US2520984A - Antenna system - Google Patents

Description

Sept. 5, 1950 F. B. WILLIAMS ETAL ANTENNA SYSTEM 3 Sheets-Sheet 1 Filed Jan. 25, 1947 Receiver FIG. 6

I INVENTOR. Fred B. Williams Fred R Hill P 1950 F. B. WILLIAMS ETAL 2,520,984

ANTENNA SYSTEM Filed Jan. 25, 1947 s Sheets-Sheet 2 FIG' I5 n6 I us R. F. AMPLIFIERC Wm H l 0: o 0) I20? LOCAL L INTERMEDIATE' i s osc lLLAToR FREQ. AMP. o 5

rm um! I 12w .0 K e o AMPLlFlER MIXER INVENTOR. Fred B. Williams By Fred P Hill p 950 F. B. WILLIAMS ETAL 2,520,984

ANTENNA SYSTEM Filed Jan. 25, 1947 '3 Sheets-Sheet 3 TO OSCILLATOR MODULATOR TO AV (1) 08 TO OSCILLATOR MODULATOR P TO AVZ Tronsmifler INVENTOR.

Fred B. Williams 7 BY FredPHill Attorney Patented Sept. 5 1 950 UNITED YS TAT ES 2,520,984

ANTENNA SY ST-EM Fred B. Williams, Lincolnwood, and'LFredI. Hill, Franklin Park, 111., negate ,to' 'M0tcr 1a, ;l,ilc,, a corporation of-Illinois Application January 25, 1-9 4Jl,:Seri al No.- '7=2 li36 19 Claims.

. L1 This invention relates to antennas and antenna systems for wave signal devices and more par- -ticularly relates'to such an antenna and antenna system for a-three dimensional conducting body as for example mobile vehicles wherein the signal' radiating or signal pickupportion of the antenna system comprises solely portions of the conducting body.

'In connection with wave signal devices for use -on-mobile craft such as automobiles, trains, boats and airplanes whether they are radio receivers or transmitters, there has always existed 1 the problem of providing effective signal pickup means in the case of a receiver or signal radiating'means in-the case'of a transmitter. This is primarily due to the fact thatgenerally a limited mounting space is providedand in-the-ease of radio receivers, for example-such limited space 'militated against obtaining adequate signal strength at the receiver .in the presence-of a 'large amount of undesirable electrical interference generallypresent in .1 connection With'the prime movers of such mobile craft.

"Although-these problems have beenpresent toagreater or lesser degreein connection with various typesyof mobile vehicles they have been especially present and-most serious=in connection with'automobiles, trucks and airplanes. -In the former, the mountingqspacehas generally been very limited whereas in connection with airplanes the question Of; providing, antenna, means which-dc not produce any additional drag or interfere with the streamlining thereof has al- .ways been a problem. In connection-With both automobiles and air-planes there arealways the,

factors of appearance, installation, and the like.

In recent years in connection with automobil es, perhaps the antenna employedmost extensively was the vertical jointed poletypeantenna which is mounted on the outsideof .an automobile body or at least extends outside and above the automobile body when in full operating position. Antennas of this type oftenare costly in an d; of themselves and the installation .problems involved are. relatively great even asidefrqrn the question of cost which is substantial. Suchantennas usually require cutting through the ,body of the automobile and in many cases, the .cut comprises a permanent. defacement. inaddi- ,tion, there has always been thecriticism .ofoutsideantennas, 0. the a automobiles-from the, appearance standpoint. Also,,such.antennas often interfere with the movement of-the automobile .while entering a garage or the like when not retracted thus requiring the operator to remember 2 to retract the antenna which is an.-ad.ditiona1 inconvenience.

Yariousparts of the automobile such as the were n tlr r o m r v n e e- 5 Jtor have. been'infsulaltedfrornthe automobile bddy an mplgv d a th a t na or i na r li 'means in the case of areceiver. However, these installations require thatthe particular .part is rp rm nentl y n la d rom ther ody us e atly increa in th ex ene f fh 'ioi ite pol yp n e n nd t th antenna mentioned above used inconneetion with .IHQLll Y hi l? 39 ta qm bi l Q /g very satisfactory-when used on the open road, 5 have beenfound to be quite unsatisfactory in 'variousshielded; areas such as under viaducts as we'll as in sections of the country such as in certainregions having eirtensive deposits of i iron ore and the-l-ike. -'It would be desirableftherefore, to providean antenna which would over- :some the objections setforth abovein :connec- -tion-with previoustypes of antennas which would in itself be; inexpensive, require noadditional installation cost, cause no defacementof the 5--mobile vehicle, and which would provide very -satisfactory operation-whether used with are-- --ceiver or a-t'ransmitten-being substantiall unaffected by adjacent bodies such as viaducts and -the -1-ike. It would furthermorebe desirable-to provide an antenna by employing therefore-part -of the -mobilel-veh'icle which-has anothenprimary :function but-would also actasan antenna. 7 There .have been numerous attempts made-to employ the .abodies. of mobile vehicles as antennas. IIn the 1 various arrangements suggested heretofore employing the automobile body .or bod of the mobile ,v ehicleitself as the antenna, difilculties have been encountered in obtaining sufficientsignal strength without too; much noiseandalsoto eliminatethe directional characteristics ,in some st rms, of heSe-entennas ;In the case rota-rewe ve 0 eXamm emphyinath car body; in one prior arttype, cf antenna very finerecep- @191 mi ht a i ins from a a t la sta .when driving along one street ,or alongonehigh- @Wl i when,chan ina i of, a e tt .:1 r9 lh mis tbecgm very ns t s egto v- Obviously, an antenna employed in connection w t eqbi fl lli e a ikelv to W .1 a e q m ste t r .fii r ti m qhamqt r sti It wouldl be desirable, therefore, to provide an antenna fonmobile vehicles employing the conducting body of a vehicle as an antenna which antenna isa loop antenna having no directional .35 characteristicsand furthermore, which antenna 3 is very satisfactory from the standpoint of signal strength and the like being much less aifected by adjacent bodies than similar devices used heretofore.

