US 2971191 A
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R. A. DAVIS SLOT TYPE ANTENNA HAVING AN AUTOTRANSFORMER COUPLING CIRCUIT Feb..7, 1961 2 Sheets-Sheet 1 Filed July 18, 1955 ROSS A. DAVIS INVENTOR.
FIG-1- FIG-6- HIS ATTORNEY Feb. 7, 1961 R. A. DAVIS 2,971,191
SLOT TYPE ANTENNA HAVING AN AUTOTRANSFORMER COUPLING CIRCUIT Filed July 18, 1955 2 Sheets-Sheet 2 BIB 108 'no 700 r IN V EN TOR.
ypiw XM HIS ATTORNEY United States Patent SLOT TYPE ANTENNA HAVING AN AUTO- TRANSFORMER COUPLING CIRCUIT Ross A. Davis, 5037 W. Pico Blvd., Los Angeles, Calif.
Filed July 18, 1955, Ser. No. 522,777
6 Claims. (Cl. 343-712) This invention is directed totransmitting or receiving antennas for structures and, more particularly, to low impedance antenna systems actively utilizing radio frequency currents flowing along the conductive boundaries surrounding discontinuities in the structures, be they mobile or fixed structures.
The invention covered herein differs from that covered in my co-pending applications, Serial No. 487,535, filed February 11, 1955, and entitled Antenna Systems, now Patent No. 2,923,813, issued February 2, 1960, and Serial No. 503,190, filed April 22, 1955, and entitled Antenna Systems, in that the structure and circuitry of the present invention insure an over-all maximum gain for the antenna system.
7 Therefore, it is an object of this invention to provide an improved radio receiving or transmitting anntena exhibiting a low impedance characteristic and utilizing as an active component a large mass of metal normally per forming other functions.
It is a further object of this invention to provide a hidden antenna system for mobile vehicles which provides optimum electromagnetic signal interception and translation to associated receiving or transmitting equipment while simultaneously providing a high degree of omnidirectivity and a minimum of electrostatic noise interception.
According to the present invention, currents which have been found to flow about the perimeter of any discontinuity in a conductive mass, such as window openings in car bodies, are coupled through novel voltage transforming coupler arrangements adjacent to or removed from at least a portion of the perimeter of any such discontinuity or opening to the antenna input or output circuits of associated radio apparatus. The inductive component of the coupler impedance is offset by the insertion of at least one capacitor in the coupler arrangement. Circuit parameters are chosen ,so that the coupler arrangement will be series resonant, and thus exhibit a minimum impedance, at or near the low end of the frequency band of the associated radio apparatus.
The features of the present invention which are be lieved to be novel are set forth with particularity in the ap pended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:
Figure 1 is a diagrammatic presentation of a first and basic embodiment of the invention applied to an automobile.
Figure 2 is a second embodiment of the present invention in which the auto-transformer coupling member is disposed adjacent to the perimeter of a discontinuity in a conductive mass, such as a window opening in an automobile.
V Figure 3 is a third embodiment of the present invention in which the auto-transformer coupling member is "ice removed from the general area of the discontinuity and pick-up leads.
Figure 4 is a sketch of a fourth embodiment of the present invention in which the auto-transformer portion of the coupling circuit is contiguous with at least a portion of the discontinuity in the conductive mass.
Figure 5 displays the embodiment of Figure 4 (with other embodiments equally applicable) as may be conveniently series coupled to the tuning portion of a first R-F amplifier.
Figure 6 is a representation of a sixth embodiment of the present invention in which the principal auto-transformer member is located in a remote place with respect to the discontinuity of a conductive mass and in which the output leads are adapted for series coupling between the capacitor and the inductor of the tuning portion of an R-F preselector, for example.
Figure 7 is a sketch of a modification of the embodiment shown in Figure 6 in which separated, non-planar portions of the conductive mass are utilized for signal detection.
