US2133855A - Antenna system for motor vehicles - Google Patents

Description

Oct. 18, 1938. G. w. FYLER ANTENNA SYSTEM FOR MOTOR VEHICLES Original Filed July 18, 1954 Inventor. George W F yler",

Patented Oct. 18, 1938 UNITED STATES ANTENNA SYSTEM FOR MOTOR VEHICLES George W. Fyler, Stratford, Conn., assignor to General Electric Company, a corporation of New York Original application July 18, 1934, Serial No. 735,756, now Patent No. 2,110,016, dated March 1, 1938. Divided and this application August 19, 1937, Serial No.'159,899

3 Claims.

This application is a division of application Serial No. 735,756, filed July 18, 1934, Patent No. 2,110,016, dated March 1, l938,for Antenna system for motor Vehicles.

My invention relates to antenna systems for radio apparatus, particularly to transmitting antennas for radio equipped motor cars, and its object is to provide an inconspicuous, simple, and eflicient antenna arrangement for such vehicles.

The invention is of particular usefulness when applied to radio equipped police motor cars, wherein it is desirable to install both a receiving antenna and a transmitting antenna for the radio system. In such installations the receiving antenna has commonly been mounted in the roof of the car and a vertical transmitting antenna extending well above the roof has been mounted in the rear of the car.

Difficulties have been encountered in the use of a transmitting antenna of the above-described vertical type installed on a motor vehicle. It has been found, for example, that the radiation of energy from this vertical transmitting antenna is far from uniform in all directions, thus seriously limiting in certain directions the distance at which speech or other signals radiated from the vehicle are of sufficient strength to be picked up by radio receiving apparatus.

It is a further disadvantage in the use of the vertical transmitting antenna when installed on a motor car that the antenna adds an undesirably conspicuous element to the car body. This latter disadvantage of the vertical antenna is of particular moment in the case of radio equipped police cars. It has been found very desirable that police motor cars be not unduly conspicuous, and therefore, that the above-described vertical type of transmitting antenna be dispensed with and that the transmitting antenna either be completely concealed or be of such nature as to escape notice.

In accordance 'with the present invention, the, above-mentioned and other difliculties are overcome by utilizing, as a transmitting antenna body or assembly, or even substantially the entire vehicle body, may be utilized as'antenna means. The above-described conductive members may be arranged to operate not only as transmitting but also as receiving antennas.

The above-mentioned conductive members perform their new electrical function as antennas only when the radio apparatus 'of the vehicle is operating; they perform their usual mechanical functions under both operating and non-operating conditions of the radio apparatus. The mounting arrangement and form of the conductive members and their means of connection to the radio apparatus all meet the requirement that it shall not be apparent to observers that these conductivemembers are intended to function as antennas. 1 1

I have discovered that the bumper members of a motor car or similar vehicle maybe utilized to great advantage as conductive members for the above-described antenna use. To operate as an antenna one or more of'the bumpers may be connected to the radio apparatus, the bumper memher or membersbeing insulated at one point at least from the vehicle.

The insulating and connection arrangements are such that the appearance of the bumper element and the adjacent portion of the vehicle is practically unchanged, or the changes in appearance are of too slight a nature to attract attention.

The antenna means, in accordance with my invention may also be constitutedby' a conductive member mounted at the rear or frontof the vehicle in or near the usual rear or,front bumper position, and projecting from the vehicle to form an antenna functioning substantially in the same manner as the antenna constituted, as above-described, by a usual bumper member.

In case one bumper member only is utilized as an antenna, it is preferable to employ the rear bumper; The radio transmitting'apparatus which supplies current to this rear bumper antenna is then conveniently mounted in a trunk or compartment at the rear of the car and is connected to the rear bumper by a transmission line which is short, thereby reducing losses in the line.

Preferably when one bumper only is employed as an antenna the bumper is insulated at one point only, as at one extremity, fromthe frame or other portion of the vehicle to which it is ad'- jacent, and is electrically connected at another point, as at the other extremity,to the vehicle. The transmission line from radio apparatus may conveniently be connected to the bumper at the I point thereof at which the bumper is insulatingly connected to the vehicle.

In this latter arrangement in which one bumper only is employed as an antenna, the bumper constitutes together with the adjacent metal portion of the vehicle a horizontal loop radiator or transmitting antenna.

By the incorporation in the radio apparatus of a suitable push-pull transmitter circuit arrangement the connection to the bumper may be made, through a two-wire transmission line, to two spaced points of the bumper, which is entirely insulated from the vehicle. In this latter circuit arrangement the bumper may be operated, for example, as a dipole antenna having a voltage node at its center.