Accordingly, it is an object of the present invention to provide a new and improved antenna system for mobile vehicles.

It is another object of the present invention to provide an antenna for three dimensional conducting bodies in which the antenna portion wholly comprises the three dimensional body portion which body portion has a primary function other than that of serving as an antenna.

It is another object of the 'present'invention to provide a pair of loop antennas which in conjunction with a special coupling circuit produce a non-directional antenna pattern and which loop antennas are formed solely of the body of mobile vehicles and consequently which eliminate installation costs and defacement of the vehicle as was required heretofore.

It is a further object of the present invention to provide an antenna system for mobile vehicles which is inexpensive, which provides more satisfactory signal reception or transmission than antennas employed heretofore and which is very pleasing in appearance.

It is another object of the present invention to provide an antenna which is formed by the conducting body of a mobile vehicle for example which provides reception or transmission at least equal to and generally superior to antennas employed heretofore with much lower installation and maintenance costs.

Still another object of the present invention is to provide an antenna system for mobile craft of improved type which has no objectional appearcircuits so as to provide a non-directional antenna. I

I Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present invention, reference may be had to the accompanying drawings in which:

Fig. 1 is a perspective view of a mobile vehicle embodying the present invention with dotted lines indicating the effective paths of the antenna loops formed of the car body itself;

Fig. 2 is an interior view of a mobile vehicle showing a specific example of terminals provided on the car body which are the terminals of a plurality of loop antennas formed solely of the mobile vehicle body; Fig. 3 is a circuit diagram of an arrangement for connecting the antenna of Figs. 1 and 2 to a radio receiver for testing purposes to show the effectiveness of first one'loop then a second loop and then both loops combined;

Fig. 4 is a diagram of the reception patterns 9;" the two loop antennas shown in Fig. 1 taken 4 separately by means of the circuit shown in Fig. 3;

Figs. 5 and 6 are representative reception pattern diagrams of loop antennas to aid in understanding the non-directional characteristics of the antenna of the present invention;

Fig. 7 is a circuit diagram by means of which the antenna of Figs. 1 and 2 may be used with any radio receiver;

Fig. 8 is a circuit diagram illustrating another embodiment for coupling the antenna of Fig. l to a radio receiver;

Fig. 9 illustrates still another modification of the arrangement shown in Fig. 8;

Figs. 10 and 11 illustrate still other modifications of the arrangement of Fig. 8;

Fig. 12 is a schematic diagram of one loop of the antenna of Fig. 1;

Fig. 13 is an equivalent circuit diagram of the schematic diagram of Fig. 10 showing a modification of the present invention;

Fig. 14 is a block diagram of the present invention as applied to a transmitter; and

Fig. 15 is a block diagram illustrating still another modification of the present invention.

In practicing the present invention, there is provided a radio receiver or a radio transmitter associated with a mobile vehicle having a conducting body generally formed of metal. In accordance with the presentinvention, this body is used as the sole signal pickup means. In connection with a radio receiver for example, connections are made to the conducting body so as effectively to provide two loop circuits displaced in phase from one another so that regardless of the orientation of the mobile vehicle with respect to a particular broadcasting station, the signal strength in the case of a receiver will be substantially constant and substantially unaffected by various bodies. adjacent thereto, such,'for example, as viaducts, overhead structures and the like. The terminals of the two loop circuits uninsulated from each other and formed wholly of the mobile vehicle body are connected through suitable means to a receiver or transmitter.

Referring now to the drawings, there is illustrated in Fig. 1 a mobile vehicle generally indicated at H]. It should be understood that although the invention is particularly disclosed in connection with its application to an automobile, it might equally be applicable for use with other 'mobile vehicles and as will become apparent as the following description proceeds, with various mobile vehicles as for example helmets and the like where it is especially desirable that the presence of an antenna is not discernible. At the present time most modern automobiles are constructed of bodies formed of conducting material, and it has been the use of such conducting or metal bodies that has militated against 'antennas being built into the motor vehicle itself since the metal body would shield the antenna. In accordance with the present invention, the mobile vehicle In specifically illustrated as an automobile is provided with a metal body ll of conventional form and as shown in Fig. 2 ofthe drawings, includes a suitable windshield l2 and a dash or instrument panel 53 adjacent which a radio receiver such as M is customarily mounted. As shown in Fig. 2 of the drawings, the body is also'provided with doors such as 55 and B6. The modern automobile is often provided with a pair of visors such as 11 and 58 which are usualiy mounted to suitable frame members such as 19 and 20, respectively.

