Multi-mode circular polarization OAM filtering antenna based on artificial surface plasmon

Abstract

The invention discloses a multi-mode circularly polarized OAM (orbital angular momentum) filtering antenna based on an artificial surface plasmon. According to the antenna, the SSPP leaky-wave antenna and the HMSIPW filter are integrated, so that efficient emission of multi-mode OAM beams is realized, and the antenna has low axial ratio, high gain and good directional diagram matching performance; the SSPP leaky-wave antenna is composed of an Archimedes spiral line type SSPP waveguide and annularly distributed patches, wherein the SSPP waveguide realizes accurate regulation and control of dispersion characteristics through the combination of periodic sawtooth comb lines and uniform spiral lines; the HMSIPW filter is composed of a dielectric substrate layer, a metalized through hole and a gradient rectangular structure, impedance matching of a micro-strip and double lines is achieved, insertion loss is reduced, and radiation performance is improved. Compared with a traditional design, a filtering function is integrated, higher harmonic radiation and low-purity high-mode OAM are inhibited through the overall design, and selectivity and radiation energy uniformity are improved.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication, and particularly to a multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmon polaritons. Background Art

[0002] Surface Plasmon Polaritons (SPPs) are surface waves that propagate along the interface between a metal and a dielectric, and their properties are determined by the interaction between light and free electrons in the metal at the interface. Due to their strong electromagnetic field localization, SPPs have important applications in fields such as enhancing the interaction between light and matter, optical sensing, and nanophotonics. However, SPPs mainly exist in the optical and infrared frequency bands. In the microwave and millimeter-wave frequency bands, metals act as perfect conductors and cannot naturally excite SPPs, which limits their applications in the low-frequency band.

[0003] To overcome this limitation, spoof surface plasmon polaritons (SSPPs) are formed by designing periodic sub-wavelength structures (such as grooved or hole arrays) on the metal surface. These structures can simulate the properties of SPPs, confine electromagnetic waves on the metal surface, and achieve SPP-like behavior in the low-frequency band. By adjusting structure parameters such as the period and unit shape, the dispersion characteristics of SSPPs can be precisely controlled, expanding their application scope in the low-frequency band.

[0004] Artificial SSPP structures combine the design flexibility of metamaterials and the electromagnetic properties of metals, and can be used to develop new microwave components and communication devices. Especially in generating orbital angular momentum (OAM) modes, SSPP provides an effective approach. By using the helical structure or other complex geometric designs of SSPP, OAM vortex modes with specific topological charges can be generated for efficient information transmission. These characteristics provide new solutions for spectrum multiplexing and high-data-rate transmission in wireless communication systems. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmon polaritons, which combines an SSPP LWA and an HMSIPW filter to generate circularly polarized OAM waves of different modes by changing the frequency.

[0006] The technical solution for achieving the object of the present invention is as follows: A multi-mode circularly polarized OAM filtering antenna based on artificial surface plasmons, which consists of two dielectric substrates. The upper dielectric substrate is a double-layer board, composed of two parts: an SSPP leaky-wave antenna and an HMSIPW filter. The lower dielectric substrate is a single-layer board, and one side of it is entirely copper. The SSPP leaky-wave antenna consists of a periodically modulated Archimedean spiral-shaped SSPP waveguide, a load resistor, and an annularly distributed patch. The HMSIPW filter consists of a dielectric substrate layer, two metal layers, and a row of metallized vias. The dielectric substrate layer is sandwiched between the top and bottom metal layers, and the metallized vias are inserted into the dielectric substrate layer to connect the two metal layers. Rectangular slot arrays are etched on the two side metal layers as SSPP structures. The excitation is fed to the HMSIPW filter through a microstrip via a trapezoidal transition structure to complete filtering, and then reaches the SSPP leaky-wave antenna through the transition part of the trapezoidal transition structure on the other side.

