Four quadrants array antenna

Abstract: A radar system and method for obtaining low sum and difference side lobe patterns from a phased array antenna comprising radiators distributed amongst four quadrants A, B, C, and D. The quadrants are arranged in a clockwise order of A, B, D, and C. Each quadrant is further divided into an inner portion and an outer portion. The monopulse sum pattern is determined by adding signals received by radiators in the A quadrant, B quadrant, C quadrant, and D quadrant. The elevation difference pattern is determined by subtracting a CD sum consisting of signals received by radiators in the C outer portion and the D outer portion from an AB sum consisting of signals received by radiators in the A outer portion and the B outer portion. The azimuth difference pattern is determined by subtracting a BD sum consisting of signals received by radiators in the B outer portion and the D outer portion from an AC sum consisting of signals received by radiators in the A outer portion and the C outer portion.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to array antennas and, more specifically, to the side lobe patterns generated by those antennas. 2. Description of the Related Art Conventional monopulse corporate-fed array antennas produce very high difference pattern side lobes in their principal planes. Referring now to Figure 1, graph 10 shows an example of a sum pattern 12 and difference pattern 14 of a conventional corporate-fed standing wave array antenna. The sum pattern 12 has low sum pattern side lobes 16. The difference pattern 14 has relatively high side lobes 18. Referring now to Figures 2 and 3, the array aperture sum amplitude distribution 20 and difference amplitude distribution 22 are usually optimized for low sum pattern side lobes 16. The optimization creates an abrupt change at the center 24 of the difference amplitude distribution 22. It is this very abrupt change, or discontinuity of the difference amplitude distribution, that produces the very high difference pattern side lobes 18. A method and system exhibiting such an abrupt change and resulting high side lobes is known from US-A-4,121,220, which more particularly relates to specific antenna radiator and equal length radiator connection configurations. There are existing approaches for achieving both low sum and difference side lobes from corporate-fed arrays. The Antenna Engineering Handbook, Third Edition, by Richard Johnson, Figure 20-44 ("Johnson") discloses a typical existing approach comprising a phase monopulse corporate-fed phased array that produces low sum and difference side lobes. Johnson discloses the pairing of radiating elements that are symmetrically opposite from the centerline of the array. The paired radiating elements are combined in a magic T to form the sum and difference patterns. This approach is relatively complex and not applicable to corporate-fed wave guide standing wave array antenna design. It is noted here, that from US-A-4,754,286 a system is known for attenuating side lobes in difference patterns. However, in this known method and system radiators from a specific quadrant are assigned to a neighboring quadrant, in stead of a quadrant in which these radiators actually lie. This reassignment is based on a statistical distribution. Therefore, a radar system comprising an array antenna of relatively simple construction that provides low difference side lobes is needed. SUMMARY OF THE INVENTION To fulfill the above and other objectives of the invention, a radar system and method for obtaining low sum and difference side lobe patterns from phased array antennas is provided. The radar system has a corporate-fed wave guide standing wave array antenna comprising radiators distributed amongst four quadrants A, B, C, and D. The quadrants are arranged in a clockwise order of A, B, D, and C. Each quadrant is further divided into an inner portion and an outer portion. The monopulse sum pattern is determined by adding signals from radiators in both the inner and outer portions of the A quadrant, B quadrant, C quadrant, and D quadrant. The elevation difference pattern is determined by subtracting signals received by radiators in the C outer portion only and the D outer portion only from signals received by radiators in the A outer portion only and the B outer portion only. The azimuth difference pattern is determined by subtracting signals received by radiators in the A outer portion only and the C outer portion only. In an aspect of the invention, the aperture array antenna is a passive phased array antenna. The passive phased array antenna has an outer quad array corporate feed that is functionally connected to the radiators in the aperture array antenna outer portions and an inner quad array corporate feed that is functionally connected to the radiators in the aperture array antenna inner portions. In an aspect of the invention, the aperture array antenna is an active aperture phased array antenna. The radar system has an active aperture phased array antenna that has an outer quad array receive corporate feed that is functionally connected to the radiators in the aperture