Linear-to-circular polarized converter based on symmetrical stepped slot and square ring metal patch

Abstract

This invention discloses a linear-to-circular polarization converter based on a symmetrical stepped-slot and square-ring metal patch, comprising, from top to bottom, a first metal patch, a first dielectric substrate, a second metal patch, a second dielectric substrate, a third dielectric substrate, and a third metal patch. The first and third metal patches are symmetrical stepped-slot metal patches of the same shape and size, while the second metal patch is a square-ring metal patch. The three metal patches form a multi-resonant structure through interlayer coupling and, together with the dielectric substrate, constitute a metasurface unit with an anisotropic response, used to control the amplitude and phase of the two orthogonal transmission components obtained by decomposing the incident linearly polarized wave. This invention can achieve the conversion of linearly polarized waves to circularly polarized transmitted waves over a wide operating frequency band and a wide incident angle range, while maintaining a low axial ratio and low insertion loss.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and more specifically relates to a linear-to-circular polarization converter based on a symmetrical stepped slot and a square ring metal patch within the field of metasurface technology. This invention can be used in communication systems such as wireless communication, radar detection, and satellite communication that require wide-angle performance of the polarization converter, enabling the conversion of linearly polarized incident waves to circularly polarized transmitted waves in the K-band and adjacent frequency bands. Background Technology

[0002] Polarization converters, as important passive microwave devices, can control the polarization state of electromagnetic waves and have wide applications in wireless communication, radar detection, and satellite navigation. Based on the different forms of interaction between electromagnetic waves and the device, polarization converters mainly include reflective, transmissive, and hybrid transmissive-reflective types. Among them, transmissive polarization converters have advantages such as high integration with feed antennas, low system profile, and ease of conformal design, making them more suitable for compact antenna front-ends and array integration scenarios. The K-band has short wavelengths, small device size, and abundant available spectrum resources. In long-distance communication, electromagnetic waves are susceptible to ionospheric scintillation, rain attenuation, and multipath reflection. Linearly polarized waves are prone to polarization rotation during transmission, leading to polarization mismatch between transmitting and receiving antennas, thus reducing system communication quality. In contrast, circular polarization has advantages such as reducing polarization mismatch and mitigating the effects of multipath effects, effectively improving the reliability of communication links. Therefore, combining linearly polarized antennas with linear-circular polarization converters to form integrated circularly polarized antenna systems has become the preferred technical solution for this frequency band, balancing performance and flexibility. Traditional transmissive polarization converters typically employ single-layer or multi-layer metal patch structures, achieving polarization conversion by introducing different transmission amplitudes and phase responses to the orthogonal polarization components. However, conventional designs struggle to simultaneously satisfy amplitude equalization and ±90° phase difference across a wide bandwidth. Furthermore, circular polarization purity deteriorates significantly under large-angle oblique incidence, leading to a rapid increase in axial ratio (AR), limiting their application in wide-beam scanning and large-angle coverage scenarios. By introducing a multi-resonant structure, effective polarization conversion responses can be formed at multiple adjacent frequency points, thereby expanding the device's operating bandwidth. Simultaneously, by combining anisotropic metasurface units to modulate the amplitude and phase of the orthogonal polarization components, and by optimizing unit period, structural symmetry, and interlayer coupling, the angular stability of the transmissive polarization converter can be improved within a certain incident angle range.