[0007] Further, the Archimedean spiral-shaped SSPP waveguide is composed of a zigzag comb-shaped line and a spiral line with a uniform width. The top layer is a comb-shaped spiral line, and the bottom layer is a uniform spiral line. The dispersion characteristics are regulated by adjusting the unit period and the sawtooth ratio. There is a stub at the end of the top-layer comb-shaped spiral SSPP waveguide, and the stub is connected to the SSPP waveguide through a load resistor. The stub is connected to the uniform spiral on the bottom layer through a metallized via.

[0008] Further, the Archimedean spiral-shaped SSPP waveguide and the annularly distributed patch generate an OAM beam through tight coupling.

[0009] Further, the patch is located on one side of the uniform spiral line, and the patch is a sequential rotation structure. Multiple patches are regarded as a uniform circular array with one element missing. Starting from the patch close to the filter structure, they rotate counterclockwise in sequence for one week. The distance from the annularly distributed patch to the origin is the same, and the distance from the patch to the Archimedean spiral-shaped SSPP waveguide decreases in sequence.

[0010] Further, the patch structure is an isosceles triangle with a pair of symmetrically chamfered corners, and semi-ellipses are added to its convex side and the two chamfered sides.

[0011] Further, the plane Cartesian coordinate equation of the Archimedean spiral is:

[0012]

[0013] where x and y are the horizontal and vertical distances from the point on the line to the origin in the rectangular coordinate system respectively, R is the distance from the starting point of the spiral to the origin of the polar coordinate, b is the distance reduced by one turn, and θ is the polar angle.

[0014] Furthermore, the HMSIPW filter is symmetrically distributed on both sides and has a rectangular slot structure in the middle, which serves as an impedance transition between the microstrip and the twin-wire waveguide.

[0015] Compared with the prior art, the remarkable advantages of the present invention are as follows: An HMSIPW filter is added between the leaky wave antenna and the feed. Without significantly increasing the size, the antenna has filtering performance. For the low-frequency part outside the passband, the modal purity is high, but the radiation pattern of the vortex wave is severely distorted and is no longer a standard donut shape, which can be filtered out; for the high-frequency part outside the passband, the high-order harmonics and the first-order harmonics are radiated simultaneously, the modal purity is low, the radiation pattern of the vortex wave is severely distorted and is no longer a standard donut shape, presenting a petal shape with scattered energy, which is not conducive to transmission and needs to be filtered out. Using an Archimedean spiral-shaped SSPP waveguide, this decreasing coupling distance generates a more uniform radiation pattern of the vortex beam. At the same time, the patches are kept in a circular distribution, with better matching and a more uniform vortex field. The symmetrically chamfered triangular patch structure maintains a low axial ratio when radiating circularly polarized waves at different frequencies. The antenna has a higher gain and better input matching throughout the passband. Brief Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the OAM filtering antenna proposed by the present invention.

[0017] Figure 2 It is another perspective schematic diagram of the OAM filtering antenna proposed by the present invention.

[0018] Figure 3 It is a schematic diagram of the SSPP leaky wave antenna.

[0019] Figure 4 It is a schematic diagram of the OAM filtering antenna proposed by the present invention, where (a) is the top view of dielectric plate 1, (b) is the bottom view of dielectric plate 1, and (c) is the metal ground of dielectric plate 2.

[0020] Figure 5 It is the S-parameter curve graph of the proposed OAM filtering antenna.

[0021] Figure 6 It is the gain curve graph of the proposed OAM filtering antenna.

[0022] Figure 7 It is the structural diagram of the SSPP waveguide unit, where (a) is the southeast isometric view, (b) is the top view, and (c) is the bottom view.

[0023] Figure 8 It is the dispersion curve graph of the SSPP waveguide unit.

[0024] Figure 9 It is the schematic diagram of the patch structure, where (a) is the complete structure and (b) is the structure without the semi-elliptical prototype.

[0025] Figure 10 It is the structural diagram of the HMSIPW unit, where (a) is the southeast isometric view and (b) is the top view.