Figure 8 is a diagram of an additional embodiment of the present invention in which a complex form of autotransformer is driven by oppositely phased sources and a single output lead is used.
Figure 9 is a pictorial representation of the embodiment shown in Figure 7, in simplified form, in which a signal from remote points is combined with a signal from an opening to provide high sensitivity and increased an gular displacement from other signals derived from th same opening.
Figure 10 is a diagram of a modification of the-embodiments of Figures 7 and 8. e
In Figure 1 window 10 delineates the discontinuity in" a conductive mass such as an automobile body of which window frame 11 is a portion. As a result of the electro-- magnetic fields which are constantly passing over the surface of the car body, currents are caused to flow in the conductive portions of the automobile body immediately surrounding Window opening 11. This current flow is also present in window frame 11 since it is assumed to be an integral portion of the car body itself;
point 13 of window frame 11 by means of conductor 23. Point 26 of sheath 18 is electrically connected to' point 13 on window frame 11. Output coaxial cable 21 is subsequently routed to the input of the receiver circuitry (not shown).
. The circuit of Figure 1 operates as follows, using instantaneous potentials in illustrating the analysis. A positive increment in the potential at point 12 on window frame 11 will be followed by a corresponding positive increment in the potential at junction 27 of conductors 16 and 19 and hence a positive potential increment at junction 27 relative to point 17 upon conductive sheath 18 will be experienced. Also, there will exist a slight positive potential at point 25 relative to point 13. The positive voltages induced in conductor 19 within sheath 18 and in the region within ferrite sheath 24 adjacent conductor 16 will add to the positive potential at point 12 to provide for an increased potential difference between conductor 19 and shielding 22, i.e., at output coaxial" cable 21. This voltage rise will add to the voltage rise" experienced at the juncture of conductors 16 and 19 so as to provide a further. increased voltage between shielding 22 of coaxial cable 21 and the inner conductor ficonductor 19).
so ast'o counteract the appreciable inductance inthe coupling circuit. One is not precluded from employing additional loops of conductor 19'through sheath 18 provided the size of capacitor 15 is alsochanged to counter= act the load change resultingfrom the increased loops. Foroptimum performance the coupling circuit in this particular application should be series resonant at or near the low end of the frequency band. It should also be mentioned that conductor14 may be shielded with ferrite metal in the neighborhood of window 10 in this'and other embodiments if desired.
In Figure 2 the periphery ofwindow 200 is in part bounded by conductive sheath 201. Points 202 and 203 on conductive sheath 201 are respectively coupled to points 204 and 205 on window frame 206, these latter points being. assumed to exhibit a. potential difference therebetween. Conductor 207 is directly connected to point 204-n window frame 206 and loops through con' ductive sheath 201 toconnect to capacitor 208. Conductor 209 joins impedance lowering capacitor 208 at junction 216 and point 210 on conductive sheath 201. Con-- ductor 211 joins with conductor 209 and loops through the lower portion of sheath 201 a chosen number of timesto emerge as inner conductor 212 of coaxial cable 213. Coaxial-cable shielding 214 is directly connected to window frame 206 in the region of point 205.
The circuit shown in Figure 2 operates as follows. A potential difference existing between points 204 and 205 on window frame 206 as a result of the passage of electromagnetic waves over the associated car body is applied to points 202 and 203 at either end of conductive sheath 201. Conductive sheath 201, its inner wire 207 and inner wire 209 of ferrite sheath 215 operate as the primary of an auto-transformer member, the secondary comprising inner conductors 211 and 212. As a result ofithe action of conductor 207 and condenser 208, a potential difference will exist between junction 216 and point 203 in the primary. As. a result of auto-transformer action, the potential difference between point 203 and junction 216 will appear as an increased potential between inner wire 212 and outer sheath 214 of coaxial line 213. The outside of the lower portion of conductive sheath 201 is magnetically shielded from external influences by ferrite sheath 215 which also increases the inductive reactance of the conductors passing therethrough. Impedance lowering capacitor 208 is inserted in series in conductor 207 (or other suitable place) so as to provide a high output driving voltage at output coaxial cable 213 and maintains as low a primary impedance as is possible. Output coaxial cable 213 is adapted for coupling to the input of associated radio circuitry.