array antenna outer portions and an inner quad array receive corporate feed that is functionally connected to the radiators in the aperture array antenna inner portions. In another aspect of the invention, the aperture array antenna is an active aperture phased array antenna. The radiators are independently controlled by corporate feed networks that transmit a sum signal and receive both sum and difference signals. The sum signal is received by an independently controllable sum aperture distribution corporate feed network. The difference signals are received by another independently controllable difference aperture distribution corporate feed network. In another aspect of the invention, the shapes of the inner and outer portions of the aperture array antenna are designed to achieve predetermined difference patterns. In another aspect of the invention the shapes of the inner and outer portions of the aperture array antenna are designed to optimize the sum, elevation difference, and azimuth difference patterns. Other and further objects and advantages will appear hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a graph of a sum pattern and difference pattern of a corporate-fed wave guide standing wave array antenna disclosed in the prior art; Figure 2 shows a graph of an array aperture sum amplitude distribution of a corporate-fed wave guide standing wave array antenna disclosed in the prior art; Figure 3 shows a graph of an array aperture difference amplitude distribution of a corporate-fed standing wave array antenna disclosed in the prior art; Figures 4A and 4B show schematic layouts of radiators on an array aperture according to embodiments of the invention; Figure 5 shows a schematic diagram of a radar system's passive aperture phased array antenna monopulse feed network according to an embodiment of the invention; Figure 6 shows a graph of an array aperture sum amplitude distribution according to an embodiment of the invention; Figure 7 shows a graph of an array aperture difference amplitude distribution according to an embodiment of the invention; Figure 8 shows a graph of a sum pattern and difference pattern of a corporate-fed wave guide standing wave array antenna according to an embodiment of the invention; Figure 9 shows a schematic diagram of a monopulse feed network for an active aperture phased array antenna according to an embodiment of the invention; and Figure 10 shows a schematic diagram of a monopulse feed network for active aperture phased array antenna with independently controllable aperture feed networks for sum and difference aperture distributions according to an embodiment of the invention. DESCRIPTIONS OF THE PREFERRED EMBODIMENTS Referring now to Figure 4A, an array aperture 100a according to an embodiment of the invention, has a surface 102a covered with radiators 104a. The surface 102a is divided into an A quadrant 106a, a B quadrant 108a, a C quadrant 110a, and a D quadrant 112a. The term "quadrant" is defined as approximately one quarter of the surface and may, or may not, have borders that align with the radii of the aperture. The clockwise order of the quadrants is the A quadrant 106a, the B quadrant 108a, the D quadrant 112a, and the C quadrant 110a. The A quadrant 106a has an a inner portion 114a and an A outer portion 116a. The B quadrant 108a has a b inner portion 118a and a B outer portion 120a. The C quadrant 110a has a c inner portion 122a and a C outer portion 124a. The D quadrant 112a has a d inner portion 126a and a D outer portion 128a. The designation "inner portion" does not imply that the inner portions for other embodiments of the invention are wholly surrounded by the outer portions, as is the case in the instant embodiment. Further, other embodiments of the invention may have discontinuous portions. Referring now to Figure 4B, wherein structures as comparable to structures of Figure 4A with the same numerical prefix according to another embodiment of the invention, an array aperture 100b comprises inner portions 114b, 118b, 122b, and 126b that extend to the perimeter 101b of the aperture. The surface 102b is divided into an A quadrant 106b, a B quadrant 108b, a C quadrant 110b, and a D quadrant 112b. The clockwise order of the quadrants is the A quadrant 106b, the B quadrant 108b, the D quadrant 112b, and the C quadrant 110b. The A, B, C, D outer portions 116b, 120b, 124b, and 128b of the array aperture 100b are adjacent the a, b, c, d inner portions 114b, 118b, 122b, and 126b. More specifically, the a inner portion 114b straddles a centerline 103 between the A quadrant 106b and the B quadrant 108b. Further, the b inner portion 118b straddles a centerline 105 between the B quadrant 106b and the D quadrant 112b. Additionally, the d inner portion 126b straddles the centerline 103 between the D quadrant 112b and the C quadrant 110b. Further, the c inner portion 122b straddles the centerline 105 between the C quadrant 110b and the A quadrant 106b. As the embodiment of Figure 4b illustrates, the term "quadrant" should be loosely interpreted to mean that a quadrant is comprised of an outer portion and an inner portion that is approximately one