[0026] Figure 11 It is the dispersion curve diagram of the HMSIPW unit structure.

[0027] Figure 12 It is the HMSIPW filter, where (a) is the southeast isometric view, (b) is the top view, and (c) is the bottom view.

[0028] Figure 13 It is the S-parameter curve diagram of the HMSIPW filter structure.

[0029] Figure 14 They are the radiation patterns of right-handed circular polarization with Phi = 0° and Phi = 90° in different modes, (a) l = +4, (b) l = +3, (c) l = +2, (d) l = +1, (e) l = 0, (f) l = -1. Specific implementation manners

[0030] The present invention proposes a multi-modal circularly polarized OAM (Orbital Angular Momentum) filtering antenna based on artificial surface plasmons. By integrating a SSPP (Spoof Surface Plasmon Polaritons) leaky-wave antenna with a HMSIPW (Half-Mode Substrate Integrated Plasmonic Waveguide) filter, this antenna achieves efficient emission of multi-modal OAM beams, featuring low axial ratio, high gain, and good pattern matching performance. The SSPP leaky-wave antenna consists of an Archimedean spiral-shaped SSPP waveguide and annularly distributed patches. Among them, the SSPP waveguide realizes precise control of dispersion characteristics through the combination of periodic sawtooth comb lines and uniform spiral lines. The phase difference between adjacent SSPP units is 48°, 52°, 56°, 60°, 64°, 68° at 4.12 GHz, 4.46 GHz, 4.80 GHz, 5.14 GHz, 5.48 GHz, 5.82 GHz. The patches are also sequentially rotationally distributed, so its first-order harmonics correspond to OAM modes (l = +4) (l = +3) (l = +2) (l = +1) (l = 0) (l = -1). The patches adopt a symmetrically chamfered triangular design, and semi-elliptical designs are added at the raised edges and symmetric chamfers to improve the coupling efficiency and axial ratio performance. The HMSIPW filter consists of a dielectric substrate layer, metallized vias, and a gradient rectangular structure, realizing impedance matching between the microstrip and the balanced line, reducing the insertion loss, and improving the radiation performance. The antenna structure is composed of two dielectric substrates, and left-handed and right-handed circularly polarized waves can be generated respectively by different placement orders. By adjusting the geometric parameters of the SSPP waveguide, specific-modal OAM vortex beams can be generated at different frequencies. The simulation results show that the antenna has a uniform pattern at the frequency points of each mode. Compared with the traditional design, the present invention integrates a filtering function, suppresses high-order harmonic radiation and low-purity high-modal OAM through overall design, increases selectivity, and improves the radiation energy uniformity. It can generate multi-modal OAM, significantly reducing the complexity of the feed source and improving the Figure 1 directivity consistency, providing technical support for efficient wireless communication.

[0031] SSPP is usually composed of a comb-shaped microstrip, and its electromagnetic response can be precisely controlled by adjusting parameters such as the size, shape, and material of the unit. Conventional SSPP vortex wave antennas, without a filtering structure, have no selectivity for generating different OAM modes at different frequencies. At some frequencies, the pattern is distorted along the way, the energy is dispersed, and the purity is low, which is not conducive to transmission. By improving the structure of the SSPP waveguide and the patch structure, improving the matching, and maintaining a low axial ratio at different frequencies. Integrating the filter with the leaky-wave antenna can improve selectivity and make the generated OAM wave more conducive to transmission.

[0032] The present invention provides a multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmonics. The filtering antenna is jointly composed of an SSPP leaky-wave antenna and a half-mode SIW filter. Through the integrated design of the SSPP leaky-wave antenna and the HMSIPW filter, the antenna realizes the efficient emission of multi-modal OAM beams and has low axial ratio, high gain, and good pattern matching performance.

[0033] The SSPP leaky-wave antenna includes a radiation structure composed of an Archimedean spiral-shaped SSPP waveguide and annularly distributed patches. The OAM beam is generated by the tight coupling between the SSPP waveguide and the patches.

