US 3827055 A
A circular phased array system is described which utilizes a lens feed to simplify the problem of commutating the RF distribution system through 360 DEG of steering of the antenna beam. The lens feed consists of a circular parallel-plate radial transmission line with a central set of probes and a ring of peripheral probes. The peripheral probes are coupled via switches to an array of radiating elements arranged in a circle. The central set of probes can be energized and phased to produce electromagnetic energy with an amplitude distribution within the parallel-plate line in any given direction. By selective settings of phase and amplitude of the energy coupled to the central set of probes to achieve the proper energy distribution to the peripheral probes and by operating the switches to determine which radiating elements are coupled to the peripheral probes, a desired directive antenna pattern with low side lobes is provided.
Claims available in
Description (OCR text may contain errors)
tates Bogner et al.
atet 1 LENS FED ANTENNA ARRAY SYSTEM  Inventors: Bruce Fredric Bogner, Mt. Holly;
David Francis Bowman, Moorestown, both of NJ.
 US. Cl 343/754, 343/876, 343/854  Int. Cl. HOlq 19/06  Field of Search 343/754, 755, 876, 854
 References Cited UNITED STATES PATENTS 3,568,207 3/l97l Boyns ct al. 343/854 Primary ExaminerEli Lieberman Attorney, Agent, or Firm-Edward J. Norton; Robert L. Troike 5 7] ABSTRACT A circular phased array system is described which utilizes a lens feed to simplify the problem of commutating the RF distribution system through 360 of steering of the antenna beam. The lens feed consists of a circular parallel-plate radial transmission line with a central set of probes and a ring of peripheral probes. The peripheral probes are coupled via switches to an array of radiating elements arranged in a circle. The central set of probes can be energized and phased to produce electromagnetic energy with an amplitude distribution within the parallel-plate line in any given direction. By selective settings of phase and amplitude of the energy coupled to the central set of probes to achieve the proper energy distribution to the peripheral probes and by operating the switches to determine which radiating elements are coupled to the peripheral probes, a desired directive antenna pattern with low side lobes is provided.
10 Claims, 14 Drawing Figures PATENIED HL 3.827, 055
sum 1 or 6 NORTH 37 $40 POWER 29 msmmumm NETWRK Hg 3 PATENTEB JUL 3 01974 SHEET 2 BF 6 PAIENTED JUL3 0 I974 sum 5 or 6 PATENTEU JUL 3 01974 SHEEF 5 UP 6 1 LENS FED ANTENNA ARRAY SYSTEM BACKGROUND OF THE INVENTION This invention relates to electronic beam steering antennas and, particularly, to a circular array of many antenna elements with means for beam steering through 360 in fine increments or continuously.
The five most common approaches to provide beam steering through 360 with such an array of antenna elements are briefly described in connection with a typical 192-element circular array, for example. A total of 48 active radiating elements are normally utilized to achieve a directional beam. A first approach is a system that uses a sector-ordering matrix to commutate the amplitude distribution and a set of phase shifters to fine-steer the beam. This first system for this application includes a 1:48 power distribution network, a total of 48 4-bit phase shifters, a 48 X 48 switch matrix with 144 transfer switches and a sector selection network. Beam steering has 11 fine steering phase shifter gradients for the 48 phase shifters and 48 sector ordering commands for the 144 switches. This system requires many diodes for the phase shifters and for transfer switching. High isolation per switch 40 db) is also a requirement. For a more detailed description of this type of system see An Electronically-Scanned Cylindrical Array Based on a Switching-and-Phasing Technique by Richard J. Giannini, in the symposium record of the December, 1969 IEEE G-AP (Antennas and Propagation Group) International Symposium, Austin, Tex.
A second approach is to employ a N X N Butler beam forming matrix to excite an array of N elements or for the 192 element array a 192 X 192 matrix. This network must employ N or 192 phase shifters for beam commutation. A proposed diode count for such a system would be about 1,536. A more detailed description of this arrangement may be had with reference to a paper entitled A Matrix Fed Circular Array for Continuous Scanning, by B. Sheleg, in the symposium record of the September, 1968 IEEE G-AP (Antennas and Propagation Group), International Symposium.
A third approach referred to as the sector beam forming technique may be provided for beam steering using a 48 X 48 Butler beam forming matrix which is used in conjunction with 48 phase shifters to index the amplitude and phase of a fixed feed network along the parts of a circular array, and a sectorselection network. A more detailed description of this may be had with reference to the article An Electronically Scanned Cylindrical Array Switched in Aximuth and Frequency Scanned in Elevation," by B. Sheleg and B. D. Wright, in Proceedings of the Conformal Array Antenna Conference, NELC, San Diego, Calif, January, 1970. This 48 X 48 Butler matrix has many disadvantages. Although the amplitude and phase distribution can be commutated together, any phase error or circuit error affects both parameters. In the example, critical cancellations through six layers of directional couplers and five layers of fixed phase shifters are required to produce the output amplitude and phase distributions. All beams generated within a sector are unique, resulting in for example 500 separate phase ramps required for 500 beam positions per quadrant. This system has relatively large insertion losses because the signal must travel in the above example through six couplers, five fixed phase shifters, long equalization lines, and through several crossover networks. For a further discussion of the diadvantages of the sector beamforming technique, see the article entitled Effects of Random Errors on the Performance of a Linear Butler Array, by M. J. Kiss, in IRE Transactions (Antennas and Propagation Group), November, 1962.
