Patent Publication Number: US-11381000-B2

Title: Low-sidelobe plate array antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 202010417832.9, filed on May 18, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     TECHNICAL FIELD 
     The invention relates to a plate array antenna, in particular to a low-sidelobe plate array antenna. 
     DESCRIPTION OF RELATED ART 
     In recent years, high-performance array antennas which have a high sensitivity, a wide band, a low profile and a low sidelobe and characterized by multiple frequency bands and low costs have been widely used in the fields of radar, communication, remote sensing and metering, and spatial technology. Existing common array antennas mainly include micro-strip array antennas and plate array antennas. 
     The micro-strip array antennas are featured by low profile, low cost and low weight and are easy to machine. However, when the frequency or antenna array size increases, the insertion loss will be increased due to conductor losses and dielectric losses of the micro-strip array antennas. Thus, the micro-strip array antennas can fulfill a wide band, but cannot fulfill high frequency, high efficiency or high gain. 
     Waveguide slot array antennas are mainstream plate array antennas used at present and are designed in such a manner that one or more slots are formed in the conductor wall of a waveguide to cut off a current line on the inner wall, part of the current across the surface of the inner wall of the waveguide bypasses the slots, the other part of the current flows across the slots in the original direction in a form of displacement current, and radiation is realized by power lines at the openings of the slots. The waveguide slot array antennas have the properties of low conductor loss, high efficiency, high performance and the like. Existing waveguide slot array antennas include waveguide slot traveling wave array antennas and waveguide slot standing wave array antennas. However, the beam direction of the waveguide slot traveling wave array antennas varies with the frequency, which results in inconsistent directions of antenna beams within a wideband range, and the waveguide slot traveling wave array antennas can only be used within an extremely narrow bandwidth, and the frequency band cannot be expanded. Because the waveguide slot standing wave array antennas are resonance antennas essentially, once the frequency deviates from the resonance frequency, the performance indicators such as the directional diagram and the sidelobe level will deteriorate drastically, so that the waveguide slot standing wave array antennas can only be used within a narrow frequency band and have a bandwidth in inverse proportion to the size of the array antennas. 
     To comply with the ever higher anti-interference requirement for radar and the development of the modern electronic industry, the antennas should have a low or extremely low sidelobe. As for traditional waveguide slot array antennas which mainly include a feed layer and a radiation layer, there are principally two solutions for reducing the sidelobe of the traditional waveguide slot array antennas at present. According to the first solution, the power distribution proportion of the feed layer is controlled to adjust the energy distribution of the radiation layer to reduce the sidelobe; however, when this solution is used to reduce the sidelobe, the main lobe will become wider, the gain will be decreased, and it is impossible to gain an extremely low sidelobe under the condition where a narrow main lobe is guaranteed and the gain is not sacrificed. According to the second solution, a polarization layer is arranged on the radiation layer to reduce the sidelobe; the polarization layer can change the polarization direction of an electric field of the radiation layer to optimize the directional diagrams of the E-plane and the H-plane of the antennas, thus obtaining a low sidelobe. However, due to the addition of the polarization layer, the cost of the antennas may be increased by 20% during mass production. 
     Chinese Invention Patent Application No. 201710429885.0 discloses a waveguide slot array antenna which comprises a radiation layer and feed layer which are arranged from top to bottom, wherein the radiation layer is constituted by a multi-layer coupled structure composed of a first radiation unit, a second radiation unit, a third radiation unit and a fourth radiation unit which are stacked from bottom to top. This waveguide slot array antenna has a wide band, a high gain and a low sidelobe, but has the following problems: 1, the radiation layer has too many structure layers which cannot be processed one by one, the assembly structure is complicated, so that mass production is unavailable; 2, the radiation layer adopts a coupling cavity divided into four parts, so that the relative bandwidth is narrow, and a wider frequency bandwidth cannot be obtained; 3, the low-sidelobe property is realized by means of repeated rotation of the several radiation units in the radiation layer, so that the efficiency of the antennas is reduced. 
     BRIEF SUMMARY OF THE INVENTION 
     The technical issue to be settled by the invention is to provide a low-sidelobe plate array antenna, which has a low sidelobe, is simple in structure, low in cost and suitable for mass production, and has a wide frequency bandwidth and high efficiency. 
     The technical solution adopted by the invention to settle the aforesaid technical issue is as follows: a low-sidelobe plate array antenna comprises a radiation layer and a feed layer, wherein the radiation layer is superimposed on the feed layer, the feed layer is used to output 4*n 2  TE10 mode signals, the radiation layer has 4*n 2  input terminals and 4*n 2  output terminals, the 4*n 2  TE10 mode signals output by the feed layer are accessed to the 4*n 2  input terminals of the radiation layer in a one-to-one correspondence, the 4*n 2  output terminals of the radiation layer are used to radiate the 4*n 2  TE10 mode signals output by the feed layer to a free space in a one-to-one correspondence, n=2 (k-1) , and k is an integer greater than or equal to 3; the radiation layer comprises a first plate and a radiation array disposed on the first plate, wherein the first plate is a rectangular plate, the radiation array is formed by n 2  radiation units which are distributed in 2 (k-1)  rows and 2 (k-1)  columns, a center distance between every two adjacent radiation unit in each row is 1.8λ, a center distance between every two adjacent radiation units in each column is 1.8λ, and λ=c/f, wherein c is a wave velocity, c=3*10{circumflex over ( )}8 m/s, and f is a center operating frequency of the low-sidelobe plate array antenna; each radiation unit comprises two first radiation assemblies and two second radiation assemblies, wherein the two first radiation assemblies are parallelly arranged left and right and are spaced apart from each other, the first radiation assembly on the left will overlap with the first radiation assembly on the right after being moved rightwards by 0.9λ, the two second radiation assemblies are also arranged left and right and are spaced apart from each other, the second radiation assembly on the left will overlap with the second radiation assembly on the right after being moved rightwards by 0.9λ, the two second radiation assemblies are located behind the two first radiation assemblies, a center distance between the second radiation assembly on the left and the first radiation assembly on the left is 0.9λ, and a center distance between the second radiation assembly on the right and the first radiation assembly on the right is 0.9λ. 
     Each first radiation assembly comprises a first rectangular bar, a first rectangular cavity, a second rectangular cavity and a third rectangular cavity, wherein the first rectangular cavity, the second rectangular cavity and the third rectangular cavity are sequentially arranged from top to bottom, a center of the first rectangular bar, a center of the first rectangular cavity, a center of the second rectangular cavity and a center of the third rectangular cavity are located on the same line which is perpendicular to the first plate and is referred to as a center line, the first rectangular bar is located in the first rectangular cavity, an upper end surface of the first rectangular bar and an upper end surface of the first rectangular cavity are located on the same plane as an upper end surface of the first plate, a front end surface of the first rectangular bar and a front end surface of the first rectangular cavity are formed and connected integrally and are attached together, a rear end surface of the first rectangular bar and a rear end surface of the first rectangular cavity are formed and connected integrally and are attached together; if the first rectangular cavity is rotated anticlockwise by 45° around the center line, a plane where the front end surface of the first rectangular cavity is located will be parallel to a plane where the front end surface of the first plate is located, and a plane where a front end surface of the second rectangular cavity is located will be parallel to a plane where a front end surface of the third rectangular cavity is located; if the second rectangular cavity is rotated anticlockwise by 67.5° around the center line, a plane where the front end surface of the second rectangular cavity is located will be parallel to a plane where the front end surface of the first plate is located, an upper end surface of the second rectangular cavity will be located on the same plane as a lower end surface of the first rectangular cavity, an upper end surface of the third rectangular cavity will be located on the same plane as a lower end surface of the second rectangular cavity, a lower end surface of the third rectangular cavity will be located on the same plane as a lower end surface of the first plate, a distance from a left end surface of the first rectangular bar to a left end surface of the first rectangular cavity is equal to a distance from a right end surface of the first rectangular bar to a right end surface of the first rectangular cavity, a distance from the front end surface to the rear end surface of the first rectangular cavity is 0.8λ, a distance from the left end surface to the right end surface of the first rectangular cavity is 0.6λ, a distance from the upper end surface to the lower end surface of the first rectangular cavity is 0.3λ, a distance from the left end surface to the right end surface of the first rectangular bar is 0.1λ, and a distance from the upper end surface to the lower end surface of the first rectangular bar is 0.1λ; a distance from the front end surface to the rear end surface of the second rectangular cavity is 0.6λ, a distance from the left end surface to the right end surface of the second rectangular cavity is 0.4λ, and a distance from the upper end surface to the lower end surface of the second rectangular cavity is 0.3λ. 
     A first rectangular matching plate and a second rectangular matching plate are arranged in the second rectangular cavity, a left side wall of the first rectangular matching plate and a left side wall of the second rectangular cavity are attached together and are formed and connected integrally, a distance from a front end surface of the first rectangular matching plate to a front end surface of the second rectangular cavity is equal to a distance from a rear end surface of the first rectangular matching plate to a rear end surface of the second rectangular cavity, a distance from a left end surface to a right end surface of the first rectangular matching plate is 0.1λ, a distance from a front end surface to a rear end surface of the first rectangular matching plate is 0.2λ. 
     An upper end surface of the first rectangular matching plate is located on the same plane as the upper end surface of the second rectangular cavity, a lower end surface of the first rectangular matching plate is located on the same plane as the lower end surface of the second rectangular cavity, and the second rectangular matching plate and the first rectangular matching plate are symmetrical left and right with respect to a left-right bisecting plane of the second rectangular cavity. 
     A distance from the front end surface to the rear end surface of the third rectangular cavity is 0.4λ, a distance from the left end surface to the right end surface of the third rectangular cavity is 0.2λ, a distance from the upper end surface to the lower end surface of the third rectangular cavity is 0.1λ, a third rectangular matching plate is arranged in the third rectangular cavity, a left side wall of the third rectangular matching plate and a left side wall of the third rectangular cavity are attached together and are formed and connected integrally, a distance from a front end surface of the third rectangular matching plate to the front end surface of the third rectangular cavity is equal to a distance from a rear end surface of the third rectangular matching plate to the rear end surface of the third rectangular cavity, an upper end surface of the third rectangular matching plate is located on the same plane as the upper end surface of the third rectangular cavity, a lower end surface of the third rectangular matching plate is located on the same plane as the lower end surface of the third rectangular cavity, a distance from a left end surface to a right end surface of the third rectangular matching plate is 0.1λ, a distance from a front end surface to a rear end surface of the third rectangular matching plate is 0.2λ, the upper end surface of the first rectangular cavity is used as an output terminal of the first radiation assembly, and the lower end surface of the third rectangular cavity is used as an input terminal of the first radiation assembly. 
     If the first radiation assembly on the left is moved downwards by 0.9λ and is then rotated clockwise by 180° around the center line, the first radiation assembly on the left will overlap with the second radiation assembly on the left; if the first radiation assembly on the right is moved downwards by 0.9λ and is then rotated clockwise by 180° around the center line, the first radiation assembly on the right will overlap with the second radiation assembly on the right. 
     The input terminals of the two first radiation assemblies and input terminals of the two second radiation assemblies are used as four input terminals of the radiation unit; the four input terminals of each radiation unit are used as four input terminals of the radiation layer, and the radiation layer has 4*n 2  input terminals; the output terminals of the two first radiation assemblies and output terminals of the two second radiation assemblies are used as four output terminals of the radiation unit, the four output terminals of each radiation unit are used as four output terminals of the radiation layer, and the radiation layer has 4*n 2  output terminals. 
     The feed layer comprises a second plate, 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units and a standard waveguide input port, wherein the
 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units and the standard waveguide input port are disposed on the second plate, and the second plate is a rectangular plate; each first-level H-type E-plane waveguide power division network unit comprises a first-level H-type E-plane waveguide power division network and a second-level H-type E-plane waveguide power divider, wherein the first-level H-type E-plane waveguide power division network comprises two first H-type E-plane waveguide power division networks and two second H-type E-plane waveguide power division networks, the two first H-type E-plane waveguide power division networks are parallelly arranged left and right and are spaced apart from each other, the first H-type E-plane waveguide power division network on the left will overlap with the first H-type E-plane waveguide power division network on the right after being moved rightwards by 1.8λ, the two second H-type E-plane waveguide power division networks are arranged left and right and are spaced apart from each other, the second H-type E-plane waveguide power division network on the left will overlap with the second H-type E-plane waveguide power division network on the right after being moved rightwards by 1.8λ, the two second H-type E-plane waveguide power division networks are located behind the two first H-type E-plane waveguide power division networks, a center distance between the second H-type E-plane waveguide power division network on the left and the first H-type E-plane waveguide power division network on the left is 1.8λ, the second H-type E-plane waveguide power division network on the left and the first H-type E-plane waveguide power division network on the left are symmetrical front and back, a center distance between the second H-type E-plane waveguide power division network on the right and the first H-type E-plane waveguide power division network on the right is 1.8λ, and the second H-type E-plane waveguide power division network on the right and the first H-type E-plane waveguide power division network on the right are symmetrical front and back.
 
