A wideband co-polarized co-transmit-receive antenna array for X-band airborne SAR

Abstract

The application provides a wideband co-transmit-receive antenna array for X-band airborne SAR, and belongs to the technical field of antenna control, and a specific scheme comprises a rectangular dielectric resonator antenna array, a dielectric substrate, a double-layer feed network, a cross-shaped slotted floor and a nylon support column; the rectangular dielectric resonator antenna array is a 4*4 array and comprises four groups of antenna subarrays with the same size and the same spacing; the dielectric substrate comprises a first dielectric substrate, a second dielectric substrate and a third dielectric substrate, and the first dielectric substrate is located below the rectangular dielectric resonator antenna array; the structure of the antenna array realizes co-transmit-receive of the same right-handed circular polarization, and the isolation of the transmit-receive ports reaches a performance of >30dB.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, and in particular to a broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR. Background Technology

[0002] Synthetic Aperture Radar (SAR), as an active microwave remote sensing system, has become an indispensable core technology in fields such as military reconnaissance, disaster emergency response, and environmental monitoring, thanks to its unique imaging capabilities that allow it to operate in all weather conditions and penetrate clouds, fog, and vegetation.

[0003] The antenna system is the core front-end component of airborne SAR, and its performance directly determines the imaging quality and mission effectiveness of the SAR system. On the one hand, the range resolution of SAR is directly proportional to the signal bandwidth, and high-resolution imaging places stringent requirements on the operating bandwidth of the antenna. Currently, traditional SAR systems typically use linearly polarized planar arrays, whose fixed polarization state is susceptible to polarization mismatch and multipath interference, and their performance degrades in depolarized environments. To overcome the shortcomings of linear polarization, circularly polarized antenna arrays are widely favored in existing technologies due to their advantages such as suppressing multipath effects and improving propagation robustness. However, existing circularly polarized antenna arrays often use microstrip antennas to meet the requirements of compactness and lightweight design, and their inherent narrow axial ratio bandwidth severely restricts the performance improvement of broadband high-resolution SAR systems. On the other hand, high-resolution airborne SAR typically employs a fully polarized transceiver mode, that is, alternately transmitting electromagnetic waves in RHCP and LHCP, and simultaneously receiving echo signals from both polarization directions after each transmission. To meet this requirement, four circularly polarized antennas are needed. However, airborne platforms are generally subject to objective constraints of limited space and load. Traditional separate transceiver antenna configurations occupy a large amount of platform space and are prone to problems such as inter-channel coupling and poor phase consistency. Summary of the Invention

[0004] To address the issues of existing separate transceiver antenna configurations occupying significant platform space and easily causing inter-channel coupling and poor phase consistency, this invention discloses a broadband co-circularly polarized co-transceiver antenna array for X-band airborne SAR. The specific technical solution includes:

