US2520988A - Car body antenna - Google Patents

Description

P 1950 w. L. EVERlTT 2,520,988

CAR BQDY ANTENNA Filed March 51, 1948 IN V EN TOR.

ZZ /L'ZZJQm/ZE 06712 2 Patented Sept. 5, 1950 CAR BODY ANTENNA William L. Everitt, Urbana, Ill., assignor to M- torola, Inc., Chicago, 111., a corporation of Illinois Application March 31, 1948, Serial No. 18,243

Claiins. (Cl. 250 33) This invention relates to car body antennas, and is particularly concerned with improvements in such antennas to facilitate the transfer of radio signals between space andthe mobile radio equipment carried by the vehicle on which antennas of this kind are employed.

"Car body antenna is the name generally given. to an antenna which utilizes the metallic body of a vehicle, such as'an automobile, truck or other craft, as a means for picking up radio signals or, in the case of a mobile transmitter, radiating such signals; Such antennas are advantageous in that they do not have'external parts projecting from the vehicle and may be less subject to fading or interference caused by the presence of structures such as buildings, power lines and viaducts near the vehicle. Heretofore the signal transfer properties of such antennas have not always been as great as desired due, it is believed, to the relatively poor electrical conductivity of the average vehicle body and the difiiculty encountered in coupling the antenna to the radio set.

An object of this invention is to improve the performance of car body antenna systems by providing a well-defined, highly conductive path or paths for current flow on the car body.

Another object is to enable the antenna and the radio equipment carried by the vehicle to be coupled together more eifectively. than was possible heretofore.

In accordance with a feature of the invention, it is proposed to for-m one or more highly conductive paths on the car body by bonding a strip of copper or other highly conductive metal to the body. This may be accomplished, for example, by sputtering the metal on the body in one or more strips extending longitudinally of the body. Each such strip forms a portion of a loop antenna which may be coupled to the radio equipment with relative ease.

The foregoing and other objects, features and advantages of the invention will be better understood by referring to the following description in conjunction with the accompanying drawing, wherein:

Fig. 1 is a perspective view of an automotive vehicle equipped with an antenna system embodying the principles of the invention; and

Fig. 2 is a schematic View showing typical coupling circuits which maybe used in connection with such a system.

In practicing the invention, two strips of metal, such as copper, having high conductance are sputtered onto the body of the vehicle, one strip extending from a rear corner of the body across the top to the opposite front corner thereof, and the other strip extending from the other rear corner of the body across the top to the other front corner thereof, crossing the first strip. Connected to one end of each of these strips is an electrical conductor which extends underneath the body in approximately the same direction as the strip. Suitable antenna coupling elements are provided for the antenna loops defined by the strips and their respective conductors. Thus, there are provided two loops having different orientations. These loops are coupled to the radio set in the correct phase relation to produce a non-directional antenna system.

Referring now to the drawings, the vehicle H! has a metallic body I 2 which extends over the top and sides of the passenger compartment of the vehicle. It is possible in accordance with prior proposals to use the vehicle body as an antenna by coupling the radio set to certain points on the body. The positions of each set of connecting points can be so selected as to give the effect of a closed loop antenna extending through the vehicle body and having a particular orientation. However, such arrangements have the disadvantage that the loops are not particularly well-defined in the vehicle body and, besides, the conductance of the metal in the body is not comparable to that of the conductors used in most conventional antennas. Moreover, the shunting effect of the body metal in the vicinity of the points where coupling is made from each loop to the radio set tends to Weaken the signal further.

I propose to remedy these shortcomings by applying strips I4 and N5 of high-conductance metal, such as copper, to the body l2. These strips l4 and I6 may be provided by sputtering the copper or other high-conductance metal on the vehicle body l2 before the body is painted. Alternatively, the strips could be sputtered on over the paint after the body has been painted and a matching coat of paint applied over each strip so that the appearance of the vehicle is not changed and to protect the coating from exposure to the elements. The strip M, as shown, extends from the rear right-hand corner of the body 12 across the top to the front left-hand corner of the body. The strip l6 extends from the rear left-hand corner of the body l2 across the top to the front right-hand corner. Each of the strips I4 and I6 is part of a loop antenna. The loop of which the strip I4 is a part is closed by an electric conductor [8 which extends beneath the body l2 and is connected to the ends 3 of the strip l4 as indicated at 20 and '22. The

conductor [8 might, for example, be a cable with a copper center. A similar conductor or cable 24 extending beneath the body I2 is connected at its ends to the strip l6 as indicated at 26 and 28 to close the loop of which this strip is a part. Suitable supporting devices (not shown) may be provided for holding the cables l8 and 24 in place.