It .is apparent that the conducting body .of a mobile vehicle such as an automobile would pro- .vide a closed loop which could be .used as an antenna which would act as a signal collector in the case of .a receiver .or a signal radiator in the case of a transmitter. Extensive tests have in? dicated that by tapping the conducting .body at spaced points a radio frequency signal can be obtained from a broadcasting station when the mobile vehicle is disposed within the range of such broadcasting station. It is not known just what path the radio frequency currents take in travelling through the loop circuit furnished by theconducting body. However, it is a well known fact that a loop antenna has a .directivity pattern somewhat in the form of a fi ure 8 with maximum radiation or reception along the plane of the loop. Consequently, tests have indicated that for certain connections made to the car body, a loop is provided which has the same directional characteristics as an equivalent loop since by properly orientating the mobile vehicle, maximum reception in the case of the receiver can beobtained for one position and substantially no reception for some other positions. In other words, the reception pattern like that of a loop antenna has a null point. It is for this reason that the use of a metal body such as the body of an automobile has not been used successfully heretofore as the loop antenna of a radio receiver associated therewith since obviously a mobile vehicle cannot satisfactorily employ a directional antenna which is the characteristic feature of a loop antenna.

Non-directional loop antennas have been employed which have substantially a circular directivity pattern. Such antennas have usually comprised two separate loop circuits displaced in space from each other by approximately ninety degrees. It is apparent that the reception patterns of each of two loop antennas might be somewhat in the form of a figure i3; and in Fig. 5, there is illustrated the reception pattern A for one loop antenna and. the reception pattern B for another loop antenna which latter is displaced in space from the former by ninety degrees. These patterns each represent the ideal reception or radiation patterns for loop antennas with no external objects affecting the field. It is apparent that if the reception patterns A and B for the two space displaced loop antennas were superimposed by direct addition or subtraction that a composite reception pattern such as is illustrated in 4 Fig. 6 by the curve C could be obtained. An examination of Fig. 6 of the drawings which shows the combination of the two patterns A and B of Fig. 5 indicates that the null point has not been eliminated but it has merely been shifted to a point between the two patterns A and B. In other words, the two radiation patterns A and B of Fig. 5 combine such that at particular points the two inphase components add and the two of opposite phase cancel toproduce a resultant field. The maximum signals of Fig. 6 are stronger than the maximum signals of either of the antennas producing the patterns A and B of Fig. 5 and also the minimum signals or null points are somewhat sharper.

If the loop antennas which are displaced in space from each other by an angle of approximately ninety degrees were connected so that the phase relationship of the signals received or transmitted were shifted such that at all angles of orientation th si nals were additive, and the signals for each :loop were of equal wmagnitude then asubstantially circular pattern wouldresult and consequently, a non-directional loop antenna would .be provided. It has been found in connection with antennas that currents are caused to flow in closed loops by the magnetic compone-nt of the electromagnetic radio waves. Thus, where interfering bodies such as overhead structures, viaducts and the like are involved loop antennas are superior to types of antenna which pick up the electric component of the electromagnetic waves since the overhead structures act as an electrostatic shield attenuating the electric component more than the magnetic component.

It is apparent that if the body of an automobile, for example, were formed of Various conducting parts insulated from .each other that the problem of employing the body as a non-directional loop antenna wouldbe considerably simplified. However, modern automobiles have their bodies formed of sheet metal stampi-ngs of substantially continuous conducting portions so that heretofore the possibility of obtaining effective space phase displaced conducting l00ps in the electrically interconnected conducting body was unknown as was also the additional problem of tapping Voltage from two closed space displaced loops. In an attempt to solve this problem, tests were made in connecting various points on the car body with a radio receiver, and it was found that for various connections to the body, effective loop circuits were provided which were orientated differently from each other as was determined by varying the position of the mobile vehicle relative to a broadcasting station to which the receiver associated with the vehicle was tuned and noting that the null points for various effective loop circuits occurred at different orientations of the automobile. Consequently, attempts were made to provide a plurality of taps on the car body which could be the terminals of a plurality of effective loops employing the car body itself as the loops which were displaced from each other suificiently to give a non-directional antenna. It was found that by trying various points on the body of the mobile vehicle for signal pickup points that various signal strengths were obtained and in addition, it was found that these various points were associated with eifective loops in the car body for the radio frequency current which loops were orientated in their eifective operation in various ways. It was found, for example, that if a tap connection to the car body were made at the support l9 for the visor ll above the windshield and at a point 22 directly below the support is below the instrument panel E3 of the mobile vehicle that a very satisfactory signal could be received. Such connections, it was found by determining the null point, provided an effective loop circuit that went from the front to the rear of the body which path might b represented by the dotted line 23 in Fig. 1 of the drawings. It should be understood that the particular paths which the radio frequency currents took through the body are unknown and probably many and diverse paths were taken. The resultant of these radio frequency'currents, however, was shown by tests to be the same as if the body were repiaced by a single loop circuit similar to the circuit 23 of Fig. 1. In other words, the conducting body of the automobile provided an efiectiv loop circult 22 which would function substantially like such a loop circuit 23 if it were built into a nonconducting body such as a plastic body for example. Tests further indicated that by making connections to the body as indicated at the visor support at the upper right-hand corner of the body II and to the point 24 on the oppositeside of the car from the point 22 that the car body ll acted as an eifective loop circuit which could be replaced by the loop circuit shown in dotted lines at in Fig. 1 of the drawings. Actual tests indicated that these effective loop circuits were displaced from each other in space by an angle in the neighborhood of forty-five degrees. Theoretically, it would be desirable for these effective loop circuits 23 and 25 to be displaced from each other by ninety degrees but it was found that a displacement around forty-five degrees was very satisfactory by virtue of the fact that the small variations in signal strength, due to the fact that the reception pattern of the substantially non-directional antenna differed slightly from a true circle, would be compensated for in modern radio receivers which employ automatic volume control or automatic gain control means. Actual tests indicated that with very sensitive receivers for example it would be possible to employ loops displaced in space from each other by an angle considerably less than forty-five degrees with fairly satisfactory results. It should be understood that the closer the phase displacement in space approaches ninety degrees, the more nearly the reception pattern in the case of a receiver approaches a true circle which is the ideal situation. With the ideal situation it would not be necessary to employ automatic volume control.