[0034] The Archimedean spiral-shaped SSPP waveguide is composed of a serrated comb line and a spiral line with a uniform width, and the dispersion characteristics are regulated by adjusting the unit period and the serration ratio.

[0035] The patch structure is a symmetrically chamfered triangle, and the chamfers are sequentially rotated and distributed around the SSPP waveguide. The patches are distributed in a ring, and the SSPP waveguide is distributed in a spiral shape. The distance between the patches and the SSPP waveguide decreases gradually.

[0036] The HMSIPW filter is composed of a dielectric substrate layer, two side metal layers, and a central metallized via. The two sides are symmetrically distributed, and a rectangular groove structure is opened in the middle as an impedance transition between the microstrip and the two-wire waveguide. The two-side gradient rectangular structure realizes the smooth transition of different impedance regions, effectively reducing the insertion loss and improving the radiation performance of the pattern.

[0037] For the patch structure, semi-elliptical designs are added to the raised edges and symmetric chamfers of the patches, improving the patch coupling efficiency and axial ratio performance.

[0038] The array surface specification of the antenna is 220mm * 220mm. The basic unit forming the SSPP waveguide is a double-sided transmission line, presenting an Archimedean spiral shape distribution. On one side, it is a serrated dressing line, and on the other side, it is a uniform line width. This double-line SSPP can reduce the unit size. Metal vias are used as substrate integrated waveguides for one week of the unit. The filtering structure is a half-mode SIW structure, with a rectangular groove opened in the center, symmetrically distributed on both sides, and at the same time, microstrip and double-line structures are on both sides respectively. A metallized via is located at the end of the spiral SSPP waveguide, connecting the side of the comb line spiral and the side of the uniform spiral. The load resistor is located on the side of the comb line, connecting a metallized via and the SSPP waveguide. The resistor can reduce reflection and improve matching. The patches are located on the side of the uniform spiral, and the patches are in a sequential rotation structure. Multiple patches are regarded as a uniform circular array with one element missing. Starting from the patch close to the filter structure, they are rotated counterclockwise for one week. The distance from the annularly distributed patches to the origin is the same, and the distance from the patches to the Archimedean spiral-shaped SSPP waveguide decreases in sequence.

[0039] The part of the filtering structure with unidirectional metallized vias and no rectangular slots is HMSIW, and the part with both metal vias and rectangular slots is HMSIPW. Therefore, the trapezoidal parts on both sides of the HMSIPW filter are transition parts, the middle is the HMSIPW unit, and a part of HMSIW with unidirectional metallized vias and no rectangular slots is connected to the trapezoidal transition parts on both sides. The HMSIPW filter is composed of trapezoidal transition - HMSIW - HMSIPW - HMSIW - trapezoidal transition in sequence. The trapezoidal transition structure on one side realizes the impedance transition between the 50Ω microstrip line and HMSIW, and the other side is the impedance transition from the SSPP waveguide twin line to HMSIW. Four progressive length rectangular HMSIPW units are used for the impedance matching between HMSIP and HWSIPW. This filter can achieve a good transition from the microstrip structure to the twin - line structure and improve the matching. HMSIPW is for realizing the band - pass filtering function. The trapezoidal transition part and HMSIW work together to achieve the impedance matching between the microstrip and HMSIPW and between HMSIPW and the SSPP twin line.

[0040] Furthermore, by adjusting the SSPP waveguide parameters, different OAM modes are generated at different frequencies.

[0041] Furthermore, the antenna can generate different circular polarizations on both sides of the dielectric substrate. On the side with the patch dielectric board, along the feeding path, the patch is excited clockwise to generate a left - hand circularly polarized wave; on the side without the patch dielectric board, along the feeding path, the patch is excited counter - clockwise to generate a right - hand circularly polarized wave.

