X-band low-profile broadband dual-circularly polarized metasurface antenna

Abstract

This disclosure presents an X-band low-profile broadband dual-circularly polarized metasurface antenna, comprising: two dielectric substrates and three metal layers, the three metal layers including a metasurface antenna layer, a microstrip feed layer, and a metal ground layer; one of the two dielectric substrates is disposed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer, forming a compact stacked structure; there is no air gap between the two dielectric substrates and the three metal layers; radiating patch units are disposed on the metasurface antenna layer with 3×3 equally spaced distributions, each radiating patch unit being a square with chamfered corners. The X-band low-profile broadband dual-circularly polarized metasurface antenna of this disclosure features a compact structure, wide operating bandwidth, a wide normal 3dB circular polarization axis, high normal gain, and multiple polarization modes.

Description

Technical Field

[0001] This disclosure relates to the field of radio frequency antenna equipment engineering technology for synthetic aperture radar systems, and specifically to an X-band low-profile broadband dual-circularly polarized metasurface antenna. Background Technology

[0002] As one of the most advanced technologies in Earth observation, Synthetic Aperture Radar (SAR) has been widely used in remote sensing, microwave mapping, and many other fields due to its all-weather and high-resolution observation capabilities. With the advancement of science and technology, the design of SAR systems also faces new challenges. X-band SAR has attracted much attention due to its small size, light weight, and mature and stable equipment, which means that the system complexity is greatly reduced. The antenna at the forefront of a spaceborne SAR system now faces high-gain performance requirements to compensate for the spatial loss of electromagnetic waves, while maintaining a small size for good integration into the electrical system. Traditional metallic reflector antennas and horn antennas have the advantages of high gain and high efficiency, but their polarization methods are too singular, and their size and weight may be too bulky to be integrated into a SAR system.

[0003] Microstrip antennas have attracted much attention in X-band SAR design. Traditional compact and high-gain antenna elements based on electric and magnetic dipoles suffer from substrate instability compared to metals in the harsh high and low temperature environments of space. Metasurface microstrip patch antennas offer advantages such as high gain, high efficiency, small size, and diverse design options. Moreover, metals are insensitive to temperature changes, making them ideal for RF front-end design in X-band airborne and spaceborne SAR systems.

[0004] In conclusion, designing and manufacturing low-profile antennas with high gain, wide bandwidth, and multiple polarization modes based on SAR systems is a problem of great significance. Summary of the Invention

[0005] This disclosure provides an X-band low-profile broadband dual-circularly polarized metasurface antenna.

[0006] In a first aspect, this disclosure provides an X-band low-profile broadband dual-circularly polarized metasurface antenna, comprising: two dielectric substrates and three metal layers, the three metal layers including a metasurface antenna layer, a microstrip feed layer and a metal ground layer; one of the two dielectric substrates is disposed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer, forming a compact stacked structure; there is no air gap between the two dielectric substrates and the three metal layers; radiating patch units are disposed on the metasurface antenna layer with 3×3 equally spaced distribution, each radiating patch unit being a square with chamfered corners.

[0007] Furthermore, the four square chamfers of the radiating patch unit are centrally symmetrically distributed, and the radiating patch units arranged in a 3×3 evenly spaced manner are centrally symmetrical about the intersection point Z of the linear polarization direction X-axis and Y-axis of the antenna.

[0008] Furthermore, the grid spacing of the 3×3 equally spaced radiating patch units on the metasurface antenna layer and the shape and size of the radiating patch units are optimized using characteristic mode theory.

[0009] Furthermore, when optimizing the grid spacing and shape of the radiating patch unit on the antenna layer using the characteristic mode theory, the first and second characteristic modes with the smallest characteristic value and the largest mode factor among the first eight characteristic modes of the radiating patch unit are used to design a broadband circularly polarized antenna, thereby obtaining the grid spacing of the radiating patch unit (1 mm) and its shape.