[0005] Rectangular dielectric resonator antenna array, dielectric substrate, double-layer feed network, cross-shaped slotted floor and nylon support column; The rectangular dielectric resonator antenna array is a 4×4 array, comprising four antenna subarrays of the same size and spacing. Each antenna subarray includes a first dielectric resonator antenna element, a second dielectric resonator antenna element, a third dielectric resonator antenna element, and a fourth dielectric resonator antenna element, excited by rotational feeding in an orthogonal order. The second, third, and fourth dielectric resonator antenna elements are formed by rotating the first dielectric resonator antenna element counterclockwise by 90°, 180°, and 270° respectively. The first dielectric resonator antenna element includes a rectangular dielectric block, two first T-shaped dielectric blocks of the same size, and two second T-shaped dielectric blocks of the same size. The dielectric substrate includes a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate, wherein the first dielectric substrate is located below the rectangular dielectric resonator antenna array; The dual-layer feed network includes an upper feed network and a lower feed network; the upper feed network is located on the upper surface of the second dielectric substrate; the lower feed network is located on the lower surface of the third dielectric substrate; the upper feed network includes a first 180° coupler, a first 90° coupler, a second 90° coupler, a first orthogonal sequence rotating feed network, a second orthogonal sequence rotating feed network, a third orthogonal sequence rotating feed network, a fourth orthogonal sequence rotating feed network, and a first feed port; the second, third, and fourth orthogonal sequence rotating feed networks are formed by rotating the first orthogonal sequence rotating feed network counterclockwise by 90°, 180°, and 270° respectively; the first orthogonal sequence rotating feed network includes a second 180° coupler, a first 90° dual-branch directional coupler, a second 90° dual-branch directional coupler, a first U-shaped transmission line, a second U-shaped transmission line, a third U-shaped transmission line, and a fourth U-shaped transmission line; The lower-level feed network includes a third 180° coupler, a third 90° coupler, a fourth 90° coupler, a fifth orthogonal sequential rotating feed network, a sixth orthogonal sequential rotating feed network, a seventh orthogonal sequential rotating feed network, an eighth orthogonal sequential rotating feed network, and a second feed port; the sixth, seventh, and eighth orthogonal sequential rotating feed networks are formed by rotating the fifth orthogonal sequential rotating feed network counterclockwise by 90°, 180°, and 270° respectively; the fifth orthogonal sequential rotating feed network includes a fourth 180° coupler, a fifth 90° coupler, a sixth 90° coupler, a fifth U-shaped transmission line, a sixth U-shaped transmission line, a seventh U-shaped dielectric resonator excitation transmission line, and an eighth U-shaped transmission line; The first 90° coupler includes a first upper coupling line, a first lower coupling line, a first shorting pin, and a first ground groove; The first feed port is connected to the first 180° coupler via a 50-ohm transmission line; the output port of the first 180° coupler is connected to the first 90° coupler and the second 90° coupler respectively, forming a 180° phase difference; the output ports of the first 90° coupler and the second 90° coupler are connected to the first orthogonal sequential rotating feed network, the second orthogonal sequential rotating feed network, the third orthogonal sequential rotating feed network, and the fourth orthogonal sequential rotating feed network respectively, forming the first-level orthogonal sequential rotating feed excitation between antenna subarrays; the output port of the second 180° coupler is connected to the first 90° dual-branch directional coupler and the second 90° dual-branch directional coupler via a 50-ohm transmission line, forming a 180° phase difference; the output ports of the first 90° dual-branch directional coupler and the second 90° dual-branch directional coupler are connected to the first U-shaped transmission line, the second U-shaped transmission line, the third U-shaped transmission line, and the fourth U-shaped transmission line respectively, forming the second-level orthogonal sequential rotating feed excitation within the antenna subarray. The second feed port is connected to the third 180° coupler via a 50-ohm transmission line; the output port of the third 180° coupler is connected to the third 90° coupler and the fourth 90° coupler, forming a 180° phase difference; the output ports of the third 90° coupler and the fourth 90° coupler are respectively connected to the fifth, sixth, seventh, and eighth orthogonal sequential rotating feed networks, forming the first-level orthogonal sequential rotating feed excitation between antenna subarrays; the output port of the fourth 180° coupler is connected to the fifth 90° coupler and the sixth 90° coupler via a 50-ohm transmission line, forming a 180° phase difference; the output ports of the fifth 90° coupler and the sixth 90° coupler are respectively connected to the fifth U-shaped transmission line, the sixth U-shaped transmission line (3245), the seventh U-shaped dielectric resonator excitation transmission line, and the eighth U-shaped transmission line, forming the orthogonal sequential rotating feed excitation within the antenna subarray. The cross-shaped slotted floor is located between the second dielectric substrate and the third dielectric substrate and is seamlessly connected; the cross-shaped slotted floor includes a ground plane and 16 cross-shaped slots; the 16 cross-shaped slots are located below the 16 rectangular dielectric blocks and their center points are vertically aligned.

[0006] By loading two sets of first T-shaped dielectric blocks and second T-shaped dielectric blocks onto the rectangular dielectric block, the impedance bandwidth is effectively widened.

[0007] By employing the aforementioned dual-layer feed network to achieve two-stage sequential rotary feed excitation, unidirectional circular polarization of dual-port excitation is obtained, and the impedance bandwidth and axial ratio bandwidth are broadened.

[0008] By employing the first 90° coupler, a flat phase difference between the output ports is obtained, thus widening the axial ratio bandwidth.

[0009] The dielectric substrates are all made of low dielectric constant thin substrates with a dielectric constant of less than 4 and a thickness of less than 1 mm. This design reduces the linewidth of each part in the double-layer power supply network. The dielectric substrates are fixed by nylon support columns.

[0010] The isolation between the first feed port and the second feed port is improved by adopting a hierarchical and non-overlapping upper and lower feed network.