A fourth technique referred to generally as the vector-transfer technique, for the above example, uses forty-eight (48) 4-bit phase shifters, a 1:48 power divider, forty-eight (48) 4-bit attenuators and forty-eight (48) single pole four throw switches (SP4T) in a sector selection network. This technique requires generally more diodes and has considerably higher loss than the other approaches. For a more complete description of this technique, see the article, Step-Scanned Circular- Array Antenna, by J. E. Boyns, C. W. Gorham, A. D. Munger, J. H. Provencher, J. Reindel and B. I. Small in- Proceedings of the Conformal Array Antenna Conference, NELC, San Diego, Calif, January, 1970.
A fifth possible technique for a ring array is the R-2R lens technique as described in the article, A Broadband Optical Feed for Circular Arrays, by J. M. Devan, J. E. Boyns and A. D. Munger in the Proceeding of the Conformal Array Antenna Conference, NELC, San Diego, Calif, January, 1970. This system requires that the angle of the feed system of a parallel plate lens by exactly twice that of the array. This would require a large diameter (or heavily loaded) lens. Moreover, it would have a very large switching matrix.
A new antenna array system is described herein which includes a parallel plate lens feed assembly. The basic array system including the parallel plate lens feed assembly is the subject of application Ser. No. 353,421 filed on the even date herewith. The basic system is exemplified by the arrangements shown in FIGS. 1 thru 3. This arrangement may require many inner probes to achieve the required highly directional pattern within the lens feed assembly. It is also desirable to further reduce the possibility of side and back lobes.
SUMMARY OF THE INVENTION Briefly, a phased array antenna system is described which includes a parallel plate lens feed assembly with a first plurality of probes arranged in a ring at the periphery of the plates and a second plurality of central probes. A plurality of radiating elements is arranged in a ring-like pattern with N times as many elements as there are probes in the first plurality of probes. A plurality of N-way switches are provided with a different N-way switch coupled to each probe of said first plurality of probes. Each of these N-way switches are coupled to N radiating elements which elements are distributed uniformly about the array. Control of the direction of the radiated beam is had by controlling the power distribution and phase of the signals to the central probes to achieve an energy distribution to the peripheral probes and by controlling the position of the N-way switches to control which antenna elements are coupled to the peripheral probes.
DETAILED DESCRIPTION A more detailed description follows in conjunction with the following drawings in which:
FIG. 1 is a sketch of a 360 electronically scanned phased array according to one embodiment of the present invention.
FIG. 2 is a sketch of the feed system in FIG. 1 showing a cross-section 'of the parallel plate radial transmission line lens feed assembly of FIG.- 1 taken along line 2-2 with the power distribution network coupled thereto.
FIG. 3 is an illustrative sketch of the fine steering portion of the array shown in FIG. 1.
FIG. 4 is a sketch of an antenna feed system in accordance with a second embodiment of the present invention.
FIG. 5 is a plan view of the radial waveguide lens feed assembly according to the second embodiment of the present invention.
FIG. 6 is a cross-sectional view of the radial parallel plate feed assembly of FIG. 5 taken along lines 6-6.
FIG. 7 is a partial cross sectional view of the parallel plate line feed assembly illustrating the probes with the center conductor having a conical taper in accordance with one embodiment of the present invention.
FIG. 8 is a sketch illustrating the coarse steering arrangement according to the second embodiment of the present invention.
FIG. 9 is a sketch of azimuth patterns illustrating how the rotatable cardioid pattern is derived.
FIG. 10 is a sketch of an azimuth pattern of a rotating phase omnidirectional pattern that is phase shifted an extra +30.
FIG. 11 is a sketch of an azimuth pattern of a rotating phase omnidirectional pattern that is phase shifted a (minus) 30.
FIG. 12 illustrates the power distribution feed network of the second embodiment of the present inventron.
FIG. 13 is a sketch of an azimuth pattern of two orthogonal figure-eight patterns.
FIG. 14 is a plan view of a radial waveguide lens feed assembly according to a third embodiment of the present invention.
