US3864689A - Hybrid scan antenna - Google Patents

Abstract

A hybrid antenna system comprises two or more wave guide antenna sections which are physically separated and separately fed with radiant energy from a single source by dividing up energy from the source and feeding it into first ends of the various sections. Phase shifters are provided such that the radiant energy fed to successive sections is shifted in phase in such a manner that the overall radiated output beam from all of these sections constitutes a single beam which may be scanned in the same manner as though all of the sections were connected together to form a single elongated wave guide antenna. The provision of the antenna in sections makes it more convenient to locate the antennas on various portions of an aircraft to realize the same effect as an elongated single waveguide type antenna.

Description

United States Patent [191 ill] 3,864,689

Young Feb. 4, 1975 HYBRID SCAN ANTENNA Primary Examiner-Eli Lieberman [76] Inventor. David Young, 627 N Attorney, Agent. or firm-Pastorrza & Kelly Beachwood Dr., Burbank, Calif. 91506 [57] ABSTRACT [22] Filed. Aug 2, 1973 A hybrid antenna system comprises two or more wave guide antenna sections which are physically separated [21] Appl. No.: 385,085 and separately fed with radiant energy from a single source by dividing up energy from the source and feeding it into first ends of the various sections. Phase liil K585331113'iii/iii:3 iioifil i hhhhhhh hhhhhhh hhhh hhhh hhh hhhhhhh hhhhgh fed [58] Field of Search 343/l00 SA 768, 771, 854, to successive sections is shifted m phase in such a manner that the overall radiated output beam from all 343/705 of these sections constitutes a single beam which may hhh resists:assesses?t en il12.15:: UNITED STATES PATENTS 1 elongated wave guide antenna. The provision of the 2,777,122 V1957 Hcdcmll" 343/763 antenna in sections makes it more convenient to lo- 3936310 5/l962 Lchim F 343/854 cate the antennas on various portions of an aircraft to 3,041,605 6/l962 GOOdWlI'l 8121i. 343/854 realize the same effect as an elongated Single wave guide type antenna.

3 Claims, 4 Drawing Figures I2 ll Synch I r F Motor I Microwave 355d Ph'use "put T COupler l Shifter PEJENTEU FEB 4 I975 SHEEi 2 [IF 2 Phase Det.

Synch Phase I Motor Shifter i i l I Microwave 3 D [3 (It) (-9-) lnput 7 Hybrid Phase Phase 3O Coupler Shifter Shifter J l 3i 33 i 39 B I Electro- 40 [4| L Mechanical Transducer 43 Position Sensor Synch Motor Phase 48 I 54\ Detector 7 5l- Microwave Digiffll m Hybrid phpse 46 Coupler Shifter HYBRID SCAN ANTENNA This invention relates generally to micro-wave antennas and more particularly to wave guide scanning type antennas used in self-contained aircraft radar systems.

BACKGROUND OF THE INVENTION In my co-pending patent application Ser. No. 353,201 filed Apr. 20, 1973, now U.S. Pat. No. 3,829,862 and entitled RIDGE SCAN ANTENNA, there is shown and described an elongated waveguide antenna which incorporates an electro-mechanical scanning means to provide for a fan-shaped radiated beam in'a vertical plane which may be scanned back and forth in azimuth. In another of my co-pending patent application Ser. No. 353,129, also filed Apr. 20, 1973 and entitled CONTINUOUS SCANNING WAVE GUIDE ANTENNA, now U.S. Pat. No. 3,803,620 issued Apr. 9, 1974 there is described an antenna system which will generate the same type of beam but wherein a continuous electro-mechanical scanning arrangement is provided.

In both of the above co-pending patent applications, the antennas involved are in the form of elongated wave guides which may have a dimension for example of feet in length. The length of the overall waveguide type of antenna is important in obtaining the necessary narrow vertical beam width. The antennas themselves are most advantageously used in perspective radar systems incorporated in an aircraft. In this respect, reference is had to my co-pending application Ser. No. 847,121 filed Aug. 4, 1969 and entitled AIR- CRAFT CONTAINED PERSPECTIVE RADAR/DIS- PLAY AND GUIDANCE FOR APPROACH AND LANDING, now U.S. Pat. No. 3,778,821, issued Dec. 11, 1973.