InFigure 3, conductive sheath 300 surrounds a portion of the periphery of window 301 which is bounded by conductive window frame or boundary 302. Again, window frame 302 is considered as the other window frames or boundaries in the previous figures, that is, being electrically integral with the conductive mass or car body associated therewith. Points 303 and 304 on window framev 302 are electrically connected to points 305 and 306,-respectively,fon the periphery'of conductive sheath 300. To point 304 is electrically connected conductor 326'which.upo1r.'passing through conductive sheath 300' and: through coaxialcshield 307 is coupled through condenser 311: to point-308'. Point 303 on window'frame It has-been discovered that" in additionto increasing the impedance and coupling coefiicient'o'f 302 is directly coupled through coaxial shield 307 via conductor 310 and through capacitor 312 to point 309. It is to be noted that an initial auto-transformer action is achieved by reasonof the disposition of conductor 326 within conductive sheath 300 so that a potential difference greater than that between points 303 and 304 will appear between points 308 and 309; Impedance lowering capacitors 311 and 312, respectively are electrically connected to the other portions of the primary313 and 318 in the ferrite sheath. The other ends ofconductors 313 and 318 are electrically connected'through conductor 317 to coaxial cable outer shield 314. The secondary 315 is joined to capacitor 312 at point 309 whichis inductive- 1y coupled with conductors 313 and 318 and which emerges as the inner conductor of output coaxial cable 316, of which shield 314 is a component part. Ferrite sheath 319 encloses and thereby increases the inductive reactance and isolation of conductors 313, 315 and 318. Condensers 311 and 312 are used to lower the primary impedance.
The embodiment shown in Figure 3 operates as follows. Initial auto-transformer action is supplied by the cooperation of conductive shield 300 and conductors 310-and 326. Coaxial shield 307 maybe of a conventional variety, or may accomplish the magnetic shielding of the conductors enclosed therein by consisting of a ferrite sheath. Capacitors 311 and 312 are placed in series with the feed-in lines so as tolower the over-all inductive imsome applications the inductive-capacitive characteristic of the coupling circuit should be resonant at a pointclose to the low end of the frequency band. Byvirtue of the unique winding of conductor 315, conductor 318, and conductor 313 and their mutual inductive coupling therebetween a second and additive auto-transformer action takes place which further serves to increase the output voltage derived at output coaxial cable 316. Conductor 317 couples conductors 313 and 318 to outer coaxial shield 314 and consequently provides a center tap. for this second auto-transformer circuitry.
The embodiment shown in Figure 4 is one of. the simplest types. Window 400 is bounded by window frame 401 which is conductive in character and which forms an integral part of the conductive car body associated therewith. Points 402 and 403 along window frame 401 are each coupled to points 404 and 405, respectively, at either end of conductive sheath 406. Conductor 407 is electrically connected to point 402 along window frame 401 and loops through conductive sheath 406 a chosen number of times to emerge therefrom and couple through capacitor 408 to finally constitute inner conductor 409 of output coaxial cable 410. Outer coaxial shield 411 is electrically connected to conductive sheath 406 at or near point 405.
The circuit of Figure 4 operates as follows. By virtue of a potential difference which exists or may exist between points 402 and 403 along window frame 401, and consequently between points 404 and 405 along conductive sheath 406 an in-phase voltage will be induced in each successive winding of conductor 407 through conductive sheath 406 to provide an increased voltage difference between inner conductor 409 of coaxial cable 410 and shield 411. Again, capacitor 408 is utilized to counteract the increased inductive impedance contributed to the coupling circuit by reason of the successive loops of'conductor 407 through conductive sheath 406'. Similar:
ly, the capacitance exhibited by capacitor 408 could be such in certain applications as to provide for the series resonant condition of the coupling circuit near the low end of the frequency band.