Referring to FIG. 1, there is illustrated a 48-element phased array antenna system 10 with 360 scan. The antenna array system 10 includes a cylindrical array support structure 15, a lens feed assembly 11, 48 radiating elements 13 and 48 feed lines 17. The lens feed assembly 11 is located coaxially within the cylindrical support structure 15 for the radiating elements 13. The 48 peripherally mounted radiating elements 13 are equally spaced about the array structure 15 and they extend in radial fashion from the center of the cylindrical structure 15. The 48 feed lines 17 are coupled between 48 outer probes 27 associated with the parallelplate transmission line lens feed assembly 11 and the radiating elements 13. The radial parallel plate transmission line lens feed assembly 11, as shown in FIGS. 1 and 2, includes a pair of parallel overlapping conductive circular plates or disks 19 and 21 with a dielectric medium 23 therebetween so as to form a transmission line. The circular plates or disks 19 and 21 are of the same diameter and totally overlap each other. The plates or disks are spaced less than a half wavelength apart so only the TEM and TE modes can propagate where N is any whole number. The edge of the disks 19 and 21 are connected to each other by a conductive band or rim 25 of conductive material to make the parallel plate lens feed assembly 11 a completely enclosed structure confining the propagated energy therein. Near the periphery of the parallel disks l9 and 21 are coupled the 48 outer probes 27 which are equally spaced from each other and are arranged in a circular pattern. Each of these outer probes 27 are coaxial probes with the outer conductor 27a (as shown in FIG. 2) coupled to the top plate 19 and with the inner conductor 27b being insulated from outer conductor 27a and extending in a coupling manner into the dielectric medium 23 located between plates 19 and 21 through a small aperture 19a in plate 19.
A second plurality of coaxial probes 29 (represented by dots in FIG. 1), sixteen 16) in number, for example, are arranged in an inner grouping or set near the center of the lens feed assembly 11. Each of the central set of probes 29 have an outer conductor 29a and an inner conductor 29b with the outer conductor 29a coupled to plate 21 and with the inner conductor 29b extending in a coupling manner into the dielectric medium 23 through an aperture 21a in plate 21. The inner probes 29 are coupled to a power distribution network 31. This power distribution network 31 in response to electromagnetic signal waves coupled to terminal 33, for example, provides energy with selected relative power levels and selected relative phases to the 16 inner or central set of probes 29. These relative power levels and phases are selected to cause a resultant radiation pattern of a certain energy distribution to be emanated towards the outer probes 27 from the central grouping or set of probes 29. This radiation pattern excites electromagnetic energy wave energy at the peripheral probes 27 according to the certain energy distribution. In the example shown in FIG. 1, a directional radiation pattern, indicated by dashed line 39, is excited whereupon the peripheral probes 27 are excited with the particular outer probe 34 receiving maximum power and the outer probes 27 extending on either side of probe 34 having symmetrically decreasing powers. The radiated pattern 39 is made sufficiently narrow, for example, so that the signal energy at those peripheral probes 27 beyond 45 on either side of probe 34 is considered negligible.
As stated previously, the peripheral probes 27 are coupled by the separate transmission lines 17 to the separate radiating elements '13 located about the array structure 15. Since the signal energy at probe 34 is maximum, maximum power is radiated out of the North-pointing radiating element 37 coupled thereto. Symmetrically decreasing power is radiated from the adjacent radiating elements 13 on either side of element 37. The resultant relatively narrow radiation pattern from the array system 10 corresponds with that within the parallel plate transmission line assembly 11 with maximum strength of the beam pointing in the generally North-pointing direction of arrow 40. No appreciable radiation occurs beyond 45 on either side of the arrow 40. The resulting pattern distribution is similar to that of dashed lines 39.
The radiated beam from the elements 13 is commutated by adjusting the relative power level and phase of the signals at the inner probes 29 via adjustments within the power distribution network 31. For example, if it is desired to radiate the relatively narrow beam with maximum strength in the pointing EAST direction of arrow 40a, the power distribution of energy coupled to undivided probes of the central probes 29 and the relative phase of that energy at the undivided probes of the central set of probes 29 is selected at the power distribution network 31 so that the pattern within assembly 11 resemble pattern 47 (shown in dashed lines) in FIG. 1. In this arrangement, maximum radiation occurs at the particular outer probe 41 of probes 27. Probe 41 is coupled via a transmission line 17 to the EAST pointing radiating element 43. No appreciable radiation occurs, in the example, beyond about i45 on either side of element 43 and therefore maximum radiation occurs in generally the EAST pointing direction. By adjusting the power ratio between the central probes 29 and the phase of the signals at the central probes 29, any selected direction of radiation within 7.5 (360/48) may be achieved. In order to collimate and/or to achieve a continuous scan or steering of the beam within finer increments, a controlled variable phase shifter 49 is coupled in each of the leads 17 between the radiating elements 13 and the probes 27.
Referring to FIG. 3, there is illustrated the manner in which the 48 variable phase shifters 49 provide beam collimation and fine beam steering within an arc of plus and minus 3.75. With the radiated pattern as illustrated by dashed lines 39 in FIG. 1, the probe 34 of probes 27 is excited with maximum power and with the power at the adjacent probes descending in a symmetrical manner from either side of the probe 34. Maximum radiation under these conditions is in the general direction of North-pointing direction arrow 40.
