US2576150A - Directive antenna system - Google Patents

Description

1951 C. M. SIMPSON 2, 7 ,150

- DIRECTIVE ANTENNA SYSTEM Filed Oct. 8, 1946 v $Sheets-Sheet 1 UNDESIRED SIGNAL T3 l A ANTENNA RESPONSE PATTERN cu FFORD M. SIMPSON Nov. 27, 1951 c. MASIMPSON 2,575,150

v DIRECTIVE ANTENNA SYSTEM Filed Oct. 8, 1946 s Sheet S-Sheet 2 ANTENNA RESPONSE PATTERN UNDESIRED SIGNAL CLIFFORD M SIMPSON 1951 c. M. SIMPSON DIRECTIVE ANTENNA SYSTEM s Sheets-Shet 3 Filed Oct. 8, 1946 CLIFFORD M.S|MPSON Mewn;

Patented Nov. 27, 1951 I UNITED STATES PATET 8 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) fI'his invention relates to anantenna system and more particularly to a directive antenna system.

Qne of the objects of this invention is to provide a directive antenna system whose properties of indicating the direction of incoming signals cannot be destroyed by undesirable signals.

Another object of this invention is to provide a direction-finding system which will exclude signals from .an unwanted direction but which will possess the direction finding properties of a conventional direction-finding system with respect to signals from any other direction.

A further object of this invention is to provide a direction-finding system which will facilitate the transmission of messages to a desired position without permitting other positions to intercept such messages. 7

Other objects and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the invention and in which:

Fig. 1 is a schematic diagram of one embodiment of this invention Fig. 1A shows in general the response pattern of I the embodiment of Fig. 1,

j 1 Figs. 2 and 3 are schematic diagrams of alternat'e embodiments of this invention Fig. 2A shows the response pattern of the embodiments illustrated in Figs.'2 and 3, and

Fig. 4 is a schematic diagram illustrating'how this invention may be used as an aid to maintaining a measure of secrecy in radio communi- "direction is effected by replacing the single nondirectional antenna located at each corner of a rhomboid' in an ordinary Adcock system with "a highly directional antenna or a combination of antennas electrically similar to each other. When no sense antennas are used, the combination at each of such corners, or collector set as it will be hereafter called, consists in one embodiment of the invention of an even number 'of antennas symmetrically arranged about a geometric center, with the outputs ofpairs of antennas in the collector set so combined that no resultant output will be obtained from the collector set for a signal coming from a specific direction. For all other directions, however, .a

combined that the properties of an Adcock array are preserved, the subject antenna arrays will indicate the direction of incoming signals while excluding interfering signals from a particular 2 5 direction. a V I I An antenna system is also contemplated in -which a sense antenna may be added at the geometric center of each antenna collector set, thus requiring that an odd number of antennas comprise each set. By causing the phase of the output from this sense antenna to be shifted approximately 90 and then combining this'output with the resultant-output from the other antennas in the set, a signal may be excluded whose direction is at right angles to the direction of the signals excluded when an even number of antennas comprise the set. Further contemplated ramifications of this system, permit the same result to be obtained by replacing the sense antenna in each collector set by one sense antenna at the geometric center of the antenna array and introducing the output from this sense antenna to the resultant output from all of the collector sets.

In Fig. l, to which reference is now had, a schematic diagram is shown of an antenna array consisting of a pair of antennas at each corner of a rhomboid. This embodiment comprises antennas I0 thru I! inclusive, transformers [8 thru 2| inclusive, and windings 3|, 32 and 33 of a goniometer 22. The antennas l0 thru ll inclusive may be ordinary vertical antennas having non-directional properties and are so, arranged that the plane containing each collector set is parallel to the plane containing the antennas of the other collector sets. Additionally, the. distances between the two antennas of each collector set are normally equal and are small as compared to the distances between'diagonal collector sets Illll and l ll5 and between the mid-points oi collector sets I'2-l3 and I6-l'l, both of which distances are normally equal. As a typical example, the distance between diagonal collector sets may be taken as M5 or 20% of the wave length of the signal being received, while the difference between the two antennas of a collector set may be taken as )g/20. Although the spacings between the'antennas in a collector set and the spacings between diagonal may be used to produce special results in accollector sets are normally equal, other spacings transformer I8 is joined to terminal 2 ;.of trans:

former 20. Voltage is derivedacross the winding 3! of the goniometer 22 by linking the cross connections to the terminals of the winding 3|.