[0011] By using orthogonal first U-shaped transmission lines and fifth U-shaped transmission lines to couple and feed a cross-shaped slotted excitation rectangular dielectric block, the mode required for broadband co-polarization operation with high isolation is excited, achieving high transmit / receive isolation while realizing co-transmit / receive operation mode.

[0012] By adjusting the spacing between rectangular dielectric blocks in the antenna subarray and the spacing between antenna subarrays, and making the spacing between antenna subarrays smaller than the spacing between rectangular dielectric blocks in the antenna subarray, the coupling is effectively reduced while the sidelobes are lowered.

[0013] The upper-layer power supply network includes a first 90° dual-branch directional coupler and a second 90° dual-branch directional coupler with a planar structure, avoiding the problem of increased sidelobes caused by slotting.

[0014] This invention discloses a broadband co-circularly polarized transmit / receive antenna array for X-band airborne SAR. This antenna array achieves co-transmit and receive with right-hand circular polarization, achieving an isolation of >30dB between the transmit and receive ports. Furthermore, the antenna array operates over a wide frequency band, with a 40% relative bandwidth in the 7.2-11 GHz range. The reflection coefficients at both the transmit and receive ports are less than -10dB, and the axial ratios are less than 3dB. Moreover, the antenna array achieves stable gain performance in the 7.3-10.4 GHz operating band, with circular polarization gains at the transmit and receive ports exceeding 9dBic and 10dBic, respectively, within this band. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a 3D structural schematic diagram of a broadband co-circular polarized co-transmit / receive antenna array for X-band airborne SAR as described in this invention. Figure 2This is a schematic diagram of the upper-layer feed network structure of a broadband co-circular polarized co-transmit / receive antenna array for X-band airborne SAR as described in this invention. Figure 3 This is a schematic diagram of the lower-layer feed network structure of a broadband co-circular polarized co-transmit / receive antenna array for X-band airborne SAR as described in this invention. Figure 4 This is a schematic diagram of the antenna subarray and the first 90° coupler structure of a broadband co-circular polarized co-transmitter antenna array for X-band airborne SAR as described in this invention. Figure 5 This is an S-parameter curve of a broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR as described in this invention. Figure 6 This is a graph showing the axial ratio and gain of a broadband co-circularly polarized co-transmitter antenna array for X-band airborne SAR as described in this invention, as a function of frequency. Figure 7 This invention describes the radiation pattern of a broadband co-circularly polarized co-transmitter antenna array for X-band airborne SAR in the 7.5 GHz E-plane. Figure 8 This invention describes the radiation pattern of a broadband co-circularly polarized co-transmitter antenna array for X-band airborne SAR in the 8.5 GHz E-plane. Figure 9 This invention describes the radiation pattern of a broadband co-circularly polarized co-transmitter antenna array for X-band airborne SAR in the 9.5 GHz E-plane. In the diagram: 1. Rectangular dielectric resonator antenna array; 11. Antenna subarray; 111. First dielectric resonator antenna element; 1111. Rectangular dielectric block; 1112. First T-shaped dielectric block; 1113. Second T-shaped dielectric block; 112. Second dielectric resonator antenna element; 113. Third dielectric resonator antenna element; 114. Fourth dielectric resonator antenna element; 2. Dielectric substrate; 21. First dielectric substrate; 22. Second dielectric substrate; 23. Third dielectric substrate; 3. Dual-layer feed network; 31. Upper layer feed network. 311. First 180° Coupler; 312. First 90° Coupler; 3121. First Upper Coupler Line; 3122. First Lower Coupler Line; 3123. First Shorting Pin; 3124. First Ground Slot; 313. Second 90° Coupler; 314. First Orthogonal Sequential Rotating Feed Network; 3141. Second 180° Coupler; 3142. First 90° Two-Branch Directional Coupler; 3143. Second 90° Two-Branch Directional Coupler. 3144, First U-shaped transmission line; 3145, Second U-shaped transmission line; 3146, Third U-shaped transmission line; 3147, Fourth U-shaped transmission line; 315, Second orthogonal sequence rotating feed network; 316, Third orthogonal sequence rotating feed network; 317, Fourth orthogonal sequence rotating feed network; 318, First feed port; 32, Lower layer feed network; 321, Third 180° coupler; 322, Third 90° coupler; 323, Fourth 90° coupler; 324, Fifth orthogonal sequence rotating feed network; 3241, Fourth 180° coupler; 3242, Fifth 90° coupler; 3243, Sixth 90° coupler; 3244, Fifth U-shaped transmission line; 3245, Sixth U-shaped transmission line; 3246, Seventh U-shaped transmission line; 3247, Eighth U-shaped transmission line; 325, Sixth orthogonal sequence rotating feed network. 326. Seventh orthogonal sequential rotating feeder network; 327. Eighth orthogonal sequential rotating feeder network; 328. Second feeder port; 4. Cross-shaped slotted floor; 41. Grounding plane; 42. Cross-shaped slot; 5. Nylon support column. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0018] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0019] The technical specifications adopted in this invention are as follows: Operating frequency band: 7.2 - 11.0 GHz Polarization mode: Right-hand circular polarization 10-dB impedance bandwidth: >40% 30-dB isolation bandwidth: >40% 3-dB axial ratio bandwidth: >40% like Figure 1 The above diagram shows a broadband co-circular polarized co-transmitter antenna array for X-band airborne SAR. The antenna array includes a rectangular dielectric resonator antenna array 1, a dielectric substrate 2, a double-layer feed network 3, a cross-shaped slotted floor 4, and nylon support columns 5.