To the right of the particular outer probe 34 in FIG. 3 are the four particular adjacent outer probes 36a, 36b, 36c and 36d. To the left of the particular outer probe 34 are the four particular adjacent outer probes 36e, 36f, 36g and 36h. Outer probe 34 is coupled via phase shifter 49 and a particular one 18 of the transmission lines 17 to radiating element 37. Outer probe 36a is coupled via phase shifter 49a and transmission line 17a to radiating element 37a. Similarly, probe 36b is coupled to radiating element 37b via line 17b and phase shifter 4%. Probe 360 is coupled to radiating element 370 via line 17c and phase shifter 49c. Probe 36d is coupled via line 17d and phase shifter 49d to radiating element 37d. To the left of North-pointing element 37 are antenna elements 37e, 37f, 37g and 37h. Probe 36e is coupled via line l7e and phase shifter 49e to radiating element 37e. Probe 36f is coupled via line 17f and phase shifter 49f to radiating element 37f. Probe 37g is coupled via line 17g and phase shifter 49g to radiating element 373. Probe 36h is coupled via line 17h and phase shifter 49b to radiating element 37h.
When the phase shifters 49 and 49a through 49h are adjusted to center the beam in the centered direction of arrow 40 in FIG. 3, the wavefront is along line 51. The phase shifter 49 and phase shifters 49a through 49h are adjusted so that the wave from element 37 is delayed relative to the waves from the adjacent radiating elements 49a through 49h and so that the waves from the radiating elements 49a through 49h on either side of radiating element 37 are delayed in decreasing amounts from element to element to the right and left of the center element 37. In other words, phase shifter 49 provides maximum delay, phase shifter 49a provides less delay, phase shifter 49b provides less delay than phase shifter 49a, phase shifter 490 provides less delay than phase shifter 49b, and phase shifter 49d provides less delay than phase shifter 490. Phase shifters 49a and 49e provide equal delay, phase shifters 49b and 49f provide equal delay, phase shifters 49c and 49g provide equal delay, and phase shifters 49a and 49h provide equal delay. The wavefront can be adjusted to be along dashed line 53 by adjusting phase shifters 49 and 49a through 49h such that each of the phase shifters 49 and 49a through 49h provide a relative delay to the corresponding waves that steadily increases to the right. The corresponding radiated beam thereby changes to the direction of arrow 55. This directional change may be in the above example at +3.75. The main beam may be rotated 3.75 in the direction of arrow 57 by reciprocally adjusting the position of the phase shifters 49 and 49a through 49h so that the relative delay to the corresponding wave steadily increases to the left thereby providing a waveform along dashed line 59.
The power distribution network 31 and the spacing and arrangement of the central set of probes 29 can be made in accordance with the teachings of C. O. Clasen, J. B. Rankin and O. M. Woodward, Jr. in an article entitled, A Radial-Waveguide Antenna and Multiple Amplifier System for Electronic Scanning, RCA Review, September, l96l, pp. 543 thru 554.
A power distribution network with a central probe or monopole, a next ring or four probes, a next ring of eight probes, a next ring of 12 probes and a final ring of 16 probes to achieve a single narrow beam in a desired direction is described in U.S. Pat. No. 3,090,956 of O. M. Woodward, Jr.
The above-described arrangements require many central probes, such as 16 and 29 in the above examples, to achieve the required highly directional pattern within the lens feed assembly. Also, the above arrangements may have difficulty in reducing side and back lobes to a sufficiently low level.
FIG. 4 illustrates a 192-element array system 60 requiring a less directional pattern within the parallel plate line lens feed assembly and having no significant back lobes and fewer significant side lobes. Referring to FIG. 4, the array system 60 includes a radial parallel plate line, lens feed assembly 61, an outer circular array structure 63, 192 radiating elements 65, transmission lines 66, 78 and 80, 48 phase shifters 64 and 48 single pole four-way (SP4T) switches 67. For purposes of illustration, however, only 24-radiating elements 680 thru 68f, 69a thru 69f, 70a thru 70f and 71a thru 71f of the I92 radiating elements 65 are drawn. There are seven radiating elements 65 -represented by dots and dashes between dots between each of the particular radiating elements 65 drawn. Also, for purposes of illustration, only a few of the transmission lines 66, 78 and 80, four-way switches 67 and phase shifters 64 are illustrated, therebeing the number of phase shifters (48) and four-way switches (48) as indicated previously.
The parallel plate line lens feed assembly 61 is similar to the lens feed assembly 11 in FIG. 1. Referring to FIGS. 5 and 6 illustrating a plan view and crosssectional view respectively of lens assembly 61, the assembly 61 includes a metal disk-shaped enclosure having a top wall 73 and a bottom wall 95 with a rim 97 therebetween. There is a central set of nine probes 75j, 75a through 75h and an outer circle of 48 outer probes 76. The assembly 61 differs from assembly 11 in that only nine probes are used to make up the central set of probes with one of the nine probes being at the center of the lens feed assembly and the surrounding set of eight probes being arranged in a single concentric circle.