In the same manner, the centers of thepr imary V windings of transformers l9 andzl are grounded,

said windings connecting antenna sets H -l3 and l6--l 1, respectively": Additionally, the secondaries of the transformers are c'r'oss-cdn'ected so that terminals 21 and 28 (if tiailsfdiiner 19 are linked to terminals 38 and 29 of transformer 2| respectively. From these cross-connections, connections are made to the terminals of the Winding 32', which is the other fixed of the goniometer 22. The winding 33 of the gonioineter is rotatable and combines vecto'ria'lly the voltages of windings 3! and 32 when rotated.

Consider now the signal 35 which is coming frornsuch a direction that its wavefront is parallel to the planes containin the collector sets. Since the wavefront will reach the antennas l0 and ll at the same time, voltages of equal ainplitude and the same phase 'Willb'e induced in these antennas and these voltages will appear at the ends of the primary winding of trans fo'riner l8. Thus, because of the fact that no voltage difference exists across the primary winding, no vvvoltage will be induced in the secondary winding of the transformer 18. Likewise, no voltage will be induced in the secondary winding of the transformer 20 becauseof equal voltages on the antennas l4 I'5 Thus the windmg 3l of -theg onioineter 22 willnot receiveexcitation-from the signal 35. in like m n er, antennas l2, l3, l6, and I] will receive 'equal voltages and thus the secondary jwindings of the transformers l9 and 21 will receive no electromotive force to be transmitted to the winding 32' o'f the goniometer 22. Since neither winding 3| nor winding 32 has voltage applied to it as a result of the signal 35 being intercepted by the -colleeto'r sets, the winding 33 of the goniometer 22 will receive no excitation when it is rotated.

, consider, however, the signal ss'tvho's wavefront is perpendicular to the pane containin the collector sets. Now, the voltage intercepted the antenna II will be different ih'phase than the signal intercepted by the antenna H). Thus 'a resultant voltage will exist between the ant'ej 'fias 111 and n and this voltage will be induced fronfl'the primary Winding to the secondary W liding o'f transformer l8. Also since the antennas and [5 are in the same os tion as the/antonnes l0 and II, respectively, with respect to the wavefront of the signal36, the same voltage difference .Will appear between the antennas l4 and I5, and'therefore across the secondary of the transformer 20, as will appear across thesecondaryof the transformer l8. By cross connectin the two secondary windings, therefore, 'the'current froin'one secondary winding will'be equal in amplitude and opposite in phase to the current from the other winding,'1eav1hg'no'tesu1taht our- 4 rent through the winding 3|. Consequently, the total reaction of the antenna collector sets l0l I and I4l5 to the signal 36 is the same as if the collector sets were replaced by the single antennas of the ordinary Adcock system.