[0042] Furthermore, adding a single - layer board with full - copper coverage on one side below the side with the patch dielectric board can reverse the polarization, change the left - hand circular polarization to right - hand circular polarization, and increase the gain. Adding a single - layer board with full - copper coverage on one side below the side without the patch dielectric board can reverse the polarization, change the right - hand circular polarization to left - hand circular polarization, and increase the gain.

[0043] The periodically modulated Archimedean spiral - shaped SSPP waveguide realizes the conversion from the SSPP wave to the radiation wave. The periodically modulated annular SSPP waveguide consists of an SSPP waveguide with a starting distance of R and N = 14 metal patches. These patches are placed equidistantly inside the SSPP. At the same time, the length between two adjacent patches of the spiral - shaped SSPP waveguide (modulation period length) is d = 6p, where p is the length of the SSPP unit. The angle between the line connecting the center of adjacent patches and the origin of coordinates is 24°, and the angles between the two sides of the unit and the origin of coordinates are 4°. The leaky - wave antenna part has a total of 85 SSPP units, of which 82 units are located on the spiral line and the remaining 3 are on the straight line, and this line is tangent to the starting point of the spiral line.

[0044] Furthermore, the basic unit period of the SSPP is 6 mm. One side of the unit is a sawtooth-shaped dressing line, and the other side has a uniform line width. By changing the unit parameters, such as the line widths on both sides and the sawtooth ratio, the dispersion curve of the unit can be adjusted. The corresponding frequencies of different OAM modes are changed.

[0045] The leaky wave antenna uses 85 SSPP units and 14 patches to prevent the interaction before the SSPP waveguide.

[0046] Furthermore, the distances from the annularly distributed patches to the origin are the same, and the distances from the patches to the Archimedean spiral-shaped SSPP waveguide decrease gradually in sequence. Through patch coupling, the current on the patches is also distributed in a circular ring, with stronger radiation ability, thus generating a more uniform vortex beam.

[0047] The SSPP waveguide is distributed in an Archimedean spiral, and its plane Cartesian coordinate equation is:

[0048] where R is the distance from the starting point of the spiral to the origin of the polar coordinates, b is the distance reduced in one turn, and θ is the polar angle.

[0049] Furthermore, the phase differences between adjacent SSPP units at 4.12 GHz, 4.46 GHz, 4.80 GHz, 5.14 GHz, 5.48 GHz, and 5.82 GHz are 48°, 52°, 56°, 60°, 64°, and 68°. The patches are distributed in a sequential rotation, so its first-order harmonics correspond to the OAM modes (l = +4)(l = +3)(l = +2)(l = +1)(l = 0)(l = -1).

[0050] Furthermore, 4 progressive length units are added before the HMSIPW to achieve the matching between the microstrip and the HMSIPW and between the twin lines and the HMSIPW, reducing the insertion loss.

[0051] Furthermore, changing the width of the HMSIPW, i.e., the position of the metallized vias, affects the lower limit of the passband cut-off frequency, and changing the length of the slot line in the middle HMSIPW affects the upper limit of the cut-off frequency.

[0052] Furthermore, the trapezoidal transition structure connects the filtering structure and the leaky wave antenna to achieve a smooth transition between different impedance regions, effectively reducing the insertion loss and improving the radiation performance of the pattern.

[0053] Furthermore, for the multi-modal circularly polarized OAM filtering antenna of the artificial surface plasmon, the distance between the two dielectric plates is 15 mm. The upper substrate uses the F4BM265 material, with a dielectric constant of 2.65, a dielectric loss tangent = 0.0013, and a thickness of 1 mm.

[0054] As a preferred method, the feeding method of the feed is microstrip feeding through a coaxial probe.

[0055] The patch is composed of a pair of right-angled triangles with symmetric cut corners rotated in sequence. Semi-ellipses are added to its convex side and the cut corner sides on both sides. The distance between the patch and the SSPP line is 1.4 mm, and the patch is excited by coupling.