     Each first H-type E-plane waveguide power division network comprises a first-level H-type E-plane waveguide power divider and four E-plane rectangular waveguide-single ridge waveguide transducers, wherein the first-level H-type E-plane waveguide power divider has an input terminal and four output terminals, divides a signal input via the input terminal thereof into four signals with the same power and phase, and outputs the four signals via the four output terminals thereof respectively, each E-plane rectangular waveguide-single ridge waveguide transducer has an input terminal and an output terminal and is used to convert a rectangular waveguide accessed to the input terminal thereof into a single ridge waveguide and output the single ridge waveguide via the output terminal thereof, the input terminals of the four E-plane rectangular waveguide-single ridge waveguide transducers are connected to the four output terminals of the first-level H-type E-plane waveguide power divider in a one-to-one correspondence, the input terminal of the first-level H-type E-plane waveguide power divider is used as an input terminal of the first H-type E-plane waveguide power division network, the output terminal of each E-plane rectangular waveguide-single ridge waveguide transducer is used as an output terminal of the first H-type E-plane waveguide power division network, and the first H-type E-plane waveguide power division network has one input terminal and four output terminals; 
     the input terminals of the two first H-type E-plane waveguide power division networks and input terminals of the two second H-type E-plane waveguide power division networks are used as input terminals of the first-level H-type E-plane waveguide power division network, four output terminals of each of the two first H-type E-plane waveguide power division networks and four output terminals of each of the two second H-type E-plane waveguide power division networks are used as output terminals of the first-level H-type E-plane waveguide power division network, and the first-level H-type E-plane waveguide power division network has four input terminals and sixteen output terminals; 
     the second-level H-type E-plane waveguide power divider has an input terminal and four output terminals and is used to divide a signal input via the input terminal thereof into four signals with the same power and phase and output the four signals via the four output terminals thereof respectively, the input terminal of the second-level H-type E-plane waveguide power divider is used as an input terminal of the first-level H-type E-plane waveguide power division network unit, the four output terminals of the second-level H-type E-plane waveguide power divider are connected to the four input terminals of the first-level H-type E-plane waveguide power division network in a one-to-one correspondence, the sixteen output terminals of the first-level H-type E-plane waveguide power division network are used as sixteen output terminals of the first-level H-type E-plane waveguide power division network unit, and the 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units have
 
             16   *       (     n     2   1       )     2           
output terminals, and the
 
             16   *       (     n     2   1       )     2           
output terminals of the
 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units are used as
 