Included in the conductors l8 and 24 'arethe.

primaries of coupling transformers 3G and 32,

respectively. The radio set 34 carried by the vehicle I is coupled to the loop antennas through the medium of the transformers 30 and 32.

It is well known that if two directional antennas having different phase orientations .are coupled to a radio set in such a manner that the antennas are displaced in phase, then it'is -pos sible to obtain a non directional field pattern for the antenna system taken as a Whole. In the present instance the loop antennas including the strips M and 45 are disposed at a substantial angle with respect to each other on the body l2 of the vehicle II). It remains only to' effect a phase displacement in the signals passing between the respective antennas and the radio set 34 in order to obtain a non-directional antenna. system. The coupling device 35 illustrated schematically in Fig. 2 and included in the radioset 3 is provided to accomplish this function.

By way of example, it will be assumed that the radio set 34 constitutes'a receiver, although it should be understood that the principles of the invention can be applied to transmitters as well. The coupling device 35 has a pair of input transformers 38 and 49, the primary windings 39 and 4| of'which are connected respectively through coaxial cables or other suitable transmission lines 42 and 44 to the secondaries of the coupling transformers 3t and 32. The secondary coils 43 and E5 of the transformers 38 and it preferably are provided with adjustable cores so that the in- .ductances of these coils may be varied Thesecondary 43 of transformer 38 is connected directly to the control grid 41 of the amplifier tube 45, which maybe a radio-frequency amplifier stage in the receiver 34. This secondary Winding 43 also is connected to a source of AVG voltage and, through a blocking capacitor 49, it is connected to one side of the primary winding 39 of the transformer 38. The primary M and secondary 15 of the input transformer 40 have a common junction, and the secondary G5 is also connected through a trimmer 58 to a junction 52. 'A

' trimmer Ed is connected between the junction 52 and the terminal of the control grid 41. The primaries of the transformers38 and 49 have-a common grounded junction 5?, and a capacitor 58 is connected between the junctions 52 and 55.

The above described circuit arrangement'of the coupling device 36 serves to shift the phase of the signals picked up through the coupling transformer 32 approximately 90 degrees with respect to the signals picked up through the coupling transformer '39. Furthermore, by interconnecting the primaries and secondaries of the transformers 38 and 43, respectively, as shown, the gain of the system is made substantially uniform throughout the frequency range. In this way the' desired non-directional field pattern for the antenna, system is, obtained, so that radio signals are received irrespective of the direction in'which the vehicle i0 is headed. "Because of the higher conductivity of the strips I4 'and'lB and the conductors l8 and 24 in comparison withathe body l2, the shunting effect of the .portions of the body 4 which are bridged across the loop is not objectionable. This shunting is minimized when the highly conductive material is placed over a body which has been painted, as the paint may be effective'as insulation. The loop circuits formed by the strips l4 and I6 and conductors l8 and 24, in addition to picking up signals directly, also pick up signals inductively from the loop circuits inherently formed in the metallic vehicle body.

The antenna system described herein is advantageous in that it provides a stronger signal with greater freedom from interference than is i possible (all other tlflngs being equal) with previously proposed types of car body antennas. The invention, of course, is not limited to the precise embodiment shown in the drawings. Broadly, it comprises a loop antenna system in which at least some portion of a loop is formed by sputtering or otherwise bonding a strip of copper or other high-conductance metal onto a vehicle body. The manner of completing the loop, and the location of the coupling elements, may be varied to fit individual needs.

Hence, while a specific embodiment has been disclosed, it is capable of modification without departing from the spirit of the invention, and it is intended that all such modifications shall be included within the scope of the appended claims.