The circuit of Figure 5 is identical in configuration and operation as. the circuit of Figure 4', but does illustrate the fact that the impedance reducing coupling capacitor may be'included within the input circuit of the associated receiver 'or radio apparatus itself. Inductor 500 and tuning capacitor 501 comprise the normal tank circuit elements of a conventional R-F preselector stage. The condenser or the inductance or both can be variable to meet maximum tuning range requirements when using several turns in the pick-up inductance. By virtue of the inclusion of capacitor 502 in the input circuitry of the R-F preselector the exciter and coupling circuitry can be and is series-coupled between inductor 500 and capacitor 501. For best tracking, the coupling circuit including capacitor 502 may be made series resonant near the low end of the band. Also, with this arrangement the LC ratio of the receiver input tank circuit will not be so greatly disturbed. It is interesting to note that capacitor 502 also serves to keep the automatic volume control voltage from being shorted out to ground. The inclusion of shielding 503 (made of ferrite material if desired) for housing conductor 504 and thereby holding down its impedance and shielding it from external electrostatic impulses in the neighborhood of window 505 is optional both in the case of the embodiment shown in Figure 5 and in all other embodiments heretofore or hereafter shown and described.
The embodiment shown in Figure 6 is similar to those heretofore mentioned with the exception of the presence 'of two final output leads and also the unique autotransformer arrangement which is enclosed by dotted lines 600. Either coupling capacitors 601 and 602 or capacitors 603 and 604, or both'sets of capacitors, may be employed to counteract the inductive impedance exhibited by the coupling circuit. Coaxial shields 605 and 606 may be intercoupled and grounded as shown. Capacitor 602 is coupled via conductor 607 to point 608 on conductive sheath 609. Capacitor 602 is also coupled via conductor 610 to coaxial cable 611 of which shield 605 is a member. Capacitor 601 is coupled via conductor 612 to join with conductor 607 at point 622 which in turn joins to point 608 on sheath 609. Conductor 613 joins with capacitor 601 at point 624 and finally emerges from the auto-transformer portion as inner conduct-or 614 of coaxial cable 615. Ferrite sheaths 616 and 617 surround the conductive wires as shown. As near critical coupling as is possible to attain and simultaneously maintain reasonable capacity loading should be made to exist between the center and two outer conductive wires within each ferrite sheath 616 and 617.
The circuit shown in Figure 6 operates as follows. A sudden increase in potential diiference between points 619 and 620 will appear as a potential increase between points 621 and 608 on conductive sheath 609 due to the connection of conductive lead 618 and condenser 602 to wire 607. Potentials of opposite polarity will exist between points 621 and 622, and points 624 and 623, due to the action of additional conductive lead 625 running from point 619 through condenser 601 to point 624, so that the current flow in conductors 607 and 612 will reinforce each other. This means that voltages will be induced in the conductorson either side of each central conductor which in turn will he stepped up by the number of turns used in the autotransformer to finally appear at coaxial cables 611 and 615 in opposite polarity on conductors 610 and 614. It is interesting to note that the auto-transformer 600 may be disposed either adjacent the car window or other associated discontinuity, or remotely from a discontinuity such as in the location of the radio receiver. Also, it is not necessary that primaries 607 and 625'have a return to a point such as 608. Experiment has shown that remarkable signal detection may be achieved by the embodiment of Figure 6.
