Low-profile low-RCS circularly polarized double-folded transmission array antenna

Abstract

The invention discloses a low-profile low-RCS (radar cross section) circular polarization double-folded transmission array antenna, which comprises a wave-absorbing type frequency selection polarizer and a double-folded transmission array antenna, and is characterized in that the wave-absorbing type frequency selection polarizer is positioned above the double-folded transmission array antenna; the wave-absorbing type frequency selection polarizer comprises a loss layer and a linear circular polarization converter with a frequency selection characteristic, wherein the loss layer and the linear circular polarization converter are separated by an air gap layer; the double-folded transmission array antenna comprises an integrated reflection-transmission metasurface and a polarization conversion metasurface, and the integrated reflection-transmission metasurface and the polarization conversion metasurface are separated by an air gap layer. According to the circularly polarized antenna, the single-station RCS reduction performance of more than 10 dB is achieved within the broadband range of 6.8-21.9 GHz, meanwhile, the radiation gain can be improved, the profile can be reduced, and the circularly polarized antenna has the advantages of being wide in band, low in profile, high in gain and low in RCS.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, specifically relating to a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer and its application. Background Technology

[0002] High-gain circularly polarized antennas are becoming increasingly important for meeting the requirements of satellite communication systems. Reflect array (RA) and transmit array (TA) antennas are widely used due to their low cost and high gain. The simplest way to achieve high gain is to increase the radiating aperture, but this is unacceptable for stealth platforms because it results in a high radar cross section (RCS). In particular, circularly polarized antennas are a highly attractive choice in communication systems due to their advantages in polarization matching and anti-jamming. Therefore, achieving both low RCS and high gain performance in circularly polarized RA / TA antennas is crucial.

[0003] In recent years, frequency-selective absorbers (FSRs) have become an attractive method for antennas to achieve out-of-band RCS reduction. Currently, many FSR structures are integrated with RA / TA to achieve low RCS performance; however, such antennas suffer from high profile height. To address this issue, a relatively low-profile (half the focal length F) low-RCS folded reflectarray antenna was proposed in J. Xu, H.-X. Xu, H. Luo, Y. Wang, and C. Wang, “A low-RCS folded reflectarray combining dual-metasurface and rasorber,” IEEE Antennas Wireless Propag. Lett., vol. 21, no. 12, pp. 2462–2466, 2022., but it lacks bistatic RCS reduction capability for cross-polarized incident waves. Furthermore, most low RCS reflection array antennas, transmission array antennas, and folded reflection array antennas are currently linearly polarized antennas; however, there are relatively few research results on RA / TA antennas that achieve low RCS circular polarization.

[0004] While a low-RCS circularly polarized reflectarray antenna was proposed in D. Kundu, A. Parameswaran, H.S. Sonalikar, D. Bhattacharya, and S. Gupta, “A low-RCS circularly polarized reflectarray antenna with a linearly polarized feed,” IEEE Trans. Antennas Propag., vol. 71, no. 8, pp. 6501–6512, 2023, the operating bandwidth of circular polarization is very narrow, only 3.3%, and the profile height is relatively high, resulting in limited RCS reduction bandwidth.

[0005] Therefore, designing a RA / TA with broadband circular polarization operation, low profile, and broadband RCS reduction performance is a technical challenge that needs to be solved. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the purpose of this invention is to propose a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on a microwave-absorbing frequency selective polarizer.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer is composed of an absorbing frequency selective polarizer and a double-folded transmission array antenna. The absorbing frequency selective polarizer is located above the double-folded transmission array antenna, and the overall structure is fed by a linearly polarized feed horn.

[0009] The absorbing frequency selective polarizer includes a loss layer and a linear-circular polarization converter with frequency selective characteristics.

[0010] The double-folded transmission array antenna includes an integrated reflective-transmitting metasurface and a polarization-converting metasurface, with each layer separated by an air gap layer.

[0011] The aperture surface of the linearly polarized feed horn is on the same horizontal plane as the lower surface of the integrated reflective-transmitting metasurface.