[0056] The antenna array surface composed of the SSPP leaky-wave antenna and the HMSIPW filter has a specification of 220 mm × 220 mm. By overall design, the high-order harmonic radiation and low-purity high-mode OAM are suppressed, the selectivity is increased, and the radiation energy uniformity is improved.

[0057] The present invention provides a multi-mode circularly polarized OAM filtering antenna based on artificial surface plasmon polaritons. The filtering structure considers the transition between the microstrip and the twin-wire, generating circularly polarized OAM beams with mode numbers of +4, +3, +2, +1, 0, -1. The filtering structure is integrated in front of the leaky-wave antenna to improve the matching. The filtering direction pattern has serious distortion, energy stray, and non-concentrated frequency bands. The high-order radiation harmonics are suppressed, and the selectivity is improved.

[0058] Compared with the traditional OAM antenna array, the SSPP-based design significantly reduces the complexity and cost of the feed network. By generating OAM vortex beams on a planar spiral structure or a periodically modulated SSPP waveguide, efficient emission of multi-mode OAM modes can be achieved.

[0059] The antenna of the present invention realizes the efficient emission of multi-mode OAM beams by integrating the SSPP leaky-wave antenna and the HMSIPW filter, and has low axial ratio, high gain and good direction pattern matching performance; the SSPP leaky-wave antenna is composed of an Archimedean spiral-shaped SSPP waveguide and an annularly distributed patch, where the SSPP waveguide realizes precise control of the dispersion characteristics through the combination of a periodic sawtooth comb line and a uniform spiral line; the HMSIPW filter is composed of a dielectric substrate layer, metallized vias and a gradient rectangular structure, realizing the impedance matching between the microstrip and the twin-wire, reducing the insertion loss and improving the radiation performance. The antenna has a uniform direction pattern at the frequency points of each mode. Compared with the traditional design, the present invention integrates the filtering function, suppresses high-order harmonic radiation and low-purity high-mode OAM through overall design, increases the selectivity and radiation energy uniformity. It can generate multi-mode OAM, significantly reduces the feed complexity, and improves the Figure 1 directivity, providing technical support for efficient wireless communication.

[0060] The following further clarifies the present invention with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0061] Embodiment

[0062] Combined withFigures 1 - 3 , this embodiment proposes a multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmons. This antenna is jointly composed of an SSPP leaky-wave antenna and an HMSIW filter. The SSPP waveguide has a double-line in a spiral shape, and the metal patches are distributed in a circular ring. The two sides of the filter are respectively a microstrip and a double-line structure. The SSPP leaky-wave antenna and the HMSIW filter are integrated on the dielectric substrate 1, and the substrate 2 is a single-layer board with copper completely covering one side. One side of the SSPP waveguide unit is a zigzag comb line, and the tooth ratio accounts for 50% in one unit, and the other side has a uniform line width. There is a metallized via at the end of the spiral SSPP waveguide, connecting the comb-line spiral side and the uniform spiral side. The load resistor connects a metallized via to the SSPP waveguide. The patch structure is a pair of symmetrically chamfered isosceles triangles, with semi-ellipses added to its protruding side and the two chamfered sides. To improve the patch coupling, the dielectric plate 2 is placed 15 mm below the patch-side layer dielectric plate 1, and a right-handed circularly polarized wave is generated on the comb-line side. The simulation shows that the impedance matching in the passband is less than -10 dB, the gain is greater than 6 dB, and OAM beams with l = +4, l = +3, l = +2, l = +1, l = 0, l = -1 modes are generated at 4.12 GHz, 4.42 GHz, 4.80 GHz, 5.14 GHz, 5.48 GHz, 5.82 GHz. This OAM filtering antenna has selectivity, a more uniform radiation pattern, and better input matching.