But a response will be obtained by the winding 32 from thereaction "o'f collector sets l2l3 and l6"ll. Considering first the collector set 5-41, the voltage induced in antenna I1 will be [different in phase than the signal intercepted by the antenna Hi. This voltage difference will appear across the terminals 29 and 30 of the transformer 2 L. Although the difference in phase between the antennas l2 and I3 will be same as the difference between antennas I6 and I1, the resultant output voltage from the collector set containing antennas l2 and I3 will be different phasefidln'the resultant output voltage "of the collector set containing antennas l6 and IT. This phenomenon occurs when the distance between the midpoints of the two collector sets is different than x. the Wave length of the signal or integral multiple thereof. Consequently, the difference vector voltage between antennas l2 and I3 is equal in amplitude to but different in phase than the difference vector voltage between antennas l6 and i1. Thus a resultant voltage will appear across the connections between transformers l9 and '2 l and this voltage will be introduced to the winding 3-2 or the gemometer 22. The feature of phase dilf er'ences between antennas of a collector set and also between collector sets is maintained for signals from any direction eiicept signals 35 and signal 45, which is travelling in a plane different in azimuth from signal 35. Since no response is obtained from signals having the direction of signals 35 and 45 and since maximum response is obtained from a signal having the direction ofsignal36 anda signal different "in animuth from signal 36, it may lee-seen that the response pattern of the "antenna array or Fig. 1 will be a figure-eight pattern, as shownin Fig. 1A. Thus, by rotating winding 33 a position may be found where no voltage is induced therein, permitting the indication of the bearing of "the received signal. I e v p The antenna system'shoiyn Fig. 2 'is physically similar to that shown ii Fig. 1 estee'ot for the addition of the an n'nas 34, '31, 3B and 3'9 and assoc ated phase shifters an, 41, 42 and 4a. In addition to being non-directional and verticfa1. the 34 is l cated in the same plane as that containing antennas lll and H and is mid way between those antennas. Antenna 3! i situated in like manner with respect "to entennas l2 and I3, antenna 38 'with frefsjpect to antennas f t and "l':5,'and antenna 39 w h respect to antennas lliand 17. The phaseshffters 10.111,}: and 43 shift by approximately '90"the phasesof thje signals "receivedby antennas 34, 3 l, 38 and 39, respectively, the reason for this shift being t at the "ve tor difference of't'he voltages'between the two outer antennas if a coilector setis apprehension out of phasewith 'the voltage vectdrof -iniddle antenna. Tlii'i's, it can be seen that the direction of the signal excluded by the 'antenna's'ysteni will no longer be the direction of sig'nal '35 "or signal 4'5. The reason for this'lies in the fact that although the resultant output, for a signal having the direction or signal [35 or 415L015 "the two 'otitjr 't t'erinas ot eaohooneotor set is zero, the

antenna an output and this iiiit,

therefore, win he "the resistant oiithuttr the complete collector 'set. is produced in such a'direction, however, that the voltage from the middle antenna, for example antenna 34, directly opposes the difference volt- If the 90 phase-shift ages between the two outer antennas, such as antennas l8 and II, a signal having the direction of the signal 36 may now be excluded from the antenna system as an undesirable signal. This can be more easily seen by discussing the action on the signal 36 of the collector set containing antennas I6, I! and 39, as shown in Fig. 2. Thus it can be seen that the voltage intercepted by the antenna H will be diflerent in phase than the signal intercepted by the antenna [6. By connecting the transformer 2| between these antennas, the vector difierence of the voltage between the antennas will be obtained. But, since the antenna 39 ismidway between the antennas I6 and H, the signal received by the antenna "39has a phase which is difierent from that of.

the two antennas by the same amount and therefore the vector of the signal intercepted by this antenna will be half way between the .voltage vectors of antennas I6 and I1. 7 vector difierence of the voltages between an- Therefore the tennas l6 and I! will form the baseof an isosceles triangle with the voltage vectors of antennas l6 and I1 and the vector ofthe voltage a of antenna 39 will lie on the altitude of this triangle. It isa basic principle of plane geometry that the base and altitude of an isosceles triangle are perpendicular to each other. If the altitude of the triangle, as represented by the signal on the antenna 39,.is shifted 90 in phase a it will be parallel to the base, as representedby-the vector difference of the voltages on the two outer antennas. If this shift is made in such a direction as to oppose the vector of the voltage .difierence the collector set containing antennas 16, I1 and 39, and each of the other collector sets, will have a resultant response of zero to the signal 36. Thus it will be seen that if a signal I having the direction of signal 36 is excluded the maximum sensitivity .willoccur from a signal 44, which is displaced 180 in azimuth with respect to signal 36, since the voltage of the middle antenna and the difference voltage between the two outer antennas now add directly in each collector set, to produce a signal of reinforced strength in the set. Consequently a cardioid pattern of sensitivity, ,as illustrated by Fig. 2A

will be produced, with,the zero sensitivity of the pattern occurring, for example, for a signal havingthe direction of-signal 36 andthe maximum sensitivity being realized for a signal of such direction as signal 44, which is displaced 180 in azimuth with respect to the signal 36. 'As for thewsignals 35 and 45, the antenna system of Fig. 2 will respond to them with outputs of equal amplitude.