             16   *       (     n     2   1       )     2           
output terminals of the feed layer and are connected to the 4*n 2  input terminals of the radiation layer in a one-to-one correspondence; the
 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units are regularly distributed in
 
             n     2   1           
rows and
 
             n     2   1           
columns at intervals to form a first-level feed network array,
 
     a center distance between every two adjacent first-level H-type E-plane waveguide power division network units in each row is 3.6λ, and a center distance between every two adjacent first-level H-type E-plane waveguide power division network units in each column is 3.6λ; 
     from the first row and the first column of the first-level feed network array, the four first-level H-type E-plane waveguide power division network units in every two rows and every two columns form a first-level network unit group, and the first-level feed network array totally includes 
               (     n     2   2       )     2         
first-level network unit groups;
 
     a third-level H-type E-plane waveguide power divider is disposed in each first-level network unit group, has an input terminal and four output terminals, and is used to divide a signal input via the input terminal thereof into four signals with the same power and phase via the four output terminals thereof respectively, the four output terminals of the third-level H-type E-plane waveguide power divider are connected to the input terminals of the four first-level H-type E-plane waveguide power division network units in the first-level network unit group in a one-to-one correspondence, the first-level network unit group and the third-level H-type E-plane waveguide power divider connected thereto form a second-level H-type E-plane waveguide power division network unit, the input terminal of the third-level H-type E-plane waveguide power divider is used as an input terminal of the second-level H-type E-plane waveguide power division network unit, 
               (     n     2   2       )     2         
second-level H-type E-plane waveguide power division network units which are distributed in
 
             n     2   2           
rows and
 
             n     2   2           
columns are obtained in total, and the
 
               (     n     2   2       )     2         
second-level H-type E-plane waveguide power division network units form a second-level feed network array;
 
     from the first row and the first column of the second-level feed network array, the four second-level H-type E-plane waveguide power division network units in every two rows and every two columns form a second-level network unit group, the second-level feed network array totally includes 
               (     n     2   3       )     2         
second-level network unit groups, the input terminal of the third-level H-type H-plane waveguide power divider of each second-level H-type E-plane waveguide power division network unit in the second-level network unit group is used as an input terminal of the second-level network unit group, and the second-level network unit group has four input terminals; a fourth-level H-type E-plane waveguide power divider is disposed in each second-level network unit group, has an input terminal and four output terminals, and is used to divide a signal input via the input terminal thereof into four output signals with the same power and phase and output the four signals via the four output terminals thereof respectively, the four output terminals of the fourth-level H-plane E-plane waveguide power divider are connected to the four input terminals of the second-level network unit group in a one-to-one correspondence, the second-level network unit group and the fourth-level H-type E-plane waveguide power divider connected thereto form a third-level H-type E-plane waveguide power division network unit, the input terminal of the fourth-level H-type E-plane waveguide power divider is used as an input terminal of the third-level H-type E-plane waveguide power division network unit,
 
               (     n     2   3       )     2         
third-level H-type E-plane waveguide power division network units which are distributed in
 
             n     2   3           
rows and
 
             n     2   3           
columns are obtained in total, and the
 
               (     n     2   3       )     2         
third-level H-type E-plane waveguide power division network units form a third-level feed network array;
 
     by this analogy, a (k−2) th -level feed network array is formed by 
               (     n     2     k   -   2         )     2         
(k−2) th -level H-type E-plane waveguide power division network units, a (k−1) th -level H-type E-plane waveguide power divider is arranged among the four (k−2) th -level H-type E-plane waveguide power division network units in the (k−2) th -level feed network array, has an input terminal and four output terminals, and is used to divide a signal input via the input terminal thereof into four signals with the same power and phase and output the four signals via the output terminals thereof respectively, the four output terminals of the (k−1) th -level H-type E-plane waveguide power divider are connected to the input terminals of the four (k−2) th -level H-type E-plane waveguide power division network units in a one-to-one correspondence, the input terminal of the (k−1) th -level H-type E-plane waveguide power divider is connected to the standard waveguide input port which is used as an input terminal of the feed layer, and the input terminal of the feed layer is connected to an external signal interface;
 