[0020] The rectangular dielectric resonator antenna array 1 is a 4×4 array, consisting of four antenna subarrays 11 of the same size and spacing. Each antenna subarray 11 includes a first dielectric resonator antenna element 111, a second dielectric resonator antenna element 112, a third dielectric resonator antenna element 113, and a fourth dielectric resonator antenna element 114, which are excited by rotating in an orthogonal order. The second dielectric resonator antenna element 112, the third dielectric resonator antenna element 113, and the fourth dielectric resonator antenna element 114 are formed by rotating the first dielectric resonator antenna element 111 counterclockwise by 90°, 180°, and 270°, respectively. The first dielectric resonator antenna element 111 consists of a rectangular dielectric block 1111, two first T-shaped dielectric blocks 1112 of the same size, and two second T-shaped dielectric blocks 1113 of the same size.

[0021] The dielectric substrate 2 is composed of a first dielectric substrate 21, a second dielectric substrate 22, and a third dielectric substrate 23. The first dielectric substrate 21 is located below the rectangular dielectric resonator antenna array 1.

[0022] The dual-layer power supply network 3 includes an upper power supply network 31 and a lower power supply network 32; the upper power supply network 31 is located on the upper surface of the second dielectric substrate 22; the lower power supply network 32 is located on the lower surface of the third dielectric substrate 23; the upper power supply network 31 is composed of a first 180° coupler 311, a first 90° coupler 312, a second 90° coupler 313, a first orthogonal sequence rotating power supply network 314, a second orthogonal sequence rotating power supply network 315, a third orthogonal sequence rotating power supply network 316, a fourth orthogonal sequence rotating power supply network 317, and a first power supply port 318; The second orthogonal sequential rotating feed network 315, the third orthogonal sequential rotating feed network 316, and the fourth orthogonal sequential rotating feed network 317 are formed by rotating the first orthogonal sequential rotating feed network 314 counterclockwise by 90°, 180°, and 270° respectively. The first orthogonal sequential rotating feed network 314 is composed of a second 180° coupler 3141, a first 90° dual-branch directional coupler 3142, a second 90° dual-branch directional coupler 3143, a first U-shaped transmission line 3144, a second U-shaped transmission line 3145, a third U-shaped transmission line 3146, and a fourth U-shaped transmission line 3147.

[0023] The lower-level power supply network 32 is composed of a third 180° coupler 321, a third 90° coupler 322, a fourth 90° coupler 323, a fifth orthogonal sequence rotating power supply network 324, a sixth orthogonal sequence rotating power supply network 325, a seventh orthogonal sequence rotating power supply network 326, an eighth orthogonal sequence rotating power supply network 327, and a second power supply port 328; the sixth orthogonal sequence rotating power supply network 325, the seventh orthogonal sequence rotating power supply network 326, the eighth orthogonal sequence rotating power supply network 327, and a second power supply port 328. The rotating power supply network 327 is composed of the fifth orthogonal sequential rotating power supply network 324 rotated counterclockwise by 90°, 180°, and 270° respectively; the fifth orthogonal sequential rotating power supply network 324 is composed of the fourth 180° coupler 3241, the fifth 90° coupler 3242, the sixth 90° coupler 3243, the fifth U-shaped transmission line 3244, the sixth U-shaped transmission line 3245, the seventh U-shaped dielectric resonator excitation transmission line 3246, and the eighth U-shaped transmission line 3247.