I claim:

1. In a vehicle having a unitary metallic body extending over the top and sides thereof and in which there is provided'a wave signal device, a loop antenna system for the vehicle comprising a strip of copper applied to the vehicle body and extending from one rear corner thereof die-gs onally across the topof the body to the oppo site front corner thereof, another strip of copper applied to the vehicle body and extending from the other rear corner thereof diagonally. across the top of the body to the other front corner thereof, a pair of antenna coupling elements for the wave signal device, electrical conductor means individually connecting each of said coupling elements in series with one of said strips thereby providing a pair of angularly spaced closed antenna loops, and a. couplingcircuit connected to said coupling means and including phase shifting means for combining the signals picked up by said antenna loops in proper phase relation to produce a non-directional antenna system.

2. In a vehicle having a unitary metallic body extending over its top and sides and in which there is provided a. wave signal device, a loop antenna system for the vehicle comprising a copper strip provided on the vehiclebody and extending from one rear corner thereof diagonally across the top of the body to the opposite front corner thereof, another copper strip provided on the vehicle body and extending from the other rear corner thereof diagonally across the top of the body to the other front corner thereof, a pair of antenna coupling transformers each including primary and secondary windings, electrical conductors respectively connecting the primary windings of said coupling transformers inseries with said strips to provide a pair of spaced loop antennas, "and a'phase-shifting input circuit connected, to the secondary windings of said coupling transformers and including phase shifting means for eifecting a phase displacement in the signals received by the two loop antennas, thereby to produce. a non-directional antenna system. a 3. In a vehicle having a unitary metallic body extending over its top and sides and in which there is provided a wave signal device, a loop antenna system comprising, thin strip-like conductors having substantially greater conductivity than the metallic vehicle body provided on the vehicle body, one of said conductors extending from one rear corner diagonally across the top of the body of the vehicle to the opposite front corner thereof, a second one of said conductors extending from the other rear corner diagonally across the top of the body of the vehicle to the other front corner thereof, a pair of antenna coupling elements, electrical conductor means respectively connecting one of said antenna coupling elements in series with a respectiv one of said strip-like conductors to provide a pair of angularly spaced closed antenna loops, and a coupling circuit connected to said antenna coupling ele ments and including phase shifting means for combining the signals in said spaced antenna loops in proper phase relation to provide a signal for said wave signal device which has a substantially non-directional characteristic.

4. In a vehicle having a unitary metallic body extending over its top and sides and in which there is provided a wave signal device, a loop antenna system comprising, thin strip-like conductors having substantially greater conductivity than the metallic vehicle body provided on the vehicle body, insulatin means positioned between said metallic vehicle body and said strip-like conductors, one of said conductors extending from one rear corner diagonally across the top of the body of the vehicle to the opposite front corner thereof, a second one of said conductors extending from the other rear corner diagonally across the top of the body of the vehicle to the other front corner thereof, a pair of antenna coupling elements, electrical conductor means respectively connecting one of said antenna coupling elements in series with a respective one of said strip-like conductors to provide a pair of angularly spaced closed antenna loops, and a coupling circuit connected to said antenna coupling elements and including phase shifting means for combining the signals in said spaced antenna loops in proper phase relation to provide a signal for said wave signal device which has a substantially non-directional characteristic.

5. In a vehicle having a unitary metallic body extending over its top and sides and in which there is provided a wave signal device, a loop antenna system comprising, thin strip-like conductors having substantially greater conductivity than the metallic vehicle body provided on the vehicle body, one of said conductors extending from one rear corner diagonally across the top of the body of the vehicle to the opposite front corner thereof and extending from both ends down the sides of the body of the vehicle,

a second one of said conductors extending from the other rear corner diagonally across the top of the body of the vehicle to the other front corner thereof and extending from both ends down the sides of the body of the vehicle, a pair of antenna coupling elements, electrical conductor means respectively connecting one of said antenna coupling elements in series with a respective one of said strip-like conductors to provide a pair of angularly spaced closed antenna loops, and a coupling circuit connected to said antenna coupling elements and including phase shifting means for combining the signals in said spaced antenna loops in proper phase relation to provide a signal for said wave signal device which has a substantially non-directional characteristic.

WILLIAM L. EVERITT.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 1,626,464 Heina Apr. 26, 1927 1,997,271 Zepler Apr. 9, 1935 2,111,398 Kippenberg Mar. 15, 1938 2,212,253 Stief Aug. 20, 1940 2,280,562 Weagant Apr. 21, 1942 2,351,947 Gabler June 20, 1944

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