     the first-level H-type E-plane waveguide power divider comprises a first conversion block, a second conversion block, a third conversion block, a fourth conversion block, a fifth conversion block, a sixth conversion block, a first rectangular block, a first metal block, a second metal block and a third metal block, wherein an upper end surface of the first conversion block, an upper end surface of the second conversion block, an upper end surface of the third conversion block, an upper end surface of the fourth conversion block, an upper end surface of the fifth conversion block, an upper end surface of the sixth conversion block, an upper end surface of the first rectangular block, an upper end surface of the first metal block, an upper end surface of the second metal block and an upper end surface of the third metal block are located on the same plane as an upper end surface of the second plate; a lower end surface of the first conversion block, a lower end surface of the second conversion block, a lower end surface of the third conversion block, a lower end surface of the fourth conversion block, a lower end surface of the fifth conversion block, a lower end surface of the sixth conversion block, a lower end surface of the first rectangular block, a lower end surface of the first metal block, a lower end surface of the second metal block and a lower end surface of the third metal block are located on the same plane as a lower end surface of the second plate; 
     the first metal block is a parallelogram block, a front end surface of the first metal block is parallel to a front end surface of the second plate, a left end surface of the first metal block will be parallel to a left end surface of the second plate after the first metal block is rotated anticlockwise by 22.5° around a center thereof, a length of the front end surface of the first metal block in the left-right direction is 0.12, length of the front end face of the first metal block in the front-back direction is 0.5λ, the length of the first metal block in the vertical direction is 0.8λ, and the first metal block will overlap with the second metal block after being moved rightwards by 0.9λ; the third metal block is located between the first metal block and the second metal block and is a parallelogram block, a front end face of the third metal block will be parallel to the front end face of the second plate after the third metal block is rotated clockwise by 12.5° around the center thereof, and the length of the front end face of the third metal block in the left-right direction is 0.6λ; the first conversion block comprises a second rectangular block and a first right triangle block, a left end face of the second rectangular block serves as a left end face of the first conversion block, the left end face of the first conversion block is connected and attached to a right end face of the first metal block, the length of a front end face of the second rectangular block in the left-right direction is 0.1λ, the length of the left end face of the second rectangular block in the front-back direction is 0.2λ, the distance from the front end surface of the second rectangular block to a front end surface of the first metal block will be equal to a distance from a rear end surface of the second rectangular block to a rear end surface of the first metal block after the second rectangular block is rotated anticlockwise by 22.5° around a center thereof, an end surface, where a first right-angle side of the first right triangle block is located, is connected and attached to a right end surface of the second rectangular block, a length of the end surface, where the first right-angle side of the first right triangle block is located, in the front-back direction is equal to a length of the left end surface of the second rectangular block in the front-back direction, an end surface, where a second right-angle side of the first right triangle block is located, is located on the same plane as the rear end surface of the second rectangular block, an included angle between the end surface where the first right-angle side of the first right triangle block is located and an end surface where a hypotenuse of the first right triangle block is located is 22.5°, and the end surface, where the hypotenuse of the first right triangle block is located, is connected to and entirely overlaps with a left end surface of the third metal block; 
     the second conversion block comprises a third rectangular block and a second right triangle block, wherein a right end surface of the third rectangular block serves as a right end surface of the second conversion block, the right end surface of the second conversion block is connected and attached to a left end surface of the second metal block, a length of a front end surface of the third rectangular block in the left-right direction is 0.1λ, a length of the right end surface of the third rectangular block in the front-back direction is 0.2λ, a distance from the front end surface of the third rectangular block to a front end surface of the second metal block is equal to a distance from a rear end surface of the third rectangular block to a rear end surface of the second metal block after the third rectangular block is rotated anticlockwise by 22.5° around a center thereof, an end surface, where a first right-angle side of the second right triangle block is located, is connected and attached to a left end surface of the third rectangular block, a length of the end surface, where the first right-angle side of the second right triangle block is located, in the front-back direction is equal to a length of the left end surface of the third rectangular block in the front-back direction, an end surface, where a second right-angle side of the second right triangle block is located, is located on the same plane as the front end surface of the third rectangular block, an included angle between the end surface where the second right-angle side of the second right triangle block is located and an end surface where a hypotenuse of the second right triangle block is located is 22.5°, and the end surface, where the hypotenuse of the second right triangle block is located, will be connected to and entirely overlap with a right end surface of the third metal block; 
     the third conversion block comprises a fourth rectangular block and a third right triangle block, wherein a front end surface of the fourth rectangular block serves as a front end surface of the third conversion block, a length of the front end surface of the fourth rectangular block in the left-right direction is 0.1λ, an end surface, where a first right-angle side of the third right triangle block is located, entirely overlaps with a rear end surface of the fourth rectangular block, a length of the end surface, where the first right-angle side of the third right triangle block is located, is equal to a length of the rear end surface of the fourth rectangular block in the left-right direction, an end surface, where a second right-angle side of the third right triangle block is located, is located on the same plane as a right end surface of the fourth rectangular block, an included angle between the end surface where the first right-angle side of the third right triangle block is located and an end surface where a hypotenuse of the third right triangle block is located is 22.5°, the end surface, where the hypotenuse of the third right triangle block is located, will be connected to and entirely overlap with the front end surface of the first metal block, the third conversion block will entirely overlap with the fourth conversion block after being moved rightwards by 0.9λ, and the rear end surface of the fourth conversion block is connected to and entirely overlaps with the front end surface of the second metal block; 
     the fifth conversion block is symmetrical with the third conversion block in the front-back direction, and a front end surface of the fifth conversion block is connected to and entirely overlaps with the rear end surface of the first metal block; 
     the sixth conversion block is symmetrical with the fourth conversion block in the front-back direction, a front end surface of the sixth conversion block is connected to and entirely overlaps with the rear end surface of the second metal block, the front end surface of the third conversion block, the front end surface of the fourth conversion block, a rear end surface of the fifth conversion block and a rear end surface of the sixth conversion block are used as the fourth output terminals of the first-level H-type E-plane waveguide power divider respectively, the front end surface of the first rectangular block is connected and attached to the rear end surface of the third metal block, a length of the first rectangular block in the left-right direction is 0.6λ, a distance from a left end of the front end surface of the first rectangular block to a left end of the rear end surface of the third metal block is equal to a distance from a right end of the front end surface of the first rectangular block to a right end of the rear end surface of the third metal block, and the rear end surface of the first rectangular block is used as the input terminal of the first-level H-type E-plane waveguide power divider. In this structure, the first-level H-type power dividers in the feed layer perform input and output in the same direction, so that the structure is compact, ultra-wideband and high-efficiency feeding of the plate antenna is realized, and miniaturization is facilitated. 
     The E-plane rectangular waveguide-single ridge waveguide transducer comprises a first rectangular metal block, wherein a rectangular port and a fourth rectangular cavity are formed in the first rectangular metal block, a rear end surface of the rectangular port is used as an input terminal of the E-plane rectangular waveguide-single ridge waveguide transducer, an upper end surface of the rectangular port is spaced apart from an upper end surface of the first rectangular metal block by a certain distance, a rear end surface of the rectangular port is located on the same plane as a rear end surface of the first rectangular metal block, an upper end surface of the fourth rectangular cavity is located on the same plane as the upper end surface of the first rectangular metal block, a left end surface of the fourth rectangular cavity is located on the same plane as a left end surface of the rectangular port, a rear end surface of the fourth rectangular cavity is connected and attached to a front end surface of the rectangular port, a lower end surface of the fourth rectangular cavity is located on the same plane as a lower end surface of the rectangular port, a right end surface of the rectangular port is spaced apart from a right end surface of the fourth rectangular cavity by a certain distance, the right end surface of the fourth rectangular cavity is spaced apart from a right end surface of the first rectangular metal block by a certain distance, a distance from the left end surface of the fourth rectangular cavity to the left end surface of the first rectangular metal block is equal to a distance from the right end surface of the fourth rectangular cavity to the right end surface of the first rectangular metal block, the lower end surface of the fourth rectangular cavity is spaced apart from the lower end surface of the first rectangular metal block by a certain distance, 
     a single ridge step, an H-plane step and an E-plane step are arranged in the fourth rectangular cavity and are all rectangular blocks, a front end surface of the single ridge step, a front end surface of the H-plane step and a front end surface of the E-plane step are connected and attached to the front end surface of the fourth rectangular cavity, a left end surface of the H-plane step is connected and attached to the left end surface of the fourth rectangular cavity, a lower end surface of the H-plane step is connected and attached to the lower end surface of the fourth rectangular cavity, a right end surface of the H-plane step is connected and attached to a left end surface of the single ridge step, a lower end surface of the single ridge step is connected and attached to the lower end surface of the fourth rectangular cavity, an upper end surface of the single ridge step is located on the same plane as the upper end surface of the fourth rectangular cavity, a right end surface of the single ridge step is connected and attached to a left end surface of the E-plane step, a right end surface of the E-plane step is connected and attached to the right end surface of the fourth rectangular cavity, and a lower end surface of the E-plane step is connected and attached to the lower end surface of the fourth rectangular cavity. 
     A length of the H-plane step in the front-back direction is half of a length of the fourth rectangular cavity in the front-back direction, a length of the H-plane step in the left-right direction is one third of a length of the fourth rectangular cavity in the left-right direction, a length of the H-plane step in the vertical direction is two fifths of a length of the fourth rectangular cavity in the vertical direction, a length of the single ridge step in the front-back direction is half of a length of the fourth rectangular cavity in the front-back direction, a length of the single ridge step in the left-right direction is one third of a length of the fourth rectangular cavity in the left-right direction, a length of the single ridge step in the vertical direction is equal to a length of the fourth rectangular cavity in the vertical direction, a length of the E-plane step in the front-back direction is equal to a length of the fourth rectangular cavity in the front-back direction, a length of the E-plane step in the left-right direction is one third of a length of the fourth rectangular cavity in the left-right direction, a length of the E-plane step in the vertical direction is a quarter of a length of the fourth rectangular cavity in the vertical direction. 
     The upper end surface of the fourth rectangular cavity serves as the output terminal of the E-plane rectangular waveguide-single ridge waveguide transducer. 
     In this structure, the single ridge step, the H-plane step and the E-plane step are arranged in the E-plane rectangular waveguide-single ridge waveguide transducer to realize impedance matching and to reduce the return loss caused by structural discontinuities, so that the plate array antenna has a good wideband transmission property, uniform feeding to the radiation units in the radiation layer is fulfilled, the dominant-mode bandwidth can be expanded, and ultra-wideband and high-efficiency feeding of the array antenna is realized. 
     Compared with the prior art, the invention has the following advantages: each radiation unit in the radiation layer is constituted by two first radiation assemblies and two second radiation assemblies, wherein the two first radiation assemblies are parallelly arranged left and right and are spaced apart from each other, the first radiation assembly on the left will overlap with the first radiation assembly on the right after being moved rightwards by 0.9λ, the two second radiation assemblies are also arranged left and right and are spaced apart from each other, the second radiation assembly on the left will overlap with the second radiation assembly on the right after being moved rightwards by 0.9λ, the two second radiation assemblies are located behind the two first radiation assemblies, a center distance between the second radiation assembly on the left and the first radiation assembly on the left is 0.9λ, and a center distance between the second radiation assembly on the right and the first radiation assembly on the right is 0.9λ; each first radiation assembly comprises a first rectangular bar, a first rectangular cavity, a second rectangular cavity and a third rectangular cavity, wherein the first rectangular cavity, the second rectangular cavity and the third rectangular cavity are sequentially arranged from top to bottom, there exists an azimuth deviation between the three rectangular cavities, a center of the first rectangular bar, a center of the first rectangular cavity, a center of the second rectangular cavity and a center of the third rectangular cavity are located on the same center line, the first radiation assembly on the left will overlap with the second radiation assembly on the left after being moved downwards by 0.9λ and then being rotated clockwise by 180° around the center line, and the first radiation assembly on the right will overlap with the second radiation assembly on the right after being moved downwards by 0.9λ and then being rotated clockwise by 180° around the center line. 