The lens feed assembly 61 can be provided by a circular disk-shaped body 93 of 0.25 inch thick dielectric material covered with a copper disk to form top wall 73 on one surface and a copper disk on the opposite surface to form bottom wall 95, a copper covering being provided around the edge of the body to form the rim 97. The dielectric body can be Z-tron-G material manufactured by the Polymer Corporation, Reading, Pa. The disk-shaped body 93 has a radius of 10.47 inches. The 48 outer probes 76 are arranged in a circle of a radius from the center of body 93 of 9.01 inches. The outer conductor 103 of each of the probes 76 is fixed to the top disk 73 as shown in FIG. 6, and the inner conductors 105 extend in an insulative manner through an aperture 104 in the top conductor disk 73 and through the dielectric body 93. The inner conductor 105 in this example extends all the way through the dielectric body 93 to the opposite conductive disk 95 at the opposite surface. In order to match the central and outer probes to the line formed, a 50-ohm conical taper 105a of the center conductor canbe utilized as shown in FIG. 7. The forty-eight (48) outer probes 76 are equally spaced on the 9.01 inch radius. The nine (9) central set of probes 75a, 75b, 75c, 75d, 75e, 75f, 75g, 75h and 75j are located near the center with probe 75j located at the center of the radial parallel plate line lens feed assembly 61 and the other eight probes 75a, 75b, 75c, 75d, 75e, 75f, 75g and 75h arranged in a circle of a radius of 1.65 inches about the center probe 75j. A description of the placement of the central probes 75a through 75h is achieved with the aid of placement lines 107 and 109 in FIG. 5. Placement line 107 is drawn through the center of assembly 61 so as to divide the lens feed assembly 61 in half with line 107 running along cross section 66 through the center of the assembly. Line 109 is drawn to intersect line 107 at the center of the assembly 61 in FIG. with line 109 orthogonal to line 107. Probe 75a is located along a radius drawn at an angle of 0, to the left of line 107. Probe 75b is located along a radius drawn at an angle of 6 to the right of line 107. Similarly, probe 75c is located along a radius drawn at an angle of 6 to the left of line 107 and probe 75d is located along a radius drawn at an angle of 0, to the right of line 107. In this example 6 29.50. Probe 75e is located along a radius drawn at an angle of 0 above line 109. Probe 75f is located along a radius drawn at an angle of 6 below line I09. Probe 75g is located along a radius drawn at an angle of 0 above line 109. Probe 75h is located along a radius drawn at an angle of 0 below line 109. In this example, 6 is equal to 29.50. Probes 75a thru 75h are locatedabout 1.65 inches from center probe 75j.
Referring to FIG. 4, each of the 48 outer probes 76 is coupled to a separate phase shifter 64 via transmission line 66. For purposes of illustration in FIG. 4, only six probes (76a thru 76]) of the outer probes 76 are shown connected to their appropriate phase shifters 64a thru 64f via lines 66. Each of the four-way switches 67a thru 67f has the common terminal coupled to one of the outer probes 76a thru 76f respectively via lead 78 and four selectable terminals at the opposite end coupled to four separate radiating elements via leads 80. These are four times as many radiating elements 65 as there are outer probes 76 (48 X 4 192). The four radiating elements 65 coupled to each four-way switch 67 are equally spaced about the total array structure 63. For example, four-way switch 67a in FIG. 4 is coupled at the one common end to probe 76a of the outer probes 76 via phase shifter 64a and is coupled at the opposite selectable terminal end at a first terminal 85 to the particular North-pointing radiating element 68a. The second terminal 86 of four-way switch 67a is coupled to the particular East-pointing radiating element 69a. The third terminal 87 of switch 67a is coupled to the particular South-pointing radiating element a. The fourth terminal 88 of switch 670 is coupled to the particular West-pointing radiating element 71a.
Coarse scanning of the antenna array system 60 is achieved by rotating the generated beam within the lens feed assembly 61 and by switching the position of four-way switches 67 to couple the outer probes 76 to a selected one of the four radiating elements 65. The switching is accomplished on an element-by-element basis as the beam is scanned about the system by switching out the element furthest from the direction of rotation and adding the next element in the direction of rotation via the four-way switches 67 as the beam is scanned about the array. Although the operation described herein is beam scanning, it is understood that the switching can be done in any desired 'order to achieve a desired beam direction.