[0063] Figure 4 For the proposed OAM filtering antenna, (a) top view of dielectric plate 1, (b) bottom view of dielectric plate 1, (c) metal ground of dielectric plate 2. The filtering antenna is jointly composed of an SSPP leaky-wave antenna and an HMSIW filter. The dielectric substrate material is F4BM265, with a dielectric constant = 2.65, a dielectric loss tangent = 0.0013, and a thickness of 1 mm. The basic unit of the SSPP waveguide is a double-sided transmission line, which is characterized by an Archimedean spiral distribution, with a zigzag comb line on one side and a uniform line width on the other side. The sizes of the two dielectric plates are both 220 mm * 220 mm.

[0064] Figure 5 For the proposed OAM filtering antenna S-parameter curve. Its -10 dB input impedance bandwidth is 3.93 GHz - 5.80 GHz.

[0065] Figure 6The gain curve of the proposed OAM filtering antenna. At 4.12 GHz (l = +4), 4.46 GHz (l = +3), 4.80 GHz (l = +2), 5.14 GHz (l = +1), 5.48 GHz (l = 0), 5.82 GHz (l = -1), the gains are 7.093 dBi, 6.174 dBi, 6.621 dBi, 6.142 dBi, 9.079 dBi, and 4.338 dBi respectively.

[0066] Figure 7 It is the SSPP waveguide unit structure (a) southeast isometric view, (b) top view, (c) bottom view. One side of the SSPP waveguide unit is a zigzag comb line, and the tooth ratio accounts for 50% in one unit, and the other side is a uniform line width.

[0067] Figure 8 It is the dispersion curve of the SSPP waveguide unit. At 4.12 GHz, 4.46 GHz, 4.80 GHz, 5.14 GHz, 5.48 GHz, 5.82 GHz, the phase difference between adjacent units is 48°, 52°, 56°, 60°, 64°, 68°. Therefore, the corresponding modes at different frequencies are 4.12 GHz (l = +4), 4.46 GHz (l = +3), 4.80 GHz (l = +2), 5.14 GHz (l = +1), 5.48 GHz (l = 0), 5.82 GHz (l = -1).

[0068] Figure 9 It is the schematic diagram of the patch structure. (a) is the complete structure, and (b) is without the semi-elliptical prototype. The patch structure in (b) is a pair of symmetrically chamfered isosceles triangles without the semi-ellipse added.

[0069] Figure 10 It is the HMSIPW unit structure. (a) is the southeast isometric view, and (b) is the top view. There are four metal vias in one unit period, a 0.3 mm rectangular slot is opened in the middle, and both sides are symmetrical.

[0070] Figure 11 It is the dispersion curve of the HMSIPW unit structure. k is the propagation constant in the propagation direction. It can be seen from the dispersion curve that HMSIPW has a band-pass characteristic. The lower cut-off frequency of the band-pass HMSIPW filter is 3.11 GHz, and the upper cut-off frequency is 5.95 GHz.

[0071] Figure 12It is a HMSIPW filter. (a) is the southeast isometric view, (b) is the top view, and (c) is the bottom view. The HMSIPW structure consists of a dielectric substrate layer, two metal layers, and a row of metallized vias. The dielectric substrate layer is sandwiched between the top and bottom metal layers, and the metallized vias are inserted into the dielectric substrate layer to connect the two metal layers. The part of the filtering structure with single-sided metallized vias and no rectangular slots is HMSIW, and the part with both metal vias and rectangular slots is HMSIPW. The trapezoidal parts on both sides of the HMSIPW filter are the transition parts, the middle is the HMSIPW unit, and a part of HMSIW with single-sided metallized vias and no rectangular slots is connected to the trapezoidal transition parts on both sides. The HMSIPW filter is composed of trapezoidal transition - HMSIW - HMSIPW - HMSIW - trapezoidal transition in sequence.

[0072] Figure 13 It is the S-parameter curve of the HMSIPW filter structure. From Figure 13 it can be seen that its -10dB input impedance bandwidth is 3.87GHz - 5.65GHz. Within 4.12GHz - 5.48GHz, S 21 is greater than -0.7dB.