[0003] Chongqing University disclosed a transparent flexible linear circular polarization converter operating at 5.8 GHz in its patent application, "A Transparent Linear Circular Polarization Converter for Microwave Wireless Power Transmission" (Patent Application No.: 202510645878.9, Application Date: 2025.05.20, Publication No.: CN 120527659 A). This linear circular polarization converter employs a five-layer stacked structure: the first and fifth layers are cross-shaped patch structures with a 45° angle and a central cross groove, using a copper microgrid with a linewidth of 0.05 mm to achieve high transparency; the second and fourth layers are PET dielectric layers; the third layer is composed of four isosceles right triangles spliced ​​together, used to regulate the coupling and phase response of the structure. This design enhances the capacitive response in a specific direction through a central slot, creating an approximately 90° phase difference between the orthogonal polarization components. Experiments at the yoz plane at the target frequency of 5.8 GHz yielded an axial ratio of 0.14 dB and an insertion loss of 0.53 dB, maintaining an axial ratio below 3 dB within a ±45° oblique incidence range. Simultaneously, the device achieves a transmittance of 73.47% in the visible light band, making it suitable for applications requiring transparent integration, such as smart windows and photovoltaic-microwave hybrid energy harvesting. However, this converter still has limitations: it is primarily optimized for a single target frequency of 5.8 GHz, and the circular polarization conversion relies on the resonant coupling response formed by a multilayer metallic microgrid structure near this frequency to achieve amplitude matching and an approximately 90° phase difference between the orthogonal polarization components. Since this amplitude matching relationship exhibits significant frequency selectivity, when the operating frequency deviates from the design point, the amplitude ratio and phase difference of the orthogonal polarization components tend to shift, leading to an increase in axial ratio. Simultaneously, deviating from the resonant matching frequency band results in a decrease in transmission coefficient and an increase in insertion loss. Therefore, this converter struggles to maintain both low axial ratio and low insertion loss across a wide bandwidth. This problem can be mitigated by introducing a multi-resonant structure in this invention, enabling multiple adjacent frequency points to form an effective polarization conversion response and maintaining amplitude matching of orthogonal polarization components over a wider bandwidth, thereby extending the device's operating bandwidth.

[0004] Hohai University disclosed a dual-layer cross-slot type linear-circular polarization converter in its patent application, "A Dual-Layer Cross-Slot Linear-Circular Polarization Converter Based on Frequency Selective Surface" (Invention Patent Application No.: 202410570651.8, Application Date: 2024.05.09, Publication No.: CN118352795 A). This converter employs a three-layer stacked structure consisting of a lower cross-slot metal layer, an intermediate dielectric layer, and an upper cross-slot metal layer. Both the upper and lower metal layers are composed of m×n cross-slot periodic units. By optimizing the width, depth, and angle of the slots within each unit, phase modulation of the orthogonal linear polarization components is achieved. Simulation and experimental data show that the converter exhibits good linear-circular polarization conversion performance with an axial ratio not exceeding 1.15 dB and an insertion loss not exceeding 0.7 dB at the test frequency range of 22-25 GHz. However, this converter still has shortcomings: it employs a double-layer cross-slot frequency selective surface, achieving amplitude matching and approximately 90° phase difference of the orthogonal polarization components through the structural equivalent response and phase delay of the upper and lower slot elements. This amplitude matching relationship depends on the structural equivalent response under specific incident conditions. As the incident angle increases, the equivalent propagation path of the electromagnetic wave, the coupling strength of the TE / TM components, and the equivalent impedance change, easily causing the amplitude ratio and phase difference of the orthogonal components to deviate from the circular polarization conversion conditions, resulting in increased axial ratio and insertion loss. Therefore, this converter struggles to maintain both low axial ratio and low insertion loss simultaneously over a wide incident angle range. This problem can be addressed by rationally designing anisotropic metasurface elements and optimizing the element period, structural symmetry, and interlayer coupling relationships to enhance the stable control capability of the amplitude and phase of the orthogonal polarization components under wide incident angle conditions, thereby reducing fluctuations in axial ratio and insertion loss caused by changes in the incident angle. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the existing technology by proposing a linear-circular polarization converter based on a symmetrical stepped gap and a square ring metal patch. This invention aims to solve the problem that existing linear-circular polarization converters are unable to maintain both low axial ratio and low insertion loss over a wide operating frequency band and wide incident angle.