Because the waveguide scanning type antennas are of long physical dimensions, there can be a serious problem in finding an acceptable location for the wave guide antenna in the aircraft. The problem is not too critical in the case of fairly large aircraft, the leading edge of the wing serving as a satisfactory location for accommodating the waveguide antenna. In fact, for fairly large aircraft, the wing flap itself constitutes an excellent location for such an antenna all as set forth and described in my further co-pending patent application Ser. No. 355,065 filed Apr. 27, 1973, and entitled FLAP ANTENNA.

However, for smaller aircraft and even in some larger types of aircraft, it is desirable to locate any antennas in suitable radomes rather than in the leading edge of wings or in other areas. 'In the case of a 10 foot long X- band antenna suitable for a perspective radar, the commercial jet radome would not be capable of accommodating the necessary structure. By using a higher frequency, for example, the Ka-band a 3 foot length wave guide antenna would operate to provide the required narrow beam width since it is equivalent in length to a 10 foot antenna operating at X-band frequency and thus could be accomodated in the radome. Of course if a Ka-band wave guide antenna of a 10 foot length or an X-band of 30 foot length could be constructed and accommodated on an aircraft, an extremely narrow beam could be generated in a vertical plane which would be very useful.

Aside from the foregoing problems of physical location of a long wave guide antenna, there are also the very serious mechanical problems involved in effecting a proper scanning in a long wave guide type of structure. For example in the ridge scan antenna as described in my heretofore referred to patent application of the same title, a ridge member is caused to reciprocate back and forth into a side opening of the waveguide antenna over its entire length to effect a shift in the phase velocity of radiation within the guide and thereby cause the desired scanning in azimuth to take place. It is vitally important that the ridge member move absolutely parallel to itself in entering and leaving the wave guide and in the case of very long wave guides for example, over wave lengths such as 10 feet for X-band or 3 feet for Ka-band, it can become a serious problem in tolerances to provide such a mechanical system for accurately moving the ridge member.

Thus from both the standpoint of physical location and the standpoint of mechanical tolerances in effecting a scanning operation, it is much easier to work with shorter length antennas. On the other hand, and as noted, the shorter length antennas are not capable of providing the desired narrow beam width of the resultant radiant energy beam in a vertical plane.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention contemplates a novel hybrid scan antenna system wherein at least two and preferably several physically separated elongated waveguide antenna sections are provided together with coupler means for receiving electro-magnetic energy from the single main source and dividing it to feed equal amounts to first ends of the antenna sections. Means are also provided for scanning in synchronism the radiant energy emitted by each of the physical separate antennas. This scanning means may take the form of ridge scanners for each particular section or continuous types scanning systems for each individual section such as described for the heretofore provided long single wave guide antenna as described in my referred to copending applications. However, because the individual sections are each substantially shorter than the over-all length of a single continuous antenna which would result if all of the sections were connected end to end, great accuracy can be realized in the scanning of the individual sections. Suitable means are provided to assure that the scanning of the individual sections is in synchronism.

In addition to the foregoing, the invention provides a phase shift means exterior of the antenna sections including means positioned to receive the energy fed to one of the sections and shift its phase relative to the energy fed to the other or preceeding section, there being provided more than one phase shifter if there are more than two sections involved. The degree of phase shifting in turn is controlled by a control means connected to the phase shift means and responsive to the scanned position of radiant energy emitted by the antennas to shift the phase of the energy fed to the one antenna and in the case of a plurality of sections successively shift the energy to the subsequent sections all in such a manner that the radiant energy from all of the sections is in the form ofa single beam which is scanned the same as though the sections were connected end to end to form a single long continuous wave guide antenna.

By adjusting the degree of phase shifting and synchronizing the phase shifting with the electromechanical scanning arrangement, the individual antenna sections can be located at various different physical portions of the aircraft and the requirement of a space on the aircraft to accommodate a single long wave guide type antenna is avoided.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be had by now referring to the accompanying drawings in which:

FIG. I is a perspective view of an aircraft incorporating the hybrid antenna of the present invention for generating a fan-shaped radar beam capable of sweeping in azimuth;

FIG. 2 is a schematic block diagram illustrating the manner in which a single radiant energy fan-shaped beam as shown in FIG. 1 can be obtained from two physically separate wave guide antenna sections in accord with a first embodiment of the invention;

FIG. 3 is a block diagram similar to FIG. 2 but showing an additional feed-back system for maintaining phase shift accuracy in the system; and

FIG. 4 illustrates a third simplified embodiment wherein a digital type phase shifter is used.