[0010] Furthermore, based on the characteristic of the current direction along the edge direction of the radiating patch unit in the characteristic mode theory, a side-feed inductive coupling excitation method is adopted in the microstrip feeder layer.

[0011] Furthermore, in the microstrip feeder layer, two side-fed microstrip lines using inductive coupling excitation are each connected to a signal input port, and the phase difference of the input signals at the signal input ports is 90 degrees. The signal input ports and signal cables are connected by blind mating using SMA and RP-SMA connectors.

[0012] The technical solutions provided in this disclosure may have the following beneficial effects:

[0013] This disclosure presents a low-profile broadband dual-circularly polarized metasurface antenna with a 3×3 subwavelength square metal patch element and its corresponding inductive microstrip side-feed structure. At 9.6 GHz, its overall low profile is only 0.06λ0. The antenna's -10 dB bandwidth is approximately 28.9% (8.35 GHz - 11.7 GHz), its normal 3 dB circular polarization axial ratio bandwidth is approximately 19.5% (8.35 GHz - 10.16 GHz), and its normal gain within the band is greater than 7.84 dBi. This disclosure achieves wide bandwidth, multi-polarization operation, and high stability requirements with a very low profile. Furthermore, it meets various specific requirements such as high operating bandwidth, good polarization axial ratio, and high normal gain for the transceiver link, optimizing and innovating the antenna structure in the transceiver mode of spaceborne synthetic aperture radar, achieving various performance indicators and possessing good practical application value.

[0014] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0015] Other features, objects, and advantages of this disclosure will become more apparent from the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings. In the drawings:

[0016] Figure 1 A schematic diagram of the overall structure of an X-band low-profile broadband dual circularly polarized metasurface microstrip patch antenna according to an embodiment of the present disclosure is shown.

[0017] Figures 2A-2B The diagram illustrates the characteristic value λn, which characterizes the importance of the characteristic current in the total current, and the mode factor MS, which characterizes the mode resonance, as a function of frequency according to an embodiment of the present disclosure.

[0018] Figure 3 A schematic diagram of the characteristic mode current distribution corresponding to characteristic modes 1-8 according to an embodiment of the present disclosure is shown.

[0019] Figure 4 A schematic diagram of the feature far-field directions corresponding to feature patterns 1-8 according to an embodiment of the present disclosure is shown.

[0020] Figure 5 A schematic diagram of an antenna feeding structure according to an embodiment of the present disclosure is shown.

[0021] Figure 6 A schematic diagram showing the effect of the feed line length l of an antenna according to an embodiment of the present disclosure on the antenna matching characteristics is shown.

[0022] Figure 7 A schematic diagram showing the amplitude of the mode weighting coefficient as a function of frequency according to an embodiment of the present disclosure is shown.

[0023] Figures 8A-8B A schematic diagram showing the S-parameter curves and impedance characteristic curves of an antenna according to an embodiment of the present disclosure is provided.

[0024] Figure 9 A schematic diagram showing the variation curve of the normal axial ratio of a metasurface antenna according to an embodiment of the present disclosure is shown.

[0025] Figure 10 A schematic diagram showing the gain in the normal direction of a metasurface antenna according to an embodiment of the present disclosure as a function of frequency is shown.

[0026] Figures 11A-11B A schematic diagram of the orientation of a metasurface antenna according to an embodiment of the present disclosure is shown.

[0027] Figure 12 A schematic diagram of a metasurface microstrip patch antenna microassembly SMA connector according to an embodiment of the present disclosure is shown. Detailed Implementation

[0028] In the following, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement them. Furthermore, for clarity, portions unrelated to the description of the exemplary embodiments have been omitted from the drawings.

[0029] In this disclosure, it should be understood that terms such as “comprising” or “having” are intended to indicate the presence of features, figures, steps, behaviors, components, parts or combinations thereof disclosed in this specification, and do not preclude the possibility of the presence or addition of one or more other features, figures, steps, behaviors, components, parts or combinations thereof.