[0012] The loss layer includes a first metal layer and a first dielectric layer, wherein the first metal layer is printed on the upper surface of the first dielectric layer;

[0013] The first metal layer consists of a square metal ring at the center, a square patch inside the square metal ring, and four T-shaped microstrip lines outside the square metal ring. The four T-shaped microstrip lines are all located on the axis of symmetry of the square metal ring passing through the midpoint of its side length. The longitudinal portion of the T-shaped microstrip line is longer than the transverse portion, and a lumped resistor is embedded in the longitudinal portion and connected to the square metal ring.

[0014] The linear-circular polarization converter includes a second metal layer, a second dielectric layer, a third metal layer, a third dielectric layer, and a fourth metal layer;

[0015] The metal patterns on the second and fourth metal layers are exactly the same, consisting of two arc-shaped metal rings and a first rectangular patch located in the center; the long side of the first rectangular patch points to the inside of the arc-shaped metal ring and is perpendicular to its edge, while the wide side is parallel to its edge.

[0016] The third metal layer consists of a patch with a central circular groove and a second rectangular patch located at the center of the circular groove; the diameter of the circular groove on the third metal layer is the same as the outer diameter of the arc-shaped metal ring on the second metal layer.

[0017] The second, third, and fourth metal layers are symmetrical about the diagonal, wherein the angle between the long side of the first rectangular patch and the positive y-axis is 45° (counterclockwise is positive), and the angle between the long side of the second rectangular patch and the positive y-axis is -45° (clockwise is negative).

[0018] The integrated reflective-transmitting metasurface includes a fifth metal layer, a fourth dielectric layer, a sixth metal layer, a fifth dielectric layer, and a seventh metal layer;

[0019] The fifth metal layer is composed of rectangular strips spaced s2 = 0.35 mm apart, with a long side of p2 = 4 mm and a wide side of s3 = 0.2 mm; the seventh metal layer is obtained by rotating the fifth metal layer 90° around the z-axis.

[0020] The sixth metal layer is an open C-shaped ring with an outer ring radius of r5 = 1.61 mm, an inner ring radius of r4 = 1.09 mm, an opening angle of θ = 10°-200°, and an opening direction with an angle of 45° or 135° with the positive y-axis.

[0021] The opening angle of the C-shaped ring on the sixth metal layer is determined by the unit position; according to the formula: The required phase compensation value at different unit locations can be calculated;

[0022] Where m and n represent the unit position, λ0 represents the wavelength of the center frequency, p is the unit period, and F is the focal length; then, based on the correspondence between the opening angle and the phase compensation value, the opening angle of the C-shaped ring at each unit position is determined.

[0023] The polarization conversion metasurface includes an eighth metal layer, a sixth dielectric layer, and a metal ground plane;

[0024] The eighth metal layer is a third rectangular patch with a long side of l7 = 3.7 mm, a wide side of w7 = 0.6 mm, and an angle of -45° between the long side and the positive y-axis (clockwise is negative).

[0025] The linearly polarized feed horn has 10-dB beamwidths of 78.3° and 71.1° in the E and H planes at 29 GHz, respectively, and a gain of 13 dBi. The unit period of the loss layer is p1 = 8 mm. The unit periods of the linear circular polarization converter, the integrated reflective-transmitting metasurface, and the polarization conversion metasurface are the same, all being p2 = 4 mm. The resistance of the lumped resistor is R = 150 Ω.

[0026] The first dielectric layer is composed of a Rogers 5880 dielectric substrate with a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of h1 = 0.508 mm; the second, third, fourth, fifth, and sixth dielectric layers are all composed of an SJ9294 dielectric substrate with a dielectric constant of 2.94 and a loss tangent of 0.0012; the thickness of the second and third dielectric layers is h2 = 0.508 mm; the thickness of the fourth and fifth dielectric layers is h3 = 1.016 mm; and the thickness of the sixth dielectric layer is h4 = 1.524 mm.

[0027] The first dielectric layer and the second dielectric layer, the third dielectric layer and the fourth dielectric layer, and the fifth dielectric layer and the sixth dielectric layer are all separated by air gap layers, with the heights of the air gap layers being t1 = 2.5 mm, t2 = 2 mm, and t3 = 15 mm, respectively.

[0028] While achieving RCS reduction performance of over 10dB in the 6.8-21.9GHz broadband range, it can also achieve circular polarization operation and radiation gain improvement in the 26-30.8GHz broadband range, featuring broadband, low profile, high gain and low RCS.