[0006] The technical approach to achieving the objective of this invention is to design a transmissive linear-circular polarization converter using a multilayer stacked structure formed by stacking three layers of metal patches and three layers of dielectric substrate. On one hand, the multi-level stepped edges and gaps in the upper and lower symmetrical stepped-gap metal patches introduce equivalent current paths of different lengths. The middle layer square ring metal patch can form an equivalent LC resonant channel and generate interlayer coupling with the upper and lower metal structures, thus jointly constituting a multi-resonant structure. This multi-resonant structure can form effective polarization conversion responses at multiple adjacent frequency points, maintaining amplitude matching and approximately ±90° phase difference between the orthogonal polarization components over a wide frequency band, thereby expanding the device's operating bandwidth. On the other hand, the upper and lower symmetrical stepped-gap metal patches, the middle layer square ring metal patch, and the dielectric layer together constitute an anisotropic metasurface unit. This unit has different equivalent current distributions, equivalent inductance and capacitance parameters, and transmission phase responses in the two orthogonal polarization directions, enabling the separate modulation of the amplitude and phase of the two orthogonal components obtained from the incident linear polarization decomposition. By employing a multi-layer metal-dielectric composite layout with symmetrical upper and lower metal patch patterns and an interlayer coupling design, the impact of incident angle variations on the amplitude ratio and phase difference of the orthogonal components can be reduced. This allows the device to maintain low axial ratio and low insertion loss transmission and polarization conversion performance over a wide incident angle range. Thus, this invention solves the problem that existing linear circular polarization converters struggle to maintain both low axial ratio and low insertion loss over a wide operating bandwidth and wide incident angle.

[0007] To achieve the above objectives, the linear-to-circular polarization converter of the present invention includes, from top to bottom, a first metal patch, a first dielectric substrate, a second metal patch, a second dielectric substrate, a third dielectric substrate, and a third metal patch; the first and third metal patches are symmetrical stepped-gap metal patches with the same shape and size; the second metal patch is a square ring metal patch; the first, second, and third metal patches form a multi-resonant structure through interlayer coupling, so that the two orthogonal transmission components obtained by decomposing the incident linear polarization wave maintain amplitude matching and a phase difference of approximately ±90° within the operating frequency band; the first metal patch, the first dielectric substrate, the second metal patch, the second dielectric substrate, the third dielectric substrate, and the third metal patch together constitute a metasurface unit with an anisotropic response, used to modulate the amplitude and phase of the two orthogonal transmission components obtained by decomposing the incident linear polarization wave, and convert the incident linear polarization wave into a circularly polarized transmission wave.

[0008] Furthermore, the first metal patch is disposed on the upper surface of the first dielectric substrate, the second metal patch is disposed on the upper surface of the second dielectric substrate, and the third metal patch is disposed on the lower surface of the third dielectric substrate.

[0009] The symmetrical stepped gap metal patch refers to a symmetrical triangular combination structure with two bases facing each other, forming a gap extending diagonally between the two symmetrical triangular metal areas, and the waist of the symmetrical triangular metal area has a continuous stepped outline.

[0010] The stepped profile refers to a structure formed by alternating connections of multiple first side segments extending along a first direction and multiple second side segments extending along a second direction, with the first direction perpendicular to the second direction. Adjacent first and second side segments are connected end to end in sequence, and the waist of the symmetrical triangular metal region has a stepped shape with progressively bent curves.

[0011] Furthermore, the second metal patch includes a square outer contour and a central circular through hole located inside the square outer contour, wherein the center of the central circular through hole coincides with the geometric center of the square outer contour.

[0012] The radius of the central circular through hole ranges as follows: ;in, This represents the free space wavelength corresponding to the operating center frequency of a linear circular polarization converter.

[0013] Furthermore, the first and third dielectric substrates are made of a first low-loss microwave dielectric material with the same relative permittivity, the range of which is [2.85, 3.3]; the second dielectric substrate is made of a second low-loss microwave dielectric material, the range of which is [2.3, 2.8]; the relative permittivity of the first low-loss microwave dielectric material is greater than that of the second low-loss microwave dielectric material; and the loss tangent of the first, second, and third dielectric substrates is not greater than 0.04.

