements, as will be desribed. All of the insulators have the same construction and only one will be described briefly, it being understood that a pair of insulators are mounted above and below the mast for each pair of dipoles. Insulator 60 is generally L-shaped and has a fiat horizontal section 61 except for a small recess to accommodate the cross arm 11 and a vertical section 63.

The dipole rod 21 is fitted into a hollow metal receiv ing socket 23 having a generally square exterior contour held between two opposing flat sections 61 and has a pin 62 extending therethrough, allowing rotation. Each dipole element is thus pivotally mounted so as to rotate in the horizontal plane containing all of the dipole elements. This rotation feature is desirable to provide easy packing and mounting of the antenna.

There is provided a spring clip 75 having a wedged aperture 76 (FIG. 4A) of approximately the same dimensions as the dipole socket. The clip is held by opposing flat sections 61.

Each insulator has a groove 64 in a slightly extending section 65 to support the wires 12, 13. Each of the insulators has narrow slots 66 extending within the arcuate portion of the insulator, each containing a conductive strip 66A, 66B (FIGS. 3, 4A) to provide the contact between the wire 12 of the dipole socket 23 and pin 62. Although not shown, a conductive wall may be provided in groove 64 to present a firm electrical contact between the internal conductor 66 of the insulator and the feed wire.

The arcuate conductive strips 66A, 66B (FIG. 3) are located on opposite quadrants of the circle defined by the two insulators; these quadrants alternate with respect to successive elements so that dipole element 21 is connected to the feed wire 12 which in turn is connected to element 30, then to 32, then to 34' and finally to 36, while the other feed wire 13 is connected to dipole elements 20', 30, 32', 34, 36, to provide successive feeds in opposing phase relation.

Takeoff terminals are shown at 68 having fastening screws 69. A metallic fitting 70 connects the terminals to the feed wire lines. A matching transformer 71 (FIG. 4A) for 75 ohm operation may be optionally used when coaxial lead-in is employed.

THE DIRECTOR ARRAY The director 40 is shown also in more detail in FIG. 5 and it will be understood that more than one director may be utilized as shown in FIG. 8. The director support is mechanically similar to the supports for the active dipoles and uses the same arcuate-shaped plastic insulators Which serve as brackets, except that internal conductors are not required.

The director is bimodal and has associated with it a stub also in the shape of an elongated wire being bent upon itself to define parallel arms 81 and 82 and a bight section 83. In this embodiment the arm 81 is longer than the arm 82. The stub is mechanically fastened to the director rod or tube by triangularly-shaped insulators of the same characteristics as the insulators 50 shown and described in connection with FIGS. 3 and 4. One arm 82 of the extension is directly connected to the director rod by a shorting clip 92.

The relative dimensions V, W, X, Y, Z are shown in the drawing, FIG. 5. For one embodiment, typical dimensions are as follows:

The bimodal director of FIG. is diagrammatically illustrated in FIG. 6 and operates essentially as a colinear element. There is shown the director as comprising three essential sections, the main section L, the extending section M, and the intermediate section N. The position of the shorting stub is shown at 92 and 83 illustrates the bight section. FIG. 6A is intended to illustrate the high band current distribution on the bimodal director element. In the case where the total length of the director element is a full-wave length, two half wave current components I1 and 12 will be induced. The current component I3 caused by the intermediate section N will be cancelled out by the component of currents I4 and I5 provided by the induced currents in the overlapping paths provided by the sections indicated at 40A (which produces 14) and 80A (which produces I5).

FIG. 6B illustrates the resulting current distribution at highband derived from the analysis of FIG. 6A.

FIG. 60 illustrates the low band current distribution. In this mode of operation, element 80 is effectively a half wave length.

These are illustrations only of the principle disclosed herein of having the length of the active and director elements increased so as to avoid pattern breakup.

Referring now to FIG. 7, there is shown an array of active elements 100 and an array of director elements 160 comprising dipole pairs 161, 162, 163, 164. Each of the dipole elements is constructed in the same manner as element 40 shown in FIGS. 2 and 5. However, in the array, each director element on a respective side of the cross arm is spaced at gradually increasing amounts. The spacing is expanded towards the front of the parasitic structure to increase the velocity to more nearly equal that free space.