quarter of the array. Referring now to Figure 5, in a radar system's passive aperture phased array antenna 129, the radiators 104 are functionally connected to an outer quad array corporate feed 130 and an inner quad array corporate feed 132. More specifically, the radiators 104 in the A, B, C, D outer portions 116, 120, 124, and 128 are functionally connected to the feed 130 and the radiators 104 in the a, b, c, d inner portions 114, 118, 122, and 126 are functionally connected to the feed 132. The feed 130 identifies and outputs the signals 134, 136, 138, and 140 coming from A, B, C, D outer portions 116, 120, 124, and 128, respectively. The feed 132 identifies and outputs the signals 142, 144, 146, and 148 coming from a, b, c, d inner portions 114, 118, 122, and 126, respectively. The outputs from the feeds 130 and 132 are combined to form a sum signal 150, an elevation difference signal 152, and an azimuth difference signal 154. To form the sum signal 150, the signals 142, 144, 146, and 148 are combined into an [a+b+c+d] signal 156 and the signals 134, 136, 138, and 140 are combined into [A+B+C+D] signal 158. The [A+B+C+D] signal 158 is then combined with the [b+c+d] signal 156 to form the sum signal 150. To form the elevation difference signal 152, the signals 138 and 140 are combined into a (C+D) signal 160 and the signals 134 and 136 are combined into an (A+B) signal 162. The (C+D) signal 160 is subtracted from the (A+B) signal 162 to form the elevation difference signal 152. To form the azimuth difference signal 154, the signal 136 is subtracted from the signal 134 to form an (A-B) signal 163, and the signal 140 is subtracted from the signal 138 to form a (C-D) signal 161. The (A-B) signal 163 and the (C-D) signal 161 are then combined to form the elevation difference signal [(A+C) - (B+D)] 154. Referring now to Figure 6, as a result of using signals from all of the radiators 104, an array aperture sum amplitude distribution 166 of the sum signal 150 is the same as the array aperture sum distribution 20 of the prior art (see Figure 2). Referring now to Figure 7, by not using the signals 142, 144, 144, and 146 from the a, b, c, d inner portions 114, 118, 122, and 126, the abrupt change of the difference amplitude distribution at the center 24 of the array aperture 22 is removed. The removal of the abrupt change results in having a difference amplitude distribution 168 with a less abrupt amplitude change at the array aperature center 170. Referring now to Figure 8, graph 172 shows a sum pattern 174, the prior art difference pattern 14, and a difference pattern 176. As there is no change in the combining of the signals 134 through 148 from the array aperture 100 of the current invention compared to the prior art, the sum pattern 174 is the same as the sum pattern 12 of the prior art. However, the result of not using the a, b, c, d signals 142 through 148 from the a, b, c, d inner portions 114, 118, 122, and 126 results in a difference pattern 176 that has much lower difference side lobes 178 compared to the relatively high difference side lobes 18 of the difference pattern 14 of the prior art. The size and shape of the difference side lobes may be predetermined by a designer of apertures choosing appropriate shapes of the A, B, C, D outer portions 116, 120, 124, and 128 and the a, b, c, d inner portions 114, 118, 122, and 126 using techniques commonly known in the art. Likewise, the size and shapes of the difference side lobes may also be optimized using techniques commonly known in the art. Referring now to Figure 9, a radar system's active aperture phased array antenna 200 is similar to the passive aperture array antenna 129 (see Figure 5) except for the feeds. The transmit sum feed and the receive sum and difference feeds are independently optimized for the best system performance, but the receive difference feed networks are not independent of the receive sum network. The antenna 200 has an outer quad array receive feed 202 functionally connected to the radiators 104 of A, B, C, D portions 116, 120, 124, and 128. The embodiment shown in Figure 9 also has an inner quad array receive feed 204 functionally connected to the radiators 104 of a, b, c, d portions 114, 118, 122, and 126. Referring now to Figure 10, a radar system's active aperture phased array antenna 210 is similar to the active aperture phased array antenna 200 but for the radiators 212 and the feeds 218 and 220. The radiators 212 are independently controlled and each radiator receives a sum signal 214 and a difference signal 216. The sum signals 214 are received by an independently controllable sum aperture feed network 218. The difference signals 216 are received by an independently controllable difference aperture feed network 220. Due to the flexibility of the feeds 218 and 220, the array aperture does not need to separate into inner portions 114, 118, 122, 126, and the outer portions 116, 120, 124, 128, to achieve predetermined array aperture amplitude distributions to obtain low sum and difference side lobe patterns because the receive difference aperture distributions are independent of the sum aperture distribution.