FIG. 8 is a sketch illustrating the switching technique. For convenience of illustration, the array of radiating elements are placed in a straight line rather than curved. Also, for purposes of illustration, only the six outer probes 76a, 76b, 76c, 76d, 76e, and 76f of the 48 outer probes 76 and six switches 67a, 67b, 67c, 67d, 67e and 67f of the 48 four-way switches 67 are illustrated. As described above, the outer probes 76 of the lens feed assembly 61 are coupled so that each outer probe 76 (48 in number) is coupled to a four-way switch 67 (48 in number) via a phase shifter 64. As mentioned previously, the four-way switch 67a coupler energy between outer probe 76a and radiating elements 68a, 69a, 70a and 71a. Similarly, four-way switch 67b couples energy between outer probe 76b and radiating elements 68b, 69b, 70b and 7 lb; four-way switch 670 couples energy between probe 760 and radiating elements 68c, 69c, 70c and 710; four-way switch 67d couples energy between probe 76d and radiating elements 68d, 69d, 70d and 71d; four-way switch 67e couples energy between probe 76c and radiating elements 68e, 69e, 70e and 71a; and four-way switch 67f couples energy between probe 76f and radiating elements 68f, 69f, 70f and 71f.
To achieve a beam directed to the northeast as indicated by arrow 73, for example, the switches 67a thru 67f are energized by a control source 87 via leads 84 to switch all of the outputs from outer probes 76a thru 76f to radiating elements 68a thru 68f via the leads 78 and 80 and phase shifters 64. The central set of probes and 75a thru 7511 are energized to produce a first cardioid pattern (shown by dashed line 81 in FIG. 8) with the maximum power divided between the outer probes 76c and 76d and lesser symmetrical powers to the outer probes 76b and 76e. Little or no appreciable power exists at the outer probes 76a and 76f. This results in an output power distribution indicated by dashed curve line 82 in FIG. 8 with the four-way switches 67a thru 67f in the position to couple the power at probes 76a thru 76f to radiating elements 68a thru 68f. This produces a beam with maximum energy in the direction of arrow 73. Since the power to the other radiating elements 69a thru 69f, 70a thru 70f and 71a thru 71f are completely switched out, no power is radiated from these elements and therefore no side or back lobe signals emit from these other elements 65, greatly reducing the possibility of back or side lobes. Also, a greater percentage of the wave energy generated by central probe 75 is this system is utilized in achieving the desired beam than in the system of FIg.
In commutating the beam about the array 60, the FIG. switches 67a thru 67f are sequentially switched element by element from the series of radiating elements 68 to the series of radiating elements 69, from the series of radiating elements 69 to the series of radiating elements 70, from the series of radiating elements 70 to the series of radiating elements 71 and from the series of radiating elements 71 back to the series of radiating elements 68. In scanning clockwise, the switches are energized in the sequence 67a, 67b, 67c, 670', 67c, 67fand back to 67a. For example, to achieve scanning from the northeast radiated position, indicated by arrow 73, to the east position indicated by arrow 83, the radiated power distribution at the particular outer probes 76a thru 76f is altered with adjustment of the power and phase at inner probes 75 and the selected position of the four-way switches 67a, 67b and 67c are switched to couple power from the probes 76a, 76b and 760 to antenna radiating elements 69a, 69b and 69c. The central set of probes 75 have their power distribution altered as indicated by pattern 810 so that the maximum power is centered at outer probe 76a with equal power at the probes 76b and 76f. A negligible low power level exists at probes 76c and 76c and a minimum power level exists at probe 76d. The result is a power distribution as indicated by curved dashed line 83 and a radiated beam with the main lobe pointing in the East direction of arrow 85. Coarse beam scanning is thereby done as discussed previously by switching on" sequentially the antenna elements 70a, 70b, 70c, 70d, 70c and 70fwhile switching off sequentially elements 69a, 69b, 69c 69f. A complete 360 scan is achieved by switching on" elements 71a, 71b, 71c 71f while switching of 70a, 70b, 70c 70f and then switching on" 68a, 68b, 68c 68fwhile switching off" elements 71a, 71b, 71c 71f. While this switching is being done, the cardioid pattern is being rotated within the lens feed assembly 61.
The fine steering to provide collimation and a continuous scan is achieved by the phase shifters 64 located between each four-way switch 67 and the outer probes 76. Control signals to the phase shifter 64 and switches 67 are provided by a control signal from source 87 via leads 84a.
The desired rotatable cardioid-like pattern as illustrated and discussed in connection with FIG. 8 is provided by generating two rotating phase omnidirectional patterns of reciprocal phase rotation represented by patterns 106 and 108 in FIG. 9 and by combining these with a uniform phase omnidirectional pattern as represented by pattern 113 in FIG. 9. The phase at the one rotating phase omnidirectional pattern 106, for example, goes clockwise from to 90, 90 to 180, 180 to 270 and 270 to 360 as shown in FIG. 9. The phase at the other rotating omnidirectional pattern 108, for example, goes clockwise from 0 to 270, 270 to 180, l80 to 90 and 90 to 0 as shown in FIG. 9. Combining these two counter rotational phase patterns results in a figure-eight pattern. By adjusting the phase between the two counter rotating omnidirectional patterns so that one is given a positive (b and the Otherjgiven an equal negative d), the orientation of the figureeight pattern can be selectably positioned in any given direction. For example, by adding a +30 to one rotating omnidirectional pattern to achieve the phase rotation shown in FIG. 10, the other rotating omnidirectional pattern should have a or 30 to achieve the other rotating phase omnidirectional pattern as shown in FIG. 11. In this case the orientation of the figureeight pattern is rotated approximately 30. Each of these two counter rotating phase omnidirectional patterns is generated by two figure-eight patterns of equal power and at phase quadrature.