It should be understood that many connections for the effective loop circuits 23 and 25 in the conducting body are possible and it is not intended in this application to limit the particular points of connection to those specifically described. There are several criteria for these points of connection, however, which are important. First of all, these points of connection should be such that two loop circuits are obtained displaced in space from each other preferably between forty-five and ninety degrees, although in some cases less than forty-five degrees is satisfactory, thereby insuring a substantially nondirectional antenna. Secondly, these points of connection should be such that they are readily available for connection to the receiver. It is apparent, for example, that a connection to a door of the automobile or some such point might be undesirable due to the awkwardness in the first place and the complications necessitated to permit movement of the door. Since the automobile receiver is customarily mounted on or adjacent to the instrument panel, it is desirable for the connections to be not too far removed therefrom thereby reducing the length of electrical connections between the receiver and the terminals on the car body which act as the antenna. The particular connection points shown in Fig. 2 by way of example are desirable in that the visor supports are already available and providing that they are electrically connected with the car body provide a very satisfactory means without the automobile manufacturer having to make any changes. The terminals or taps such as 22 and 24 could be provided in the manufacture of the automobile as by providing a screw welded directly to the body for example. Actually, the manufacturer would not need to cooperate in any way whatever since the body is 8 usually provided with numerous openings in th general area around the terminals 22 and 24 through which a suitable bolt or other connecting means might be extended. In any event, the particular connections on the car body such as |9,'22, 23 and 24 could be determined by each manufacturer so as to provide the most desirable connection points for every automobile whereby the automobile would be provided, with substantially no additional cost, with a built-in wave signal antenna. In this way, a radio installation for an automobile whether it involved a radio transmitter or a radio receiver or both would require no antenna expense nor antenna installation expense. 1

In Fig. 3 there is illustrated a circuit diagram of a testing device generally indicated at 30 which enables one to determine experimentally the most effective connections on an automobile body whereby such body formed of conducting material may provide a non-directional loop antenna. It should be understood that such a testing device 35 could be employed in connection with any mobile vehicle and reference to its use with automobile bodies is by way of example only. As illustrated, the testing circuit 33 of Fig. 3 comprises three coaxial cables designated at 3!, 32 and 33, respectively, which coaxial cables are provided with a common ground connection 33. These cables 3i to 33 are connected to a pair of primary windings 34' and 35 having a common connection 36. The common connection 35 is connected to the coaxial cable 33 while the other terminals of the windings 34 and 35 are connected to the coaxial cables 3! and 32, respectively. A secondary winding 31 is inductively coupled to the windings 3 2 and 35 and is connected in parallel with a variable capacitor 38 to provide a tuned circuit generally indicated at 39. A suitable amplifier comprising the electron discharge valve ill is provided whose plate circuit includes a source of potential generally designated at 4! and a tuned circuit 42. The output of the amplifier 5G is connected through a suitable coupling capacitor 43 with a coaxial cable 44 leading to the conventional receiver in the case of a radio receiver. 'The coaxial cables 3| to 33 are adapted to be connected in a predetermined manner to the taps provided on the automobile body which effectively are the terminals of the loop circuits in the conducting body. By shorting one of the coaxial cables as by means of a shorting plug such as is indicated at 45 in Fig. 3 of the drawings, it is possible to operate the receiver from one loop circuit at a time or from both loop circuits. For example, if the coaxial cable 3! were connected to the terminals l9 and 22 and the coaxial cable 32 were connected to the terminals 29 and 24 with the loop antenna 23 being referred to as antenna No. 1 and the loop antenna 25 being referred to as antenna No. 2, it is possible to obtain the directivity patterns of each of these antennas separately by orientating the automobile relative to a particular broadcasting station. If the shorting plug 45, for example, were connected to short 7 the coaxial cable 32,then the reception pattern actual tests for antenna N0. 2 is illustrated by the curve F in Fig. 4 of the drawings. By shorting the coaxial cable 33 with the shorting plug 45, a reception pattern for the combined antennas could. be obtained. It is apparent that with such an arrangement themanufacturer of an automobile could readily find the most desirable connections for a non-directional loop antenna employing the automobilebody which would give the desired signal strength and furthermore, would be located in a mostsatisfactory position for mak ing. electrical connections to a wave signal tic-- vice while requiring substantially no expense in the manufacture thereof.