Referring first to FIG. 1, there is shown an aircraft l equipped with hybrid antenna sections l1, 12, 13, 14, and in accord with the present invention. The physical location of these sections, one of which is shown in the nose portion of the aircraft and the remaining on leading edge portions of the wings is arranged to provide for a single fan-shaped radiant energy beam 16 which may be swept in azimuth as indicated by the double headed arrow the same as though the individual sections were all connected end to end to provide a single elongated continuous wave guide antenna.

It will be evident from FIG. 1 that if the antenna sections were connected together as described, there would be no convenient physical location on the air- I craft to accommodate such a long antenna. However,

by providing the antenna in hybrid sections as shown, the sections themselves can be properly accommodated.

Referring now to FIG. 2 there is shown a first system for assuring that the individual hybrid antenna sections function in such a manner as to provide for an overall single radiated beam of narrow beam width. In FIG. 2, the antenna sections 11 and 12 described in FIG. 1 are shown the separation spacing being greatly exaggerated. In this respect, there is no problem in locating one of the sections ahead or behind the other as long as their longitudinally separated distance is not great. For example, the antenna sections 12 and 13 of FIG. 1 are translationally displaced so that the antenna section 13 is ahead of the antenna section 12. However, if the antenna section 13 were moved back to a projected position in alignment or close to alignment with the antenna section 12, its physical separation at the adjacent ends would be small and it is important that this distance be kept small.

As shown in FIG. 2, there is provided a first synchronous motor 17 for driving a suitable scanning element in the antenna section 12. A second synchronous motor 18 in turn drives the corresponding scanning element in the antenna section 11 and is maintained in exact synchronism with the synchronous motor 17 as by the resolver 19.

If a ridge type scan member is employed such as described in my heretofore referred to co-pending patent application, it will be appreciated that control of the ridge for the shorter length sections 11 and 12 can more readily be carried out and with greater accuracy than is possible for a single ridge in a wave guide of twice the length of either of the individual sections.

Referring to the lower portion of FIG. 2, there is shown a micro-wave input line 20 which would be a feeding wave guide from a single source of electromagnetic energy. This input passes through a hybrid coupler means 21 which simply functions to divide the energy and feed it in equal amounts to first ends of the antenna sections as indicated by the lines 22 and 23. A phase shift means in the form ofa phase shifter 24 exterior of the antenna sections is positioned to receive energy from the line 23 and shift its phase relative to the energy in line 22 fed to the other of the said sections.

The system is completed by control means in the form of the connection 25 from the synchronous motor 18 to the phase shifter 24 which functions to supply a signal to the phase shifter in response to the scan position of the radiant energy emitted by the antennas. This scanned position is a function of the position of the ridge member in the event ridge scanning is employed which in turn is determined by the position of the synchronous motor at any instance in time. The signal to the phase shifter 24 from the line 25 shifts the phase of the energy fed to the antenna 11 in such a manner that the radiant energy from the sections 10 and 11 is in the form of a single beam which scans the same as though the sections were connected end to end to form a single long continuous wave guide antenna.

The result of the phase shifting can be best understood by referring to the wave fronts of the radiated energy in FIG. 2 wherein the portion 26 of the wave front would represent energy from the antenna section 12 and the dashed portion 27 would represent energy from the section 11 at a given scan position. Essentially, the action of the phase shifter 24 shifts the energy wave front 27 to the position 27' in exact alignment with the wave front 26 so that there results the single radiant energy beam as described.

The amount of phase shift is different for each scan position. For example, when the radiated beam is directed forwardly along a line perpendicular to the longitudinal axis of the antenna sections; that is, broadside, no phase shift between the energy at the input lines 22 and 23 to the sections respectively, takes place. As the beam scans past broadside, then the phase shifter 24 acts to shift the phase of the energy fed to the one antenna section 11 in a continuous manner such as to bring about the condition of a simulated single beam as described with respect to the scanned position illustrated in FIG. 2.

It will be understood that the FIG. 2 relates to only two antenna sections and that in actuality, several sections may be provided to provide the equivalent wave front of a single elongated antenna of length equal to the sum of the total number of sections. Further phase shifters corresponding to the phase shifter 24 would be provided for the subsequent antenna sections so that the final overall radiated beam would have a flat wave front corresponding to the line 26 and 27' of FIG. 2.