FIG. 12 illustrates the feed system 117 for properly exciting the inner probes to produce the selected cardioid type energy distribution within the parallel plate line lens feed assembly 61 and to commutate these distributions within the assembly 61 by means of phase settings to the phase shifters.
The center probe 75j in FIGS. 5 and 12 excites a uniform phase omnidirectional radial pattern within the radial parallel plate transmission line lens feed assembly 61. Each of probes 75a and 75b are excited at a given phase and probes 75c and 75d are excited with equal power as probes 75a and 75b but at a 180 phase difference to produce the first figure-eight pattern as illustrated by line in FIG. 13. The probes 75e and 75f are excited with equal power and in phase. The phase of the signals at probes 75e and 75f are at phase quadrature with the phase of the signals at probes 75a and 75b Probes 75g and 75h are excited with equal power as probes 75e 75f but at a 180 phase difference to provide the second figure-eight pattern in phase quadrature as illustrated by line 111 in FIG. 13.
Referring to FIG. 12, the probes 75a and 75b are coupled to arms 120a and 12% of hybrid 120. The hybrids herein may be, for example, rat race hybrids. The summing lead 1200 of hybrid 120 is coupled to hybrid at arm 125a. The difference lead 120d of hybrid 120 is open circuited at the end. Similarly, probes 75c and 750' are coupled respectively to arms 121a and l21b of hybrid 121. The summing arm 121c of hybrid 121 is coupled to hybrid 125 at arm 125b. The difference lead 121d of hybrid 121 is open circuited at the end. The summing arm 125a of hybrid 125 is terminated in an open circuit, and the difference arm 125d is coupled to point 126. Signals coupled at point 126 are divided equally at hybrid 125 with the signals applied to hybrid 120 being out of phase with respect to those at hybrid 121. This phase and power relationship provides for the first figure-eight pattern 110 in FIG. 13.
Similarly, probes 75e and 75f are coupled to arms 127a and 127b respectively of hybrid 127. The summing arm 127c of hybrid 127 is coupled to arm 131a of hybrid 131. The difference arm 127d is terminated in an open circuit. The probes 75g and 75h are coupled to arms 129a and 12% respectively of hybrid 129. The summing arm 129c of hybrid 129 is coupled to arm l31b of hybrid 131. The difference arm 129d is terminated in an open circuit. The summing arm 1310 is terminated in an open circuit and the difference arm 131d is coupled to point 128. A signal at point 128 is coupled equally to hybrids 127 and 129 with the signals coupled to hybrid 127 being 180 out of phase with respect to signals coupled to hybrid 129. This phase and power :relationship provides for the second figure-eight pattern.
The two rotating omnidirectional patterns 106 and 108 in FIG. 9 with opposite phase rotation is provided by coupling the 3 db 90 (quadrature) coupler 140 between the points 126 and 128 at one end and the points 141 and 143 at the opposite end. One half the signal at point 141 is coupled to point 126 and the other half of the signal is phase shifted 90 to point 128. Similarly, half of the signal at point 143 is coupled to point 128 and the other half of the signal is coupled to point 126 with 90 phase shift. In the case of reciprocal operation signals at either points 126 or 128 are equally divided and coupled 90 out of phase to points 141 and 143.
By adjusting the relative phase shift of the two rotating omnidirectional patterns, as mentioned previously, the adjustable direction figure-eight pattern is provided. This adjustment of relative phase shift is accomplished by phase shifters 145 and 147 located between hybrid 149 and points 141 and 143. The phase adjustment of phase shifters 145 and 147 is made so that phase shifter 145 be made to provide a negative 4) phase shift, for example 30, when phase shifter 147 provides a positive d: or in the example +30. The result is the two counter rotating phase omnidirectional patterns in FIGS. and 11 and a resultant figure-eight pattern. The summing arm 149c of hybrid 149 is coupled to port 151 of directional coupler 150. The difference arm 149d is coupled to difference port 157. The signal information at this difference arm 149d is that from a figure'eight pattern orthogonally oriented to the selected figure-eight pattern as illustrated by pattern 118 in FIG. 9. To achieve the desired cardioid shape, the uniform phase omnidirectional pattern (represented by pattern 113 in FIG. 9) is added to the selectable figure-eight pattern. The power ratio of the uniform phase omnidirectional pattern 113 relative to the figure-eight pattern is in the order of 3 to I. This can be achieved by a 6 db directional coupler 150 whereby 75 percent of the power at sum terminal 155 is applied to terminal 153 of coupler 150 and 25 percent of this power is applied to sum port 1490 of hybrid 149. The result is a selected cardioid pattern illustrated by pattern 119 in FIG. 9. At the difference arm 149d of hybrid 149 is provided the results of a figure-eight pattern illustrated by pattern 118 with the null pointing in the direction of the maximum signal strength of the selected cardioid-like pattern 119 as shown in FIG. 9.