When a bumper is arranged as hereinbefore described to operate as an antenna, a desirable form of the bumper includes a main body portion and reentrant end portions the bumper being mechanically connected to the vehicle at the inner extremities of the reentrant portions,

there being preferably no metal struts or similar members in electrical contact with and extending across the bumper. In a bumper of this form no portion thereof is short-circuited by conductive struts or similar elements, the full length of the bumper being thereby availabl as a radiator of signal energy.

It has been suggested heretofore to employ as automobile radio antennas metallic members under and spaced from the running board, vor to employ metallic members in the roof of the car. It will be noted that such running board and roof top antennas are primarily capacitive antennas, that is, they consist of a large area of metal connected by a shielded lead-in to the receiver (or transmitter) located at any point in the car; As radiators of. radio frequency energy such capacitive antennas are definitely inferior to my bumper antenna, which is an inductive radiator. At very high frequencies, for example 30 megacycles, the roof antenna and the running board antenna require considerable charging current due to their low capacitive reactance, and since the .radiation resistance must be low the losses in the coupling and tuning circuits associated with these antennas are inherently high. The bumper antenna being an inductive device has an appreciable radiation resistance particularly at high frequencies, and its inductive reactance is not excessive. It is by analysis a low loss conducting loop reasonably isolated from the car. The inductance of the bumper antenna simply requires additional voltage for feeding the antenna and, in general, the voltage supply in a transmitter is normally nearly correct for easily feeding the bumper antenna without complicated loading circuits. A capacitive antenna, however, requires high current and low voltage with consequent losses in conducting members. Thus the bumper antenna is more eflicientas a radiating device than the above-mentioned running board or roof antennas. Also, the field pattern of. the bumper antenna is nearly circular and thus normally most desirable. Since the running board antenna is definitely more shielded than the bumper antenna by the car body and chassis structure its field pattern tends to be more peaked in the. direction of the side of the car.

Further, the location of the bumper on an automobile is such that an antenna constituted by the bumper is more isolated from the automobile body than either the roof antenna or the running board antenna. In the latter case the metallic member constituting the antenna must be located several inches below the running board to be effective for radio operation between the automobile and distant radio stations or sets, yet must be reasonably well spaced from the ground to prevent its being knocked off when going over bumps. Since, as above explained, it is a capacitive antenna, it does not have good radiating properties due to its being within a few inches of the ground and the capacitive changes due to variations in this spacing tend to cause frequency variations and wide variations in output in a car transmitter. The bumper antenna, however, being an inductive instead of a capacitive device is not appreciably affected by variations of. the spacing to ground, particularly since it is normally higher than the usual running board type of antenna, and therefore, considerably farther from the ground. From the mechanical standpoint it is to be noted that the running board antenna is objectionable since it is liable to damage by water sprayed from the front wheels in wet weather, and from stones picked up by the front wheels.

It has also been suggested heretofore to employ as automobile antennas fortransmission over a very short distance metallic members mounted under the automobile body and closely adjacent the metal under parts thereof, or else mounted under and very closely adjacent to the metal running board. Such antennas operate as closed loops disposedin a vertical plane and signals from these antennas have practically no influence upon distant radioreceiving sets due to the shielding of the antenna loop from above and laterally by the metal body and running board. My bumper antenna, however, being well isolated from the metal elements of the automobile and being located well above the ground beyond an extremity of the automobile, is substantially free from the shielding and excessive reflection effects of the automobile body metal elements. Due to this isolation from the end of the automobile body and to the substantial height above the ground the bumper operates in connection with the adjacent metal portion of the automobile body as a horizontal loop antenna with relatively high efficiency in all directions between the automobile and distant radio sets or stations. 7

In characterizing the bumper antenna system as inductive it will be understood that the system is inductive when the length of the wave has a definite relation to the length of the antenna, the frequency being below the valueat which the reactance of the system becomes capacitive. It will be further understood that in operation of the antenna system which includes the bumper connected as a dipole antenna, the coupling adjustment in the antenna systemwill under certain conditions determine whether the reactance is inductive or capacitive.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Figs. 1 and 2 are respectively a longitudinal plan View and a perspective view of a radio-equipped motor vehicle in which my invention has been embodied; Fig. 3 illustrates an insulating means for connecting a bumper inconspicuously to a motor vehicle; Fig. 4 is a circuit diagram illustrating connections, through a transmission line, from radio transmitting apparatus to one point of a bumper constituting part of a loop antenna; Fig. 5 is a circuit diagram similar to that of Fig. 4 but illustrating connections to two points of a bumper operating as a dipole antenna; and Fig. 6 illustrates signal radiation patterns of a bumper type transmitting antenna and of a vertical type vehicle antenna.

In Figs. 1 and 2, the numeral Ill designates a motor vehicle for police or other use, in which is installed a two-way radio communication system comprising radio signal generating apparatus ll preferably mounted in a trunk or compartment 12 at the rear of the vehicle and connected to suitable microphone, loudspeaker and control means installed toward the front of, or other suitable position in the vehicle and indicated generally by the numeral l3.