A further advantage of the hybrid scanner described in FIG. 2 in addition to the advantage of spaced location and better tolerances in the mechanical scanning is the fact that less energy is lost in the overall hybrid antenna system. For example, considering an X-band antenna feet long there is a three decibel power loss. If two 10 foot antennas are combined as illustrated in FIG. 2, the total loss would still only be three decibels while the loss of an equivalent straight 20 foot antenna would be 6 decibels. Thus the two antenna sections function twice as efficiently as an equivalent single long antenna. Clearly greater efficiency will be achieved for a larger number of sections.

Another advantage of providing antenna sections rather than a single elongated antenna is that each section is less sensitive to aircraft changes in structure due to variations in wing loading by way of example. In other words, variations in the wing loading would be less likely to affect the synchronous motor driving of the individual sections as opposed to driving a single long antenna.

FIG. 3 illustrates a system similar to FIG. 2 but wherein a feedback mechanism has been provided to maintain absolute accuracy in the phase shifting of the energy fed to one antenna relative to the energy fed to the other.

As shown, there are provided antenna sections 11 and 12 wherein there corresponding electromechanical scanning mechanisms which might take the form of individual ridges are driven in synchronism by a synchronous motor 28. In the showing of FIG. 3, the ridge for the one antenna 11 is indicated as being driven by the synchronous motor 28 by the dash line 29. It will be understood that a separate synchronous motor could be utilized and it should also be understood that the section 11 need not be in alignment with section 12 but could still be driven by the same synchronous motor through suitable displacing gears.

As in the case of FIG. 2, there is provided a microwave input line 30 passing to a coupler 31 dividing the radiant energy into equal amounts for feeding along lines 32 and 33 to first ends of the antennas l2 and 11 respectively. However, the energy in the line 33 first passes through a plus-minus feedback controlled phase shifter 34 and thence to a plus phase shifter 35 prior to being fed into the one antenna 11. The energy at the other end of the one antenna 11 passes into a minus phase shifter 36 and thence to one side of a feedback phase detector 37. The other side of the phase detector 37 receives energy from the other end of the other antenna 12 as indicated by the line 38 to provide for an error signal on an output line 39 passing to the plusminus feedback controlled phase shifter 34.

The phase shifter 35 is controlled by an input signal line 40 and the phase shifter 36 is simultaneously controlled by the same signal on a line 41. It will be understood that the minus phase shifter 36 shifts the phase in an exactly opposite direction to the plus phase shift by the phase shifter 35. The controlled signals on line 40 and 41 are derived from an electro-mechanical transducer position sensor 42 responsive to the position of the scanning means as indicated by the dashed line 43.

In the operation of the circuit of FIG. 3, the phase shifter 35 shifts the phase of the energy fed to the antenna section 11 in such a manner that the wave front radiated therefrom is in proper flat relationship or alignment with the wave front radiated from the antenna section 12. The proper alignment is maintained for the various scanner positions in azimuth by continuously shifting the phase of the phase shifter 35 through the electro-mechanical transducer position sensor 42 and signal line 40 all as is accomplished by the corresponding elements as described in FIG. 2. However, in FIG. 3 the minus phase shifter 36 receives the energy from the other end of the antenna section 11 and shifts its phase in a manner precisely opposite to the phase shifter 35 so that the input to one side of the phase detector 37 is in phase with the energy fed on line 33 passing through the plus-minus phase shifter 34 to the phase shifter 35. As stated, the energy from the other end of the antenna section 12 passes in line 38 to the phase detector 37 and this energy should be directly in phase with the energy passed to the first side since the phase shift accomplished by the phase shifter 35 has been canceled out be the phase shifter 36. However, should there be any mechanical differences or discrepancies in the synchronizing of the mechanical scanning of the two antenna sections resulting in a slight phase shifting, the phase detector 37 will detect any such slight difference in phases of the energy fed to the respective sections and provide an error signal on the line 39 which passes to the plus-minus feedback controlled phase shifter 34. This phase shifter will effect a slight shift in the phase of the energy on line 33 to phase shifter 35 in a proper direction to null any error signal from the phase detector 37 so that the desired proper phase relationship is maintained notwithstanding the presence of slight mechanical differences in the mechanical scanning operations of the sections.