[0029] An application of a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on a microwave-absorbing frequency selective polarizer, which operates with circular polarization in a broadband range of 26-30.8 GHz and is used for low-detectability Ka-band satellite communication applications in a broadband range of 6.8-21.9 GHz.

[0030] Compared with existing technologies, it has the following beneficial effects:

[0031] 1. This invention designs a linear-to-circular polarization converter that maintains in-band linear-to-circular polarization conversion while exhibiting good frequency selectivity characteristics; when integrated with a loss layer, it forms an absorbing frequency selective polarizer, simultaneously achieving in-band linear-to-circular polarization conversion and out-of-band absorption.

[0032] 2. This invention combines an absorbing frequency selective polarizer with a double-folded transmission array antenna, achieving out-of-band RCS reduction over a wide bandwidth while maintaining good in-band radiation characteristics of the antenna.

[0033] 3. The double-fold design of the transmission array antenna in this invention is specifically manifested in that the electromagnetic waves emitted by the feed horn are reflected back and forth three times between the upper and lower surfaces of the transmission array antenna, thereby reducing the antenna profile to one-quarter of the original while still maintaining a high aperture efficiency.

[0034] 4. This invention operates in the Ka band (26-30.8GHz) and has an RCS reduction capability of more than 10dB in the frequency range of 6.8-21.9GHz, which can meet the low detectability requirements of Ka band satellite communication applications. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the structure of a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer, provided in an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the unit structure of an absorbing frequency selective polarizer provided in an embodiment of the present invention.

[0038] Figure 3 This is a schematic diagram of the unit structure of the loss layer provided in an embodiment of the present invention.

[0039] Figure 4 This is a schematic diagram of the unit structure of a linear-circular polarization converter provided in an embodiment of the present invention.

[0040] Figure 5(a) shows the S-parameter simulation results of the absorbing frequency selective polarizer provided in the embodiment of the present invention.

[0041] Figure 5(b) shows the simulation results of the absorption rate of the frequency selective polarizer provided in the embodiment of the present invention.

[0042] Figure 6 This is a schematic diagram of the unit structure of the integrated reflective-transmitting metasurface provided in an embodiment of the present invention.

[0043] Figure 7 The following are schematic diagrams of other configurations of the open C-shaped ring in the integrated reflective-transmitting metasurface provided in the embodiments of the present invention, wherein (a) is an I-shaped structure and (b) is a cross-shaped structure.

[0044] Figure 8(a) shows the simulation results of the reflection amplitude and phase of the integrated reflective-transmitting metasurface provided in the embodiment of the present invention.

[0045] Figure 8(b) shows the simulation results of the transmission amplitude and phase of the integrated reflective-transmitting metasurface provided in the embodiment of the present invention.

[0046] Figure 9(a) is a schematic diagram of the phase distribution required for different unit positions provided in the embodiments of the present invention.

[0047] Figure 9(b) is a schematic diagram of the distribution of C-shaped rings with openings at different unit positions provided in the embodiments of the present invention.

[0048] Figure 10 This is a schematic diagram of the unit structure of the polarization conversion metasurface provided in an embodiment of the present invention.

[0049] Figure 11 The following are schematic diagrams of other configurations of the third rectangular patch on the top layer of the polarization conversion metasurface provided in the embodiments of the present invention, wherein (a) is a double L-shaped structure and (b) is an arrow-shaped structure.

[0050] Figure 12(a) shows the normalized gain simulation results of the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer provided in the embodiment of the present invention at 29 GHz in the xoz plane.

[0051] Figure 12(b) shows the normalized gain simulation results of the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer provided in the embodiment of the present invention at 29 GHz in the yoz plane.

[0052] Figure 13(a) shows the simulation results of the actual gain and aperture efficiency of the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on the absorbing frequency selective polarizer provided in the embodiment of the present invention.

[0053] Figure 13(b) shows the simulation results of the axial ratio of the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on the absorbing frequency selective polarizer provided in the embodiment of the present invention.

[0054] Figure 14 The simulation results show the comparison of the single-station RCS of a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer, as provided in the embodiments of the present invention, with that of a metal plate of the same size.