[0014] Furthermore, the first dielectric substrate and the third dielectric substrate have the same thickness, and the range of their values ​​is as follows: The thickness of the second dielectric substrate is less than the thicknesses of the first and third dielectric substrates, and its value range is: The range of the total thickness of the linear-circular polarization converter along the stacking direction is: .

[0015] Furthermore, the projected outer contour of the linear-circular polarization converter perpendicular to the stacking direction is a square, and the range of values ​​for the side length of the square is: .

[0016] Furthermore, the first metal patch, the second metal patch, and the third metal patch are all conductive metal layers made of the same material, and the conductive metal layer is made of any one of copper, aluminum, silver, gold, or other alloy materials.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] First, this invention employs a multi-resonant structure composed of upper and lower symmetrical stepped-gap metal patches and a middle square-ring metal patch. This structure maintains good amplitude matching and a phase difference of approximately ±90° for the orthogonal polarization components over a wide frequency band, overcoming the limitation of operating bandwidth caused by existing linear-circular polarization converters that mainly rely on a single resonance or single-frequency optimization. This allows the invention to form an effective polarization conversion response at multiple adjacent frequency points, thereby maintaining both low axial ratio and low insertion loss over a wide operating frequency band.

[0019] Secondly, this invention employs an anisotropic metasurface unit composed of upper and lower symmetrical stepped-gap metal patches, a middle square-ring metal patch, and a dielectric layer. This overcomes the shortcomings of existing linear-circular polarization converters, which are prone to shifts in the amplitude ratio and phase difference of orthogonal polarization components over a wide incident angle range, leading to increased axial ratio and insertion loss. This anisotropic metasurface unit can modulate the amplitude and phase of the two orthogonal components obtained from the decomposition of the incident linear polarization wave. Combined with the symmetrical multilayer metal-dielectric composite layout of the upper and lower metal patches and the interlayer coupling design, it reduces the impact of incident angle variations on polarization conversion performance, thereby enabling this invention to maintain both low axial ratio and low insertion loss over a wide incident angle range. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the linear-circular polarization converter of the present invention;

[0021] Figure 2 This is a top view of the first metal patch 4 and the third metal patch 6 in the linear-circular polarization converter of the present invention.

[0022] Figure 3 This is a top view of the second metal patch 5 in the linear-circular polarization converter of the present invention;

[0023] Figure 4 The transmission coefficient response curves of the u-polarization component in the range of 16 GHz to 26 GHz under different incident angles are shown below.

[0024] Figure 5 The transmission coefficient response curves of the v polarization component in the range of 16 GHz to 26 GHz under different incident angles are shown below.

[0025] Figure 6 The phase difference response curves of u and v polarization components in the range of 16 GHz to 26 GHz under different incident angles are shown for this invention.

[0026] Figure 7 The axial ratio response curves of this invention in the range of 16GHz to 26GHz under different incident angles are shown below.

[0027] Figure 8 The insertion loss response curves of this invention are shown in the range of 16 GHz to 26 GHz at different incident angles. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0029] Reference Figure 1 The overall three-dimensional structure of the linear-circular polarization converter of the present invention will be further described.

[0030] The transmissive linear-circular polarization converter unit of the present invention has a multi-layer stacked structure, comprising, from top to bottom, a first metal patch 4, a first dielectric substrate 1, a second metal patch 5, a second dielectric substrate 2, a third dielectric substrate 3, and a third metal patch 6. In terms of spatial arrangement, the first metal patch 4 is disposed on the upper surface of the first dielectric substrate 1, the second metal patch 5 is disposed on the upper surface of the second dielectric substrate 2, and the third metal patch 6 is disposed on the lower surface of the third dielectric substrate 3. The first metal patch 4 and the third metal patch 6 have identical shapes and sizes, and are located at the top and bottom layers of the unit structure, respectively. This symmetrical three-layer metal-dielectric composite layout effectively forms a multi-level coupled resonant network, providing a solid structural foundation for the polarization control of transmitted waves.