The schematic diagram of Fig. 3 contemplates the use of either sixteen or seventeen antennas, with four collector sets arranged at the four corners of a rhomboid and each collector set comprising four antennas arranged in a conventional Adcock set up. The antennas 46, 41, 48 and 49 comprise one collector set;v another set is composed of antennas 58, 5|, 52 and 53; a third set consists of antennas 54, 55, 56 and '51; and the last set, of antennas 58, 59, 69 and 6|. A sense collector set 18 is normally located at the geometric center of the four collector sets. The

antennas of each set are cross-connected inthe "conventional manner and the'cross-connect'ions are linked to the fixed windings of a goniometer.

. Thus thecross-Tcom'iections or antennas 46 *and a 48 is connected through a conventional Adcock arrangement. to the winding 62 of the goniometer 65. In like manner, antennas 59 and 52, 54. :and

56, and 58 and 68- are connected tothe-fixed windings 66, and 14 of the goniometers 69,13

: and 11, respectively. Likewise, antennas 41 and -49, 5| and 53,55 and 5'1, and 59 and 6| are connected through a conventional Adcock arrangement to windings 63, 61, II and 15 of the goniometers 65, 69, I3 and 11, respectively. 'The rotatable windings 6'4, 68, I2 and 16 of thegoniometers 65, 69, 13 and TI, respectively, are so arranged that the signal from theunwanted direction is excluded in each goniometer. Since the position of the rotating winding is the deciding factor,

it'may be seen that the corresponding antennas of each collectorset do not have to belocated in'a definite pattern with respectto each other.

If, then, the rotatable windings ofthe goniometers which are used in connection with the diagonal collector sets are connected together and connections are made from these diagonallyconnected goniometers to the fixed windings of a fifth goniometer, the. rotatable windings of this latter goniometer will be able to give the directions of incoming signals without any difficulty being presented by the signals from the undesirable direction. In this application, however, the rotatable-windings must remain in a fixed position once theyhave been adjusted to exclude the undesirable signals. Thus the ro'tatable windings 64 and'12 of goniometers 65 and 13, respectively, are connected together and the fixed winding 19 of the goniometer 82 is placed "in-parallel with these windings.

The rotatable windings 68 and 16 of the goniometers 69 and IT, respectively, are also connected in parallel with the fixed winding 88 of the goniometer 82.

Since the signal from the undesirable direction has already been excluded from the goniometers 65, 69, 13 and 71, the rotatable winding 8| of the goniometer 82 will be free to give the direction of any other incoming signals. The response pattern which will result is similar to the figure eight pattern shown in Fig. 1A, except that the null point of the figure eight may be changed merely by varying the position of the rotatable windings 64, 68, 12 and I6.

The above situation is particularly advantageous when used in such a situation as is diagrammed in Fig. 4. Assume that the friendly ship 83 desires to transmit 'a message 'to the friendlyst'ation 85 but is afraid to transmit this message openly and directly because of the danger that an unfriendly ship such as the ship 84 will intercept the message and thus be able 1 to determine the position of the ship 83. If, now, the friendly station 86 sends out'a'continuous and strong signal and the ship83 sends out a' weaker signal at the same frequency, the

signal from the ship 83 being modulated, howfrom the station 86.

a Referringagain to Fig. 3, the sense-collector each of said sets cross connected with that associated with the set diagonally opposed thereto, a goniometer having a pair of fixed windings and a rotatable winding, one of said fixed windings adapted to receive the resultant output signal from one pair of said diagonally opposed antenna sets, the other of said fixed winding adapted to receive the resultant signal from the other of said diagonally opposed sets, whereby there is induced in said rotatable winding a resultant voltage signal indicative of the direction of the incoming signal.