[0055] The following are the labeling instructions in the diagram: 1. Linearly polarized feed horn; 2. Loss layer; 21. First metal layer; 211. Square metal ring; 212. Square patch; 213. T-shaped microstrip line; 213a. Vertical portion; 213b. Lateral portion; 214. Lumped resistor; 22. First dielectric layer; 3. Linearly polarized converter; 31. Second metal layer; 311. Arc-shaped metal ring; 312. First rectangular patch; 32. Second dielectric layer; 33. Third metal layer; 331. Patch with a circular groove in the center; 332. Second rectangular patch; 34. Third dielectric layer; 35. Fourth metal layer; 4. Integrated reflective-transmitting metasurface; 41. Fifth metal layer; 42. Fourth dielectric layer; 43. Sixth metal layer; 44. Fifth dielectric layer; 45. Seventh metal layer; 5. Polarization conversion metasurface; 51. Third rectangular patch; 52. Sixth dielectric layer; 53. Metal ground plane. Detailed Implementation

[0056] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0057] This invention discloses a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer, such as... Figure 1-14 As shown.

[0058] The present invention relates to a low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer. The antenna consists of an absorbing frequency selective polarizer and a double-folded transmission array antenna, with the absorbing frequency selective polarizer positioned above the double-folded transmission array antenna. The overall antenna structure is fed by a linearly polarized feed horn 1.

[0059] The absorbing frequency selective polarizer includes a loss layer 2 and a linear-circular polarization converter 3 with frequency selective characteristics;

[0060] The double-folded transmission array antenna includes an integrated reflective-transmitting metasurface 4 and a polarization-converting metasurface 5, with each layer separated by an air gap layer.

[0061] The aperture surface of the linearly polarized feed horn 1 is on the same horizontal plane as the lower surface of the integrated reflective-transmitting metasurface.

[0062] In one embodiment, such as Figure 1As shown, the structure involved in this invention consists of a double-folded transmission array antenna and a microwave-absorbing frequency-selective polarizer loaded on top, separated by an air gap layer with a height t2 = 2 mm; the linearly polarized feed horn 1 used has 10-dB beamwidths of 78.3° and 71.1° in the E-plane and H-plane at 29 GHz, respectively, with a gain of 13 dBi; the overall antenna structure has dimensions of 112 mm × 112 mm and a cross-sectional height of 24.58 mm (excluding the linearly polarized feed horn 1).

[0063] Furthermore, such as Figure 2 As shown, the unit period of the top loss layer 2 in the absorbing frequency selective polarizer is twice that of the bottom linear-circular polarizer 3, and the height of the air gap layer between them is t1 = 2.5 mm.

[0064] The loss layer 2 includes a first metal layer 21 and a first dielectric layer 22, with the first metal layer 21 printed on the upper surface of the first dielectric layer 22;

[0065] The first metal layer 21 consists of a square metal ring 211 located at the center, a square patch 212 located inside the square metal ring, and four T-shaped microstrip lines 213 located outside the square metal ring. The four T-shaped microstrip lines 213 are all located on the axis of symmetry of the square metal ring 211 passing through the midpoint of its side length. The longitudinal portion 213b of the T-shaped microstrip line 213 is longer than the transverse portion 213a, and the longitudinal portion 213b embeds a lumped resistor 214 and is connected to the square metal ring 211.

[0066] In a specific embodiment, see Figure 3 The cell period of loss layer 2 is p1 = 8 mm. The outer ring length of the square metal ring 211 located in the center is l1 = 3.8 mm and the width is w1 = 0.3 mm. The side length of the square patch 212 located inside the square metal ring is l2 = 2 mm. The length of the transverse portion 213a of the T-shaped microstrip line 213 located outside the square metal ring is l3 = 1.8 mm and the width is w3 = 0.3 mm. The length of the longitudinal portion 213b is l4 = 1.7 mm and the width is w4 = 0.3 mm. The lumped resistor 214 embedded in the longitudinal portion 213b of the T-shaped microstrip line 213 adopts the 0201 package size and has a resistance value of R = 150 Ω.

[0067] Furthermore, the first dielectric layer 22 is composed of a Rogers 5880 dielectric substrate with a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of h1 = 0.508 mm.