[0031] The first dielectric substrate 1 and the third dielectric substrate 3 are made of a first low-loss microwave dielectric material with the same relative permittivity, and the second dielectric substrate 2 is made of a second low-loss microwave dielectric material; the relative permittivity of the first low-loss microwave dielectric material is greater than that of the second low-loss microwave dielectric material. The first dielectric substrate 1 and the third dielectric substrate 3 have the same thickness, and the thickness of the second dielectric substrate 2 is less than that of the first dielectric substrate 1 and the third dielectric substrate 3.

[0032] like Figure 2As shown, the first metal patch 4 and the third metal patch 6, projected onto a plane perpendicular to the stacking direction, form a symmetrical triangular combination structure with two opposing bases. A gap extending obliquely is formed between the two symmetrical triangular metal regions. This gap, together with the continuous stepped contour, alters the surface current path, causing different equivalent inductance, capacitance, and transmission phase responses in the two orthogonal polarization directions. Furthermore, the waists of these symmetrical triangles are constructed as continuous stepped contours, formed by alternating connections of multiple first side segments extending along a first direction and multiple second side segments extending along a second direction. The first and second directions are perpendicular, and adjacent first and second side segments are connected end-to-end, resulting in a stepped shape with progressively bent waists for the symmetrical triangular metal regions. This specially designed stepped edge effectively extends the physical transmission path of the surface current in terms of electromagnetic properties, creating a strong equivalent inductance and capacitance loading effect. This effect can significantly increase the phase accumulation between the two orthogonal polarization components without increasing the dielectric thickness, providing structural support for accurately achieving the required ±90° phase difference.

[0033] like Figure 3 As shown, the second metal patch 5, disposed on the upper surface of the second dielectric substrate 2, projects onto a horizontal plane as a square frame with a circular through-hole at its geometric center, forming a square ring structure with a central circular through-hole. The center of the central circular through-hole coincides with the geometric center of the square outer contour. In practical applications, the outer edge of this square ring structure and the edge of the inner circular hole together form an LC equivalent resonant cavity with a wide bandwidth response. Its special feature is that the presence of the circular hole provides a coupling path and reduces the overall Q value of the structure, effectively exciting multimode resonance. The second metal patch 5 can generate strong near-field electromagnetic coupling with the first metal patch 4 and the third metal patch 6, effectively reducing the transmission insertion loss of the entire metasurface while broadening the polarization conversion bandwidth.

[0034] This embodiment uses a center frequency of 21 GHz as an example for design. The unit period (square side length) is taken as 2.88 mm (corresponding to approximately... Both the first and third dielectric substrates are made of Rogers RO3003 material with a relative permittivity of 3.0, and each has a thickness of 0.508 mm (approximately...). The second dielectric substrate is made of Taconic TLY-5 material with a relative permittivity of 2.55 and a thickness of 0.1 mm (corresponding to approximately...). The radius of the central hole in the second metal patch is 1.4 mm (corresponding to approximately...). The remaining dimensions can be obtained through electromagnetic simulation optimization.

[0035] The effects of the present invention will be further explained below with reference to simulation experiments.

[0036] 1. Simulation experimental conditions:

[0037] The simulation experiments of this invention were performed using the commercial electromagnetic simulation software ANSYS HFSS 2022 R1. The simulation object was the periodic unit structure of the transmissive linear-circular polarization converter described in this invention. During the simulation, periodic master-slave boundary conditions and Floquet ports were set to simulate the electromagnetic response of an infinite periodic array structure under plane wave incident conditions.

[0038] In the simulation experiment of this invention, the incident wave is a uniformly linearly polarized plane wave with a propagation direction along the z-axis and an electric field vector along the y-axis. To analyze the circular polarization formation process of the transmitted field, the transmitted linearly polarized field is decomposed into u-polarization components and v-polarization components on two orthogonal substrates, and the transmission coefficient, phase response, phase difference, axial ratio, and insertion loss of the two orthogonal transmission components are extracted respectively.

[0039] To verify the polarization conversion performance of this invention over a wide bandwidth and wide incident angle range, the simulation frequency range was set to 16 GHz to 26 GHz, and the incident angles θ were set to 0°, 15°, 30°, 45°, and 60°, respectively. These incident angles cover typical operating conditions from normal incidence to large-angle oblique incidence and can be used to evaluate the wide-angle stability of the linear-circular polarization converter of this invention.

