Title:

United States Patent 3631503

Abstract:

The apparatus of the present invention provides a space-fed antenna system with a capability of forming highly efficient, multiple simultaneous beams over a broad instantaneous frequency bandwidth. The space-fed antenna system consists of a feed-through lens with a high-performance feed system. This invention employs the technique of resolving the radiating array of the feed-through lens into subarrays which overlap each other completely over the entire radiating aperture. Each of the subarrays has a truncated sinx/x amplitude distribution across the entire radiating aperture where x is linear distance therealong, thus producing a radiation pattern closely rectangular in shape. The rectangular subarray pattern is ideal, since it maximizes the array gain and minimizes the grating lobe level for a given system bandwidth. Therefore, this overlapping subarray technique allows the antenna to perform over a wide instantaneous bandwidth with a minimum number of subarrays or time delay phase shifters. Use of this technique tends to minimize cost, since the cost of such a system is reflected in the number of subarrays required

Inventors:

Tang, Raymond (Anaheim, CA)

Wong, Nam San (La Habra, CA)

Wong, Nam San (La Habra, CA)

Application Number:

04/821209

Publication Date:

12/28/1971

Filing Date:

05/02/1969

Export Citation:

Assignee:

HUGHES AIRCRAFT CO.

Primary Class:

Other Classes:

342/371, 343/782

International Classes:

Field of Search:

343/753,754,755,776,777,778,779,853,854,782

View Patent Images:

US Patent References:

3553692 | N/A | 1971-01-05 | Drabowitch | |

3380052 | Multibeam antenna system | 1968-04-23 | Drabowitch et al. | |

3305867 | Antenna array system | 1967-02-21 | Miccioli et al. | |

3295134 | Antenna system for radiating directional patterns | 1966-12-27 | Lowe |

Primary Examiner:

Lieberman, Eli

Claims:

We claim

1. A distributionally integrated subarray antenna comprising a feed-through lens having a radiating aperture and a pickup aperture; means having no less than one input and a plurality of outputs for producing no less than one phase front at said plurality of outputs; means including a multibeam matrix having a number of subarray input terminals equal to said plurality of outputs and responsive to said no less than one phase front thereat and additionally including an output feed array for simultaneously forming a plurality of substantially orthogonal overlapping beams and for directing said overlapping beams toward said pickup aperture of said feed-through lens, thereby to generate no less than one main beam from said radiating aperture; and means including switchable time-delay phase shifters disposed in series with said subarray input terminals for compensating for differences in arrival time of off-broadside wavefronts incident on said radiating aperture.

2. The distributionally integrated subarray antenna as defined in claim 1 additionally including phase shifters in said feed-through lens and means coupled to said phase shifters for scanning said main beam.

3. The distributionally integrated subarray antenna as defined in claim 1 additionally including an anechoic chamber surrounding the volume intermediate said output feed array and said radiating aperture.

4. A distributionally integrated subarray antenna capable of generating multiple simultaneous beams over a broadband of frequencies with high antenna aperture efficiency, said subarray antenna comprising a feed-through lens defining a radiating aperture; a first two-dimensional multibeam matrix having a first plurality of inputs and a corresponding plurality of outputs for producing a discrete phase front corresponding to each of said inputs at said plurality of outputs; and means including a feed array and a second two-dimensional multibeam matrix having inputs corresponding to respective subarray input terminals, said inputs being coupled to said plurality of outputs of said first multibeam matrix to energize said inputs so connected with said respective discrete phase fronts thereby to form beams corresponding to said respective subarray input terminals having sin x/x amplitude distributions where x is linear distance about each phase center and for directing said beams toward said feed-through lens thereby generating a cluster of simultaneous beams in space having a direction corresponding to said respective input terminals of said first matrix.

5. The distributionally integrated subarray antenna capable of generating multiple simultaneous beams over a broad band of frequencies with high antenna aperture efficiency as defined in claim 4 additionally including means disposed intermediate said subarray input terminals of said second two-dimensional multibeam matrix and said plurality of output terminals of said first two-dimensional multibeam matrix for compensating for differences in arrival time for off-broadside wavefronts incident on said radiating aperture.

6. A distributionally integrated subarray antenna comprising a planar radiating array, a planar pickup array having elements corresponding, respectively, with the elements of said radiating array; a controllable phase shifter interconnected between each element of said radiating array and corresponding elements of said pickup array; means including a first matrix having no less than one input and a first plurality of outputs corresponding, respectively, to subarray input terminals for producing no less than one phase front thereat, a feed array disposed to illuminate said planar pickup array; means including a second matrix interconnected between said feed array and said subarray input terminals for generating a second plurality of substantially orthogonal overlapping beams whereby said overlapping beams illuminate said pickup array thereby to generate a main beam from said planar radiating array; and means coupled to said phase shifters for scanning said main beam.

7. The distributionally integrated subarray antenna as defined in claim 6 wherein said first matrix is a corporate feed.

8. The distributionally integrated subarray antenna as defined in claim 6 wherein said first and second matrices are Butler matrices, said second matrix having more inputs than the number of subarray input terminals with the excess inputs being terminated with impedances substantially equal to the characteristic impedance thereof.

9. The distributionally integrated subarray antenna as defined in claim 6 additionally including a time-delay phase shifter interposed between each subarray input terminal and a corresponding input to said second matrix; and means connected to said time-delay phase shifter for controlling said time-delay phase shifter in a manner to compensate for differences in arrival time of off-broadside wavefronts incident on said radiating array.

10. A distributionally integrated subarray antenna comprising a feed-through lens defining a radiating aperture; a corporate feed having an input and a first plurality of outputs corresponding, respectively, to subarray input terminals; means disposed intermediate said respective subarray input terminals and said outputs of said corporate feed for compensating for differences in arrival time for off-broadside wavefronts incident on said radiating aperture; a planar feed array; means including a two-dimensional multibeam matrix having a second plurality of inputs and a corresponding second plurality of outputs interconnected from said subarray input terminals to said feed array for illuminating said feed-through lens with a first plurality of substantially orthogonal overlapping beams having sin x/x amplitude distribution where x is linear distance about each phase center corresponding, respectively, to said subarray input terminals whereby the radiation pattern from said radiating aperture corresponding to each subarray terminal has a rectangular configuration.

1. A distributionally integrated subarray antenna comprising a feed-through lens having a radiating aperture and a pickup aperture; means having no less than one input and a plurality of outputs for producing no less than one phase front at said plurality of outputs; means including a multibeam matrix having a number of subarray input terminals equal to said plurality of outputs and responsive to said no less than one phase front thereat and additionally including an output feed array for simultaneously forming a plurality of substantially orthogonal overlapping beams and for directing said overlapping beams toward said pickup aperture of said feed-through lens, thereby to generate no less than one main beam from said radiating aperture; and means including switchable time-delay phase shifters disposed in series with said subarray input terminals for compensating for differences in arrival time of off-broadside wavefronts incident on said radiating aperture.

2. The distributionally integrated subarray antenna as defined in claim 1 additionally including phase shifters in said feed-through lens and means coupled to said phase shifters for scanning said main beam.

3. The distributionally integrated subarray antenna as defined in claim 1 additionally including an anechoic chamber surrounding the volume intermediate said output feed array and said radiating aperture.

4. A distributionally integrated subarray antenna capable of generating multiple simultaneous beams over a broadband of frequencies with high antenna aperture efficiency, said subarray antenna comprising a feed-through lens defining a radiating aperture; a first two-dimensional multibeam matrix having a first plurality of inputs and a corresponding plurality of outputs for producing a discrete phase front corresponding to each of said inputs at said plurality of outputs; and means including a feed array and a second two-dimensional multibeam matrix having inputs corresponding to respective subarray input terminals, said inputs being coupled to said plurality of outputs of said first multibeam matrix to energize said inputs so connected with said respective discrete phase fronts thereby to form beams corresponding to said respective subarray input terminals having sin x/x amplitude distributions where x is linear distance about each phase center and for directing said beams toward said feed-through lens thereby generating a cluster of simultaneous beams in space having a direction corresponding to said respective input terminals of said first matrix.

5. The distributionally integrated subarray antenna capable of generating multiple simultaneous beams over a broad band of frequencies with high antenna aperture efficiency as defined in claim 4 additionally including means disposed intermediate said subarray input terminals of said second two-dimensional multibeam matrix and said plurality of output terminals of said first two-dimensional multibeam matrix for compensating for differences in arrival time for off-broadside wavefronts incident on said radiating aperture.

6. A distributionally integrated subarray antenna comprising a planar radiating array, a planar pickup array having elements corresponding, respectively, with the elements of said radiating array; a controllable phase shifter interconnected between each element of said radiating array and corresponding elements of said pickup array; means including a first matrix having no less than one input and a first plurality of outputs corresponding, respectively, to subarray input terminals for producing no less than one phase front thereat, a feed array disposed to illuminate said planar pickup array; means including a second matrix interconnected between said feed array and said subarray input terminals for generating a second plurality of substantially orthogonal overlapping beams whereby said overlapping beams illuminate said pickup array thereby to generate a main beam from said planar radiating array; and means coupled to said phase shifters for scanning said main beam.

7. The distributionally integrated subarray antenna as defined in claim 6 wherein said first matrix is a corporate feed.

8. The distributionally integrated subarray antenna as defined in claim 6 wherein said first and second matrices are Butler matrices, said second matrix having more inputs than the number of subarray input terminals with the excess inputs being terminated with impedances substantially equal to the characteristic impedance thereof.

9. The distributionally integrated subarray antenna as defined in claim 6 additionally including a time-delay phase shifter interposed between each subarray input terminal and a corresponding input to said second matrix; and means connected to said time-delay phase shifter for controlling said time-delay phase shifter in a manner to compensate for differences in arrival time of off-broadside wavefronts incident on said radiating array.

10. A distributionally integrated subarray antenna comprising a feed-through lens defining a radiating aperture; a corporate feed having an input and a first plurality of outputs corresponding, respectively, to subarray input terminals; means disposed intermediate said respective subarray input terminals and said outputs of said corporate feed for compensating for differences in arrival time for off-broadside wavefronts incident on said radiating aperture; a planar feed array; means including a two-dimensional multibeam matrix having a second plurality of inputs and a corresponding second plurality of outputs interconnected from said subarray input terminals to said feed array for illuminating said feed-through lens with a first plurality of substantially orthogonal overlapping beams having sin x/x amplitude distribution where x is linear distance about each phase center corresponding, respectively, to said subarray input terminals whereby the radiation pattern from said radiating aperture corresponding to each subarray terminal has a rectangular configuration.

Description:

BACKGROUND OF THE INVENTION

Phased array antennas are generally required to operate over a large instantaneous bandwidth with only a small tolerable amount of pulse dispersion. Conventional subarray antennas have been built with physically identifiable blocks of arrays which receive time-delayed electromagnetic signals from a corporate feed power divider. The size of each subarray must be small enough relative to the length of the pulsed signal in order to minimize dispersion. Subarray antennas of this type were plagued by high grating lobes and antenna gain losses and required a large number of time delay phase shifters as a result of the restricted subarray size.

SUMMARY OF THE INVENTION

Phased array antennas of large instantaneous bandwidth are generally dispersive in the transmission of electromagnetic pulses. Conventional subarray antenna systems provide some compensation of the above defect but pay a large penalty in sidelobe level and antenna gain. In accordance with the present invention, a subarray antenna system is provided wherein the optimum sin x/x amplitude excitation of each subarray is achieved by means of a system of arrays. The overlapping sin x/x aperture illuminations of the subarrays allow amplitude tapering to be applied to the subarray feeding coefficients without loss of subarray aperture size. This capability provides subarray radiation pattern control in a manner to enhance the antenna gain and suppress grating lobes without the requirement of a large number of subarrays. Further applications of this invention include the capability of generating multiple simultaneous beams by the replacement of the corporate feed with a multiple beam matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of the subarray antenna of the present invention;

FIG. 2 is a diagram of the feed array in the apparatus of FIG. 1;

FIG. 3 is a diagram of the connections to the multibeam matrix from the corporate feed in the apparatus of FIG. 1;

FIG. 4 is a schematic of a contemporary time-delay phase shifter;

FIGS. 5 and 5A illustrate the basic configuration and the signal flow through the apparatus of FIGS. 1 and 8, respectively;

FIG. 6 illustrates the effects of scanning a contemporary subarray pattern with respect to its concomitant array pattern;

FIG. 7 illustrates the effect of scanning the "rectangular" subarray pattern with respect to the array pattern in the apparatus of FIG. 1; and

FIG. 8 illustrates a block diagram of the subarray antenna of FIG. 1 modified to provide multiple beams.

DESCRIPTION

Referring now to FIG. 1 of the drawings, there is shown a schematic block diagram of the high performance distributionally integrated subarray antenna of the present invention. In particular, the subarray antenna comprises a feed-through lens 10 which constitutes, for example, a circular planar array made up of approximately 1,800 double-ended radiating modules 11, each having a radiating element 12 at the output extremity thereof, a pickup element 13 at the input extremity and an electronically controllable phase shifter 14 in between. The respective radiating elements 12 form a radiating array 15 which is the final radiating aperture of the antenna, and the respective pickup elements 13 form a pickup array 16 of the lens. Each of the controllable phase shifters 14 are individually connected to a phase shifter control apparatus 17 which is capable of making corrections for the spherical aberration of the lens, as well as introducing appropriate phase shifts for scanning the radiated beam of the radiating array 15. The radiating elements 12 and 13 may be implemented with horn radiators or dipoles interconnected with coaxial lines.

The primary pickup array 16 of the feed-through lens 10 is illuminated through an anechoic (reflectionless) chamber 19 by an 8×8 two-dimensional feed (64 elements) array 20 with square element lattice as shown in FIG. 2. The anechoic chamber 19 may be provided, for example, by a truncated conical conductive shell lined with pyramidal shaped electromagnetic absorbing material and feed array 20 may be implemented with open-ended waveguide radiators to make maximum usage of available area. The feed array 20 has a one-to-one correspondence between the outputs from a multibeam matrix 22 which in this case also has 8×8 elements and may be of the Butler, Blass or equivalent type. Butler matrices are described in an article entitled "Beam-Forming Matrix Simplifies Design of Electronically Scanned Antennas," by J. Butler and R. Lowe, page 170 in Electronic Design, Vol. 9, Apr. 12, 1961. An n x n matrix constitutes a first stack of n, n-input, n-output linear matrices with outputs connected straight through to respective inputs of a similar second vertical stack of linear matrices. Each linear matrix generates beams in two dimensions only. A signal applied to an input of the first stack generates an output from the n outputs of the corresponding linear matrix of the first stack which, in turn, generate outputs from all n^{2} outputs of the second stack. These output signals combine to form a pencil beam having a discrete direction corresponding to the input selected.

Inputs 23 of the multibeam matrix 22 correspond to radiated pencil beams of the feed array 20 whose peak intensities fall within the aperture plane of the pickup array 16. Inputs to the multibeam matrix 22 that correspond to beams that do not illuminate the pickup array 16 are terminated into matched loads 21, FIGS. 3 and 5.

Referring to FIG. 3, there is shown a diagram of the layout of the input ports of a Butler-type multibeam matrix 22, wherein the shaded ports around the periphery and at the inner corners thereof are terminated into matched loads 21 and the remaining ports (see FIG. I) are connected through time-delay phase shifters 24 to a corporate feed 25. Details of a corporate feed are described in connection with FIG. 38(a), Pages 11-53 of Radar Handbook, Merrill I. Skolnik, Editor-in-Chief. Corporate feed 25 has an input terminal 26 which constitutes the input-output port to the antenna system. In the transmit mode the corporate feed 25 divides energy from terminal 26 thereof equally and transfers each divided signal with equal phase shifts to the respective output terminals thereof. These output terminals of corporate feed 25 are connected to the respective time-delay phase shifters 24. In the opposite direction (receive mode) the corporate feed 25 adds the signals from the time-delay phase shifters 24 in a coherent manner and makes the resulting signal available at the terminal 26. The time delay phase shifters 24 are controlled by a phase shifter control apparatus 27 to compensate for off-broadside beams from radiating array 15 in a manner hereinafter described in connection with FIG. 5.

Referring to FIG. 4, there is shown an implementation of one of the time-delay phase shifters 24. In particular, a time-delay phase shifter may be provided with switchable-type circulators 30, 31, 32, 33, 34, 35, 36, 37 having an input 38 to circulator 30 and an output 39 from circulator 37. Reference connections 40, 41, 42, 43 are made between circulators 30, 31; 32, 33; 34, 35; and 36, 37, respectively, with TEM line. In addition, a connection 44 of TEM line having a length that is one wavelength, i.e., 1λ, longer than the reference connection 40 is made between circulators 30, 31; a connection 45 of TEM line having a length that is two wavelengths, i.e., 2λ, longer than the reference connection 41 is made between circulators 32, 33; and a connection 46 of TEM line having a length that is four wavelengths, i.e., 4λ, longer than the reference connections 42 is made between circulators 34, 35. The length of delay line 47 between the nth pair of circulators 36, 37 increases over the reference line 43 in a binomial manner; i.e., is 2^{}(n^{-1}) λ wavelength long. This process is continued until the total line length of all the delay lines equals the required time delay of the radiating aperture of the final array in the desired beam scan direction. The switching mechanisms of circulators 30-37 are coupled to the phase shifter control apparatus 27. Delays of from zero to seven wavelengths in increments of one wavelength can be switched in by appropriate combinations of connections 44, 45, 46 in place of the reference connections 40, 41, 42.

Referring to FIG. 5, there is shown a two-dimensional diagram of the apparatus of FIG. 1. The theory of operation of this system can be qualitatively described by considering the signal flow through FIG. 5 in the transmit mode of operation. A signal to be transmitted is applied to corporate feed 25 by way of input terminal 26. Corporate feed 25 divides and delivers the power of the input signal equally with the same phase shift to the respective output terminals thereof. These output signals progress through the time-delay phase shifters 24 to inputs of matrix 22 i.e., unshaded parts of FIG. 3 which illuminate the aperture of array 16. The delay introduced by time-delay phase shifters 24 will be hereinafter explained. As is well known, each input to the matrix 22 generates a beam pattern in a different direction, the center inputs having the least deflection from a normal to the array 20. For the purpose of simplicity, only two illumination patterns are illustrated. Accordingly, each unshaded input port of the multibeam matrix 22 shown in FIG. 3 of the drawings represents a subarray input terminal. The apertures of these subarrays overlap each other and each extends completely across the entire radiating aperture of the feed-through lens 10. Solid line 50 and dashed line 51 illustrate by way of example the phase distributions across the feed array 20 for two subarray input terminals 23. The solid line pattern 52 and the dashed line pattern 53 constitute the concomitant sin x/x illumination patterns corresponding to the two subarrays inputs with the phase distributions 50, 51, respectively. The illumination pattern 52 generates a corresponding sin x /x amplitude distribution across the radiating aperture represented by the solid line 54. Similarly, illumination pattern 53 generates a corresponding sin x/x amplitude distribution across the radiating aperture represented by dashed line 55. The peak of the sin x/x amplitude distributions 54, 55 are designated as phase centers 56, 57, respectively of the corresponding subarrays. Phase centers 56, 57, 58, 59, 60, 61, together with the phase centers of the other subarrays are spaced so that the sin x/x amplitude distributions intersect at the -4 db. points down from the peaks of the sin x/x distributions. In so doing, the various subarrays are said to be orthogonal; i.e., there is a minimum amount of mutual coupling between the respective subarrays.

For a given beam scan direction in the receive mode corresponding to an incident plane wave front 62, there is a delay of τ_{1} and τ_{2} in arriving at phase centers 58, 59, respectively, over the time required to reach the phase center 61 at the right edge of the array 15, as viewed in the drawing. Appropriate compensation, then, is to introduce delays of τ_{1} and τ_{2} in the time delayers 24 corresponding to the phase centers 61, 60, respectively. Similar compensating delays τ_{3} τ_{n} are introduced in the remaining time delayers 24. These time delays are switched into the delayers 24 by the phase shifter control apparatus 27. When delayed in this manner, the leading edges of an incident pulsed signal along the plane wavefront 62 arrives at the output 26 of the corporate feed 25 at the same time, thus farming a broadband instantaneous signal at the output 26. Stated differently, in the absence of delays introduced by time-delay phase shifters 24, a short pulse arriving at phase center 58 along phase front 62 would be delayed τ_{1} behind the same pulse arriving at phase front 61 resulting in substantial dispersion if not properly compensated.

Thus for each signal applied to a subarray input terminal, i.e., for each one of the outputs of time delayers 24, FIG. 5, the resulting excitations at the feed horns of feed array 20 are uniform in amplitude and progressive in phase across the radiating aperture thereof. The illumination pattern of the feed array 20 is the Fourier transform of this aperture distribution and is therefore a sin x/x type pattern because a rectangular and sin x/x are Fourier pairs. This sin x/x illumination pattern is picked up by the receiving aperture of the pickup array 16. The phase error components of the signals at the array 16 due to the spherical aberration of the feed-through lens 10 are compensated for by the phase shifters 11 in the lens 10. Hence, the illumination across the final radiating array 15 of the feed-through lens 10 corresponding to each array input 23 is still approximately a sin x/x distribution. This sin x/x distribution in turn provides a subarray radiation pattern which is approximately rectangular in shape, and very nearly achieves the goal of an ideal "rectangular" subarray radiation pattern. Each of the rectangular subarray patterns can be steered to various scan angles in space by setting the phase shifts of the constant phase-type phase shifters 11 in the feed-through lens 10 with the phase shifter control apparatus 17. The location of the peak of the sin x/x distribution is determined by the phase distribution across the feed array 20 corresponding to the excitation at a given subarray input terminal. These peaks correspond to the phase centers of the subarrays. Since the input of each subarray yields a different, progressive phase shift across the feed array 20, the phase centers of the subarrays will be distributed across the final radiating array 15 of the antenna. The time delays required for signals to travel from the phase centers of the subarrays to a plane wavefront corresponding to a given scan angle is provided by the time-delay phase shifters 24 at the subarray input terminals. A conventional corporate feed 25 or matrix feed can be used to provide uniform or other excitations of the subarrays.

Since the excitation at each subarray input terminal yields an aperture distribution across the feed array 20 which is uniform in amplitude and progressive in phase, uniform excitation of all the subarray input terminals by the corporate feed 25 yields a sin x/x type distribution for each subarray across the feed array 20. The primary illumination pattern of the feed array 20 with all the subarray input terminals excited is therefore a rectangular or sector beam pattern with steep dropoffs at the edges of the feed-through lens 10. Hence, the spillover loss of this feed system is extremely small. For example, for a 1°×1° circular planar array system with a f/d=1/2, the spillover loss is less than 0.25 db. The sector beam primary pattern also provides a fairly uniform illumination across the central portion of the radiating aperture of lens 10 with a small amount of amplitude taper near the edges of the lens due to optical spreading of the signal. The aperture efficiency of the final radiating aperture with all the subarray input terminals uniformly excited is approximately 90 percent. The peak sidelobe level corresponding to this aperture distribution is approximately 23 db.

Referring to FIGS. 6 and 7, there is illustrated the manner in which a rectangular subarray pattern improves broadband operation of the antenna system. Referring particularly to FIG. 6, there is shown the effects of scanning the subarray pattern with respect to array pattern for an antenna having nonoverlapping subarrays. The subarray pattern scans with respect to the array pattern as a function of frequency, since the constant phase-type phase shifter in the lens is only adjusted properly at one frequency, namely, midband. The amount of scanning depends upon the instantaneous bandwidth of the signal or the length of the pulsed signal. The function u, FIG. 6, varies as 2π/λd sin θ where d is the spacing between elements of the feed-through lens 10 and "θ" is the angle off-broadside. Solid line 70 represents a typical subarray pattern at a given scan angle, "θ," and the peaks 71, 72, 73 represent the main beam and the grating lobes of the array factor of the subarrays. The overall pattern of the antenna system is the product of the array factor with the subarray pattern 70. As long as the grating lobes of the array factor 72, 73 are located at the null locations of the subarray pattern 70, there is negligible drop in amplitude of the main beam and grating lobes are small. As the subarray pattern 70 is scanned, however, to a position represented by dashed line 74, there is a gain drop in the main beam to point 75 and an objectionable increase in grating lobes to points 76, 77.

Referring to FIG. 7, there is shown the effects of scanning the "rectangular" subarray pattern 80 with respect to the array factor of the antenna system of FIG. 1. As before, function u varies as 2π/λd sin θ. The scanned "rectangular" subarray pattern, as shown in the drawing, is represented by the dashed line 82. Since the patterns 80, 82 are of substantially constant amplitude, there is no gain reduction in the main beam 71. Also, since the subarray pattern 82 does not overlap the grating lobes 72, 73 of the array factor, there is no substantial increase in the magnitudes of the grating lobes as represented by points 83, 84.

Referring to FIG. 8, there is shown the antenna system of FIG. 1 with the corporate feed 25 replaced with a 6×6 multibeam matrix 90 having outputs 91 corresponding to each of the time delay phase shifters 24 and inputs 92 corresponding to each of the outputs 91. In FIG. 5A, the multibeam matrix 90 is substituted for the corporate feed in the diagram of FIG. 5. In operation, one of the inputs 92 generates a broadside phase front at the outputs 91, whereby by the multibeam matrix 90 performs the same function as the corporate feed 25. Other inputs 92 by definition of a multibeam matrix generate phase fronts at the outputs 91 that are at varying angles with broadside. These phases add to the phase shifts introduced by the time-delay phase shifters 24 to generate a cluster of beams having different directions. In the event these are outputs 91 from the multibeam matrix 90 which cannot be used; i.e., cannot be connected to time-delay phase shifters 24, they are terminated. Thus, the multibeam matrix 90 when substituted for the corporate feed in the apparatus of FIG. 1, provides a simultaneous cluster of beams that are directed in different directions over a wide angular sector of space. Operation of the apparatus of FIG. 8 in other respects is the same as for the antenna system of FIG. 1. Thus, each of the plurality of beams at the output can be simultaneously scanned by the feed-through lens 10.

Phased array antennas are generally required to operate over a large instantaneous bandwidth with only a small tolerable amount of pulse dispersion. Conventional subarray antennas have been built with physically identifiable blocks of arrays which receive time-delayed electromagnetic signals from a corporate feed power divider. The size of each subarray must be small enough relative to the length of the pulsed signal in order to minimize dispersion. Subarray antennas of this type were plagued by high grating lobes and antenna gain losses and required a large number of time delay phase shifters as a result of the restricted subarray size.

SUMMARY OF THE INVENTION

Phased array antennas of large instantaneous bandwidth are generally dispersive in the transmission of electromagnetic pulses. Conventional subarray antenna systems provide some compensation of the above defect but pay a large penalty in sidelobe level and antenna gain. In accordance with the present invention, a subarray antenna system is provided wherein the optimum sin x/x amplitude excitation of each subarray is achieved by means of a system of arrays. The overlapping sin x/x aperture illuminations of the subarrays allow amplitude tapering to be applied to the subarray feeding coefficients without loss of subarray aperture size. This capability provides subarray radiation pattern control in a manner to enhance the antenna gain and suppress grating lobes without the requirement of a large number of subarrays. Further applications of this invention include the capability of generating multiple simultaneous beams by the replacement of the corporate feed with a multiple beam matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of the subarray antenna of the present invention;

FIG. 2 is a diagram of the feed array in the apparatus of FIG. 1;

FIG. 3 is a diagram of the connections to the multibeam matrix from the corporate feed in the apparatus of FIG. 1;

FIG. 4 is a schematic of a contemporary time-delay phase shifter;

FIGS. 5 and 5A illustrate the basic configuration and the signal flow through the apparatus of FIGS. 1 and 8, respectively;

FIG. 6 illustrates the effects of scanning a contemporary subarray pattern with respect to its concomitant array pattern;

FIG. 7 illustrates the effect of scanning the "rectangular" subarray pattern with respect to the array pattern in the apparatus of FIG. 1; and

FIG. 8 illustrates a block diagram of the subarray antenna of FIG. 1 modified to provide multiple beams.

DESCRIPTION

Referring now to FIG. 1 of the drawings, there is shown a schematic block diagram of the high performance distributionally integrated subarray antenna of the present invention. In particular, the subarray antenna comprises a feed-through lens 10 which constitutes, for example, a circular planar array made up of approximately 1,800 double-ended radiating modules 11, each having a radiating element 12 at the output extremity thereof, a pickup element 13 at the input extremity and an electronically controllable phase shifter 14 in between. The respective radiating elements 12 form a radiating array 15 which is the final radiating aperture of the antenna, and the respective pickup elements 13 form a pickup array 16 of the lens. Each of the controllable phase shifters 14 are individually connected to a phase shifter control apparatus 17 which is capable of making corrections for the spherical aberration of the lens, as well as introducing appropriate phase shifts for scanning the radiated beam of the radiating array 15. The radiating elements 12 and 13 may be implemented with horn radiators or dipoles interconnected with coaxial lines.

The primary pickup array 16 of the feed-through lens 10 is illuminated through an anechoic (reflectionless) chamber 19 by an 8×8 two-dimensional feed (64 elements) array 20 with square element lattice as shown in FIG. 2. The anechoic chamber 19 may be provided, for example, by a truncated conical conductive shell lined with pyramidal shaped electromagnetic absorbing material and feed array 20 may be implemented with open-ended waveguide radiators to make maximum usage of available area. The feed array 20 has a one-to-one correspondence between the outputs from a multibeam matrix 22 which in this case also has 8×8 elements and may be of the Butler, Blass or equivalent type. Butler matrices are described in an article entitled "Beam-Forming Matrix Simplifies Design of Electronically Scanned Antennas," by J. Butler and R. Lowe, page 170 in Electronic Design, Vol. 9, Apr. 12, 1961. An n x n matrix constitutes a first stack of n, n-input, n-output linear matrices with outputs connected straight through to respective inputs of a similar second vertical stack of linear matrices. Each linear matrix generates beams in two dimensions only. A signal applied to an input of the first stack generates an output from the n outputs of the corresponding linear matrix of the first stack which, in turn, generate outputs from all n

Inputs 23 of the multibeam matrix 22 correspond to radiated pencil beams of the feed array 20 whose peak intensities fall within the aperture plane of the pickup array 16. Inputs to the multibeam matrix 22 that correspond to beams that do not illuminate the pickup array 16 are terminated into matched loads 21, FIGS. 3 and 5.

Referring to FIG. 3, there is shown a diagram of the layout of the input ports of a Butler-type multibeam matrix 22, wherein the shaded ports around the periphery and at the inner corners thereof are terminated into matched loads 21 and the remaining ports (see FIG. I) are connected through time-delay phase shifters 24 to a corporate feed 25. Details of a corporate feed are described in connection with FIG. 38(a), Pages 11-53 of Radar Handbook, Merrill I. Skolnik, Editor-in-Chief. Corporate feed 25 has an input terminal 26 which constitutes the input-output port to the antenna system. In the transmit mode the corporate feed 25 divides energy from terminal 26 thereof equally and transfers each divided signal with equal phase shifts to the respective output terminals thereof. These output terminals of corporate feed 25 are connected to the respective time-delay phase shifters 24. In the opposite direction (receive mode) the corporate feed 25 adds the signals from the time-delay phase shifters 24 in a coherent manner and makes the resulting signal available at the terminal 26. The time delay phase shifters 24 are controlled by a phase shifter control apparatus 27 to compensate for off-broadside beams from radiating array 15 in a manner hereinafter described in connection with FIG. 5.

Referring to FIG. 4, there is shown an implementation of one of the time-delay phase shifters 24. In particular, a time-delay phase shifter may be provided with switchable-type circulators 30, 31, 32, 33, 34, 35, 36, 37 having an input 38 to circulator 30 and an output 39 from circulator 37. Reference connections 40, 41, 42, 43 are made between circulators 30, 31; 32, 33; 34, 35; and 36, 37, respectively, with TEM line. In addition, a connection 44 of TEM line having a length that is one wavelength, i.e., 1λ, longer than the reference connection 40 is made between circulators 30, 31; a connection 45 of TEM line having a length that is two wavelengths, i.e., 2λ, longer than the reference connection 41 is made between circulators 32, 33; and a connection 46 of TEM line having a length that is four wavelengths, i.e., 4λ, longer than the reference connections 42 is made between circulators 34, 35. The length of delay line 47 between the nth pair of circulators 36, 37 increases over the reference line 43 in a binomial manner; i.e., is 2

Referring to FIG. 5, there is shown a two-dimensional diagram of the apparatus of FIG. 1. The theory of operation of this system can be qualitatively described by considering the signal flow through FIG. 5 in the transmit mode of operation. A signal to be transmitted is applied to corporate feed 25 by way of input terminal 26. Corporate feed 25 divides and delivers the power of the input signal equally with the same phase shift to the respective output terminals thereof. These output signals progress through the time-delay phase shifters 24 to inputs of matrix 22 i.e., unshaded parts of FIG. 3 which illuminate the aperture of array 16. The delay introduced by time-delay phase shifters 24 will be hereinafter explained. As is well known, each input to the matrix 22 generates a beam pattern in a different direction, the center inputs having the least deflection from a normal to the array 20. For the purpose of simplicity, only two illumination patterns are illustrated. Accordingly, each unshaded input port of the multibeam matrix 22 shown in FIG. 3 of the drawings represents a subarray input terminal. The apertures of these subarrays overlap each other and each extends completely across the entire radiating aperture of the feed-through lens 10. Solid line 50 and dashed line 51 illustrate by way of example the phase distributions across the feed array 20 for two subarray input terminals 23. The solid line pattern 52 and the dashed line pattern 53 constitute the concomitant sin x/x illumination patterns corresponding to the two subarrays inputs with the phase distributions 50, 51, respectively. The illumination pattern 52 generates a corresponding sin x /x amplitude distribution across the radiating aperture represented by the solid line 54. Similarly, illumination pattern 53 generates a corresponding sin x/x amplitude distribution across the radiating aperture represented by dashed line 55. The peak of the sin x/x amplitude distributions 54, 55 are designated as phase centers 56, 57, respectively of the corresponding subarrays. Phase centers 56, 57, 58, 59, 60, 61, together with the phase centers of the other subarrays are spaced so that the sin x/x amplitude distributions intersect at the -4 db. points down from the peaks of the sin x/x distributions. In so doing, the various subarrays are said to be orthogonal; i.e., there is a minimum amount of mutual coupling between the respective subarrays.

For a given beam scan direction in the receive mode corresponding to an incident plane wave front 62, there is a delay of τ

Thus for each signal applied to a subarray input terminal, i.e., for each one of the outputs of time delayers 24, FIG. 5, the resulting excitations at the feed horns of feed array 20 are uniform in amplitude and progressive in phase across the radiating aperture thereof. The illumination pattern of the feed array 20 is the Fourier transform of this aperture distribution and is therefore a sin x/x type pattern because a rectangular and sin x/x are Fourier pairs. This sin x/x illumination pattern is picked up by the receiving aperture of the pickup array 16. The phase error components of the signals at the array 16 due to the spherical aberration of the feed-through lens 10 are compensated for by the phase shifters 11 in the lens 10. Hence, the illumination across the final radiating array 15 of the feed-through lens 10 corresponding to each array input 23 is still approximately a sin x/x distribution. This sin x/x distribution in turn provides a subarray radiation pattern which is approximately rectangular in shape, and very nearly achieves the goal of an ideal "rectangular" subarray radiation pattern. Each of the rectangular subarray patterns can be steered to various scan angles in space by setting the phase shifts of the constant phase-type phase shifters 11 in the feed-through lens 10 with the phase shifter control apparatus 17. The location of the peak of the sin x/x distribution is determined by the phase distribution across the feed array 20 corresponding to the excitation at a given subarray input terminal. These peaks correspond to the phase centers of the subarrays. Since the input of each subarray yields a different, progressive phase shift across the feed array 20, the phase centers of the subarrays will be distributed across the final radiating array 15 of the antenna. The time delays required for signals to travel from the phase centers of the subarrays to a plane wavefront corresponding to a given scan angle is provided by the time-delay phase shifters 24 at the subarray input terminals. A conventional corporate feed 25 or matrix feed can be used to provide uniform or other excitations of the subarrays.

Since the excitation at each subarray input terminal yields an aperture distribution across the feed array 20 which is uniform in amplitude and progressive in phase, uniform excitation of all the subarray input terminals by the corporate feed 25 yields a sin x/x type distribution for each subarray across the feed array 20. The primary illumination pattern of the feed array 20 with all the subarray input terminals excited is therefore a rectangular or sector beam pattern with steep dropoffs at the edges of the feed-through lens 10. Hence, the spillover loss of this feed system is extremely small. For example, for a 1°×1° circular planar array system with a f/d=1/2, the spillover loss is less than 0.25 db. The sector beam primary pattern also provides a fairly uniform illumination across the central portion of the radiating aperture of lens 10 with a small amount of amplitude taper near the edges of the lens due to optical spreading of the signal. The aperture efficiency of the final radiating aperture with all the subarray input terminals uniformly excited is approximately 90 percent. The peak sidelobe level corresponding to this aperture distribution is approximately 23 db.

Referring to FIGS. 6 and 7, there is illustrated the manner in which a rectangular subarray pattern improves broadband operation of the antenna system. Referring particularly to FIG. 6, there is shown the effects of scanning the subarray pattern with respect to array pattern for an antenna having nonoverlapping subarrays. The subarray pattern scans with respect to the array pattern as a function of frequency, since the constant phase-type phase shifter in the lens is only adjusted properly at one frequency, namely, midband. The amount of scanning depends upon the instantaneous bandwidth of the signal or the length of the pulsed signal. The function u, FIG. 6, varies as 2π/λd sin θ where d is the spacing between elements of the feed-through lens 10 and "θ" is the angle off-broadside. Solid line 70 represents a typical subarray pattern at a given scan angle, "θ," and the peaks 71, 72, 73 represent the main beam and the grating lobes of the array factor of the subarrays. The overall pattern of the antenna system is the product of the array factor with the subarray pattern 70. As long as the grating lobes of the array factor 72, 73 are located at the null locations of the subarray pattern 70, there is negligible drop in amplitude of the main beam and grating lobes are small. As the subarray pattern 70 is scanned, however, to a position represented by dashed line 74, there is a gain drop in the main beam to point 75 and an objectionable increase in grating lobes to points 76, 77.

Referring to FIG. 7, there is shown the effects of scanning the "rectangular" subarray pattern 80 with respect to the array factor of the antenna system of FIG. 1. As before, function u varies as 2π/λd sin θ. The scanned "rectangular" subarray pattern, as shown in the drawing, is represented by the dashed line 82. Since the patterns 80, 82 are of substantially constant amplitude, there is no gain reduction in the main beam 71. Also, since the subarray pattern 82 does not overlap the grating lobes 72, 73 of the array factor, there is no substantial increase in the magnitudes of the grating lobes as represented by points 83, 84.

Referring to FIG. 8, there is shown the antenna system of FIG. 1 with the corporate feed 25 replaced with a 6×6 multibeam matrix 90 having outputs 91 corresponding to each of the time delay phase shifters 24 and inputs 92 corresponding to each of the outputs 91. In FIG. 5A, the multibeam matrix 90 is substituted for the corporate feed in the diagram of FIG. 5. In operation, one of the inputs 92 generates a broadside phase front at the outputs 91, whereby by the multibeam matrix 90 performs the same function as the corporate feed 25. Other inputs 92 by definition of a multibeam matrix generate phase fronts at the outputs 91 that are at varying angles with broadside. These phases add to the phase shifts introduced by the time-delay phase shifters 24 to generate a cluster of beams having different directions. In the event these are outputs 91 from the multibeam matrix 90 which cannot be used; i.e., cannot be connected to time-delay phase shifters 24, they are terminated. Thus, the multibeam matrix 90 when substituted for the corporate feed in the apparatus of FIG. 1, provides a simultaneous cluster of beams that are directed in different directions over a wide angular sector of space. Operation of the apparatus of FIG. 8 in other respects is the same as for the antenna system of FIG. 1. Thus, each of the plurality of beams at the output can be simultaneously scanned by the feed-through lens 10.