For the purpose of coupling the two loop antennas such as 23 and 25 effectively tormed'as a part of the mobile vehicle.- body of Fig. 1 to a radio receiver so as to provide a non-directional loopantenna, various coupling circuits: may be employed. In Fig. 7 there is illustrated a coupling circuit whereby any present radio receiver installation inv a mobile vehicle may be converted to employ the automobile body as. a non-directionalloop antenna. This coupling circuit, generally desi nated at. 5.9 in Fig. 7, comprises the coaxial cables 3i and 32 which are adapted to be connected to the terminals l9. and 22 and 25)- and 24, respectively. The coaxial cable 31 terminates in a primary winding 53, while the coaxial cable 32. terminates. in a primary winding 54. These primary: windings. 53 and 5.4. are inductively coupled with tuned. circuits 55 and 56, respectively, comprising the secondary windings and 53. and the variable capacitors 59 andftiil. Thetuned circuits 55 and 5c are arranged tobe supplied to the input circuits of a. twin triodc am.- plifier 61. having anodes E2 and 63, a cathode 64 and control electrodes 65 and 6.6.. The cathode 64. is grounded as indicated at 61.. The signal from. loop- No. 1 appears in. amplifiedform in. the. plate circuit. comprising anode 62, while similarly the signal picked up. by the loop No. 2 appears inampliiied form at. the plate circuit of anode; 5.3. In order to combine these signals suitable phase shifting. means, comprising a, capacitor t8- and resistor 69. are provided in the plate circuit of the twin triode 6i comprising the anode 52 thereby causing a 90.- degree phase shift of the signals picked up by antenna. No. l. or whatever amount. of phase shift. is desired in order to cause the reception patterns to combine into. a

substantially circular pattern. A suitable source of +3 potential is provided as indicated at 1.!!- whijch is connected throughsuitable resistors ii. and '12 to the anode: 53. and through a suitable resistor '43 to the anode 52'. The. total resistance of the series resistors Ti and 52 connected to the anode is equal to that. of the single resistor 13' connected to the anode. 621. The reason for this arrangement is to tak care of the. decrease in the signal. strength obtained from the loop. No. 1 produced by the phase. shifting elements- 63 and 6353. It is desirabl to. decrease the signal strength. of the signals which are not shifted in phase so that the, two. signals. after the phaseshifting operation is. performed are. substantially equal. The. output signal is obtained. at the terminal 'l' i between the resistors ii and E2 in the case of the radio irequency signal appearing in the. circuit including the anode 53'. With. the arrangement described. thus far, it is desirable to provide an impedance transforming device which may take the form of a cathode follower gen-- erali'y at 25 whereby the highirnpedance output of the amplifier circuit may be. coupled to a low input impedance. radio receiver through! the it coaxial transmission line 15a, for example. It is well known that a cathode follower circuit has an inherently low output impedance and a high input impedance. It should be understood that any other suitable impedance matching circuit maybe employed if desired.

In order that the non-directional loop. antennaformed of the conducting body of a mobile vehicle may be satisfactorily coupled to a radio receiver Without employing additional tubes or the like, the arrangement illustrated in- Fig. 8. of the. drawings maybe employed. The coaxial cables. 35. and 22 are adapted to be connected to the; input circuit of a radio receiver of which the. first tube or electron discharge Valve 16 is illus-- trated. Such electron discharge valve might. be a radio frequency amplifier or the like. It will be understood that in conventional radio re.- ceivers a tuned circuit such as is. indicated at. 11 is connected to the input circuit of electron discharge valve lt. Sucha tuned circuit may in clude a fixed inductance and. a variable capacitance, or a fixed capacitance and a variable inductance. As illustrated in Fig- 8, a Variable, capacitance i8 is illustrated. and a fixed inductance generally indicated at i9 is also provided which: comprises the two. sections um andv 191); A suitable padding condenser fit.- is provided for causing tracking with the other tuned circuits in the radio receiver and an automatic volume controlcircuit including the resistor 81 is normally connectedto the electron discharge valve it through; tuned circuit 1?. A ground connection for the tuned circuit. T! is indicated. at 8.2..

For the purpose of coupling the. loop antennas connected to coaxial cables 31 and 32 to the tuned circuit l! in a manner to produce the de-- sired phase shift mentioned above which phase shift may be with reference to only one of the received signals or which phase shift may be with. reference to both of the received signals, there is provided the coupling circuit. comprising phaseshifting resistances 82 and S3 and; coupling meansdi and With this arrangement, the radio frequency signal from coaxial cable 31 is inductively coupled through coupling. means. 84. comprising a winding inductively related with: the winding 19. The series resistor 82 causes a phaseshift of 45 degrees or thereabouts in one direc-- tion of the radio frequency signal supplied through coaxial cable 34. The radio frequency signal supplied through the coaxial cable 32 on the other hand is shifted in phase in the other direction by an. amount of theorder of id-degreesby means of a parallel resistor 85. In this case the capacitor 85 directly couples the coaxial cable 5.2 with one end of the inductive winding 7.9.. The coupling capacitor 85 also prevents theautcmatic volume control circuit including the resistor 8! from being shorted to ground. Themagnitude of the resistors 82 and 83 are varied to. give the desired phase shift between the two input signals and then the inductive coupling of the coupling means 84. is adjusted to give the same input sensitivity as that of the capacitive coupling means 85 to insure equal signals from each loop antenna. Actual tests on the circuit of Fig. 8 have indicated it to be very satisfactory. In view of the detailed description included above, the operation of the coupling means of Fig. 8 will. be understood. by those skilled in the art.