     The first rectangular cavity, the second rectangular cavity and the third rectangular cavity in the first radiation assembly are stacked in presence of an azimuth deviation to form a three-layer coupled structure so as to optimize a multi-level radiation structure of traditional plate antennas into a one-level radiation structure, so that the profile height of the plate antennas is greatly decreased, and higher assembly precision can be realized easily. 
     The low-profile and miniaturized design restrains the property of cross polarization of the traditional plate antennas, obviously improves the gain and aperture efficiency of the plate antennas; in addition, the first rectangular bar located in the first rectangular cavity can better restrain cross polarization and reduce the sidelobe; therefore, the low-sidelobe plate array antenna of the invention has a low sidelobe, is simple in structure, low in cost and suitable for mass production, and has a wide frequency bandwidth and high efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a first exploded view of a low-sidelobe plate array antenna of the invention. 
         FIG. 2  is a second exploded view of the low-sidelobe plate array antenna of the invention. 
         FIG. 3  is a top view of a radiation layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 4  is a bottom view of the radiation layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 5  is a perspective view of a first radiation assembly of the radiation layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 6  is a top view of a feed layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 7  is a bottom view of the feed layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 8  is an exploded view of a first-level H-type E-plane waveguide power divider of the feed layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 9  is an exploded view of an E-plane rectangular waveguide-single ridge waveguide transducer of the feed layer of the low-sidelobe plate array antenna of the invention. 
         FIG. 10  is a simulated curve chart of the reflection coefficient of the low-sidelobe plate array antenna of the invention. 
         FIG. 11  is an H-plane directional diagram of the low-sidelobe plate array antenna of the invention. 
         FIG. 12  is an E-plane directional diagram of the low-sidelobe plate array antenna of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be further expounded below in conjunction with the accompanying drawings and embodiments. 
     Embodiment: as shown in  FIG. 1  and  FIG. 2 , a low-sidelobe plate array antenna comprises a radiation layer  1  and a feed layer  2 , wherein the radiation layer  1  is superimposed on the feed layer  2 , the feed layer  2  is used to output 4*n 2  TE10 mode signals, the radiation layer  1  has 4*n 2  input terminals and 4*n 2  output terminals, the 4*n 2  TE10 mode signals output by the feed layer  2  are accessed to the 4*n 2  input terminals of the radiation layer  1  in a one-to-one correspondence, the 4*n 2  output terminals of the radiation layer  1  are used to radiate the 4*n 2  TE10 mode signals output by the feed layer  2  to a free space in a one-to-one correspondence, n=2 (k-1) , and k is an integer greater than or equal to 3; as shown in  FIG. 3 - FIG. 5 , the radiation layer  1  comprises a first plate  3  and a radiation array disposed on the first plate  3 , wherein the first plate  3  is a rectangular plate, the radiation array is formed by n 2  radiation units  4  which are distributed in 2 (k-1)  rows and 2 (k-1)  columns, a center distance between every two adjacent radiation unit  4  in each row is 1.8λ, a center distance between every two adjacent radiation units  4  in each column is 1.8λ, and λ=c/f, wherein c is a wave velocity, c=3*10{circumflex over ( )}8 m/s, and f is a center operating frequency of the low-sidelobe plate array antenna; each radiation unit  4  comprises two first radiation assemblies  5  and two second radiation assemblies  6 , wherein the two first radiation assemblies  5  are parallelly arranged left and right and are spaced apart from each other, the first radiation assembly  5  on the left will overlap with the first radiation assembly  5  on the right after being moved rightwards by 0.9λ, the two second radiation assemblies  6  are also arranged left and right and are spaced apart from each other, the second radiation assembly  6  on the left will overlap with the second radiation assembly  6  on the right after being moved rightwards by 0.9λ, the two second radiation assemblies  6  are located behind the two first radiation assemblies  5 , a center distance between the second radiation assembly  6  on the left and the first radiation assembly  5  on the left is 0.9λ, and a center distance between the second radiation assembly  6  on the right and the first radiation assembly  5  on the right is 0.9λ. 
     Each first radiation assembly  5  comprises a first rectangular bar  7 , a first rectangular cavity  8 , a second rectangular cavity  9  and a third rectangular cavity  10 , wherein the first rectangular cavity  8 , the second rectangular cavity  9  and the third rectangular cavity  10  are sequentially arranged from top to bottom, a center of the first rectangular bar  7 , a center of the first rectangular cavity  8 , a center of the second rectangular cavity  9  and a center of the third rectangular cavity  10  are located on the same line which is perpendicular to the first plate  3  and is referred to as a center line, the first rectangular bar  7  is located in the first rectangular cavity  8 , an upper end surface of the first rectangular bar  7  and an upper end surface of the first rectangular cavity  8  are located on the same plane as an upper end surface of the first plate  3 , a front end surface of the first rectangular bar  7  and a front end surface of the first rectangular cavity  8  are formed and connected integrally and are attached together, a rear end surface of the first rectangular bar  7  and a rear end surface of the first rectangular cavity  8  are formed and connected integrally and are attached together; if the first rectangular cavity  8  is rotated anticlockwise by 45° around the center line, a plane where the front end surface of the first rectangular cavity  8  is located will be parallel to a plane where the front end surface of the first plate  3  is located, and a plane where a front end surface of the second rectangular cavity  9  is located will be parallel to a plane where a front end surface of the third rectangular cavity  10  is located; if the second rectangular cavity  9  is rotated anticlockwise by 67.5° around the center line, a plane where the front end surface of the second rectangular cavity  9  is located will be parallel to a plane where the front end surface of the first plate  3  is located, an upper end surface of the second rectangular cavity  9  will be located on the same plane as a lower end surface of the first rectangular cavity  8 , an upper end surface of the third rectangular cavity  10  will be located on the same plane as a lower end surface of the second rectangular cavity  9 , a lower end surface of the third rectangular cavity  10  will be located on the same plane as a lower end surface of the first plate  3 , a distance from a left end surface of the first rectangular bar  7  to a left end surface of the first rectangular cavity  8  is equal to a distance from a right end surface of the first rectangular bar  7  to a right end surface of the first rectangular cavity  8 , a distance from the front end surface to the rear end surface of the first rectangular cavity  8  is 0.8λ, a distance from the left end surface to the right end surface of the first rectangular cavity  8  is 0.6λ, a distance from the upper end surface to the lower end surface of the first rectangular cavity  8  is 0.3λ, a distance from the left end surface to the right end surface of the first rectangular bar  7  is 0.1λ, and a distance from the upper end surface to the lower end surface of the first rectangular bar  7  is 0.1λ; a distance from the front end surface to the rear end surface of the second rectangular cavity  9  is 0.6λ, a distance from the left end surface to the right end surface of the second rectangular cavity  9  is 0.4λ, and a distance from the upper end surface to the lower end surface of the second rectangular cavity  9  is 0.3λ. 
     A first rectangular matching plate  91  and a second rectangular matching plate  92  are arranged in the second rectangular cavity  9 , a left side wall of the first rectangular matching plate and a left side wall of the second rectangular cavity  9  are attached together and are formed and connected integrally, a distance from a front end surface of the first rectangular matching plate to a front end surface of the second rectangular cavity  9  is equal to a distance from a rear end surface of the first rectangular matching plate to a rear end surface of the second rectangular cavity  9 , a distance from a left end surface to a right end surface of the first rectangular matching plate is 0.1λ, a distance from a front end surface to a rear end surface of the first rectangular matching plate is 0.2λ. 
     An upper end surface of the first rectangular matching plate  91  is located on the same plane as the upper end surface of the second rectangular cavity  9 , a lower end surface of the first rectangular matching plate  91  is located on the same plane as the lower end surface of the second rectangular cavity  9 , and the second rectangular matching plate  92  and the first rectangular matching plate  91  are symmetrical left and right with respect to a left-right bisecting plane of the second rectangular cavity  9 . 
     A distance from the front end surface to the rear end surface of the third rectangular cavity  10  is 0.4λ, a distance from the left end surface to the right end surface of the third rectangular cavity  10  is 0.2λ, a distance from the upper end surface to the lower end surface of the third rectangular cavity  10  is 0.1λ, a third rectangular matching plate  101  is arranged in the third rectangular cavity  10 , a left side wall of the third rectangular matching plate  101  and a left side wall of the third rectangular cavity  10  are attached together and are formed and connected integrally, a distance from a front end surface of the third rectangular matching plate  101  to the front end surface of the third rectangular cavity  10  is equal to a distance from a rear end surface of the third rectangular matching plate to the rear end surface of the third rectangular cavity  10 , an upper end surface of the third rectangular matching plate  101  is located on the same plane as the upper end surface of the third rectangular cavity  10 , a lower end surface of the third rectangular matching plate is located on the same plane as the lower end surface of the third rectangular cavity  10 , a distance from a left end surface to a right end surface of the third rectangular matching plate is 0.1λ, a distance from a front end surface to a rear end surface of the third rectangular matching plate  101  is 0.2λ, the upper end surface of the first rectangular cavity  8  is used as an output terminal of the first radiation assembly  5 , and the lower end surface of the third rectangular cavity  10  is used as an input terminal of the first radiation assembly  5 . 
     If the first radiation assembly  5  on the left is moved downwards by 0.9λ and is then rotated clockwise by 180° around the center line, the first radiation assembly  5  on the left will overlap with the second radiation assembly  6  on the left; if the first radiation assembly  5  on the right is moved downwards by 0.9λ and is then rotated clockwise by 180° around the center line, the first radiation assembly  5  on the right will overlap with the second radiation assembly  6  on the right. 
     The input terminals of the two first radiation assemblies  5  and input terminals of the two second radiation assemblies  6  are used as four input terminals of the radiation unit  4 ; the four input terminals of each radiation unit  4  are used as four input terminals of the radiation layer  1 , and the radiation layer  1  has 4*n 2  input terminals; the output terminals of the two first radiation assemblies  5  and output terminals of the two second radiation assemblies  6  are used as four output terminals of the radiation unit  4 , the four output terminals of each radiation unit  4  are used as four output terminals of the radiation layer  1 , and the radiation layer  1  has 4*n 2  output terminals. 
     In this embodiment, as shown in  FIG. 6  and  FIG. 7 , the feed layer  2  comprises a second plate  11 , 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units  12  and a standard waveguide input port  13 , wherein the
 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units  12  and the standard waveguide input port  13  are disposed on the second plate  11 , and the second plate  11  is a rectangular plate; each first-level H-type E-plane waveguide power division network unit  12  comprises a first-level H-type E-plane waveguide power division network and a second-level H-type E-plane waveguide power divider  14 , wherein the first-level H-type E-plane waveguide power division network comprises two first H-type E-plane waveguide power division networks  15  and two second H-type E-plane waveguide power division networks  16 , the two first H-type E-plane waveguide power division networks  15  are parallelly arranged left and right and are spaced apart from each other, the first H-type E-plane waveguide power division network  15  on the left will overlap with the first H-type E-plane waveguide power division network  15  on the right after being moved rightwards by 1.8λ, the two second H-type E-plane waveguide power division networks  16  are arranged left and right and are spaced apart from each other, the second H-type E-plane waveguide power division network  16  on the left will overlap with the second H-type E-plane waveguide power division network  16  on the right after being moved rightwards by 1.8λ, the two second H-type E-plane waveguide power division networks  16  are located behind the two first H-type E-plane waveguide power division networks  15 , a center distance between the second H-type E-plane waveguide power division network  16  on the left and the first H-type E-plane waveguide power division network  15  on the left is 1.8λ, the second H-type E-plane waveguide power division network  16  on the left and the first H-type E-plane waveguide power division network  15  on the left are symmetrical front and back, a center distance between the second H-type E-plane waveguide power division network  16  on the right and the first H-type E-plane waveguide power division network  15  on the right is 1.8λ, and the second H-type E-plane waveguide power division network  16  on the right and the first H-type E-plane waveguide power division network  15  on the right are symmetrical front and back.
 