[0030] It should also be noted that, unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other. This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] Based on the background technology, this invention proposes a metasurface microstrip patch antenna for synthetic aperture radar systems and its manufacturing method, addressing the need for high-performance multi-polarization X-band antennas. It adopts a double-layer dielectric substrate structure, which has a low profile, is easy to process, and has a compact structure. It features a wide operating bandwidth, a wide normal 3dB circular polarization axis, high normal gain, and multiple polarization modes, making it more suitable for various applications.

[0032] To achieve the above objectives, the technical solution of this invention is as follows: an X-band low-profile broadband dual-circularly polarized metasurface antenna for synthetic aperture radar (SAR). To meet the requirements of small antenna size and low profile thickness for SAR systems, the overall thickness of this antenna is approximately 3.8 mm. It is compactly stacked from two Rogers dielectric substrates and three metal layers (metasurface antenna layer, microstrip feed layer, and metal ground layer). Dielectric substrates with a thickness of approximately 1 mm are disposed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer. There are no air gaps between the two dielectric substrate layers and the three metal layers. In some embodiments, to improve antenna design efficiency, effectively improve impedance matching characteristics, and enhance antenna performance to meet the needs of SAR systems, the arrangement spacing of the 3×3 equally spaced rectangular unit grids on the metasurface antenna layer and the shape and size of the square corner-cut radiating patches are analyzed and improved using characteristic mode theory. By orthogonally expanding the current on the conductor surface using the method of moments, and then weighting and calculating the values ​​of each characteristic current and the field generated by the characteristic current, the shape, size and arrangement of the radiation layer are optimized and reconstructed.

[0033] In some embodiments, based on the characteristic that the current direction is along the edge of the radiating element patch in the characteristic mode theory, the present invention employs a side-fed inductive coupling excitation method in the microstrip feed layer. This feeding structure can effectively excite the two dominant characteristic modes, achieving excellent antenna operating bandwidth while maintaining good circular polarization characteristics.

[0034] In some embodiments, SMA and RP-SMA connectors are used for blind mating in this invention. This ensures that the internal radiation modules can be independently debugged and repeatedly plugged and unplugged, while also ensuring the combined installation of the modules to achieve high-quality signal transmission and suppress signal leakage to a large extent.

[0035] In some embodiments, the present invention achieves excellent performance with a normal 3dB circular polarization axial ratio bandwidth of approximately 19.5% (8.35GHz-10.16GHz) and a normal gain greater than 7.84dBi in the frequency band by optimizing the antenna structure of the metasurface layer. This ensures the consistency of amplitude and phase under high-precision multi-polarization transmission and corresponding reception modes (H polarization mode, V polarization mode and HV / VH polarization mode, LHCP left-hand circular polarization, RHCP right-hand circular polarization), thus providing a guarantee for the consistency of transmitted and received signals of the synthetic aperture radar system.

[0036] The design scheme described in this invention also provides a new approach to finding high-performance synthetic aperture radar antenna designs from the perspective of characteristic modes.

[0037] Figure 1 A schematic diagram of the overall structure of an X-band low-profile broadband dual-circularly polarized metasurface microstrip patch antenna according to an embodiment of this disclosure is shown. Figure 1 As shown, this metasurface microstrip patch antenna is used for detection by synthetic aperture radar.

[0038] This metasurface microstrip patch antenna is composed of two Rogers dielectric substrates (with corresponding parameters: dielectric constant εr: 2.2, loss tangent tanδ: 0, dielectric density: 1e+3 kg / m³) compactly stacked with three metal layers, resulting in an overall thickness of only about 3.8 mm. Dielectric substrates with a thickness of approximately 1 mm are placed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer. There are no air gaps between the two dielectric substrate layers and the three metal layers. The metal layers and the cross-section are as shown... Figure 1 As shown.