Aswasmentioned above, many radio receivers employed in connection with mobile vehicles such. as automobiles employ as. the tuning means thereof variable inductances rather than the 11 variable capacitance such as I8. In Fig. 9 there is illustrated a portion of the coupling circuit of Fig. 8 showing the same electron discharge valve I6 having its input circuit connected to a tuned circuit 98 including a variable iron core inductance SI and a substantially fixed capacitance 92 which may be variable to the extent of providing the necessary trimmer action. The coupling means 84 having the same reference numeral as the corresponding means in Fig. 8 of the drawings comprises'a few turns wound in inductive relation with inductance SL The problem involved in this arrangement is to get the same amount of mutual coupling throughout the entire tunin range or throughout the entire movement of the movable core 93.

In the arrangements described thus far for coupling the two loop circuits to a radio receiver so as to effectively provide a non-directional loop antenna, phase shifting means employing resistors and the like have been described. It will be apparent that changes in temperature of the ambient medium and the like will cause a change in the resistance of such resistors whereby the desired ninety degree phase shift will not be realized. In Fig. 10 there is illustrated a phase shift ing circuit in which the ninety degree phase shift once it is obtained will be insured regardless of temperature changes and the like. The corresponding parts of Fig. 10 are designated by the same reference numeralsas in Fig. 8. In order to couple the two loop antennas to the radio receiver in Fig. 10, there are provided two tunable resonant circuits 94 and 95. The resonant circuit 94 comprises a variable inductance 96 preferably of the so-called permeability tuned type and a suitable capacitor 9! which is adjustable for trimming purposes. The tuned circuit 95 includes a similar variable inductance or tuning inductance 98 and a capacitor 99 also variable for trimmer purposes. In addition, the tuned circuit 95 includes a winding I comprising a few turns inductively coupled with the winding 96, the number of turns being a small percentage of the number of turns in the inductance 98. Actually, the inductances 9S andQB comprise the secondary windings oftransformers having primary windings IIII and I02 respectively. The primary windings are connected to the coaxial cables 3! and 32, respectively, with suitable capacitors I93 and I04 shunted across the primary windings NH and I02, respectively. Each of the resonant circuits 94 and 95 are provided with a common ground indicated at HTS which ground is connected to each resonant circuit at a point adjacent on terminal of the capacitors 9'! and 99, respectively. It is apparent that the current and voltage of resonant circuit 94 are in phase as is also the case with reference to the resonant circuit 95. The currents in the resonant circuits S4 and 95 can also be adjusted to be in phase. The voltage across winding 580 which is inductively coupled with the winding 96 causes a component of current to flow in the resonant circuit 94 which is ninety degrees out of phase with the current flowing in resonant circuit 54 whereby the two components of wave signal current from the effective loop circuits 23 and 25 are displaced electrically by ninety degrees and supplied through a suitable coupling capacitor It! to the electron discharge valve 15. Preferably, the plate circuit of electron discharge valve i8 is connected through a broad band coil generally designated at I08 to the next stage of the receiver such as the oscillator-modulator; It will be understood that. n 1. he

ninety degree phase shift between the wave signal components obtained from loop No. -1 and circuit 94' includes a series winding I09 while the resonant circuit includes a series winding IIIl inductively coupled with the winding I09. The phase shift in this case will be identical with that discussed in Fig. 10 and for the same reasons. The circuits of FigslO and 11 have considerable advantage over the circuits previously described and the following three advantages are obtainable therewith: (1) Greater sensitivity; (2) Full ninety degree phase shift which is not possible with phase shifting circuits employing resistance and inductance; and (3) A constant phase shift across the entire frequency band.

From the above discussion, it will be appreciated that each of the loop antennas such as 23 and 25 forming an integral part of the conducting body of the mobile vehicle are essentially closed loops across a portion of which the input to the wave signal device is connected. In Fig. 12 there is illustrated a schematic diagram of one of the loop circuits such as 23 for example to which is connected the coaxial cable 3|. It is noted that between the terminals I9 and 22 there is a conducting portion I I I which to a certain extent short circuits or provides a short circuit across the loop circuit 23 and across the coaxial cable 3 I. Axially, this short circuit portion represented by the numeral I I I in Fig. 12 of the drawings is a small inductance for high frequency currents designated by the numeral III in the equivalent circuit diagram of Fig. 13 of the drawings. The part of the inductance of the total loop circuit of the automobile or mobile vehicle body loop across which it is convenient to make the connections is a small portion of the total in- 1' ductance of the loop. A considerably improved performance can be obtained in accordance with the present invention by adding the capacitor II2 across the terminals I9 and 22, for example, which capacitor II2 has such a value as to tune the inductance III of the car loop circuit 23 between the terminals I9 and 22 to resonance within the frequency range of the wave signal device associated therewith. The resonant circuit formed of the inductance III and the capacitor II2 provides a very high impedance or substantial open circuit between the points I9 and 22 thereby eliminating the short circuit across the terminals of the loop. 7

Although the invention heretofore has been described primarily in connection with a wave signal receiver, it will be understood that the antenna system of the present invention is equally applicable for use with radio transmitters. In Fig. 14 there is illustrated in block diagram a non-directional loop antenna formed of the car body of Fig. 1 shown schematically by the loop portions 23 and 25 which are connected by suitable connections IM and H3 respectively with the transmitter H5. It will be understood that for certain applications the same antenna formed of the body of the mobile vehicle may be used both for a wave signal receiver or a wave signal transmitter in a manner well understood by those skilled in the art.

A thou coaxial 0r shielded cables have been transmission is provided.

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1 3 described for making connections between the antenna and the receiver, it will be understood that for many applications ordinary connections may be employed.