[0068] The linear-circular polarization converter 3 includes a second metal layer 31, a second dielectric layer 32, a third metal layer 33, a third dielectric layer 34, and a fourth metal layer 35;

[0069] The metal patterns on the second metal layer 31 and the fourth metal layer 35 are exactly the same, both consisting of two arc-shaped metal rings 311 and a first rectangular patch 312 located in the center; the long side of the first rectangular patch 312 points to the inside of the arc-shaped metal rings 311 and remains perpendicular to their edges, while the wide side remains parallel to their edges.

[0070] The third metal layer 33 is composed of a patch 331 with a central circular groove and a second rectangular patch 332 located at the center of the circular groove; the diameter of the circular groove on the third metal layer 33 is the same as the outer diameter of the arc-shaped metal ring 311 on the second metal layer 31.

[0071] The second metal layer 31, the third metal layer 33, and the fourth metal layer 35 are symmetrical about the diagonal. The angle between the long side of the first rectangular patch 312 and the positive y-axis is 45° (counterclockwise is positive), and the angle between the long side of the second rectangular patch 332 and the positive y-axis is -45° (clockwise is negative).

[0072] In a specific embodiment, see Figure 4 The unit period of the linear-circular polarization converter 3 is p2 = 4 mm; the inner ring radius of the arc-shaped metal ring 311 on the second metal layer 31 is r1 = 1 mm and the outer ring radius is r2 = 1.5 mm; the length of the first rectangular patch 312 located at the center is l5 = 1.1 mm and the width is w5 = 0.5 mm; the distance between the two arc-shaped metal rings 311 is s1 = 1.32 mm; the radius of the circular groove at the center of the patch 331 located on the third metal layer 33 is r3 = 1.5 mm; the length of the second rectangular patch 332 is l6 = 1.8 mm and the width is w6 = 0.5 mm.

[0073] Furthermore, the second dielectric layer 32 and the third dielectric layer 34 are composed of an SJ9294 dielectric substrate with a dielectric constant of 2.94, a loss tangent of 0.0012, and a thickness of h2 = 0.508 mm.

[0074] Furthermore, please see [link / reference] Figure 2 After integrating the loss layer 2 with the linear-circular polarization converter 3, an absorbing frequency selective polarizer is obtained.

[0075] To verify the in-band linear-to-circular polarization conversion capability and out-of-band absorption capability of the frequency selective absorbing polarizer in this embodiment of the invention, its S-parameters and absorption rate were simulated, and the results are shown in Figure 5.

[0076] Specifically, referring to Figure 5(a), it can be observed that for the y-polarized wave emitted by the double-folded transmission array antenna, after passing through the absorber-type frequency selective polarizer, the transmission coefficient S of the y-polarized wave converted into a left-hand circular polarization (LHCP) wave is... 21y_LHCPThe reflection coefficient S of the y-polarized wave is consistently greater than -1.8 dB in the 26-32 GHz frequency range. 11y_y It remains below -10dB within the 8-32GHz frequency range.

[0077] Specifically, referring to Figure 5(b), it can be seen that the absorption rate of the frequency selective polarizer remains above 80% in the frequency range of 6.91-21.13 GHz (101.4%); moreover, when the oblique incident angle is within 30°, the absorption rate of 80% remains basically stable, showing good angular stability.

[0078] The integrated reflective-transmitting metasurface 4 includes a fifth metal layer 41, a fourth dielectric layer 42, a sixth metal layer 43, a fifth dielectric layer 44, and a seventh metal layer 45;

[0079] The fifth metal layer 41 is composed of rectangular strips spaced s3 = 0.35 mm apart, with a long side p2 = 4 mm and a wide side s3 = 0.2 mm; the seventh metal layer 45 is obtained by rotating the fifth metal layer 41 by 90° around the z-axis.

[0080] The sixth metal layer 43 is an open C-shaped ring with an outer ring radius r5 = 1.61 mm, an inner ring radius r4 = 1.09 mm, an opening angle θ = 10°-200°, and an opening direction with an angle of 45° or 135° with the positive y-axis.

[0081] The opening angle of the C-shaped ring 43 on the sixth metal layer is determined by the unit position; according to the formula: The required phase compensation value at different unit locations can be calculated;

[0082] Where m and n represent the unit position, λ0 represents the wavelength of the center frequency, p is the unit period, and F is the focal length; then, based on the correspondence between the opening angle and the phase compensation value, the opening angle of the C-shaped ring 43 at each unit position is determined.