It is understood that the well known reciprocal theory of antennas applies and whatever performs for generating a radiated pattern performs in the reverse when a radiated pattern is received.
A difficulty may be encountered due to cross coupling between the inner probes 75. Isolation between points 126 and 128 and point 130 along center probe 75j is had by adjusting the lengths of the difference arm stubs 120d, 121d, 127d and 129d in hybrids 120, 121, 127 and 129 and the summing arm stubs 1250 and 1310 in hybrids 125 and 131. The adjustment of the length of these stubs is done empirically by varying the stub lengths until minimum cross coupling occurs.
The above-described parallel plate line lens feed assembly 61 including the feed distribution network 117 in FIG. 12 was built and tested over a frequency range of 1,250 1,325 MHz. With equal to 0 (zero degrees 6 phase shift) at phase shifter 145 and 147 the peak of the sum distribution (maximum field strength) of the cardioid-like pattern was aligned with the sixth probe 76 to the right of outer probe 760. Also the null of the difference distribution was aligned with this same sixth probe to the right of probe 76a. When 80 is applied to phase shifter 147 and 80 is applied to phase shifter 145, the pointing direction changed with the peak of the cardioid-like pattern (maximum field strength) pointing between the sixteenth and seventeenth probe to the right of probe 76a. The amplitude and phase levels did not change as the distribution was commutated.
In optimizing the system, the central set of probes 75a thru 75h are arranged with a degree of arc (20 for example) between the probes of a pair being between 50 and Further in optimizing the system the radius or distance from the center probe j to one of the other central set of probes 75a thru 75h is between 0.2 to 0.4 wavelengths in the dielectric medium of the assembly 61.
In accordance with another embodiment shown in FIG. 14 of the present invention, the assembly 161 includes a central set of five probes 175. The five probes are arranged as shown in FIG. 14 with a central probe The paired probes in FIG. -5 are replaced by single probes 175a thru 175d placed on a line bisecting the arc of the replaced probes 75 in FIG. 5 and located considerably closer to the center probe 175j.
What is claimed is:
l. A ring-like antenna array system comprising:
a pair of parallel overlapping conductive plates spaced from each other with a dielectric medium therebetween to form a transmission line,
a first plurality of probes being arranged in a ring-like pattern near the periphery of the parallel overlapping conductive plates, each of said first plurality of probes having a portion hereof extending into the field region of said transmission line,
means including a second plurality of probes being grouped in a pattern near the center of said parallel conductive plates for generating a radiated pattern of electromagnetic energy with a selected amplitude distribution of that energy within said transmission line to thereby excite a given group of said first plurality of probes,
a plurality of radiating elements arranged in a ringlike pattern, the number of said radiating elements being N times as many elements as there are probes in the first plurality of probes, where N is an integer greater than one,
a plurality of N-way switches, said switches being equal in number to said first plurality of probes,
each of said N-way switches being electrically coupled to a different one of said first plurality of probes, N number of said radiating elements being selectively coupledto each N-way switch, said N radiating elements coupled to each switch being equally spaced about the array,
and means for changing the selected switch positions of said N-way switches to determine the radiating elements electrically coupled to each of said first plurality of probes and thereby control with the generating means the direction of the beam radiated from the system.
2. The combination of claim 1 including collimating means coupled between said first plurality of probes and said N-way switches.
3. The combination in claim 2 where N is four.
4. The combination in claim 2 wherein said collimating means includes a variable phase shifter coupled between each N-way switch and one of said first plurality of probes.
5. The combination in claim 1 wherein said means for generating a radiated pattern within said transmission line includes a power distribution network so arranged as to produce a rotatable cardioid-like pattern and a difference mode pattern within the region bounded by the plates.
6. The combination in claim 5 wherein said means for generating said rotatable cardioid-like pattern further includes a pair of phase shifters and a coupler, a first of said phase shifters being arranged to provide a phase shift equal in phase shift but of opposite sign to that provided by the second of said phase shifters.
7. The combination in claim 6 wherein said coupler is arranged to combine the power of a fixed omnidirectional pattern and the resultant power from said two counter rotating omnidirectional patterns.
8. The combination in claim 1 wherein said second plurality of probes is five probes with one central probe and four probes arranged in a circle coaxially with the central probe.
9. The combination in claim 1 wherein said second plurality of probes is nine with one center probe and eight probes arranged in a circle coaxially with the center probe.
10. The combination in claim 9 wherein said eight coaxially arranged second plurality of probes are distributed in pairs such that each pair is of are from the next adjacent pair of probes.