[0039] The aforementioned three metal layers include a metasurface antenna layer, a microstrip feed layer, and a metal ground layer. The metasurface antenna layer is disposed on the upper surface of the first dielectric substrate. The microstrip feed layer is disposed on the bottom surface of the first dielectric substrate and the upper surface of the second dielectric substrate. It consists of two symmetrically positioned side-fed microstrip obtuse-angled zigzag feed lines and corresponding rectangular tuning stubs perpendicularly intersecting at point Z. One end of each microstrip feed line is flush with the lateral edge of the first dielectric substrate, and the other end is directly connected to a square metal patch with chamfered corners placed at point Z, forming the antenna's feed portion to generate inductively coupled excitation. The metal ground layer is disposed on the bottom surface of the second dielectric substrate. It is a complete, uncut copper ground layer with a gold-plated surface, providing a reference level and reflecting electromagnetic waves generated by the feed layer and the radiating layer.

[0040] The radiating layer of this metasurface microstrip patch antenna, i.e., the metasurface antenna layer, comprises a dielectric substrate and nine equally spaced rectangular radiating patch units arranged in a 3×3 pattern. These radiating patches evolved from traditional square patches with chamfered corners. As the operating frequency increases, the relative proportion of the chamfered corners around the radiating patches increases. To provide good dual-circular polarization radiation capability, each radiating patch is square in shape with four square chamfered corners. The four square chamfered corners of each radiating patch are centrally symmetrically distributed, and the nine equally spaced radiating patches are centrally symmetrical about the intersection point Z of the antenna's linear polarization directions X and Y axes.

[0041] In some embodiments, to improve antenna design efficiency, effectively enhance impedance matching characteristics, and improve antenna performance to meet the needs of synthetic aperture radar systems, the arrangement spacing and shape dimensions of the nine equally spaced radiating patch grids on the metasurface antenna layer are analyzed and improved using characteristic mode theory. The optimized shape parameters of the X-band (λ = 3.125 cm) radiating patch in this example are shown in Table 1. On the metasurface antenna layer, the side length of each square radiating patch unit is a = 7.3 mm, and the center distance between two adjacent radiating patch units is b = 8.3 mm. Where c is the side length of the metal square chamfered patch in the microstrip feed layer, d1 and l are the cross-sectional width and length of the rectangular tuning branch in the microstrip feed layer, and d2 is the cross-sectional width of the side-fed microstrip obtuse-angled polygonal feed line.

[0042] Table 1

[0043] a b c <![CDATA[d1]]> <![CDATA[d2]]> l 7.3 8.3 9.6 1.2 3.1 9.5

[0044] The characteristic mode theory described herein is based on the method of moments (MoM) for orthogonal expansion of the currents on the conductor surface. Then, weighted calculations are performed on each characteristic current and the field it generates, enabling analytical solutions for electromagnetic problems with complex geometries and various boundary conditions. Furthermore, it possesses clear physical concepts and meanings, combining the advantages of both numerical and analytical methods. In this invention, the conductor surface can be the radiating surface of an antenna, the feed surface, or the surface of a metal mesh, etc. Therefore, this invention utilizes characteristic mode theory to optimize and reconstruct the shape and size arrangement of the radiating layer of a low-profile broadband dual-circularly polarized metasurface antenna for synthetic aperture radar (SAR), providing a new approach to designing high-performance SAR antennas from the perspective of characteristic modes.