One embodiment of the parasitic array is shown in FIG. 8 and comprises seven dipole pairs 171, 172, 173, 174, 175, 176, 177. The relative spacing between successive elements is shown on the drawing and is repeated here:

Parasitic elements: Spacing, inches TRIMODAL OPERATION FIG. 9 shows an embodiment of an antenna also operative for the UHF band, while FIG. 10 illustrates diagrammatically the director element for trimodal operation. In FIG. 9, there is shown an active UHF dipole element 200 having a length of 5 /2 inches for each arm. A director 210 and an active dipole 202 are positioned before and after the element 200 respectively.

The interlaced director embodiment is shown in FIG. 10. The director elements 210, 210' and 210" (FIGS. 9, 10) are of the same form. In FIG. 10, between the two elements 210', 210", is a UHF active dipole comprising two rod elements 214 each cut to approximate half wave length UHF. The UHF element 214 does not interfere at all with operation at the low or high TV bands.

While the principles of the invention have been described in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A mutliband antenna for use in the TV and FM bands, said TV and FM bands including the 54-108, 174-216 mc. bands comprising:

an array of active dipole elements the length of successive elements varying according to a predetermined ratio, each element being equally spaced from the preceding element,

means for feeding each of successive elements in opposing phase relationship,

said first active dipole elements each having at least one physically and electrically spaced, capacitively coupled, substantially parallel, extension member mounted adjacent thereto,

and at least one parasitic director element mounted in front of the active elements, said capacitively coupled element being disconnected in the 54-108 mc. band.

2. The antenna of claim 1 in which a plurality of director elements are mounted parallel to each other to form a director array,

said director elements being variably spaced one from the other in progressively increasing space sequence away from said active elements.

3. The antenna of claim 1, in which the elongated element includes a hairpin-shaped member having two parallel extending elements, connected at one of their adjacent ends.

4. The antenna of claim 3 in which said director element includes at least one elongated conductive element spaced adjacent and parallel thereto over a predetermined length thereof and extending beyond said active element and a conductive stub coupling said elongated and director element.

5. The antenna of claim 1 in which the effective length of each of the first active elements including the respective extension is /2 A at approximately 174 mc., whereby the total dipole length of said first active dipole element is 1 A the impedance of the capacitive coupling being substantially minimal at 174 mc.

6. The antenna of claim 9 in which said first active dipole has a total length of /2 A at 108 mc., and the longest dipole of said array being resonant at 54 mc.

7. The antenna of claim 5 including an interlaced, colinear UHF active element.

8. In sub-combination, an antenna for use in the TV and FM bands, said TV and FM bands including the 54-108, 174-216 mc. bands, including at least one pair of active dipole antenna elements,

and at least one elongated electrically spaced but capacitively coupled conductive element physically spaced adjacent and parallel to said active element over a predetermined length and extending beyond said active element and supporting means closely supporting said element adjacent to said extension, said capacitively coupled element being electrically disconnected in the 54108 mc. band.

9. The antenna of claim 8, in which the elongated element includes a hairpin-shaped member having two parallel extending elements, connected at one of their adjacent ends.

References Cited UNITED STATES PATENTS 2,417,808 3/1947 Carter 343833 X 2,598,005 5/1952 Lippit 343-815 X 2,622,197 12/1952 Cruser 343-802 2,885,675 5/1959 Simon et a1. 343895 X 2,975,423 3/1961 Wells 343-833 Re. 25,604 6/ 1964 Greenberg 343-7925 X FOREIGN PATENTS 229,354 9/ 1958 Australia.

HERMAN KARL SAALBACH, Primary Examiner SAXFIELD CHATMON, JR., Assistant Examiner U.S. Cl. X.R. 343-802, 815, 812

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,534 369 October 13, 1970 Norman J. Rea

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 36, claim reference numeral "9" should read Signed and sealed this 6th day of April 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, JR.

Attesting Officer Commissioner of Patents

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