     Each first H-type E-plane waveguide power division network  15  comprises a first-level H-type E-plane waveguide power divider  17  and four E-plane rectangular waveguide-single ridge waveguide transducers  18 , wherein the first-level H-type E-plane waveguide power divider  17  has an input terminal and four output terminals, divides a signal input via the input terminal thereof into four signals with the same power and phase, and outputs the four signals via the four output terminals thereof respectively, each E-plane rectangular waveguide-single ridge waveguide transducer  18  has an input terminal and an output terminal and is used to convert a rectangular waveguide accessed to the input terminal thereof into a single ridge waveguide and output the single ridge waveguide via the output terminal thereof, the input terminals of the four E-plane rectangular waveguide-single ridge waveguide transducers  18  are connected to the four output terminals of the first-level H-type E-plane waveguide power divider  17  in a one-to-one correspondence, the input terminal of the first-level H-type E-plane waveguide power divider  17  is used as an input terminal of the first H-type E-plane waveguide power division network  15 , the output terminal of each E-plane rectangular waveguide-single ridge waveguide transducer  18  is used as an output terminal of the first H-type E-plane waveguide power division network  15 , and the first H-type E-plane waveguide power division network  15  has one input terminal and four output terminals. 
     The input terminals of the two first H-type E-plane waveguide power division networks  15  and input terminals of the two second H-type E-plane waveguide power division networks  16  are used as input terminals of the first-level H-type E-plane waveguide power division network, four output terminals of each of the two first H-type E-plane waveguide power division networks  15  and four output terminals of each of the two second H-type E-plane waveguide power division networks  16  are used as output terminals of the first-level H-type E-plane waveguide power division network, and the first-level H-type E-plane waveguide power division network has four input terminals and sixteen output terminals; the second-level H-type E-plane waveguide power divider  14  has an input terminal and four output terminals and is used to divide a signal input via the input terminal thereof into four signals with the same power and phase and output the four signals via the four output terminals thereof respectively, the input terminal of the second-level H-type E-plane waveguide power divider  14  is used as an input terminal of the first-level H-type E-plane waveguide power division network unit  12 , the four output terminals of the second-level H-type E-plane waveguide power divider  14  are connected to the four input terminals of the first-level H-type E-plane waveguide power division network in a one-to-one correspondence, the sixteen output terminals of the first-level H-type E-plane waveguide power division network are used as sixteen output terminals of the first-level H-type E-plane waveguide power division network unit  12 , and the 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units  12  have
 