In the coupling circuits for coupling the nondirectional loop antenna formed of the body of the mobile vehicle described above, the phase shifting means employed cause a loss of signal strength in connection with the signal associated with at least one of the loop circuits and since it is necessary for the signal strength of each loop circuit to be the same, it effectively causes a reduction in the signal. strength available. In addition to the loss due to the phase shifting operation required the mixing of the two radio frequency signals in the antenna coil causes the Q, of the secondary coil to be low and to provide very little gain. It is awell known fact that the local oscillator circuit of most modern radio receivers, for example, provides very satisfactory means for shifting the phase of the signals. and inaddition, ample power is available. at. that point. for accomplishing this purpose. Accordingly, in Fig. there is. illustrated inblock diagram the loop circuits 23 and of Fig. 1 which are individually connected through separate radio frequency amplifiers HG-and I H, respectively; and through separate mixer stages H8 and H 9, respectively, which are associated with a. common local oscillator stage I20. The outputs of the local oscillator should be ninety degrees out of phase with each other to produce the desired phase shift in themixer whereby the output circuits of the mixer may be combined and fed. to an intermediate frequency amplifier I21 and thence to the remaining stages of the radio receiver. With this arrangement, the loss in signal strength at the antenna circuit is eliminated and the phase shift is obtained at the local oscillator where plenty of power is available; It will be understood that the circuits will not be unduly complicated by employing the arrangement of Fig. 15 since the two separate radio frequency amplifiers may be embodied in a dual tube asmay also the mixer stages H 8 and H19 From the above description, it is apparent that by means of the present invention the body of a mobile vehicle. or the body of some other device such as a helmet or the like having another primary function may be employed as a non-direc tional loop antenna for a wave signal device whether it be a transmitter or areceiver. Furthermore, with the present invention, the directional characteristics heretofore preventing the use of such bodies as the antennas have been eliminated and a non-directional loop antenna less affected than priorantennas by adjacent objects which interfere with radio reception or In addition, there is no outside apparatus detracting from the appearance of the mobile craft and no defacement of the body is required in order to provide a satisfactory antenna. It will be understood that if the automobile manufacturers, for' example, should go to plastic bodies that a non-directional loop antenna for such type of vehicle: can readily be provided by the manufacturer in molding the body initially.

It will be apparent to those skilled in. the art that the present invention is not limited to the particular constructions shown and that changes and modifications may be made without departing'from the spirit and scope thereof. It isaimed 14 in the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be se cured by Letters Patent of the United States. is:

1'. Anantenna system including a three dimensional conducting body which defines a plurality of closed. loop circuits effectively extending in planes disposed at angles with. respect to each other, a plurality of taps. on. said body constituting the terminals of said loop. circuits, all oi. said loop circuitslbeing defined substantially entirely by electrically interconnected portions of said: conducting body, and means including aphase shifter for connecting said loop circuits so as to provide a non-directional antenna.

2. An antenna for" a mobile vehicle having a body formed of conducting material, a plurality of taps on said body so positioned to serve as terminals of a plurality of physically displaced loop circuits in said conducting body, each loop cir cuit being defined substantially entirely by pertions of said conducting body, and means for coupling said loop circuits together in such phase relation as to provide a substantially non-directional antenna.

3. In. a wave signal; system for an automobile having a. metal body, an antenna including a plurality of loop circuits wholly defined in said metal body, at least tWo of said loop circuitsbeing efiectively. displaced from each other, and" means including a phase shifter for coupling said two loop circuits to a Wave signal device in such phase relation as to. provide a substantially non-directional antenna.

4. In a wave signal system for amobile vehicle having a conducting body, said body defining a pair of loop: circuits the planes of" which are displaced. from each. other by an: angle oi the order of forty-five degrees, a plurality of taps on said body at readily available points within said body constituting terminals on: said loop circuits, and means for connecting the terminals of saidtwo loop circuits to a. wave signal device so that said loop circuits act as. a non-directional antenna.

5*. In a wave signal receiver for a mobile vehicle having'a metal body, said body defining a pair of efiiective loop: circuits displaced from each other by an. angle of the order of forty-five degrees, a plurality of taps on said body at readily available points within said body constituting terminals on said loop. circuits, and means for connecting said loop circuits to said WZ/VG signal receiver including phase shifting means for shifting the relative phase positions of the Wave signals received by said loop circuits sothat the phases thereof at said receiver add vectorially; whereby a non-directional antenna is provided forsaid mobile vehicle.

6. An antenna system for an automobile having a metal body and a windshield, said body defining a plurality of loop circuits effectively extending in planes disposed at. angl'eswith respect to each other, a plurality of pairs of electrical connections to said body, one of said pairs of connections being. disposed at one side of the interior of said body adjacent an upper. and a lower corner of said windshield, said pairs of connections constituting. the terminals of said loop circuits, all of said loopv circuits being. defined substantially entirely by electrically interconnected. portions of said. metal body, and means for coupling said pairs of connections together in such phase relation as. to provide a. substantially non-directional. antenna. system.

assaosa '7. In a wave signal receiver for a mobile vehicle having a metal body, said body defining a pair of independent effective loop circuits extending in planes displaced from each other an angle of betw en forty-five and ninety degrees, a plurality of electrical connections on said body at readily available points at the interior of said body constituting terminals on said effective loop circuits, and means for connecting said loop circuits to a wave signal receiver disposed within said body including phase shifting means for shifting the relative phase of the wave signals received by said loop circuits so that a non-directional antenna is provided for said receiver.