[0083] The correspondence between the aperture angle and the phase compensation value is shown in Figure 8(b), where the transmission phase is the phase compensation value.

[0084] In a specific embodiment, see Figure 6 The unit period p2 of the integrated reflective-transmitting metasurface 4 is 4 mm; the open C-shaped ring 43 on the sixth metal layer has two states: when the angle between the opening direction and the positive y-axis is 45°, it is unit 0; when the angle between the opening direction and the positive y-axis is 135°, it is unit 1, and the transmission phase difference between unit 0 and unit 1 is 180°.

[0085] Furthermore, the fourth dielectric layer 42 and the fifth dielectric layer 44 are composed of an SJ9294 dielectric substrate with a dielectric constant of 2.94, a loss tangent of 0.0012, and a thickness of h3 = 1.016 mm.

[0086] In this embodiment of the invention, the open C-shaped ring 43 on the sixth metal layer can also have other configurations to achieve the same effect; see [link to relevant documentation]. Figure 7 The I-shaped structure (a) and the cross-shaped structure (b) are tilted at 45 degrees.

[0087] In order to realize the double-fold design of the transmission array antenna in the embodiment of the present invention, the integrated reflective-transmitting metasurface 4 needs to achieve total reflection of the incident y-polarized wave and convert the incident x-polarized wave into y-polarized transmission.

[0088] Furthermore, in order to convert the spherical wave emitted by the linearly polarized feed horn 1 into a plane wave, the integrated reflective-transmitting metasurface 4 needs to perform phase compensation on the transmitted y-polarized wave, which is achieved by changing the opening angle θ and opening direction (45° or 135°) of the C-shaped ring 43.

[0089] To verify the reflection and transmission characteristics of the integrated reflective-transmitting metasurface 4 in this embodiment of the invention, the simulation results are shown in Figure 8.

[0090] Specifically, referring to Figure 8(a), it can be seen that the reflection amplitude of the integrated reflective-transmitting metasurface 4 remains within -0.01dB in the frequency range of 26-32GHz, the reflection phase is around 180°, and the reflection characteristics remain stable when the oblique incident angle is within 30°, showing good angular stability.

[0091] Specifically, referring to Figure 8(b), it can be seen that when the opening angle θ of the C-shaped ring changes from 0° to 200°, and the opening direction changes from 45° to 135°, a continuous 360° change in the transmission phase can be achieved, and the transmission amplitude remains within -3dB throughout the entire change process.

[0092] Furthermore, the required phase compensation values ​​at different unit locations are calculated according to the formula, and then mapped one-to-one with the distribution of the open C-shaped ring 43. The final phase distribution and the distribution of the open C-shaped ring 43 are as follows: Figure 9(a) and 9(b) As shown.

[0093] The polarization conversion metasurface 5 includes an eighth metal layer 51, a sixth dielectric layer 52, and a metal ground plane 53;

[0094] Air gaps separate the first dielectric layer 22 from the second dielectric layer 32, the third dielectric layer 34 from the fourth dielectric layer 42, and the fifth dielectric layer 44 from the sixth dielectric layer 52.

[0095] The eighth metal layer 51 is a third rectangular patch with a long side l7 = 3.7 mm and a wide side w7 = 0.6 mm. The angle between the long side and the positive y-axis is -45° (negative for clockwise).

[0096] In a specific embodiment, see Figure 10 The unit cell period of the polarization conversion metasurface 5 is p2 = 4 mm; the sixth dielectric layer 52 is composed of an SJ9294 dielectric substrate with a dielectric constant of 2.94, a loss tangent of 0.0012, and a thickness of h4 = 1.524 mm.

[0097] In this embodiment of the invention, the third rectangular patch 51 on the eighth metal layer can also have other configurations to achieve the same effect; see [link to relevant documentation]. Figure 11 The double L-shaped structure (a) and arrow-shaped structure (b) are symmetrical about the diagonal.

[0098] Furthermore, by loading the integrated reflective-transmitting metasurface 4 on top of the polarization conversion metasurface 5, separated by an air gap layer with a height of t3 = 15 mm, a double-folded transmission array antenna can be obtained.