The configuration of Figure 7 is identical to that of Figure 6 with the exception that a remotely situated driving point such as a point on a tender well (point 700) may comprise one of the driving leads of the circuit. If the potential at point 706 is increasing positively with respect to point 707, and the potential at point 700 is increasing negatively with respect to point 708 and such a condition exists at condensers 701 and 702, the phasing will be correct for driving opposite legs of the auto-transformer and attaining maximum output at the two output coaxi-als. This additional driving method was introduced primarily to improve signal displacement between two points of pick-0E in a common discontinuity when the angle of displacement in that opening is not sufiicient. If the driving voltages are properly phased, ideal signal conditions can be obtained through this method and also maximum angular displacement of this signal combination with respect to another using the same opening for the second signal may be realized. Auto-transformer unit 703 may be located remotely with respect to the signal pick-01f points and may be conveniently situated in proximity to the radio equipment proper. Again, coupling capacitors 701 and 702 are series connected to the input lead so as to reduce the inductive reactance or impedance of the lead-in wires and, in particular, of auto-transformer unit 703. Additional or substituted capacitors 704 and 705 may be utilized in the output of the coupler circuit if desired.
In Figure 8, window 800 is bounded by window frame 801, points 802 and 803 of which are electrically connected to points 804 and 805, respectively, of conductive sheath 806. Inner conductor 807 of conductive sheath 806 is connected to point 808 on Window frame 801 and is routed through conductive sheath 806 to couple to capacitor 809 the remaining side of which is coupled to junction point 810 via conductor 811. Junction point 810 is directly connected to point 808 and also to point 812 on outer sheath 813. Conductor 814 is routed from point 802 on window frame 801 to capacitor 815 the opposite side of which is connected to conductor 816 which is routed through outer sheath 813 to constitute, ultimately, inner conductor 816 of output coaxial cable 817. Coaxial shield 818 of coaxial cable 817 is directly connected to outer sheath 813. Point 819 on outer sheath 813 is directly connected through point 821 to point 805 on conductive sheath 806. Conductor 820 is connected between junctions 821 and 822. Ferrite sheath 823 encloses conductors 811, 816 and 820, as shown, to increase the inductive reactance thereof and also to prevent the loading thereof by the surrounding low impedance conductive mass.
The circuit in Figure 8 operates as follows. Assume point 802 and point 803 (to a lesser degree) are increasing positively in potential with respect to point 808 on window frame 801. An in-phase voltage will be induced in conductor 807 by current flow in conductive sheath 806 so that conductor 811 will be positive at junction 810 with respect to the associated sideof capacitor 809. A voltage of like polarity will appear across conductor, 820 by reason of the voltage difference, between points 802 and 803 on window frame 801. The voltages of conductors 811 and 820 combine to induce an increased voltage in conductor 816 in the region of ferrite sheath 823. This induced voltage will be in phase with the voltage induced in conductor 816 in the region of outer sheath 813 by the increased potential difference across outer sheath 813 so as to provide a greatly increased voltage difierence between inner conductor 816 and coaxial shield 818 of output coaxial cable 817. Again, capacitors 809 and 815, together with capacitor 824, if required, are employed to lower the impedance ofthe coupling circuit and hence to increase the sensitivtiy of the system.
In Figure 9 (which is in the main similar to Figure 1) an external driving voltage is obtained from another portion of the car as, for example, wheel well 900 which adds to the voltage derived from window 901 so as to add to the final voltage output existing between shield 902 and inner conductor 903 of coaxial cable 904 and also assists in displacing the signal at a greater angle than could be attained by using signals from the one openingalone; Also, capacitor 905 and capacitor 906 (if necessary) may be utilized to counterbalance the inductive reactance' exhibited by the coupling circuit. As with the cables in the other embodiments, cable 907 will have a lowcharacteristic impedance. Again, ferrite sheath 908 in addition to increasing the impedance of conductors 903 and 909 therewithin magnetically shields conductors 909 and 910 from extraneous loading and other influences.
The embodiment of Figure 10 is similar to the circuit of Figure 6, in that the same dual drive system is utilized in'the principal signal pick-up circuitry associated with.
discontinuity 1000 in Figure 10 as was utilized in connection with the discontinuity in Figure 6. However, in Figure 10 dual pick-up points are also utilized along auxiliary discontinuity 1001. The signals from the auxiliary discontinuity 1001 are combined in phase with those from the principal discontinuity 1000 through conductors that are common to both transformer sections 1002 and 1003. Extensions of inner conductors 1004 and 1005 form the common links between sections 1002 and 1003 thus producing an additive combination of the signals in both circuits. Impedance lowering condensers 1006, 1007, 1008, 1009, 1010 and 1011 may be added to permit series connection of the transformer sections 1002 and 1003 into the input tuning circuits of associated radio apparatus.