             16   *       (     n     2   1       )     2           
output terminals, and the
 
             16   *       (     n     2   1       )     2           
output terminals of the
 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units  12  are used as
 
             16   *       (     n     2   1       )     2           
output terminals of the feed layer  2  and are connected to the 4*n 2  input terminals of the radiation layer  1  in a one-to-one correspondence; the
 
               (     n     2   1       )     2         
first-level H-type E-plane waveguide power division network units  12  are regularly distributed in
 
             n     2   1           
rows and
 
             n     2   1           
columns at intervals to form a first-level feed network array.
 
     A center distance between every two adjacent first-level H-type E-plane waveguide power division network units  12  in each row is 3.6λ, and a center distance between every two adjacent first-level H-type E-plane waveguide power division network units  12  in each column is 3.6λ. 
     From the first row and the first column of the first-level feed network array, the four first-level H-type E-plane waveguide power division network units  12  in every two rows and every two columns form a first-level network unit group, and the first-level feed network array totally includes 
               (     n     2   2       )     2         
first-level network unit groups.
 
     A third-level H-type E-plane waveguide power divider is disposed in each first-level network unit group, has an input terminal and four output terminals, and is used to divide a signal input via the input terminal thereof into four signals with the same power and phase via the four output terminals thereof respectively, the four output terminals of the third-level H-type E-plane waveguide power divider are connected to the input terminals of the four first-level H-type E-plane waveguide power division network units  12  in the first-level network unit group in a one-to-one correspondence, the first-level network unit group and the third-level H-type E-plane waveguide power divider connected thereto form a second-level H-type E-plane waveguide power division network unit, the input terminal of the third-level H-type E-plane waveguide power divider is used as an input terminal of the second-level H-type E-plane waveguide power division network unit, 
               (     n     2   2       )     2         
second-level H-type E-plane waveguide power division network units which are distributed in
 
             n     2   2           
rows and
 
             n     2   2           
columns are obtained in total, and the
 
               (     n     2   2       )     2         
second-level H-type E-plane waveguide power division network units form a second-level feed network array;
 
     from the first row and the first column of the second-level feed network array, the four second-level H-type E-plane waveguide power division network units in every two rows and every two columns form a second-level network unit group, the second-level feed network array totally includes 
               (     n     2   3       )     2         
second-level network unit groups, the input terminal of the third-level H-type H-plane waveguide power divider of each second-level H-type E-plane waveguide power division network unit in the second-level network unit group is used as an input terminal of the second-level network unit group, and the second-level network unit group has four input terminals; a fourth-level H-type E-plane waveguide power divider is disposed in each second-level network unit group, has an input terminal and four output terminals, and is used to divide a signal input via the input terminal thereof into four output signals with the same power and phase and output the four signals via the four output terminals thereof respectively, the four output terminals of the fourth-level H-plane E-plane waveguide power divider are connected to the four input terminals of the second-level network unit group in a one-to-one correspondence, the second-level network unit group and the fourth-level H-type E-plane waveguide power divider connected thereto form a third-level H-type E-plane waveguide power division network unit, the input terminal of the fourth-level H-type E-plane waveguide power divider is used as an input terminal of the third-level H-type E-plane waveguide power division network unit,
 
               (     n     2   3       )     2         
third-level H-type E-plane waveguide power division network units which are distributed in
 
             n     2   3           
rows and
 
             n     2   3           
columns are obtained in total, and the
 
               (     n     2   3       )     2         
third-level H-type E-plane waveguide power division network units form a third-level feed network array.
 
     By this analogy, a (k−2) th -level feed network array is formed by 
               (     n     2     k   -   2         )     2         
(k−2) th -level H-type E-plane waveguide power division network units, a (k−1) th -level H-type E-plane waveguide power divider is arranged among the four (k−2) th -level H-type E-plane waveguide power division network units in the (k−2) th -level feed network array, has an input terminal and four output terminals, and is used to divide a signal input via the input terminal thereof into four signals with the same power and phase and output the four signals via the output terminals thereof respectively, the four output terminals of the (k−1) th -level H-type E-plane waveguide power divider are connected to the input terminals of the four (k−2) th -level H-type E-plane waveguide power division network units in a one-to-one correspondence, the input terminal of the (k−1) th -level H-type E-plane waveguide power divider is connected to the standard waveguide input port  13  which is used as an input terminal of the feed layer  2 , and the input terminal of the feed layer  2  is connected to an external signal interface.
 