[0024] The first 90° coupler 312 includes a first upper coupling line 3121, a first lower coupling line 3122, a first shorting pin 3123, and a first ground groove 3124; The first feed port 318 is connected to the first 180° coupler 311 via a 50-ohm transmission line; the output port of the first 180° coupler 311 is connected to the first 90° coupler 312 and the second 90° coupler 313 respectively, forming a 180° phase difference; the output ports of the first 90° coupler 312 and the second 90° coupler 313 are connected to the first orthogonal sequence rotating feed network 314, the second orthogonal sequence rotating feed network 315, the third orthogonal sequence rotating feed network 316, and the fourth orthogonal sequence rotating feed network 317 respectively, forming the first stage between the antenna subarrays 11. Orthogonal sequential rotational feeding excitation; the output port of the second 180° coupler 3141 is connected to the first 90° dual-branch directional coupler 3142 and the second 90° dual-branch directional coupler 3143 respectively through 50-ohm transmission lines to form a 180° phase difference. The output ports of the first 90° dual-branch directional coupler 3142 and the second 90° dual-branch directional coupler 3143 are connected to the first U-shaped transmission line 3144, the second U-shaped transmission line 3145, the third U-shaped transmission line 3146, and the fourth U-shaped transmission line 3147 respectively to form the second-stage orthogonal sequential rotational feeding excitation within the antenna subarray 11.

[0025] The second feed port 328 is connected to the third 180° coupler 321 via a 50-ohm transmission line; the output port of the third 180° coupler 321 is connected to the third 90° coupler 322 and the fourth 90° coupler 323, forming a 180° phase difference; the output ports of the third 90° coupler 322 and the fourth 90° coupler 323 are respectively connected to the fifth orthogonal sequence rotating feed network 324, the sixth orthogonal sequence rotating feed network 325, the seventh orthogonal sequence rotating feed network 326, and the eighth orthogonal sequence rotating feed network 327, forming an antenna subarray. The first-stage orthogonal sequential rotational feeding excitation of the 11 subarrays is formed; the output port of the fourth 180° coupler 3241 is connected to the fifth 90° coupler 3242 and the sixth 90° coupler 3243 respectively through 50-ohm transmission lines to form a 180° phase difference. The output ports of the fifth 90° coupler 3242 and the sixth 90° coupler 3243 are connected to the fifth U-shaped transmission line 3244, the sixth U-shaped transmission line 3245, the seventh U-shaped dielectric resonator excitation transmission line 3246, and the eighth U-shaped transmission line 3247 respectively to form the orthogonal sequential rotational feeding excitation within the subarray 11.

[0026] The cross-shaped slotted floor 4 is located between the second dielectric substrate 22 and the third dielectric substrate 23, and is seamlessly connected; the cross-shaped slotted floor 4 includes a ground plane 41 and 16 cross-shaped slots 42; the 16 cross-shaped slots 42 are located below the 16 rectangular dielectric blocks 1111, and their center points are vertically aligned.

[0027] Furthermore, the rectangular dielectric block, the first T-shaped dielectric block, and the second T-shaped dielectric block all use dielectric substrates with a relative permittivity greater than 9 and a thickness greater than 3.5 mm. By loading two sets of first T-shaped dielectric blocks and second T-shaped dielectric blocks onto the rectangular dielectric block, the impedance bandwidth is effectively broadened. Ultimately, the rectangular dielectric block has a permittivity of 9.8 and dimensions of 10.5 mm × 9.5 mm × 3.6 mm; the first T-shaped dielectric block has a permittivity of 9.8 and dimensions of 10.5 mm × 1.5 mm × 3.6 mm and 1 mm × 0.5 mm × 3.6 mm; and the second T-shaped dielectric block has a permittivity of 9.8 and dimensions of 9.5 mm × 1.5 mm × 3.6 mm and 1 mm × 0.5 mm × 3.6 mm.

[0028] Furthermore, by employing the aforementioned dual-layer feeding network, two-stage sequential rotary feeding excitation is achieved, resulting in unidirectional circular polarization of the dual-port excitation and effectively broadening the impedance bandwidth and axial ratio bandwidth.