[0045] The radiating layer antenna structure described in this invention is similar to a patch-type artificial magnetic conductor, with the antenna body being a two-dimensional array plane with grid slots. Its eigenvalue λn, characterizing the importance of the characteristic current in the total current, varies with frequency as shown in the curve. Figure 2A As shown, the mode factor MS, which characterizes the mode resonance condition, varies with frequency as follows: Figure 2B As shown. Simulation results of the first eight characteristic modes of the radiating patch antenna reveal that, within the 7GHz-11GHz frequency range, the eigenvalues ​​of the first two modes are smaller and the mode factors are larger compared to the latter six modes. According to characteristic mode theory, the closer the eigenvalue λn of a characteristic mode is to 0, the easier it is for that mode to resonate; when the mode factor MS = 1, this frequency point is the resonant frequency of the metasurface. Figures 2A-2B It can be seen that at a frequency of approximately 8.65 GHz, the eigenvalues ​​of modes 1 and 2 are 0, and the mode factor reaches 1. At this point, modes 1 and 2 exhibit the strongest radiation capability, approaching a resonant state, and can be considered the dominant modes of this metasurface structure. Other characteristic modes have smaller eigenvalues ​​and weaker radiation capabilities within the investigated frequency band. The characteristic mode currents and characteristic far-field directions corresponding to modes 1-8 are shown below. Figure 3 and Figure 4As shown. Simulation results of eigenvalues ​​and mode factors indicate that modes 1 and 2 have strong resonance characteristics within the frequency band and are easily excited. The far-field radiation characteristics of each mode are observed below. Among the first eight modes, only modes 1 and 2 have maximum radiation directions along the normal direction. Mode 1 is a linearly polarized mode along the X-axis, and mode 2 is a linearly polarized mode along the Y-axis. Modes 3 and 4, and modes 5 and 6 have maximum far-field radiation directions in the horizontal plane, with weak normal radiation. The mode currents are relatively uniformly distributed and orthogonal on each patch, and the eigenvalues ​​are basically the same in the studied frequency band. Due to the symmetry of the antenna structure, modes 3 and 4, and modes 5 and 6 can be approximated as degenerate modes. Similarly, the degenerate mode patterns of modes 7 and 8 exhibit split lobes, with large horizontal sidelobes, making them unsuitable as primary excitation modes. Since both Mode 1 and Mode 2 achieve their strongest radiation capability at 8.65 GHz and their far-field polarization directions differ by 90 degrees, Mode 1 and Mode 2 are used to design a broadband circularly polarized antenna, thereby determining the arrangement spacing of the rectangular unit grid and the shape and size of the square corner-cut radiating patch.

[0046] As can be seen from the aforementioned characteristic mode analysis, the characteristic current at the edge of the feed patch for modes 1 and 2 is relatively strong, and the current direction is along the edge of the patch. Therefore, this invention adopts a side-fed inductive coupling excitation method in the microstrip feed layer, which consists of two symmetrical side-fed microstrip obtuse-angled zigzag feed lines and corresponding rectangular tuning branches that intersect perpendicularly at point Z. One end of the microstrip feed line is flush with the lateral edge of the first dielectric substrate, and the other end is directly connected to a metal square patch with chamfered corners placed at point Z, forming the feed part of the antenna, which can effectively implement inductive excitation for the two characteristic modes. The corresponding structure is as follows: Figure 1 and Figure 5 As shown.

[0047] Figure 6 A schematic diagram illustrating the effect of the feed line length l on the antenna matching characteristics according to an embodiment of the present disclosure is shown. In order to obtain a better operating bandwidth and comprehensively consider the various electrical performance requirements of the antenna, the present invention utilizes characteristic mode theory to optimize the design of the coupling excitation structure. The corresponding feed structure dimensions are: c = 9.6 mm, l = 9.5 mm, d1 = 1.2 mm and d2 = 3.1 mm, as shown in Table 1.

[0048] For the antenna after the excitation source is applied, the mode weighting coefficient directly reflects the magnitude of the mode's contribution to the total current density. Figure 7The amplitude curves of the mode weighting coefficients versus frequency show that, after adding the excitation source, the amplitudes of the mode weighting coefficients for modes 1 and 2 are larger in the 7GHz-11GHz frequency band, which can be considered as the modes mainly excited in this frequency band. Therefore, the antenna feeding structure in this example can effectively excite the radiating layer of the metasurface antenna, achieving excellent antenna operating bandwidth while realizing good circular polarization characteristics.