Referring now to FIG. 4 there is shown a simplified embodiment of the invention wherein rather than continuously varying the phasewith the scanning of one section relative to another, a digital type phase shifter is utilized.

Referring in detail to FIG. 4 the antenna sections 11 and 12 are scanned synchronously as by a synchronous motor 44 and suitable coupling connection 45. A micro-wave input line 46 passes through a coupling 47 to divide energy along lines 48 and 49 to first ends of the antennas l2 and 11 respectively.

The digital phase shifter is characterized in that it will shift the phase of an incoming signal in a discreet step rather than in a continuous manner in response to an input signal. For example, it might effect a phase shift whenever it receives such an input signal.

Control of the digital phase shifter 50 is accomplished by passing energy on lines 51 and 52 into the two sides of a phase detector 53, the output line 54 of which provides an input signal to the digital phase shifter 50. The phase detector 53 is arranged to provide such an input signal only when the energy on the lines 51 and 52 is out of phase by a predetermined amount.

In considering the operation of the circuit of FIG. 4, it will be understood that in the absence of any phase shifter 50, the resultant beam from the radiation from each of the antenna sections 11 and 12 would alternately peak and null as scanning took place. For example, when scanning is directly broadside and no phase shift is required between the energy supplied on lines 48 and 49, the wave front of the energy radiated would be flat and in a peak condition. However, when the angle of scan to either side of broadside assumes certain values one radiation would cancel the other and there would result a null. For example, if the two wave guide sections were each 10 feet long and at X-band each would have its own approximate 0.8 beam width and in combination the beam width would be 0.4. However, the 0.4 beam while scanning would null out about every 0.8. This result would not seem to be a very useful antenna but in reality, the nulls are very narrow and in the presence of strong signals the nulls would not be very prominent on a practical radar display. In essence, then, the hybrid antenna in its most simplified version might function to some extent without any phase shift.

In the circuit of FIG. 4, however, a compromise phase shift system is provided which will fill in the nulls and peaks of the resultant output beam. While this system is not as satisfactory as that described in conjunction with FIGS. 2 and 3 wherein automatic continous phase shifting takes place so that the beam is always peaked, it is far more economical and may be sufficiently practical for practical applications.

Considering the actual manner in which the filling in t e ll P l .t sp ase tQLSS is s to provide anTnput signal on the line 54 whenever the phase of the input energies supplied by leads 51 and 52 approaches a predetermined difference; for example, when the two input energies approach 180 out of phase. Generation of the input signal on the line 54 will then digitally shift the phase shifter 50 and if this phase shifter is set for shifting phase in 180 steps, the phase on the line 51 will be shifted 180 and thus will be appreaching a condition in phase with the energy on line 52. Thus a condition wherein there would normally be a null is filled in by the sudden reversal of the phase on the line 51 due to actuation of the digital type phase shifter. The wave front of the resultant output beam as far as peaks and nulls are concerned would appear scalloped. By providing digital stepping of the phase shifter 50in shorter steps; for example, 90 or even 45,

the number of scallopes would increase and would all be shallower and clearly as the number of digital phase shifts steps were made still shorter, the operation would approach that of the FIG. 2 embodiment.

From the foregoing description, it will be evident that the present invention has provided unique hybrid antenna systems wherein the advantages of a long antenna, tolerances in mechanical scanning, and efficient use of power are all realized.

In essence, the present invention combines the most advantageous features of a completely electronic scanning antenna and a completely mechanical scanning antenna. The use of total electronic scanning antenna systems is much too complex and expensive for many current and future applications but the present invention takes advantage of the small, rapid electronic phase shifter design used only a few times and combines it with the mechanical or ridge scanner type of antenna, thus utilizing the best of both techniques.

Moreover, each of the hybrid sections are the same and thus can be economically manufactured. In any particular application, any number of sections to make up an overall antenna may be selected depending upon the economics, size of the aircraft, and beam width desired.

What is claimed is:

l. A hybrid scan antenna comprising, in combination:

a. at least two physically separated elongated wave guide antenna sections;

b. coupler means for receiving electromagnetic energy from a single source and dividing it to feed equal amounts to said antenna sections;

c. mechanical means for scanning radiant energy emitted by each of said antennas, said scanning being sychronized;

d. phase shift means exterior of the antenna sections including means positioned to receive the energy fed to one of said sections and shift its phase relative to the energy fed to the other of said sections; and,

e. control means connected to said phase shift means and responsive to the scanned position of radiant energy emitted by the antennas to cause the phase shift means to shift the phase of the energy fed to said one antenna in a manner such that said radiant energy is in the form of a single beam which is scanned the same as though the sections were connected end to end to form a single long continuous wave guide antenna, said phase shift means shifting the phase of energy received thereby in a continuous manner as a linear function of a varying input signal, said control means including means for deriving said varying input signal for the phase shift means from said mechanical means for scanning radiant energy.