[0029] Furthermore, by employing the first 90° coupler, a flatter output phase can be obtained, effectively widening the axial ratio bandwidth.

[0030] Furthermore, all dielectric substrates are low-dielectric-constant thin substrates with a dielectric constant of less than 4 and a thickness of less than 1 mm. This design effectively reduces the linewidth of each part of the double-layer feed network, making the layout more flexible and effectively reducing coupling. The dielectric substrates are fixed by nylon support pillars. Ultimately, the dielectric constant of the first dielectric substrate is 3, and its dimensions are 136.4 mm × 136.4 mm × 0.73 mm; the dielectric constant of the second dielectric substrate is 3.5, and its dimensions are 136.4 mm × 136.4 mm × 0.43 mm; the dielectric constant of the third dielectric substrate is 3.5, and its dimensions are 136.4 mm × 136.4 mm × 0.43 mm; the diameter of the nylon support pillars is 2 mm.

[0031] Furthermore, by adopting a layered and non-overlapping design of upper and lower feed networks, the isolation between the first feed port and the second feed port is effectively improved.

[0032] Furthermore, by employing orthogonal first and fifth U-shaped transmission lines coupled to feed a cross-shaped slotted excitation rectangular dielectric block, the mode required for broadband co-polarization operation with high isolation can be effectively excited, achieving high transmit / receive isolation while realizing a co-transmit / receive operating mode. The final dimensions of the cross-shaped slot are 13.5mm × 0.9mm and 13mm × 1mm.

[0033] Furthermore, the upper-layer power supply network consists of a first 90° dual-branch directional coupler and a second 90° dual-branch directional coupler with a planar structure, which can effectively avoid the problem of increased sidelobe size caused by slotting.

[0034] Furthermore, by adjusting the spacing between the rectangular dielectric blocks in the antenna subarray and the spacing between the antenna subarrays, and making the spacing between the antenna subarrays smaller than the spacing between the rectangular dielectric blocks in the antenna subarray, the coupling can be effectively reduced while the sidelobes are lowered. The final spacing between the rectangular dielectric blocks in the antenna subarray is 26 mm, and the spacing between the antenna subarrays is 25.7 mm. The final overall size of the antenna array is 136.4 mm × 136.4 mm × 5.19 mm, which is only 3.27λ × 3.27λ × 0.12λ, where λ is the free wavelength corresponding to the lowest frequency.

[0035] like Figure 5 As shown, the broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR proposed in this invention exhibits a return loss greater than 10 dB at both the transmit and receive ports within the 7.2 GHz ~ 11.0 GHz (41.8%) frequency band, demonstrating good impedance matching of the antenna across this wide frequency range; simultaneously, the isolation between the transmit and receive ports is greater than 30 dB.

[0036] like Figure 6 The figure shows the axial ratio and gain curves as a function of frequency for a broadband co-circularly polarized co-transmitter antenna array for X-band airborne SAR according to the present invention. The results show that the axial ratio of the antenna array proposed in this invention is less than 3dB in the 7.2GHz ~ 11.0 GHz (41.8%) frequency band, indicating that the proposed broadband co-circularly polarized co-transmitter antenna array has good circular polarization performance. Within the 7.2GHz ~ 11.0 GHz frequency band, the transmit gain is greater than 9 dBic, reaching a maximum of 15.1 dBic; the receive gain is greater than 10 dBic, reaching a maximum of 14.3 dBic.