[0040] 2. Simulation content and result analysis:

[0041] The simulation experiments of this invention include four parts: The first simulation experiment simulates the transmission coefficients of the u-polarized and v-polarized components in the transmitted field to verify the amplitude matching of the two orthogonal transmission components; the second simulation experiment simulates the phase difference between the u-polarized and v-polarized components to verify whether the two orthogonal transmission components meet the phase conditions required to form a circularly polarized wave; the third simulation experiment simulates the axial ratio of the linear circular polarization converter of this invention to verify its circular polarization conversion bandwidth and stability over wide incident angles; the fourth simulation experiment simulates the insertion loss of the linear circular polarization converter of this invention to verify its low-loss transmission performance over a wide bandwidth and under wide incident angle conditions.

[0042] For linear-circular polarization conversion, the two orthogonal components in the transmitted field must simultaneously satisfy two conditions: approximately equal amplitude and a phase difference of approximately ±90°. The amplitude matching condition determines the closeness of the major and minor axes of the synthesized polarization ellipse, while the phase difference condition determines the rotational characteristics of the synthesized electric field vector. When both conditions are satisfied, the transmitted wave can form a low-axial-ratio circularly polarized wave.

[0043] Figure 4 and Figure 5 The figures show the transmission coefficient response curves of the u-polarization component and the v-polarization component in the transmitted field at different incident angles θ. Figure 4 and Figure 5 The horizontal axis represents frequency in GHz, and the vertical axis represents transmission coefficient. The curves marked with rhombuses, left-facing triangles, right-facing triangles, circles, and pentagrams in the figure correspond to the simulation results for incident angles θ of 0°, 15°, 30°, 45°, and 60°, respectively.

[0044] Depend on Figure 4 and Figure 5 It can be seen that within the frequency sweep range of 16 GHz to 26 GHz, the transmission coefficients of the u-polarized and v-polarized components fluctuate with frequency and incident angle, but the two orthogonal transmission components maintain a good amplitude matching relationship overall. This result indicates that the symmetrical stepped-gap metal patch and square ring metal patch in this invention can effectively modulate the amplitude of the two orthogonal components obtained from the decomposition of the incident ray-polarized wave, providing amplitude conditions for the formation of circularly polarized transmission waves.

[0045] Figure 6 The phase difference response curves between the u-polarized component and the v-polarized component in the transmitted field at different incident angles θ are shown. Figure 6 The horizontal axis represents frequency in GHz, and the vertical axis represents phase difference in degrees. The curves marked with rhombuses, left-facing triangles, right-facing triangles, circles, and pentagrams in the figure correspond to the simulation results for incident angles θ of 0°, 15°, 30°, 45°, and 60°, respectively.

[0046] Depend on Figure 6 It can be seen that within the frequency sweep range of 16 GHz to 26 GHz, the phase difference between the two orthogonal transmission components is generally maintained around ±90° (mainly -90° in this embodiment, equivalent to 270°). The phase jumps appearing in the figure are mainly caused by the phase being displayed in a 360° period and do not affect the equivalent phase difference relationship between the two orthogonal transmission components. This result shows that the structure of the present invention can meet the phase conditions required for linear circular polarization conversion over a wide frequency band and wide incident angle range.

[0047] comprehensive Figure 4 , Figure 5 The quadrature component amplitude response and Figure 6As can be seen from the phase difference response of the orthogonal components, the present invention can simultaneously maintain the amplitude matching of the two orthogonal transmission components and the phase difference of approximately ±90° (mainly -90° in this embodiment) over a wide frequency band and a wide incident angle range, thereby achieving a stable conversion of incident linearly polarized waves to circularly polarized waves.