5. A directive antenna system, having substantially zero responsiveness to incoming signals from a certain direction but finite responsiveness to signals from all other directions, said system comprising, four identical antenna sets containing three non-directional antennas in each set, said sets arranged at the four corners of a rhomboid, with the antennas of each set located in coplanar relationships, the antennas in each set being further arranged such that one antenna is mid way between the other two antennas, means for directly combining the outputs from the outer antennas of each set, means for shifting the phase of the output from the middle antenna in each set by approximately 90, means for combining the phase-shifted output of said middle antenna with the combined output of said outer antennas, means for pairing the outputs of diagonal sets to produce difierence voltages, and goniometer means for combining the difference voltages to produce a resultant voltage signal indicative of the direction of the incoming signal.

6. A directive antenna system having substantially zero responsiveness to signals from a certain direction but finite responsiveness to signals from all other directions, said system comprising, four identical antenna collector sets containing four non-directional antennas in each set, said sets arranged at the four corners of a rhomboid, the four antennas of each set arranged in a conventional Adcock arrangement at the four corners of a smaller rhomboid, a separate goniometer associated with each of said collector sets and having two fixed windings and a rotatable winding, means for connecting each pair of diagonal antennas in an Adcock set to a fixed winding of its respective goniometer, the rotatable winding of each of said goniometers being positioned to exclude an incoming signal arriving from a specific direction, means for combining the outputs from the goniometers of diagonal antenna sets to produce difierence voltages, a goniometer common to all collector sets and having two fixed windings and a rotatable winding, one of said fixed winding adapted to receive the output signal from one pair of said diagonally opposed collector sets, the other of said fixed winding being adapted to receive the output signal from the other pair of diagonally opposed sets, whereby there is introduced in the rotatable winding of said last named goniometer a resultant voltage signal indicative of the direction of the incoming signal.

7. A directive antenna system having substantially zero responsiveness to signals from a certain direction but finite responsiveness to signals from unwanted directions, said system comprising, four identical antenna collector sets containing four non-directional antennas in each set, said antenna sets arranged at the four corners of a rhomboid, a non-directional antenna located at the geometric center of said rhomboid, the four antennas comprising each set arranged in a conventional Adcock arrangement at the four corners of a smaller rhomboid, a separate goniometer associated with each of said collector sets and having two fixed windings and a rotatable winding, means for connecting each pair of diagonal antennas in an Adcock set to a fixed winding of its respective goniometer the rotatable winding of each of said goniometers being positioned to exclude an incoming signal arriving from a Specific direction, means for combining the outputs from the goniometers of diagonial antenna sets to produce difierence voltages, a goniometer common to all collector sets and having two fixed windings and a rotatable winding, one of said fixed windings adapted to receive the output signal from one pair of said diagonally opposed collector sets, the other of said fixed windings being adapted to receive the output signal from the other pair of diagonally opposed sets, means for shifting by the phase of the output from the antenna located at the center of the four collector sets, and means for introducing said phase-shifted output to the rotatable winding of said last-named goniometer, whereby there is introduced in said rotatable winding a resultant voltage signal indicative of the direction of the incoming signal.

8. A direction finding antenna system for nullifyin-g the effect of undesired signals from a given direction comprising a first and second pair of antenna elements located respectively along two lines at right angles to each other which cross at the geometrical center of said elements, a goniometer transformer having a first and second winding fixed at right angles to each other and a third winding inductively coupled thereto, said third winding being rotatable relative to said first and second winding, means for differentially coupling said first and second pair of antenna elements respectively to said first and second windings, said antenna elements having directional characteristics providing a minimum response in the same given direction, a non-directional antenna means located at the geometrical center of each of said antenna elements, phasing means for displacing the phase of the voltage in each of said non-directional antenna means by 90 degrees, means coupling the output of said phasing means to the said third winding of said goniometer transformer.

CLIFFORD M. SIMPSON.

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

FOREIGN PATENTS Number Country Date 501,959 Germany July 14, 1930 694,209 Germany July 27, 1940 491,127 Great Britain Aug. 26, 1938 63,207 Norway Feb. 10, 1941

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