[0073] From Figure 14 it can be seen that they are the radiation patterns of right-handed circular polarization with Phi = 0° and Phi = 90° in different modes. (a) l = +4, (b) l = +3, (c) l = +2, (d) l = +1, (e) l = 0, (f) l = -1. For mode l = +4, the divergence angle is 46°; for mode l = +3, the divergence angle is 31°; for mode l = +2, the divergence angle is 21°; for mode l = +1, the divergence angle is 14°; for mode l = 0, the main lobe direction is 1°; for mode l = -1, the divergence angle is 12°.

Claims

1. A multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmons, characterized in that, It consists of two layers of dielectric substrates. The upper dielectric substrate is a double-layer board, which is composed of two parts: an SSPP leaky-wave antenna and an HMSIPW filter. The lower dielectric substrate is a single-layer board, and one side of it is entirely copper. The SSPP leaky-wave antenna is composed of a periodically modulated Archimedean spiral-shaped SSPP waveguide, a load resistor, and an annularly distributed patch. The HMSIPW filter is composed of a dielectric substrate layer, two metal layers, and a row of metallized vias. The dielectric substrate layer is sandwiched between the top and bottom metal layers, and the metallized vias are inserted into the dielectric substrate layer to connect the two metal layers. Rectangular slot arrays are etched on the two side metal layers as SSPP structures. The excitation is fed to the HMSIPW filter through a microstrip via a trapezoidal transition structure to complete filtering, and then reaches the SSPP leaky-wave antenna through the transition part of the trapezoidal transition structure on the other side.

2. The multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmons according to claim 1, wherein The Archimedean spiral-shaped SSPP waveguide is composed of a zigzag comb-like line combined with a spiral line of uniform width. The top layer is a comb-shaped spiral line, and the bottom layer is a uniform spiral line. The dispersion characteristics are regulated by adjusting the unit period and the sawtooth ratio. There is a stub at the end of the top-layer comb-shaped spiral SSPP waveguide, and the stub is connected to the SSPP waveguide through a load resistor. The stub is connected to the uniform spiral shape of the bottom layer through a metallized via.

3. The multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmon according to claim 2, characterized in that, The Archimedean spiral-shaped SSPP waveguide and the annularly distributed patch generate an OAM beam through tight coupling.

4. The multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmons according to claim 2, wherein The patch is located on one side of the uniform spiral line, and the patch is a sequential rotation structure. Multiple patches are regarded as a uniform circular array with one element missing. Starting from the patch close to the filter structure, it rotates counterclockwise for one week. The distances from the annularly distributed patches to the origin are the same, and the distances from the patches to the Archimedean spiral-shaped SSPP waveguide decrease in sequence.

5. The multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmons according to claim 4, wherein The patch structure is a pair of symmetrically chamfered isosceles triangles, with semi-ellipses added to its protruding side and the two chamfered sides on both sides.

6. The multi-modal circularly polarized OAM filtering antenna based on artificial surface plasmons according to claim 2, wherein The plane Cartesian coordinate equation of the Archimedean spiral is: Wherein, x and y are the distances of a point on the line to the origin in the horizontal and vertical directions in a rectangular coordinate system respectively, R is the distance from the starting point of the helix to the origin of the polar coordinate system, b is the distance reduced per revolution, and θ is the polar angle.

7. The multimodal circularly polarized OAM filtering antenna based on artificial surface plasmons according to claim 1, wherein The HMSIPW filter is symmetrically distributed on both sides, with a rectangular slot structure in the middle, serving as an impedance transition between the microstrip and the two-wire waveguide.

8. The multimodal circularly polarized OAM filtering antenna based on artificial surface plasmon according to claim 1, characterized in that The distance between the two layers of dielectric substrates is 15 mm. The upper substrate uses F4BM265 material, with a dielectric constant of 2.65 and a thickness of 1 mm.

9. The multimodal circularly polarized OAM filtering antenna based on artificial surface plasmons according to claim 1, wherein The sizes of the two dielectric plates are both 220 mm * 220 mm.

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