[0099] To verify the radiation characteristics of the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on the absorbing frequency selective polarizer, the normalized gain pattern, actual gain, aperture efficiency, and axial ratio of the xoz and yoz planes of the embodiment of the present invention at 29 GHz were simulated, and the results are shown in Figures 12 and 13.

[0100] Specifically, referring to Figures 12(a) and 12(b), it can be observed that at 29 GHz, the 3-dB beamwidths of the antenna in the xoz and yoz planes are 6.1° and 5.4°, respectively. Furthermore, the cross-polarization in the wide-side radiation direction is less than -20 dB, and the sidelobe level remains essentially below -10 dB.

[0101] Specifically, referring to Figures 13(a) and 13(b), it can be seen that the antenna provides a 20.7% 3-dB gain bandwidth (26-32 GHz), with a peak gain of 26.1 dB at 31 GHz, corresponding to a peak aperture efficiency of 30.3%. Furthermore, the 3-dB axial ratio bandwidth in the 26-30.8 GHz frequency range is 16.9%.

[0102] To verify the out-of-band RCS reduction capability of the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency-selective polarizer, the monostatic RCS of the antenna in this embodiment was simulated and compared with that of a metal plate of the same size. The results are as follows: Figure 14 As shown.

[0103] Specifically, see Figure 14 It can be observed that, compared to a metal plate of the same size, the antenna achieves an RCS reduction of more than 10dB in the 6.8-21.9GHz broadband range.

[0104] In summary, the low-profile, low-RCS circularly polarized double-folded transmission array antenna based on an absorbing frequency selective polarizer provided by this invention achieves circular polarization operation and improved radiation gain in a broadband range of 26-30.8 GHz, while also achieving an RCS reduction performance of over 10 dB in a broadband range of 6.8-21.9 GHz, meeting the low detectability requirements of Ka-band satellite communication applications. This invention employs a carefully designed linear-to-circular polarization converter to maintain in-band linear-to-circular polarization conversion while exhibiting excellent frequency selectivity. Integrated with a loss layer, it forms an absorbing frequency selective polarizer, simultaneously achieving in-band linear-to-circular polarization conversion and out-of-band absorption. Furthermore, its co-design with a double-folded transmission array antenna maintains good in-band radiation characteristics while achieving out-of-band RCS reduction across a wide broadband range. The double-folded design of the transmission array antenna in this invention reduces the antenna profile to one-quarter of its original size, resulting in broadband, low-profile, high-gain, and low-RCS characteristics.

[0105] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A low-profile, low-RCS circularly polarized double-folded transmission array antenna, characterized in that: It includes an absorbing frequency selective polarizer and a double-folded transmission array antenna, wherein the absorbing frequency selective polarizer is located above the double-folded transmission array antenna; The absorbing frequency selective polarizer includes a loss layer (2) and a linear-circular polarization converter (3) with frequency selective characteristics, and the loss layer (2) and the linear-circular polarization converter (3) are separated by an air gap layer. The double-folded transmission array antenna includes an integrated reflective-transmitting metasurface (4) and a polarization conversion metasurface (5), which are separated by an air gap layer.

2. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 1, characterized in that: The loss layer (2) includes a first metal layer (21) and a first dielectric layer (22), wherein the first metal layer (21) is printed on the upper surface of the first dielectric layer (22); The first metal layer (21) is composed of a square metal ring (211) located in the center, a square patch (212) located inside the square metal ring, and four T-shaped microstrip lines (213) located outside the square metal ring. The four T-shaped microstrip lines (213) are all located on the axis of symmetry of the square metal ring (211) through the midpoint of the side length. The longitudinal portion (213b) of the T-shaped microstrip line (213) is longer than the transverse portion (213a), and the longitudinal portion (213b) embeds a lumped resistor (214) and is connected to the square metal ring (211).

3. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 1, characterized in that: The linear-circular polarization converter (3) includes a second metal layer (31), a second dielectric layer (32), a third metal layer (33), a third dielectric layer (34), and a fourth metal layer (35); The metal patterns on the second metal layer (31) and the fourth metal layer (35) are exactly the same, both consisting of two arc-shaped metal rings (311) and a first rectangular patch (312) located in the center; the long side of the first rectangular patch (312) points to the inside of the arc-shaped metal ring (311) and remains perpendicular to its edge, while the wide side remains parallel to the edge of the arc-shaped metal ring (311); The third metal layer (33) is composed of a patch (331) with a central circular groove and a second rectangular patch (332) located at the center of the circular groove; the diameter of the circular groove on the third metal layer (33) is the same as the outer diameter of the arc-shaped metal ring (311) on the second metal layer (31); The second metal layer (31), the third metal layer (33) and the fourth metal layer (35) are all symmetrical about the diagonal. The angle between the long side of the first rectangular patch (312) and the positive y-axis is 45°, and the angle between the long side of the second rectangular patch (332) and the positive y-axis is -45°.

4. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 1, characterized in that: The integrated reflective-transmitting metasurface (4) includes a fifth metal layer (41), a fourth dielectric layer (42), a sixth metal layer (43), a fifth dielectric layer (44), and a seventh metal layer (45); The fifth metal layer (41) is composed of rectangular strips arranged in parallel at intervals; the seventh metal layer (45) is obtained by rotating the fifth metal layer (41) around the z-axis by 90°; the sixth metal layer (43) is an open C-shaped ring with the opening direction at an angle of 45° or 135° to the positive y-axis direction.

5. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 1, characterized in that: The polarization conversion metasurface (5) includes an eighth metal layer (51), a sixth dielectric layer (52), and a metal ground plane (53); The eighth metal layer (51) is a third rectangular patch, and the angle between the long side of the third rectangular patch and the positive y-axis is -45°.

6. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 4, characterized in that: The rectangular strip spacing of the fifth metal layer (41) is s2 = 0.35 mm; the width of the rectangular strip is s3 = 0.2 mm; The sixth metal layer (43) has an outer ring radius r5 = 1.61 mm, an inner ring radius r4 = 1.09 mm, and an opening angle θ = 10°-200°.

7. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 6, characterized in that: The method for determining the opening angle θ of the C-shaped ring (43) on the sixth metal layer is as follows: Calculate the required phase compensation value Φ(m,n) at different element locations: Where m and n represent the unit position, λ0 represents the wavelength of the center frequency, p is the unit period, and F is the focal length; Based on the calculated required phase compensation value, determine the opening angle of the C-shaped ring (43) at each unit position.

8. The low-profile, low-RCS circularly polarized double-folded transmission array antenna according to claim 5, characterized in that: The third rectangular patch (51) has a long side l7 = 3.7 mm and a wide side w7 = 0.6 mm.

9. The low RCS circularly polarized double-folded transmission array antenna according to any one of claims 1-8, characterized in that: The linearly polarized feed horn (1) has a 10-dB beamwidth of 78.3° and 71.1° in the E-plane and H-plane at 29 GHz, and a gain of 13 dBi; the unit period of the loss layer (2) is p1 = 8 mm; the unit periods of the linear circular polarization converter (3), the integrated reflective-transmitting metasurface (4), and the polarization conversion metasurface (5) are the same, with a unit period of p2 = 4 mm; the resistance of the lumped resistor (214) is R = 150 Ω.

10. The low RCS circularly polarized double-folded transmission array antenna according to any one of claims 1-8, characterized in that: The first dielectric layer (22) is composed of a Rogers 5880 dielectric substrate with a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of h1 = 0.508 mm; the second dielectric layer (32), the third dielectric layer (34), the fourth dielectric layer (42), the fifth dielectric layer (44), and the sixth dielectric layer (52) are all composed of an SJ9294 dielectric substrate with a dielectric constant of 2.94 and a loss tangent of 0.0012; the thickness of the second dielectric layer (32) and the third dielectric layer (34) is h2 = 0.508 mm; the thickness of the fourth dielectric layer (42) and the fifth dielectric layer (44) is h3 = 1.016 mm; and the thickness of the sixth dielectric layer (52) is h4 = 1.524 mm. The first dielectric layer (22) and the second dielectric layer (32), the third dielectric layer (34) and the fourth dielectric layer (42), and the fifth dielectric layer (44) and the sixth dielectric layer (52) are all separated by air gap layers, with the heights of the air gap layers being t1 = 2.5 mm, t2 = 2 mm, and t3 = 15 mm, respectively.

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