It should be noted that although throughout this discussion the ferrite sheath has been described as surrounding the signal conductors, it is equally feasible to surround the adjacent conductive material or insert therewitlu'n ferrite material so as to eliminate any loading of adjacent signal carrying wiresand so as to raise the impedance of such conductive material and attain higher voltages between separated points thereon.
Various departures may be made from the embodiments shown in the various figures without departing from the scope of this invention. For example, instead of crossing the window or opening the lead wires may be suitably shielded from external influences and routed along the periphery of the window. Any auto-transformer device disclosed may employ one or more conductor loops depending upon the particular design of the coupling circuit that is needed. In addition, a single or dual driving voltage may be obtained from a remote part of the automobile or other metal mass relative to the radio receiver or transmitter, such as from a wheel well or other enclosed discontinuity, and the wires be subsequently routed through a low impedance cable and capacitance coupled to the radio set or an additional autotransformer device. Auto-transformers in the various embodiments may or may not be center tapped, as is desired. Rather than take only one space-phased signal from two displaced points on the conductive boundary of a discontinuity which the accompanying figures suggest, two or more signals from additional appropriately displaced, pick-off points on the same boundary may be obtained and subsequently combined to insure optimum omnidirectivity of the antenna system. All of the embodiments presented have proven or appear to demonstate the soundness of utilizing the concept of choosing at least two points from the boundary of at least one conductive mass between which points there exists a potential difierence by virtue of their being so displaced as to provide the desired angulardisplacement of signals, loopingconductive wires coupled to such points so as to generate an auto-transformer effect, and employing coupling capacitors to counterbalance the inductive reactance of the coupling circuit.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its} broader aspects, and, therefore, the aim in the appendedclaims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
1. An antenna system including: a conductive struc of said edge at a plurality of points spaced along its length whereby said part of said primary portion attains a potential gradient along its length corresponding to the gradient of said contiguous firstportion of said edge; an exciter wire and a capacitor connected in series and coupled between a second portion of said edge remote from said first portion and said primary portion of said auto-transformer, said secondary portion being adapted for coupling to radio apparatus.
2. Apparatus according to claim 1 in which said part of said primary portion comprises an electrically conductive sheath.
3. Apparatus according to claim 1 in which said second portion of said conductive edge is onthe opposite side of said area from said first portion of said edge.
4. Apparatus according to claim 2vin which said autotransformer includes, in addition to said sheath, a first conductor passing through said sheath at least once and having an input terminal and an output terminal; a second conductor in close proximity with a portion of said first conductor and coupled between said first conductor input terminal and said second point on said conductive sheath; and a sheath of high magnetic permeability in close proximity to said first and second conductors.
5. Apparatus according to claim 1 in which the magnitude of said capacitor is chosen to producev series resonance of said exciter wire in the range of operatingfrequencies of said radio apparatus. v
6. Apparatus according to claim 4 in which said exciter wire is shielded in the region proximate to said nonconductive area.
' References Cited in the file of this patent UNITED. STATES PATENTS 1,875,952 Taylor v Sept. 6, 1932 2,481,978 Clough Sept. 13, 1949 2,520,986 Williams et' al Sept. 5, 1950 2,575,471 Schweiss'et -al Nov. 20, 1951 2,637,814 Johnson May 5, 1953 2,687,475 Sheldorf Aug. 24, 1954 2,781,512 Robinson Feb. 12, 1957 2,825,061 Rowland Feb. 25, 1958 FOREIGN PATENTS 535,055 Great Britain Mar. 27, 1941 Marc: