Abstract:
Antennas having a circular array of radiating elements are arranged to enable continuous 360 degree scanning of a sum and difference beam pattern. With a 108 element circular array, a sub array of 27 contiguous elements may be step scanned to 108 positions while maintaining sum and difference antenna patterns. Each scan step may require only two switch adjustments, one to initiate excitation of a contiguous leading element and terminate excitation of the trailing element, and the other to change coupling of a middle element from a divided power port of a left power divider to such a port of a right power divider. Configurations using sub arrays whose element complement is not evenly divisible into the total number of array elements, using sub arrays consisting of an odd number of radiating elements, or employing minimized feed network complexity are disclosed.

Description:
RELATED APPLICATIONS 
     (Not Applicable) 
     FEDERALLY SPONSORED RESEARCH 
     (Not Applicable) 
     BACKGROUND OF THE INVENTION 
     This invention relates to antennas and, more particularly, to electronic scanning of a circular array antenna with excitation of a sum and difference beam pattern. 
     Electronic scanning of a circular array of radiating elements represents a long term problem area in antenna technology, particularly in the context of continuous circular scanning of a composite sum and difference beam pattern. The basic geometry of a circular array and the objective of providing the capability of uninterrupted and continuous scanning (e.g., from zero degrees to 360 degrees azimuth and continuing past 360 degrees) introduce complexities of signal switching and beam management and control. While solutions may have been proposed, no solutions free of operational limitations or of a high level of technical complexity are known. 
     Accordingly, objects of the present invention are to provide new and improved curved linear array antennas and such antennas having one or more of the following characteristics and capabilities: 
     circular arrays with continuously scannable beam patterns; 
     scannable sum and difference composite beam patterns; 
     stepped scanning of sum and difference beam patterns, with only two switch activations per step; 
     circular arrays with simplified switching networks; 
     stepped beam patterns formed by progressively modified element sub array; 
     circular scanning with a number of sub array elements not evenly divisible into the total array complement; and 
     circular scanning with sub arrays having an odd number of elements. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an array antenna, with scannable beam sum and difference excitation, includes a circular array of radiating elements arranged to provide a beam pattern upon excitation of radiating elements of a sub array consisting of a fixed number of radiating elements of the array. First and second power dividers each have a first port and a plurality of divided power ports. A circuit device, coupled to the first ports of the first and second power dividers, is arranged to provide at a sum port a signal representative of a sum of signals from the power dividers and at a difference port a signal representative of a difference between signals from the power dividers. Switching devices are coupled between the radiating elements and the divided power ports of the first and second power dividers and arranged to provide the beam pattern by coupling the first and second power dividers to respective first left and first right subsets of a sub array of the radiating elements. A control facility is arranged to control the switching devices to scan the beam pattern by coupling the first power divider to a successive left subset of the radiating elements and the second power divider to a successive right subset of the radiating elements. Such successive left subset includes at least one radiating element not included in the first left subset and the successive right subset includes at least one radiating element not included in the first right subset. This switching protocol can then be repeated for continuing 360 degree scanning of the sum and difference pattern. 
     Also in accordance with the invention, an array antenna, with scannable beam excitation, includes a circular array of radiating elements arranged to provide a beam pattern upon excitation of a sub array consisting of a fixed number of radiating elements of the array and a power divider with a first port and a number of divided power ports equal to that fixed number. Switching devices are coupled between the radiating elements and the power divider and arranged to provide the beam pattern by coupling the power divider to the sub array of the radiating elements. A control facility is arranged to control the switching devices to scan the beam pattern by coupling the power divider to successive sub arrays, each modified from the preceding sub array by initiating coupling to a radiating element contiguous in a forward beam scan direction and terminating coupling to the trailing radiating element of the preceding sub array, to enable continuous 360 degree scanning. 
     For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a circular array of radiating elements usable with the invention. 
     FIG. 2 illustrates a scannable beam array antenna arranged to enable a beam pattern formed by excitation of a sub array of eight radiating elements of the FIG. 1 array to be scanned with 360 degree continuous scanning. 
     FIG. 3 provides exemplary settings for four of the 24 beam scan positions for an eight element sub array of the FIG. 2 array antenna. 
     FIG. 4 illustrates a scannable beam array antenna arranged to enable continuous circular scanning of a beam pattern including both sum and difference excitation. 
     FIG. 5 provides exemplary settings for four of the 24 beam scan positions for an eight element sub array of the FIG. 4 array antenna. 
     FIG. 6 provides computed sum and difference beam patterns for the eight element scannable beam pattern of the FIG. 3 array antenna. 
     FIG. 7 provides component data for a FIG. 3 type array antenna using excitation of sub arrays of different numbers of the radiating elements of a 108 element circular array. 
     FIG. 8 illustrates an array antenna, with a scannable sum and difference beam pattern, using a sub array of 28 radiating elements which is not evenly divisible into the 108 total number of radiating elements in a circular array. 
     FIG. 9 provides exemplary power divider to radiating element switched interconnections for selections of the 108 beam scan positions of the FIG. 8 array antenna, with fly-back switch positioning at the end of each 360 degree scan cycle. 
     FIG. 10 illustrates an array antenna with a scannable sum and difference beam pattern excited via a simplified switching configuration involving dissipative termination of one divided power port of each power divider. 
     FIG. 11 provides exemplary switch connection data for switching devices of the FIG. 10 array antenna. 
     FIG. 12 provides exemplary power divider to radiating element switched interconnections for selections of the 108 beam scan positions of the FIG. 10 array antenna. 
     FIG. 13 illustrates a  21  element circular array version of the FIG. 10 array antenna, showing detail on simplified switched interconnections enabling continuous 360 degree scanning of a beam pattern with sum and difference excitation 
    
    
     DESCRIPTION OF THE INVENTION 
     The invention relates to scanning the beam of a circular array antenna or, more generally, the beam of an antenna having a linear (e.g., curved) array of radiating elements. More particularly, consideration is directed to circuit aspects of scanning a beam characterized by sum and difference excitation, in the context of a circular array of radiating elements. Such scanning may take the form of progressively stepping the beam to a succession of azimuth positions around a horizontally aligned circular array, of stepping the beam from one azimuth to some other selected azimuth, or of other scanning protocol. 
     As an aid to understanding, there will first be described the scanning of a simple focused beam which does not involve sum and difference excitation. FIG. 1 shows a circular array  30 , including 24 radiating elements  1 - 24 . If the elements are spaced by 0.4 wavelength, at a frequency in an operating frequency range, then the diameter of the FIG. 1 circle in wavelengths will be 9.6 wavelengths. 
     One-third of the 24 elements (e.g., a sub array of any eight contiguous elements) can be excited to provide a focused beam pattern. FIG. 2 shows a switching and phasing configuration arranged to enable excitation of a sub array of any eight contiguous radiating elements of array antenna  32 . In FIG. 2 are included eight single-pole triple-throw (SP3T) switching devices, a representative one of which is identified at  34  (the eight SP3T switching devices are shown as units  1 - 8 ). These SP3T switching devices are arranged to enable excitation of any eight element sub array to provide a beam pattern at any one of 24 azimuth positions or to rotate the beam by stepping the selection of eight elements to 24 successive eight element sub arrays around the circular array of radiating elements. The term “circular” is defined generically, for present purposes, to include elliptical and other configurations of radiating elements extending 360 degrees around a point. 
     By way of example, in FIG. 2 the darker couplings to the radiating elements represent excitation of the sub array formed by elements  18 - 24  and  1 . With radiating elements  1 - 24  of FIG. 2 representing the circular array of FIG. 1, the beam pattern provided by the eight element sub array can be stepped 15 degrees in azimuth clockwise by switching SP3T No.3 from its center port (i.e., its first port) to its center port (i.e., its second port). Thus, the power divider  38  is coupled to a successive sub array modified by initiating coupling to a radiating element contiguous in a forward beam scan direction (element  2 ) and terminating coupling to the trailing radiating element of the initial sub array (element  18 ). This stepping process can be continued indefinitely, e.g., by subsequently switching SP3T No.4 from its first port to its second port, etc. 
     In this configuration, eight phase shifters, a representative one of which is indicated at  36 , are provided for use to focus the beam pattern for desired shape in the circular array context. The phase shifters can be adjusted to provide appropriate relative phases of excitation of the radiating elements. In this example of excitation of the initial sub array of elements  18 - 24  and  1 , the center elements  21  and  22  are set for a first phase (i.e., identified as phase value  01 ), elements  20  and  23  are set to phase value  02 , elements  19  and  24  are set to phase value  03  and elements  18  and  1  are set to phase value  04 . Determination of the relative phase values and adjustment of the phase shifters to provide these values can be implemented using known techniques to provide relative phasing and beam shaping as appropriate in particular applications. 
     The nominal beamwidth of the beam pattern for the eight element sub array of this example is 6.9 degrees, with 15 degree separations between the 24 beam positions. The specific settings of the SP3T switching devices and the phase shifters (value  01 ,  02 ,  03  or  04 ) for the elements  18 - 24  and  1  of the initial sub array (shown as beam number  1 ) and three successive beam positions are shown by way of example in FIG.  3 . For finer adjustment while the beam is at any of the 24 positions, the beam may be scanned or pointed in azimuth (i.e., within its basic 15 degree sector) by superimposing on the phase factors for basic beam focusing, additional phase factors determined to be effective for scanning the beam to a desired pointing alignment within its 15 degree sector. Such additional phase factors can be determined by known beam scan techniques, as appropriate in particular applications. As shown in FIG. 2, this antenna configuration includes an 8-way power divider  38  and an input/output beam port  39 . Since antenna elements are typically reciprocal devices, the FIG. 2 antenna may be used for signal reception, signal transmission, or both. For present purposes, a “power divider” is a device having power divider/combiner capabilities, which includes a plurality of divided power ports and a combined power input/output or first port and may comprise one or more units. Not shown in FIG. 2 is a control facility arranged to control settings of the SP3T switching devices and phase shifters to provide settings for selected or predetermined beam scanning. Such a facility with suitable programming, as discussed with reference to FIG. 4, can be provided by skilled persons, once they have an understanding of the antenna configuration and its operation as described. 
     Referring now to FIG. 4, there is illustrated an array antenna  40 , which provides an electronically scannable beam with simultaneous sum and difference excitation. Thus, the sum excitation provides a beam pattern as discussed with reference to FIG. 2, while the difference excitation provides a beam pattern having a central null. Such patterns are illustrated in FIG. 6 (sum pattern shown solid and difference pattern shown dashed). 
     Maintaining the null of the difference excitation at the center of the active aperture (the aperture as determined by the selected sub array of radiating elements) is accomplished by certain circuit changes. Thus, the SP3T switching devices, of FIG. 2, are replaced with eight single-pole six-throw (SP6T) switching devices, a representative one of which is identified at  44 , and at each radiating element a single-pole double-throw (SP2T) switching device is added, with a representative one thereof identified at  42 . As a result, the number of couplings (e.g., interconnecting cables) between the switching devices and the radiating elements (now via the SP2T switching devices) increases by a factor of two. 
     As illustrated in FIG. 4, for sum and difference excitation of array antenna  40  first and second 4-way power dividers  46  and  48  are provided and the divided power ports of each power divider are coupled to four of the eight SP6T switching devices  42 , via the phase shifters  36 , as shown. Also included is a four port circuit device  50 , shown as a 180 degree hybrid junction, which has first and second ports  51  and  52  respectively coupled to the first and second power dividers  46  and  48 , and also includes a sum beam port  53  and a difference beam port  54 . For signal reception, circuit device  50  functions in the manner of a known form of hybrid junction, to provide a sum beam port output at  53  representing the result of addition of signals from power dividers  46  and  48  (e.g., providing a beam pattern as shown solid in FIG. 6) and a difference beam port output at  54  representing the result of subtraction of signals from the power dividers (e.g., providing a beam pattern as shown dashed in FIG.  6 ). In use for signal transmission, an input signal to sum beam port  53  provides a radiated beam pattern similar to that provided by the FIG. 2 array antenna. While a difference beam may also be transmitted, typically, only a sum beam is transmitted. 
     Operationally, the example of excitation of a radiating element sub array of elements  22 - 24  and  1 - 5  is represented by the darker coupling lines in FIG.  4 . As shown, the left side elements  22 - 24  and  1  are excited via power divider  46  and the right side elements  2 - 5  are excited via power divider  48 . In this manner sum and difference excitation are provided in conjunction with circuit device  50 , as described. To step the beam pattern on 15 degree increments to the right in FIG. 4, switched port position  4  of SP6T No.2 is selected in order to excite radiating element  2  (in place of radiating element  22 , which had been excited via position  3  of SP6T No.2). At the same time, switched portion  5  of SP6T No. 6 is selected in order to excite radiating element  6  switched port position  5  of SP6T No. 6 is selected in order to excite radiating element  6  (in place of radiating element  2 , which had been excited via position  4  of SP6T No.6). In this manner, the beam pattern is stepped one interval to the right to excite the sub array of elements  23 ,  24  and  1 - 6 , while providing excitation of the four right side elements (i.e., now elements  23 ,  24 ,  1  and  2 ) via power divider  48  and excitation of the four left side elements (i.e., now elements  3 - 6 ) via power divider  46 , to maintain the sum and difference excitation. It should be noted that, with operation as described, a sum and difference beam pattern is stepped from one position to a successive position with activation of only two switching devices (e.g., SPGT Nos.2 and 6). 
     Thus, by inclusion and operation of the 24 SP2T switching devices, one for each of the 24 radiating elements, each such element may be coupled to either power divider  46  or power divider  48 , as appropriate to maintain sum and difference excitation. The specific settings of the SP6T and SP2T switching devices of FIG. 4, as well as the associated basic phase shifter settings, for the  22 ,  23  and  1 - 5  element sub array example (shown as beam number  1 ) and three successive beams are shown by way of example in FIG.  5 . By logical continuation of this switching protocol the beam pattern of array antenna  40  of FIG. 4 can be stepped through all 24 beam positions at 15 degree steps, returning to the beam number  1  position and repeated continuously, if desired. It will further be evident, that the beam pattern can be scanned directly to any beam position by selection of the appropriate switching device and phase shifter settings. As discussed above, for more precise beam scanning or steering within a 15 degree sector, while the beam remains at one of the 24 stepped positions, additional phase factors suitable for such scan adjustment or steering of the beam may be superimposed on the phase factors provided for basic beam focusing purposes. 
     Also included, as an element of array antenna  40  of FIG. 4, is control facility  60 , which may be a suitable computer-based processor or other device or apparatus arranged to provide control signals or other indicia effective to control the settings of the SP6T and SP2T switching devices and the phase shifters. While representative couplings are shown from control facility  60  to representative elements  44 ,  42  and  36 , such couplings will typically be provided to each of the switching devices and phase shifters, as appropriate in particular embodiments of array antennas. Suitable control facility configurations and programming may be implemented using known techniques by skilled persons who have an understanding of the invention. Also, with such understanding, appropriate variations of control facility  60  may be implemented for the array antennas of each of the accompanying figures and variations thereof, with changes and adjustments as appropriate to particular embodiments. 
     With reference to the above description of operation of the FIG. 4 antenna, control facility  60  may be arranged to control the switching devices  42  and  44  to scan the beam pattern (with sum and difference excitation) by coupling the first power divider  46  from a first left subset (e.g., elements  22 - 24  and  1 ) to a successive left subset (e.g., elements  23 ,  24 ,  1  and  2 ). For the same beam scan step, the second power divider  48  is coupled from a first right subset (e.g., elements  2 - 5 ) to a successive right subset (e.g., elements  3 - 6 ). In this manner, each successive left subset includes one radiating element not included in the preceding or initial left subset, and each successive right subset includes one radiating element not included in the preceding or initial right subset. At the same time, the successive sub array of radiating elements, which consists of these left and right subsets also includes one element (e.g., element  2 ) not included in the preceding or initial sub array and excludes one element (e.g., element  22 ) which was included in the preceding or initial sub array. In these examples based on stepping the beam pattern of an eight element sub array to successive 15 degree sectors, eight contiguous elements are excited, with the next contiguous element in the beam step direction newly excited (e.g., element  2 ), excitation of the trailing element terminated (e.g., element  22 ) and excitation of the other six elements maintained from one sub array to the successive sub array (e.g., elements  23 - 1 ). In other implementations different sub array and subset excitation protocols may be employed as appropriate. 
     FIG. 6 shows computed sum and difference patterns for an example of a circular array antenna of the type shown in FIG.  4 . For this example, 108 radiating elements were included with element spacing of 0.4 wavelength and nominal beamwidth of 4.8 degrees. The circular array diameter was 13.75 wavelengths, with switching step size of 3.33 degrees. 
     FIG. 7 lists data as to complements of power dividers and switching devices for other possible sub arrays usable with a circular array of 108 radiating elements, under the conditions that the sub array consists of an even number of radiating elements and 108 divided by the number of elements in the sub array is an integer. Thus, for example, for an array antenna of a configuration similar to that of FIG. 4, if a sub array size of 18 elements is selected, two 9-way power dividers and 18 single-pole 12-throw (SP12T) switching devices would be employed in a FIG. 4 type configuration. As described for the FIG. 4 antenna, with these antenna configurations, complete 360 degree scan is achieved while requiring the activation of only two switching devices per step. 
     As described above, a beam pattern is scanned by exciting a sub array of contiguous radiating elements and then exciting a different sub array to point the beam pattern in a new direction. So long as the sub array includes an even number of radiating elements and the total number of elements divided by the number of elements in the sub array is an integer, considerations which arise in the case of non-integer sub array choices are not relevant. 
     FIG. 8 illustrates a circular array antenna configuration operable with use of an excited sub array which includes a number of radiating elements such that the total number of elements in the array antenna is not divisible by the number of elements in a sub array without a remainder. Thus, for a 108 element array and a 28 element sub array, 108/28=3.857. 
     As shown in FIG. 8, array antenna  70  includes a 108 element circular array, with each element excited via one of 108 single-pole triple-throw (SP3T) switching devices, as represented by box  72 . Elements of antenna  70  are generally of the same basic type as elements of antenna  40  of FIG. 4, subject to changes in switching capacity, etc. Thus, while antenna  40  includes power dividers, phase shifters and switching devices shown as discrete elements, such as  46 ,  36  and  44 , similar types of elements are included in boxes  74  and  75  of antenna  70 , with the addition of an attenuator associated with each of the 14 power divider ports of each power divider. In this example an attenuator associated with each power divider divided power port provides additional flexibility in relative excitation of the elements of a sub array. Whereas in FIG. 4, the SP6T switching devices associated with each 4-way power divider are coupled to the 24 radiating elements via 24 interconnecting cables, the SP9T switching devices associated with each 14-way power divider of FIG. 8 are coupled to the 108 radiating elements via 121 cables as represented by boxes  76  and  77 . 
     Basically, in the FIG. 8 antenna, the SP3T switching device associated with each radiating element enables operation with overlapping scan (extending beyond 360 degrees) such that after stepping through 108 beam positions (each step involving activation of two switching devices) all switches are activated (termed “fly-back switching”) to return the beam pattern and all switching devices to their original position/activation. Thus, fly-back switching can be provided at the end of a scan stepping cycle covering 360 degrees in azimuth, in order to couple the two power dividers to the same radiating elements to which they were respectively coupled at the start of the scan stepping cycle. In this manner, a different switching protocol is employed to provide the 360 degree scanning capability. This is illustrated in FIG. 9, which lists couplings of the 28 SP9T switching devices to the 28 elements of the excited sub array for nine representative beam scan positions, including such couplings for the start and fly-back beam positions and for the scan position prior to the fly-back beam positions. There is thus provided an electronic scan control configuration which enables full 360 degree scanning with use of a sub array which includes a number of sub array elements such that the total number of elements in the array is not evenly divisible by the number of sub array elements. 
     FIG. 10 illustrates a circular array antenna  80  including 108 radiating elements, wherein a sub array of 27 elements is excited by use of a switching network which is further reduced or minimized as to complexity. Antenna  80  enables a sub array consisting of an odd number of elements to be stepped through 108 beam positions for scanning of a sum and difference beam pattern. In FIG. 10, the combination of two 14-way power dividers  82  and  83 , 28 SP2T switching devices represented by boxes  84  and  85  and 27 SP4T switching devices represented by box  87  are arranged as shown, with inclusion of attenuators and phase shifters. The 27 SP2T switching devices are coupled via 108 cables represented by box  88  to the circular array of 108 radiating elements represented by box  89 . Couplings of the 27 SP4T switching devices are as shown in FIG.  11 . For a sampling of beam scan steps, power divider to radiating element couplings are listed in FIG. 12, with step  109  bringing the beam back to its zero step position. Basic scan stepping involves the following. The excited sub array includes 27 contiguous elements. For each step, the SP4T switch coupled to the left element is switched to the next position to the right and is connected to the right power divider. The center element is connected to the left power divider  82  and the signal available relative to that element is completely attenuated by the associated attenuator (as indicated by the center zero in the top line of data in FIG. 12, representing power divider ports). One divided power port of power divider  83  is terminated, so that there is an aggregate total of 27 divided power ports in active use. The arrangement enables each divided power port in use to be switched from one radiating element to another one displaced by 27 elements. Each element can be coupled to either power divider and the signal from any element can be completely attenuated. 
     With reference to the reduced or minimized switching network of antenna  80  described with reference to FIG. 10, FIG. 13 illustrates interconnections in the context of a 21 element array antenna  90 , having seven element sub array scannable sum and difference excitation. As shown, in antenna  90  two 4-way power dividers  46  and  48  are coupled to eight SP2T switching devices, of which device  92  is representative. In this case, as to each of the power dividers, one of the coupled SP2T switching devices has one of its ports terminated. The eight SP2T switching devices represented by device  92  are coupled to seven additional SP2T switching devices, of which device  94  is representative. These seven SP2T switching devices are in turn coupled to a seven element excited sub array via phase shifters (e.g., shifter  36 ) and seven SP3T switching devices, of which device  96  is representative. Operationally, under the control of control facility  60 ′ beam scan stepping is implemented using a protocol consistent with the power divider to radiating element couplings listed in FIG. 12 for the FIG. 10 array antenna. In this example, the signal available at the center radiating element of the seven element sub array is completely attenuated. Thus, all seven elements of the sub array are used for signal transmission, however signals from only the outer six elements are used during reception. 
     On an overview comparison basis, it will be seen that the switching network of antenna  90  is of reduced complexity, as compared to that of antenna  40  of FIG.  4 . While the numbers of radiating elements in total and in the excited sub array are not the same in the two antennas, they are relatively similar. Thus, depending upon the specific application and other factors, a configuration of the type shown in FIG. 13 may provide advantages in some applications, while a configuration of the type shown in FIG. 4 may be preferable in other applications. 
     While there have been described the currently preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made without departing from the invention and it is intended to claim all modifications and variations as fall within the scope of the invention.