[0037] Figures 7-9 The diagram shows the radiation pattern of a broadband co-circularly polarized co-transmitter antenna array for X-band airborne SAR described in this invention at 7.5 GHz, 8.5 GHz, and 9.5 GHz. When φ = 0°, at 7.5 GHz, the difference between the right-hand circular polarization and left-hand circular polarization of the transmitting antenna is 27.2 dB, and the difference between the right-hand circular polarization and left-hand circular polarization of the receiving antenna is 30.7 dB; at 8.5 GHz, the difference between the right-hand circular polarization and left-hand circular polarization of the transmitting antenna is 21.1 dB, and the difference between the right-hand circular polarization and left-hand circular polarization of the receiving antenna is 35.0 dB; at 9.5 GHz, the difference between the right-hand circular polarization and left-hand circular polarization of the transmitting antenna is 16.9 dB, and the difference between the right-hand circular polarization and left-hand circular polarization of the receiving antenna is 37.7 dB. This demonstrates that the broadband co-circularly polarized co-transmitter antenna array proposed in this invention has excellent right-hand circularly polarized signal transmission and reception capabilities.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR, characterized in that, include: A rectangular dielectric resonator antenna array (1), a dielectric substrate (2), a double-layer feed network (3), a cross-shaped slotted floor (4), and nylon support columns (5); The rectangular dielectric resonator antenna array (1) is a 4×4 array, comprising four antenna subarrays (11) of the same size and spacing; each antenna subarray (11) includes a first dielectric resonator antenna element (111), a second dielectric resonator antenna element (112), a third dielectric resonator antenna element (113), and a fourth dielectric resonator antenna element (114), which are excited by rotating in an orthogonal order; the second dielectric resonator antenna element (112), the third dielectric resonator antenna element (113), and the fourth dielectric resonator antenna element (114) are formed by rotating the first dielectric resonator antenna element (111) counterclockwise by 90°, 180°, and 270° respectively; the first dielectric resonator antenna element (111) includes a rectangular dielectric block (1111), two first T-shaped dielectric blocks (1112) of the same size, and two second T-shaped dielectric blocks (1113) of the same size. The dielectric substrate (2) includes a first dielectric substrate (21), a second dielectric substrate (22), and a third dielectric substrate (23), wherein the first dielectric substrate (21) is located below the rectangular dielectric resonator antenna array (1); The dual-layer power supply network (3) includes an upper power supply network (31) and a lower power supply network (32); the upper power supply network (31) is located on the upper surface of the second dielectric substrate (22); the lower power supply network (32) is located on the lower surface of the third dielectric substrate (23); the upper power supply network (31) includes a first 180° coupler (311), a first 90° coupler (312), a second 90° coupler (313), a first orthogonal sequence rotating power supply network (314), a second orthogonal sequence rotating power supply network (315), a third orthogonal sequence rotating power supply network (316), a fourth orthogonal sequence rotating power supply network (317), and a first power supply port (318). The second orthogonal sequence rotating feed network (315), the third orthogonal sequence rotating feed network (316), and the fourth orthogonal sequence rotating feed network (317) are formed by rotating the first orthogonal sequence rotating feed network (314) counterclockwise by 90°, 180°, and 270° respectively; the first orthogonal sequence rotating feed network (314) includes a second 180° coupler (3141), a first 90° dual-branch directional coupler (3142), a second 90° dual-branch directional coupler (3143), a first U-shaped transmission line (3144), a second U-shaped transmission line (3145), a third U-shaped transmission line (3146), and a fourth U-shaped transmission line (3147); The lower-level feed network (32) includes a third 180° coupler (321), a third 90° coupler (322), a fourth 90° coupler (323), a fifth orthogonal sequence rotating feed network (324), a sixth orthogonal sequence rotating feed network (325), a seventh orthogonal sequence rotating feed network (326), an eighth orthogonal sequence rotating feed network (327), and a second feed port (328); the sixth orthogonal sequence rotating feed network (325), the seventh orthogonal sequence rotating feed network (326), and the eighth orthogonal sequence rotating feed network (327) are all part of the feed network. The sequential rotating feed network (327) is formed by rotating the fifth orthogonal sequential rotating feed network (324) counterclockwise by 90°, 180°, and 270° respectively; the fifth orthogonal sequential rotating feed network (324) includes a fourth 180° coupler (3241), a fifth 90° coupler (3242), a sixth 90° coupler (3243), a fifth U-shaped transmission line (3244), a sixth U-shaped transmission line (3245), a seventh U-shaped dielectric resonator excitation transmission line (3246), and an eighth U-shaped transmission line (3247); The first 90° coupler (312) includes a first upper coupling line (3121), a first lower coupling line (3122), a first shorting pin (3123), and a first floor groove (3124). The first feed port (318) is connected to the first 180° coupler (311) via a 50-ohm transmission line; the output port of the first 180° coupler (311) is connected to the first 90° coupler (312) and the second 90° coupler (313) respectively, forming a 180° phase difference; the output ports of the first 90° coupler (312) and the second 90° coupler (313) are connected to the first orthogonal sequence rotating feed network (314), the second orthogonal sequence rotating feed network (315), the third orthogonal sequence rotating feed network (316), and the fourth orthogonal sequence rotating feed network (317) respectively, forming the first phase difference between the antenna subarrays (11). The first-stage orthogonal sequential rotational feeding excitation; the output port of the second 180° coupler (3141) is connected to the first 90° dual-branch directional coupler (3142) and the second 90° dual-branch directional coupler (3143) respectively through 50-ohm transmission lines to form a 180° phase difference, and the output ports of the first 90° dual-branch directional coupler (3142) and the second 90° dual-branch directional coupler (3143) are connected to the first U-shaped transmission line (3144), the second U-shaped transmission line (3145), the third U-shaped transmission line (3146), and the fourth U-shaped transmission line (3147) respectively to form the second-stage orthogonal sequential rotational feeding excitation in the antenna subarray (11); The second feed port (328) is connected to the third 180° coupler (321) via a 50-ohm transmission line; the output port of the third 180° coupler (321) is connected to the third 90° coupler (322) and the fourth 90° coupler (323) to form a 180° phase difference; the output ports of the third 90° coupler (322) and the fourth 90° coupler (323) are respectively connected to the fifth orthogonal sequence rotating feed network (324), the sixth orthogonal sequence rotating feed network (325), the seventh orthogonal sequence rotating feed network (326), and the eighth orthogonal sequence rotating feed network (327) to form an antenna subarray. (11) The first-stage orthogonal sequential rotational feeding excitation; the output port of the fourth 180° coupler (3241) is connected to the fifth 90° coupler (3242) and the sixth 90° coupler (3243) respectively through 50-ohm transmission lines to form a 180° phase difference. The output ports of the fifth 90° coupler (3242) and the sixth 90° coupler (3243) are connected to the fifth U-shaped transmission line (3244), the sixth U-shaped transmission line (3245), the seventh U-shaped dielectric resonator excitation transmission line (3246), and the eighth U-shaped transmission line (3247) respectively to form the orthogonal sequential rotational feeding excitation in the antenna subarray (11); The cross-shaped slotted floor (4) is located between the second dielectric substrate (22) and the third dielectric substrate (23) and is seamlessly connected; the cross-shaped slotted floor (4) includes a ground plane (41) and 16 cross-shaped slots (42); the 16 cross-shaped slots (42) are located below the 16 rectangular dielectric blocks (1111) with their center points vertically aligned.

2. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: By loading two sets of first T-shaped dielectric blocks (1112) and second T-shaped dielectric blocks (1113) onto the rectangular dielectric block (1111), the impedance bandwidth is effectively widened.

3. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: By employing the dual-layer feed network (3), two-stage sequential rotary feed excitation is achieved, resulting in unidirectional circular polarization of the dual-port excitation and broadening the impedance bandwidth and axial ratio bandwidth.

4. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: By employing the first 90° coupler (312), a flat phase difference between the output ports is obtained, thus widening the axial ratio bandwidth.

5. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: The dielectric substrates (2) are all made of low dielectric constant thin substrates with a dielectric constant of less than 4 and a thickness of less than 1 mm. This setting reduces the line width of each part in the double-layer power supply network (3). The dielectric substrates (2) are fixed by nylon support columns (5).

6. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: The isolation between the first feed port (318) and the second feed port (328) is improved by using an upper-layer feed network (31) and a lower-layer feed network (32) in a layered and non-overlapping manner.

7. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: By using orthogonal first U-shaped transmission line (3144) and fifth U-shaped transmission line (3244) to couple and feed cross-shaped slot (42) to excite rectangular dielectric block (1111), the mode required for broadband co-polarization operation with high isolation is excited, achieving high transmit / receive isolation while realizing co-transmit / receive operation mode.

8. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: By adjusting the spacing between rectangular dielectric blocks (1111) in the antenna subarray (11) and the spacing between antenna subarrays (11), and making the spacing between antenna subarrays (11) smaller than the spacing between rectangular dielectric blocks (1111) in the antenna subarray (11), the sidelobes are reduced while effectively reducing coupling.

9. A broadband co-circularly polarized co-transmit / receive antenna array for X-band airborne SAR according to claim 1, characterized in that: The upper-layer power supply network (31) includes a first 90° dual-branch directional coupler (3142) and a second 90° dual-branch directional coupler (3143) with a planar structure, to avoid the problem of increased sidelobe due to slotting.

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