[0048] Figure 7 The axial ratio response curves of the linear circular polarization converter of the present invention at different incident angles θ are shown. Figure 7 The horizontal axis represents frequency in GHz, and the vertical axis represents axial ratio in dB. The curves marked with rhombuses, left-facing triangles, right-facing triangles, circles, and pentagrams in the figure correspond to the simulation results for incident angles θ of 0°, 15°, 30°, 45°, and 60°, respectively.

[0049] According to the standard in engineering applications, a shaft ratio of less than 3 dB is considered acceptable for circular polarization performance. Figure 7 It can be seen that within a wide incident angle range of θ = 0° to 60°, this invention exhibits a relatively wide axial ratio acceptable frequency band. The relative bandwidth is calculated according to the following formula:

[0050]

[0051] in, Indicates relative bandwidth. This indicates the upper limit frequency of the band with an axial ratio of less than 3 dB. This indicates the lower limit frequency of the frequency band where the axial ratio is less than 3 dB. The center frequency.

[0052] The operating frequency bands and relative bandwidths of the linear circular polarization converter of the present invention with an axial ratio of less than 3 dB under different incident angles are shown in the table below.

[0053] Table 1. Operating frequency bands with an axial ratio less than 3 dB at different incident angles.

[0054] 0° 16.60~24.68 39.15 15° 16.60~24.77 39.50 30° 16.68~24.93 39.56 45° 16.74~25.07 39.85 60° 16.84~25.19 39.73

[0055] As shown in Table 1, when θ=0°, the frequency range with an axial ratio less than 3 dB is 16.60 GHz to 24.68 GHz, with a relative bandwidth of approximately 39.15%; when θ=60°, the frequency range with an axial ratio less than 3 dB is 16.84 GHz to 25.19 GHz, with a relative bandwidth of approximately 39.73%. The common frequency band with an axial ratio less than 3 dB stably covers the range of 16.84 GHz to 24.68 GHz under different incident angles. This result demonstrates that the present invention can maintain good circular polarization conversion performance under both wide bandwidth and wide incident angle conditions.

[0056] Figure 8 The insertion loss response curves of the transmissive linear circular polarization converter of the present invention are shown at different incident angles θ. Figure 8 The horizontal axis represents frequency in GHz, and the vertical axis represents insertion loss in dB. The curves marked with rhombuses, left-facing triangles, right-facing triangles, circles, and pentagrams in the figure correspond to the simulation results for incident angles θ of 0°, 15°, 30°, 45°, and 60°, respectively.

[0057] Depend on Figure 8 As can be seen, within the sweep frequency range of 16 GHz to 26 GHz, the insertion loss at different incident angles is generally less than 3 dB, indicating that the linearly circularly polarized converter of this invention exhibits low-loss transmission characteristics over a wide bandwidth and wide incident angle range. Specifically, within the sweep frequency range of 16 GHz to 26 GHz, as the incident angle θ increases from 0° to 60°, the insertion loss increases slightly with the increase of the incident angle, with the maximum insertion loss increasing from 1.65 dB to 2.13 dB, but always remaining below 3 dB. This result demonstrates that this invention can maintain low-loss transmission over a wide bandwidth and wide incident angle range.

[0058] The simulation experiments above show that the linear-circular polarization converter described in this invention exhibits excellent transmission and polarization conversion performance within a sweep frequency range of 16 GHz to 26 GHz. Within a wide incident angle range of 0° to 60°, the common operating frequency band with an axial ratio of less than 3 dB stably covers approximately 16.84 GHz to 24.68 GHz, and the overall insertion loss is less than 3 dB. This demonstrates that this invention, through the formation of a multi-resonant structure using upper and lower symmetrical stepped-gap metal patches and a middle square-ring metal patch, can extend the operating bandwidth of the linear-circular polarization converter. Simultaneously, through anisotropic metasurface units and symmetrical coupling structures, the influence of incident angle variations on the amplitude and phase of the orthogonal polarization components can be reduced, improving polarization conversion stability under wide incident angle conditions. This solves the problem that existing linear-circular polarization converters struggle to maintain both low axial ratio and low insertion loss within a wide operating frequency band and wide incident angle range.