     As show in  FIG. 8 , the first-level H-type E-plane waveguide power divider  17  comprises a first conversion block  19 , a second conversion block  20 , a third conversion block  21 , a fourth conversion block  22 , a fifth conversion block  23 , a sixth conversion block  24 , a first rectangular block  25 , a first metal block  26 , a second metal block  27  and a third metal block  28 , wherein an upper end surface of the first conversion block  19 , an upper end surface of the second conversion block  20 , an upper end surface of the third conversion block  21 , an upper end surface of the fourth conversion block  22 , an upper end surface of the fifth conversion block  23 , an upper end surface of the sixth conversion block  24 , an upper end surface of the first rectangular block  25 , an upper end surface of the first metal block  26 , an upper end surface of the second metal block  27  and an upper end surface of the third metal block  28  are located on the same plane as an upper end surface of the second plate  11 ; a lower end surface of the first conversion block  19 , a lower end surface of the second conversion block  20 , a lower end surface of the third conversion block  21 , a lower end surface of the fourth conversion block  22 , a lower end surface of the fifth conversion block  23 , a lower end surface of the sixth conversion block  24 , a lower end surface of the first rectangular block  25 , a lower end surface of the first metal block  26 , a lower end surface of the second metal block  27  and a lower end surface of the third metal block  28  are located on the same plane as a lower end surface of the second plate  11 . 
     The first metal block  26  is a parallelogram block, a front end surface of the first metal block  26  is parallel to a front end surface of the second plate  11 , a left end surface of the first metal block  26  will be parallel to a left end surface of the second plate  11  after the first metal block  26  is rotated anticlockwise by 22.5° around a center thereof, a length of the front end surface of the first metal block  26  in the left-right direction is 0.1λ, a length of the front end surface of the first metal block  26  in the front-back direction is 0.5λ, a length of the first metal block  26  in the vertical direction is 0.8λ, and the first metal block  26  will overlap with the second metal block  27  after being moved rightwards by 0.9λ. 
     The third metal block  28  is located between the first metal block  26  and the second metal block  27  and is a parallelogram block, a front end surface of the third metal block  28  will be parallel to the front end surface of the second plate  11  after the third metal block is rotated clockwise by 12.5° around a center thereof, and a length of the front end surface of the third metal block  28  in the left-right direction is 0.6λ. 
     The first conversion block  19  comprises a second rectangular block  29  and a first right triangle block  30 , a left end surface of the second rectangular block  29  serves as a left end surface of the first conversion block  19 , the left end surface of the first conversion block  19  is connected and attached to a right end surface of the first metal block  26 , a length of a front end surface of the second rectangular block  29  in the left-right direction is 0.1λ, a length of the left end surface of the second rectangular block  29  in the front-back direction is 0.2λ, a distance from the front end surface of the second rectangular block  29  to a front end surface of the first metal block  26  will be equal to a distance from a rear end surface of the second rectangular block  29  to a rear end surface of the first metal block  26  after the second rectangular block  29  is rotated anticlockwise by 22.5° around a center thereof, an end surface, where a first right-angle side of the first right triangle block  30  is located, is connected and attached to a right end surface of the second rectangular block  29 , a length of the end surface, where the first right-angle side of the first right triangle block  30  is located, in the front-back direction is equal to a length of the left end surface of the second rectangular block  29  in the front-back direction, an end surface, where a second right-angle side of the first right triangle block  30  is located, is located on the same plane as the rear end surface of the second rectangular block  29 , an included angle between the end surface where the first right-angle side of the first right triangle block  30  is located and an end surface where a hypotenuse of the first right triangle block  30  is located is 22.5°, and the end surface, where the hypotenuse of the first right triangle block  30  is located, is connected to and entirely overlaps with a left end surface of the third metal block  28 . 
     The second conversion block  20  comprises a third rectangular block  31  and a second right triangle block  32 , wherein a right end surface of the third rectangular block  31  serves as a right end surface of the second conversion block  20 , the right end surface of the second conversion block  20  is connected and attached to a left end surface of the second metal block  27 , a length of a front end surface of the third rectangular block  31  in the left-right direction is 0.1λ, a length of the right end surface of the third rectangular block  31  in the front-back direction is 0.2λ, a distance from the front end surface of the third rectangular block  31  to a front end surface of the second metal block  27  is equal to a distance from a rear end surface of the third rectangular block  31  to a rear end surface of the second metal block  27  after the third rectangular block  31  is rotated anticlockwise by 22.5° around a center thereof, an end surface, where a first right-angle side of the second right triangle block  32  is located, is connected and attached to a left end surface of the third rectangular block  31 , a length of the end surface, where the first right-angle side of the second right triangle block  32  is located, in the front-back direction is equal to a length of the left end surface of the third rectangular block  31  in the front-back direction, an end surface, where a second right-angle side of the second right triangle block  32  is located, is located on the same plane as the front end surface of the third rectangular block  31 , an included angle between the end surface where the second right-angle side of the second right triangle block  32  is located and an end surface where a hypotenuse of the second right triangle block  32  is located is 22.5°, and the end surface, where the hypotenuse of the second right triangle block  32  is located, will be connected to and entirely overlap with a right end surface of the third metal block  28 . 
     The third conversion block  21  comprises a fourth rectangular block  33  and a third right triangle block  34 , wherein a front end surface of the fourth rectangular block  33  serves as a front end surface of the third conversion block  21 , a length of the front end surface of the fourth rectangular block  33  in the left-right direction is 0.1λ, an end surface, where a first right-angle side of the third right triangle block  34  is located, entirely overlaps with a rear end surface of the fourth rectangular block  33 , a length of the end surface, where the first right-angle side of the third right triangle block  34  is located, is equal to a length of the rear end surface of the fourth rectangular block  33  in the left-right direction, an end surface, where a second right-angle side of the third right triangle block  34  is located, is located on the same plane as a right end surface of the fourth rectangular block  33 , an included angle between the end surface where the first right-angle side of the third right triangle block  34  is located and an end surface where a hypotenuse of the third right triangle block  34  is located is 22.5°, the end surface, where the hypotenuse of the third right triangle block  34  is located, will be connected to and entirely overlap with the front end surface of the first metal block  26 , the third conversion block  21  will entirely overlap with the fourth conversion block  22  after being moved rightwards by 0.9λ, and the rear end surface of the fourth conversion block  22  is connected to and entirely overlaps with the front end surface of the second metal block  27 . 
     The fifth conversion block  23  is symmetrical with the third conversion block  21  in the front-back direction, and a front end surface of the fifth conversion block  23  is connected to and entirely overlaps with the rear end surface of the first metal block  26 . 
     The sixth conversion block  24  is symmetrical with the fourth conversion block  22  in the front-back direction, a front end surface of the sixth conversion block  24  is connected to and entirely overlaps with the rear end surface of the second metal block  27 , the front end surface of the third conversion block  21 , the front end surface of the fourth conversion block  22 , a rear end surface of the fifth conversion block  23  and a rear end surface of the sixth conversion block  25  are used as the fourth output terminals of the first-level H-type E-plane waveguide power divider  17  respectively, the front end surface of the first rectangular block  25  is connected and attached to the rear end surface of the third metal block  28 , a length of the first rectangular block  25  in the left-right direction is 0.6λ, a distance from a left end of the front end surface of the first rectangular block  25  to a left end of the rear end surface of the third metal block  28  is equal to a distance from a right end of the front end surface of the first rectangular block  25  to a right end of the rear end surface of the third metal block  28 , and the rear end surface of the first rectangular block  25  is used as the input terminal of the first-level H-type E-plane waveguide power divider  17 . 
     In this embodiment, as shown in  FIG. 9 , the E-plane rectangular waveguide-single ridge waveguide transducer  18  comprises a first rectangular metal block  35 , wherein a rectangular port  36  and a fourth rectangular cavity  37  are formed in the first rectangular metal block  35 , a rear end surface of the rectangular port  36  is used as an input terminal of the E-plane rectangular waveguide-single ridge waveguide transducer  18 , an upper end surface of the rectangular port  36  is spaced apart from an upper end surface of the first rectangular metal block  35  by a certain distance, a rear end surface of the rectangular port  36  is located on the same plane as a rear end surface of the first rectangular metal block  35 , an upper end surface of the fourth rectangular cavity  37  is located on the same plane as the upper end surface of the first rectangular metal block  35 , a left end surface of the fourth rectangular cavity  37  is located on the same plane as a left end surface of the rectangular port  36 , a rear end surface of the fourth rectangular cavity  37  is connected and attached to a front end surface of the rectangular port  36 , a lower end surface of the fourth rectangular cavity  37  is located on the same plane as a lower end surface of the rectangular port  36 , a right end surface of the rectangular port  36  is spaced apart from a right end surface of the fourth rectangular cavity  37  by a certain distance, the right end surface of the fourth rectangular cavity  37  is spaced apart from a right end surface of the first rectangular metal block  35  by a certain distance, a distance from the left end surface of the fourth rectangular cavity  37  to the left end surface of the first rectangular metal block  35  is equal to a distance from the right end surface of the fourth rectangular cavity  37  to the right end surface of the first rectangular metal block  35 , the lower end surface of the fourth rectangular cavity  37  is spaced apart from the lower end surface of the first rectangular metal block  35  by a certain distance. 
     A single ridge step  38 , an H-plane step  39  and an E-plane step  40  are arranged in the fourth rectangular cavity  37  and are all rectangular blocks, a front end surface of the single ridge step  38 , a front end surface of the H-plane step  39  and a front end surface of the E-plane step  40  are connected and attached to the front end surface of the fourth rectangular cavity  37 , a left end surface of the H-plane step  39  is connected and attached to the left end surface of the fourth rectangular cavity  37 , a lower end surface of the H-plane step  39  is connected and attached to the lower end surface of the fourth rectangular cavity  37 , a right end surface of the H-plane step  39  is connected and attached to a left end surface of the single ridge step  38 , a lower end surface of the single ridge step  38  is connected and attached to the lower end surface of the fourth rectangular cavity  37 , an upper end surface of the single ridge step  38  is located on the same plane as the upper end surface of the fourth rectangular cavity  37 , a right end surface of the single ridge step  38  is connected and attached to a left end surface of the E-plane step  40 , a right end surface of the E-plane step  40  is connected and attached to the right end surface of the fourth rectangular cavity  37 , and a lower end surface of the E-plane step  40  is connected and attached to the lower end surface of the fourth rectangular cavity  37 . 
     A length of the H-plane step  39  in the front-back direction is half of a length of the fourth rectangular cavity  37  in the front-back direction, a length of the H-plane step  39  in the left-right direction is one third of a length of the fourth rectangular cavity  37  in the left-right direction, a length of the H-plane step  39  in the vertical direction is two fifths of a length of the fourth rectangular cavity  37  in the vertical direction, a length of the single ridge step  38  in the front-back direction is half of a length of the fourth rectangular cavity  37  in the front-back direction, a length of the single ridge step  38  in the left-right direction is one third of a length of the fourth rectangular cavity  37  in the left-right direction, a length of the single ridge step  38  in the vertical direction is equal to a length of the fourth rectangular cavity  37  in the vertical direction, a length of the E-plane step  40  in the front-back direction is equal to a length of the fourth rectangular cavity  37  in the front-back direction, a length of the E-plane step  40  in the left-right direction is one third of a length of the fourth rectangular cavity  37  in the left-right direction, a length of the E-plane step  40  in the vertical direction is a quarter of a length of the fourth rectangular cavity  37  in the vertical direction. 
     The upper end surface of the fourth rectangular cavity  37  serves as the output terminal of the E-plane rectangular waveguide-single ridge waveguide transducer  18 . 
     The low-sidelobe plate array antenna of the invention is simulated. A simulated curve chart of the reflection coefficient S 11  of the low-sidelobe plate array antenna of the invention is shown in  FIG. 10 . An H-plane directional diagram of the low-sidelobe plate array antenna of the invention is shown in  FIG. 11 . An E-plane directional diagram of the low-sidelobe plate array antenna of the invention is shown in  FIG. 12 . As shown in  FIG. 10 , within the frequency range of 70-85 GHz, the reflection coefficient of the low-sidelobe plate array antenna of the invention is superior to −20 dB, and the relative bandwidth under −10 dB is greater than 30%. As shown in  FIG. 11 , the H-plane peak gain of the low-sidelobe plate array antenna of the invention is greater than 33 dB. As shown in  FIG. 12 , the E-plane peak gain of the low-sidelobe plate array antenna of the invention is greater than 33 dB.