The receiving antenna may be of any suitable or usual form, such as a wire or other antenna member (not shown) which may be mounted in the roof of the vehicle or in any other suitable position.

In order to radiate speech or other signals effectively from the vehicle without at the same time adding to the vehicle an antenna element which is conspicuous, or which is even noticeable to an observer of the vehicle, the generating apparatus l l is arranged to supply its output energy to one or both of the bumpers I4 and I5.

In the present embodiment of the invention the rear bumper l4 alone is preferably utilzed for this purpose, and this bumper is preferably so mounted that it is insulated at one point from the 1 vehicle by an insulating fastening means [6 and electrically connected at another point by a suitable fastening means IT.

The bumper l4 may be of any usual form but it is preferable that the form be such that the full length of the bumper may be utilized as a radiator of energy. In the present embodiment of the invention the bumper comprises a main portion l8 and two reentrant portions [9 and 20 the extremities of which are connected respectively to the vehicle by the fastening means It and H.

The insulating fastening means I6, as shown in greater detail in Fig. 3, may comprise a bolt 2| within a mica insulating sleeve 22, and insulating rings 23, preferably of mica sheets tightly pressed and formed into solid blocks by a suitable binder.

As shown in Fig. 4, the radio apparatus l I may comprise an output circuit 24 which is connected to the bumper l4, preferably at the insulating fastening means [5, through a transmission line 25. The transmission line may comprise a metal conductor 26 inclosed in a tubular shield member 21 from which the wire is insulated by spaced insulating discs 28.

As shown partially in diagram in Fig. 5, the radio apparatus designated in Figs. 1 and 2 by the numeral I I may comprise, instead of the output circuit 24 illustrated in Fig. 4, a push-pull output circuit 29 connected, through a two-wire transmission line, to two spaced points, as 30, 3|, on the bumper, which in this case is completely insulated from the vehicle. With this latter circuit and connection arrangement, the bumper may be operated as a dipole antenna having a voltage node at its center.

Referring to the signal radiation patterns illus trated in Fig. 6, curve 32 is a typical field pattern given by a vehicle transmitter antenna of the hereinbefore mentioned vertical type mounted at the rear of the vehicle and extending above the roof. It will be observed that the radiation efficiency with this antenna is far from uniform in all directions, the ratio of maximum radiation, in a certain direction, to the minimum, in another direction, being as great as twenty to one.

Curve 33 is a typical field pattern given by the antenna constituted by a bumper antenna such as bumper 14. This pattern 33 shows that the radiation of signal energy, from the bumper antenna in accordance with the present invention, is far more nearly uniform in all directions than in the case of the vertical antenna above-described, and that the radiation efficiency of the bumper antenna is fully adequate for efiicient radio reception in all directions from the vehicle. The field pattern illustrated in curve 33 was given by a bumper arranged as shown in Figs. 1, 2 and 4 wherein one end of the bumper is electrically connected to the car frame and the other end, insulated from the car frame, is connected to the radio apparatus. In this arrangement the antenna current flows around the horizontal loop enclosed by the bumper and the car frame. The radiation pattern given by the bumper when insulated at both ends and fed at the central portion by a two-wire transmission line as in the arrangement as illustrated in Fig. 5 is, however, essentially the same as the radiation pattern given by the bumper arrangement illustrated in Figs. 1, 2 and 4 due to the circulating current through the two end insulators.

I have described my invention in a particular embodiment for purposes of illustration. It will be understood, however, that the invention is susceptible of various changes and modifications without departing from the scope of the invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination with a vehicle, of a radio apparatus mounted on said vehicle, a bumper mechanically connected to an end of said vehicle and electrically insulated throughout its length from said vehicle, push-pull transmitttr means in said radio apparatus, and means to connect said push-pull transmitter means to two spaced points of said bumper whereby said bumper operates as a dipole antenna having a voltage node at its center.

2. The combination with a vehicle, of a radio apparatus mounted on said vehicle, a bumper mechanically connected to an end of said vehicle and electrically insulated throughout its length from said vehicle, and means to connect said radio apparatus to two spaced points of said bumper, whereby said bumper operates as a dipole antenna.

3. In combination, a vehicle, a radio apparatus mounted on said vehicle, a metallic bar member mechanically connected to said vehicle at an end thereof and spaced from said end a substantial distance, said metallic member extending transversely of said vehicle a distance substantially equal to the width of said vehicle, said bar member being insulated throughout its length from said vehicle, and means to connect said radio apparatus to two spaced points of said bar member, whereby said bar member operates as a dipole antenna.

GEORGE W. FYLER.

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