Claims: A corporate-fed phased array antenna system for obtaining low sum and difference side lobe patterns comprising: a. an aperture array antenna comprising a surface covered with radiators, the surface being divided into an A quadrant, a B quadrant, a C quadrant, and a D quadrant, wherein the clockwise order of the quadrant is A, B, D, and C, ; b. sum means for determining a monopulse sum pattern by adding signals received by radiators in the A quadrant, B quadrant, C quadrant, and D quadrant; c. elevation difference means for determining a monopulse elevation difference pattern ΔE and d. azimuth difference means for determining a monopulse azimuth difference pattern ΔAZ, characterized in that each quadrant comprises an inner portion and an outer portion and in that the elevation difference means for determining a monopulse elevation difference pattern ΔE are arranged for subtracting a CD sum consisting of signals received by radiators in the outer portions only of the C quadrant and the D quadrant from an AB sum consisting of signals received by radiators in the outer portions only of the A quadrant and the B quadrant, and in that the azimuth difference means for determining a monopulse azimuth difference pattern ..AZ are arranged for subtracting a BD sum consisting of signals received by radiators in the outer portions only of the B quadrant and the D quadrant from an AC sum consisting of signals received by radiators in the outer portions only of the A quadrant and the C quadrant. The system of claim 1 further comprising: a. an outer quad array corporate feed functionally connected to the radiators in the aperture array antenna outer portions and functionally connected to the sum means, elevation difference means and azimuth difference means; and b. an inner quad array corporate feed functionally connected to the radiators in the aperture array antenna inner portions and functionally connected to the sum means, wherein the aperture array antenna is passive. The system of claim 1 further comprising: a. an outer quad array receive corporate feed is functionally connected to the radiators in the active aperture array antenna outer portions and functionally connected to the sum means, elevation difference means and azimuth difference means; and b. an inner quad array receive corporate feed is functionally connected to the radiators in the aperture array antenna inner portions and functionally connected to the sum means, wherein the aperture array antenna is an active aperture phased array antenna. The system of claim 1, 2 or 3 wherein: a. radiators are independently controlled and transmit a sum signal and receive a sum signal and two difference signals; b. the sum means comprises an independently controllable sum aperture distribution feed network that receives signals from the radiators; c. the elevation difference means and azimuth difference means comprise an independently controllable difference aperture distribution feed network that receives signals from the radiators; and d. the aperture array antenna is an active aperture phased array antenna. A process for obtaining low sum and difference side lobe patterns from a corporate-fed phased array antenna system comprising the steps of: a. providing an aperture array antenna comprising a surface covered with radiators, the surface being divided into an A quadrant, a B quadrant, a C quadrant, and a D quadrant, wherein the clockwise order of the quadrants is A, B, D, and C; b. determining a monopulse sum pattern by adding signals received by the A quadrant, B quadrant, C quadrant, and D quadrant; c. determining a monopulse elevation difference pattern ΔEL; and d. determining a monopulse azimuth difference pattern ΔAZ, characterized in that each quadrant comprises an inner portion and an outer portion, in that determening a monopulse elevation difference pattern ΔEL comprises subtracting a CD sum consisting of signals received by the radiators in the outer portions only of the C and D quadrants from an AB sum consisting of signals received by radiators in the outer portions only of the A and B quadrants; and determining a monopulse azimuth difference pattern ΔAZ comprises subtracting a BD sum consisting of signals received by radiators in the outer portions only of the B and D quadrants from an AC sum consisting of signals received by radiators in the outer portions only of the A and C quadrants. The process of claim 5, further comprising the steps of: a. directing signals from radiators in the outer quadrants through an outer quad array corporate feed prior to the determining steps; and b. directing signals from radiators in the inner quadrants through an inner quad array corporate feed prior to the determining steps, wherein the aperture array antenna is passive. The process of claim 5, further comprising the steps of: a. directing signals from radiators in the outer quadrants through an outer quad array receive corporate feed prior to the determining steps; and b. directing signals from radiators in the inner quadrants through an inner quad array receive corporate feed prior to the determining steps, wherein the aperture array antenna is an active phased array antenna. The process of claim 5, further comprising the steps of: a. directing sum signals from the radiators to an independently controllable sum aperture distribution network prior to the determining a monopulse sum step, wherein the radiators are independently controlled; and b. directing difference signals from the radiators to an independently controllable difference aperture distribution network prior to the steps of determining a monopulse elevation difference and determining a monopulse azimuth difference, wherein the aperture array antenna is an active aperture phased array antenna. The process of any of the claims 5-8 further comprising the step of designing and selecting the shapes of the inner and outer portions of the aperture array antenna to achieve a predetermined difference pattern. The process of any of the claims 5-8 further comprising the step of designing and selecting the shapes of the inner and outer portions of the aperture array antenna to optimize the sum, elevation difference, and azimuth difference patterns.

Inventors: WONG SAM H, WONG, SAM H.
Applicants: BOEING NORTH AMERICAN INC, BOEING NORTH AMERICAN, INC.
Application year: 1999
Main classification: H01Q3
IPC codes: H01Q21, H01Q3, H01Q25