[0049] Figures 8A-8B A schematic diagram showing the S-parameter curves and impedance characteristic curves of an antenna according to an embodiment of the present disclosure is provided. Figures 8A-8B As shown, its reflection coefficient has a -10dB bandwidth of approximately 28.9% (8.35GHz-11.7GHz), which is basically the same as the frequency band of the two excited modes. The resonant point corresponds to the mode weighting coefficient curves of mode 1 and mode 2. Figure 9 A schematic diagram showing the variation curve of the normal axial ratio of a metasurface antenna according to an embodiment of the present disclosure is shown. Figure 10 This diagram illustrates a curve showing the gain along the normal direction of a metasurface antenna according to an embodiment of the present disclosure as a function of frequency. Figure 9 and Figure 10 As can be seen, the normal 3dB circular polarization axial ratio bandwidth is approximately 19.5% (8.35-10.16GHz), and the normal gain is higher than 7.84dBi within this frequency band, exhibiting good circular polarization characteristics.

[0050] Figures 11A-11B A schematic diagram of the radiating pattern of a metasurface antenna according to an embodiment of this disclosure is shown. Within the operating frequency band, the antenna's maximum radiation direction is essentially in the normal direction. The 3dB beamwidth of the antenna's E-plane radiation pattern is 62 degrees, and the 3dB beamwidth of the H-plane is 58 degrees, with relatively small sidelobes. Within the circularly polarized operating frequency band of 8.35-10.16 GHz, the antenna's normal radiation gain varies between 7.84 dBi and 9.56 dBi, exhibiting high gain within the operating frequency band. This provides excellent wideband, wide beamwidth, and high-gain characteristics, ensuring the consistency of amplitude and phase under high-precision multi-polarization transmission and corresponding reception modes (H-polarization mode, V-polarization mode, and HV / VH polarization mode; LHCP left-hand circular polarization; RHCP right-hand circular polarization), thus guaranteeing the consistency of the transmitted and received signals of the synthetic aperture radar system.

[0051] Figure 12 This diagram illustrates a micro-assembly SMA connector for a metasurface microstrip patch antenna according to an embodiment of this disclosure. The present invention employs SMA and RP-SMA connectors for blind mating. This ensures that the internal radiating modules can be independently debugged and repeatedly plugged and unplugged, while also guaranteeing the combined installation of modules, achieving high-quality signal transmission and significantly suppressing signal leakage.

[0052] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

Claims

1. An X-band low-profile broadband dual-circularly polarized metasurface antenna, characterized in that, include: The device consists of two dielectric substrates and three metal layers. The three metal layers include a metasurface antenna layer, a microstrip feed layer, and a metal ground layer. One of the two dielectric substrates is disposed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer, forming a compact stacked structure. There is no air gap between the two dielectric substrates and the three metal layers. The metasurface antenna layer is provided with 3×3 equally spaced radiating patch units, each of which is a square with chamfered corners. The four square chamfers of the radiating patch unit are centrally symmetrically distributed, and the radiating patch units arranged in a 3×3 evenly spaced manner are centrally symmetrical about the intersection point Z of the antenna's linear polarization direction X-axis and Y-axis. The grid spacing and shape and size of the radiating patch units arranged in a 3×3 equally spaced manner on the metasurface antenna layer are optimized using characteristic mode theory. When optimizing the grid spacing and shape of the radiating patch unit on the antenna layer using the characteristic mode theory, the first and second characteristic modes with the smallest characteristic value and the largest mode factor among the first eight characteristic modes of the radiating patch unit are used to design a broadband circularly polarized antenna, resulting in a grid spacing of 1 mm and a shape of the radiating patch unit. Based on the characteristic of current direction along the edge of the radiating patch unit in the characteristic mode theory, a side-feed inductive coupling excitation method is adopted in the microstrip feeder layer.

2. The X-band low-profile broadband dual-circularly polarized metasurface antenna according to claim 1, characterized in that, In the microstrip feeder layer, two side-fed microstrip lines using inductive coupling excitation are each connected to a signal input port, and the phase difference of the input signals at the signal input ports is 90 degrees. Furthermore, the signal input ports and signal cables are connected by blind mating using SMA and RP-SMA connectors.

Images