8. In a Wave signal receiver fora mobile vehicle having a conducting body, a plurality of on said body at readily available points within said body constituting terminals on a pair of effective loop circuits wholly defined in said conducting body, said loop circuits being displaced from each other by an angle of the order of fortyfive degrees, and coupling means for connectingv said loop circuits to said wave signal receiver including phase shifting means for shifting the relative phase positions of the wave signals re-.

ceived by said loop circuits so that a non-directional antenna is provided for said receiver, one of said coupling means comprising an inductive element.

9. An antenna for a radio transmitter in a mobile vehicle having a conducting body which defines a plurality of closed loop circuits effectively extending in planes disposed at angles with respect to each other, a plurality of terminals on said body constituting taps on said loop circuits, each loop circuit being defined substantially entirely by portions of said conducting body, and means for coupling said transmitter to said terminals whereby said body acts as a nondirec tional antenna. a

10. In a wave signal receiver of the superheterodyne type for a mobile vehicle having a conducting body, said body defining a pair of effective loop circuits extending in planes disposed with respect to each other at a substantial angle, a plurality of taps on said body at readily available points within said body constituting terminals on said effective loop circuits, means for individually connecting said loop circuits to said Wave signal receiver, and means at the output of the local oscillator of said receiver for (30.1 bining the signals received by said loop circuits so that a substantially non-directional antenna is provided for said mobile vehicle.

11. An antenna system for an automobile having a metal body and a Windshield, said body defining a plurality of effective loop circuits extending in planes disposed at angles with respect to each other, a plurality of pairs of electrical connections to said body, one of said pairs of connections being disposed at oneside of the interior of said body adjacent an upper and a lower corner of said windshield, another of said pairs of connections being disposed at the other side of the interior of said body adjacent an upper and a lower corner of said windshield, said pairs of connections constituting the terminals of said loop circuits, all of said loop circuits being defined substantially entirely by electrically interconnected portions of said metal body, and means for coupling said pairs of connections together in such phase relation as to provide a substantially non-directional antenna system.

'12. An antenna system for an automobile having a metal body and a windshield, said body defining a plurality of loop circuits extending in planes disposed at angles with respect to eachother, a plurality of pairs of electrical connections to said body, one of said pairs of connections being disposedat one side of the interior of said body adjacent an upper and a lower corner of said windshield, said pairs of con ections constituting the terminals of said loop circuits, and means for coupling said pairs of connections together in such phase relation as to provide a substantially non-directional antenna system.

13. In a Wave signal system for an apparatus having a conducting three dimensional body which defines a pair of independent closed circuits having substantially different orientations, a plurality of taps on said body at relatively available points constituting the terminals on said closed circuits Wholly defined in said conducting body, means for connecting said terminals to a wave signal device, and phase shifting means connected to said last-mentioned means including a pair of magnetically coupled tuned circuits for shifting the relative phase of the currents obtained from saidclosed circuits so that said closed circuits effectively provide a non-directional antenna.

14. In a Wave signal system for an apparatus having a conducting three dimensional body which defines a, pair of independent closed cir ouits having substantially difierent orientations, a plurality of taps on said body at relatively available points constituting the terminals on said closed circuits Wholly defined in said conducting body, means for connecting said terminals to a Wave signal device, and phase shifting means connected to said last-mentioned mean including a pair of tuned circuits, one of said tuned circuits including a, winding inductively coupled with the other tuned circuit.

15. An antenna system in accordance with claim 1 in which said connecting means includes means for tuning the short conducting portion of each loop circuit between the terminals thereof whereby said short conducting portion in effect becomes an open circuit.

16. An antenna system for a radio set mounted in a vehicle, such system comprising a three-dimensional conductive vehicle body of such configuration as to define a plurality of loop circuits effectively extending in planes disposed at substantial angles with respect to each other, all of said loop circuits being defined substantially entirely by electrically interconnected portions of said conducting body, and means for coupling said loops individually to the radio set in such phase relation as to make the antenna syste non-directional;

17. An antenna system for a radio set mounted in a vehicle, such system comprising a three-dimensional conductive vehicle body of such configuration as to define a pair of closed loop circuits eiiectively extending in planes disposed at substantial angles with respect to each other, said body having a primary function other than that d of providing said loops, with each loop circuit being defined substantially entirely by portions of said conducting body, and means for coupling said loops individually to the radio set in such phase relation as to make the antenna system nondirectional.

18. An antenna system for a radio set or the like mounted in a vehicle, such system comprising a three-dimensional conductive vehicle body of such configuration as to define a plurality of loop circuits effectively extending in separate planes at least two of which are angularly displaced by a substantial amount, each of said loop circuits being defined substantially entirely by portions of said conducting body, and means for coupling said loops individually to the radio set 5 in such phase relation as to make the antenna system non-directional.

19. An anterma for a radio set mounted in a vehicle, such system comprising a three-dimensional conductive vehicle body of such configuration that said body afiords two crossed loop circuits therein, two pairs of taps on said body, each pair being located on one of said loop circuits, and means for coupling said pairs of taps to the radio set including phase-shifting means for obtaining us a resultant antenna pattern which is substantially non-directional.

FRED B. WILLIAMS. FRED P. HILL.

1s 7 REFERENCES CITED 1 5 The following references are of'record in the file of this patent: I

v n UNITED STATES PATENTS Number

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