2. An antenna according to claim 1, in which said phase shift means includes a plus-minus feedback controlled phase shifter, a plus phase shifter, a minus phase shifter, and a feedback phase detector, said plus-minus feedback controlled phase shifter receiving radiant energy fed to one of said sections and passing it through said plus phase shifter, the output from said plus shifter passing to the first end of said one antenna section, said minus phase shifter receiving energy from the other end of said one section and shifting its phase in a manner opposite to the phase shift by said plus phase shifter to provide energy to one side of said feedback phase detector so that said energy is in phase with the phase of the energy supplied from said plus-minus feedback controlled phase shifter, radiant energy from the other end of the other of said antenna sections passing to the other side of said feedback phase detector, said feedback phase detector providing an output error signal proportional to any phase difference of the energy received in its sides to said plus-minus feedback controlled phase shifter to effect a correction in the phase of the energy passed to said plus phase shifter in a manner to reduce the error signal towards zero, said control means connecting to both said plus and minus phase shifters to simultaneously control the phase shifts thereof which take place in opposite directions, in accordance with the scan position of the radiant energy emitted by the antennas.

3. An antenna according to claim 1, in which said phase shift means comprises a digital type phase shifter for shifting the phase of energy fed thereto in discrete steps in response to an input signal, said control means comprising a phase detector having its sides connected to receive radiant energy fed to said first ends and providing said input signal to said phase shifter whenever the difference in phase of said energy reaches a predetermined amount.

Claims (3)

1. A hybrid scan antenna comprising, in combination: a. at least two physically separated elongated wave guide antenna sections; b. coupler means for receiving electromagnetic energy from a single source and dividing it to feed equal amounts to said antenna sections; c. mechanical means for scanning radiant energy emitted by each of said antennas, said scanning being sychronized; d. phase shift means exterior of the antenna sections including means positioned to receive the energy fed to one of said sections and shift its phase relative to the energy fed to the other of said sections; and, e. control means connected to said phase shift means and responsive to the scanned position of radiant energy emitted by the antennas to cause the phase shift means to shift the phase of the energy fed to said one antenna in a manner such that said radiant energy is in the form of a single beam which is scanned the same as though the sections were connected end to end to form a single long continuous wave guide antenna, said phase shift means shifting the phase of energy received thereby in a continuous manner as a linear function of a varying input signal, said control means including means for deriving said varying input signal for the phase shift means from said mechanical means for scanning radiant energy.

2. An antenna according to claim 1, in which said phase shift means includes a plus-minus feedback controlled phase shifter, a plus phase shifter, a minus phase shifter, and a feedback phase detector, said plus-minus feedback controlled phase shifter receiving radiant energy fed to one of said sections and passing it through said plus phase shifter, the output from said plus shifter passing to the first end of said one antenna section, said minus phase shifter receiving energy from the other end of said one section and shifting its phase in a manner opposite to the phase shift by said plus phase shifter to provide energy to one side of said feedback phase detector so that said energy is in phase with the phase of the energy supplied from said plus-minus feedback controlled phase shifter, radiant energy from the other end of the other of said antenna sections passing to the other side of said feedback phase detector, said feedback phase detector providing an output error signal proportional to any phase difference of the energy received in its sides to said plus-minus feedback controlled phase shifter to effect a correction in the phase of the energy passed to said plus phase shifter in a manner to reduce the error signal towards zero, said control means connecting to both said plus and minus phase shifters to simultaneously control the phase shifts thereof which take place in opposite directions, in accordance with the scan position of the radiant energy emitted by the antEnnas.

3. An antenna according to claim 1, in which said phase shift means comprises a digital type phase shifter for shifting the phase of energy fed thereto in discrete steps in response to an input signal, said control means comprising a phase detector having its sides connected to receive radiant energy fed to said first ends and providing said input signal to said phase shifter whenever the difference in phase of said energy reaches a predetermined amount.

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