Claims

1. A linear-circular polarization converter based on symmetrical stepped gaps and square ring metal patches, comprising a first metal patch (4), a first dielectric substrate (1), a second metal patch (5), a second dielectric substrate (2), a third dielectric substrate (3), and a third metal patch (6) arranged sequentially from top to bottom, characterized in that: The first metal patch (4) and the third metal patch (6) are symmetrical stepped slot metal patches with the same shape and size; the second metal patch (5) is a square ring metal patch; the first metal patch (4), the second metal patch (5), and the third metal patch (6) form a multi-resonant structure through interlayer coupling, so that the two orthogonal transmission components obtained by the decomposition of incident ray polarized wave maintain amplitude matching and a phase difference of about ±90° within the working frequency band; the first metal patch (4), the first dielectric substrate (1), the second metal patch (5), the second dielectric substrate (2), the third dielectric substrate (3), and the third metal patch (6) together constitute a metasurface unit with anisotropic response, which is used to modulate the amplitude and phase of the two orthogonal transmission components obtained by the decomposition of incident ray polarized wave, and convert the incident ray polarized wave into a circularly polarized transmission wave.

2. The linear-circular polarization converter according to claim 1, characterized in that, The first metal patch (4) is disposed on the upper surface of the first dielectric substrate (1), the second metal patch (5) is disposed on the upper surface of the second dielectric substrate (2), and the third metal patch (6) is disposed on the lower surface of the third dielectric substrate (3).

3. The linear-circular polarization converter according to claim 2, characterized in that, The symmetrical stepped gap metal patch refers to a symmetrical triangular combination structure with two bases facing each other, forming a gap extending diagonally between the two symmetrical triangular metal areas, and the waist of the symmetrical triangular metal area has a continuous stepped outline.

4. The linear-circular polarization converter according to claim 3, characterized in that, The stepped profile refers to a structure formed by alternating connections of multiple first side segments extending along a first direction and multiple second side segments extending along a second direction, with the first direction perpendicular to the second direction. Adjacent first and second side segments are connected end to end in sequence, and the waist of the symmetrical triangular metal region has a stepped shape with progressively bent curves.

5. The linear-circular polarization converter according to claim 4, characterized in that, The second metal patch (5) includes a square outer contour and a central circular through hole located inside the square outer contour, wherein the center of the central circular through hole coincides with the geometric center of the square outer contour.

6. The linear-circular polarization converter according to claim 5, characterized in that, The radius of the central circular through hole ranges as follows: ;in, This represents the free space wavelength corresponding to the operating center frequency of a linear circular polarization converter.

7. The linear-circular polarization converter according to claim 6, characterized in that, The first dielectric substrate (1) and the third dielectric substrate (3) are made of a first low-loss microwave dielectric material with the same relative permittivity, and the range of its permittivity is [2.85, 3.3]; the second dielectric substrate (2) is made of a second low-loss microwave dielectric material, and the range of its relative permittivity is [2.3, 2.8]; the relative permittivity of the first low-loss microwave dielectric material is greater than that of the second low-loss microwave dielectric material; the loss tangent of the first dielectric substrate (1), the second dielectric substrate (2) and the third dielectric substrate (3) is not greater than 0.

04.

8. The linear-circular polarization converter according to claim 7, characterized in that, The first dielectric substrate (1) and the third dielectric substrate (3) have the same thickness, and their values ​​range as follows: ; The thickness of the second dielectric substrate (2) is less than the thickness of the first dielectric substrate (1) and the third dielectric substrate (3), and its value range is: The range of the total thickness of the linear-circular polarization converter along the stacking direction is: .

9. The linear-circular polarization converter according to claim 1, characterized in that, The linear-circular polarization converter has a square outer contour projected perpendicular to the stacking direction, and the range of values ​​for the side length of the square is: .

10. The linear-circular polarization converter according to claim 1, characterized in that, The first metal patch (4), the second metal patch (5) and the third metal patch (6) are all conductive metal layers made of the same material, and the conductive metal layers are made of any one of copper, aluminum, silver, gold or other alloy materials.

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