Filtering folding transmission array antenna with broadband, high gain and circular polarization

Abstract

The invention belongs to the technical field of communication, and particularly relates to a broadband, high-gain and circularly-polarized filtering folded transmission array antenna, which comprises a planar integrated feed source antenna, an SIW-Mini-SMP transition structure, a reflection type cross polarization converter RCPC and a transmission type metasurface TMMS capable of effectively generating circularly-polarized electromagnetic waves. The working frequency range of the antenna is 12.0 GHz to 18.3 GHz, the antenna covers the whole Ku wave band, the bandwidth is 41.6%, and the antenna has remarkable broadband characteristics; high gain is kept in the working frequency band, the peak gain is 22.64 dBic, and the advantage of high gain is shown.

Description

Technical Field

[0001] This invention belongs to, but is not limited to, the field of communication technology, and particularly relates to a broadband, high-gain, circularly polarized filtered folded transmission array antenna. Background Technology

[0002] With the rapid development of 5G / 6G mobile communication, satellite interconnection, and radar technology, modern advanced wireless communication systems are placing higher demands on the overall performance of antennas. On the one hand, they must meet the requirements of high gain, low loss, and low profile characteristics; on the other hand, they must integrate more functions while achieving broadband performance. Folded transmission array antennas, as a novel electromagnetic wavefront modulation device that combines the advantages of high gain and low profile, have achieved continuous breakthroughs in recent years.

[0003] Traditional folded transmission arrays, due to structural limitations, struggle to simultaneously achieve high gain and a large gain bandwidth across a wide frequency range. Furthermore, existing broadband designs are often affected by factors such as dispersion, resulting in a practically usable bandwidth significantly smaller than the designed bandwidth. In addition, multi-functional integration of traditional antennas is a current research hotspot. Existing multi-functional integration schemes typically achieve this by loading reconfigurable devices or employing mode multiplexing. The challenge of this approach lies in balancing antenna electromagnetic performance, size, and design complexity.

[0004] In 2022, Li Tangjing of the Air Force Engineering University proposed a circularly polarized folded transmission array. This array achieved a conversion from linear to circular polarization by introducing a transceiver metasurface, and utilized the polarization-conversion reflective surface to alter the propagation path of electromagnetic waves, thereby effectively reducing the antenna profile. However, the proposed transmission array's -3 dB bandwidth was only 15.8%, insufficient for operation over a wide frequency range. Furthermore, out-of-band interference energy was not effectively suppressed, which to some extent reduced the radiation performance stability and anti-interference capability of the transmission array in high-dynamic environments.

[0005] Therefore, how to balance broadband and high gain in folded transmission arrays, and further integrate electromagnetic properties such as circular polarization and filtering, remains a technical challenge that needs to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a broadband, high-gain, circularly polarized filtered folded transmission array antenna.

[0007] The specific implementation of the present invention is as follows: a broadband, high-gain, circularly polarized filtered folded transmission array antenna, the device comprising: a planar integrated feed antenna, a SIW-Mini-SMP transition structure, a reflective cross-polarization converter RCPC, and a transmission metasurface TMMS capable of generating circularly polarized electromagnetic waves.

[0008] The feed antenna serves as the feed source for the entire antenna array and has filtering characteristics; the SIW-Mini-SMP transition structure serves as the connection between the feed source and the test equipment; the TMMS function is to convert x-polarized waves into right-hand circularly polarized RHCP waves and suppress the passage of y-polarized waves; while the RCPC realizes the mutual conversion between x- and y-polarized waves.

[0009] Furthermore, the overall structure of the device employs a folding mechanism to reduce the profile height to approximately one-third of that of a traditional transmission array, while maintaining good performance through reasonable polarization control. The top of the transmission metasurface can be tuned to adjust the radiation phase, forming a circularly polarized emission wave that approximates a plane wave, thereby improving the aperture efficiency of the folded transmission array. To achieve broadband characteristics and meet the requirements for radiation pattern stability, a substrate integrated waveguide (SIW) aperture-coupled feed structure is used, integrating the magnetoelectric dipole feed source into the bottom cross-polarization converter. This design leverages the compactness and low-loss characteristics of SIW, thereby improving overall performance and maintaining consistent operating efficiency over a wide frequency range in the Ku band. To minimize losses caused by the SIW structure and facilitate measurement, a miniature Mini-SMP connector is used to connect to the GCPW.

[0010] Furthermore, the feed antenna employs a magnetoelectric dipole as the feed source; the substrate-integrated waveguide aperture serves as the feeding section for coupled feeding; four rectangular patches with metal through-holes serve as the radiating section; the bandpass filter structure includes the waveguide itself, the resonant SIW back cavity in substrate 4, and the openings on the magnetoelectric dipole patches; wherein, the inherent high-pass characteristics of the waveguide are used to achieve suppression of the lower sideband outside the Ku band, and the resonant SIW back cavity in substrate 4 and the openings on the magnetoelectric dipole patches generate radiation nulls Hnull_1 and Hnull_2 in the upper sideband, respectively; in addition, an additional SIW back cavity is designed on substrate 3 to enhance the gain stability of the feed source, while reducing the frequency shift and impedance mismatch caused by the mutual coupling between the feed source and surrounding adjacent components.

[0011] Furthermore, the SIW-Mini-SMP transition structure is a broadband, low insertion loss coplanar waveguide GCPW to SIW transition structure, comprising a Mini-SMP connector, a GCPW excitation section, a transition section, and an SIW waveguide section; the Mini-SMP connector is model GPPO-JHD12 to ensure impedance matching and external connection; the center conductor of the GCPW is chamfered to improve matching efficiency; the transition section from GCPW to SIW is a quadrilateral transition structure, which further improves matching efficiency compared to the triangular transition structure.

[0012] Furthermore, the reflective cross-polarization converter (RCPC) is composed of a double-sided copper-clad dielectric substrate, with the dielectric material being F4B; the top layer is a set of arrow patterns placed diagonally, and the bottom layer is metal.

[0013] Furthermore, the transport-type metasurface TMMS consists of a horseshoe-shaped patch at the bottom, metallized vias, a metal ground, an asymmetric H-shaped aperture patch at the top, and two dielectric substrates; the horseshoe-shaped patch at the bottom includes a notch with an angle of θ. d The annular pores can absorb x-polarized waves and reflect y-polarized waves.

[0014] Furthermore, the device employs a new gain bandwidth enhancement method and applies a gain prediction model for the transmission array antenna; it quantifies the trend of the transmission array gain bandwidth with the key parameters; it expands the traditional spatial phase error factor calculation formula (1), and the design bandwidth can be expressed by the spatial phase dispersion error, the design bandwidth can be expressed by formula (2), and the gain of the array antenna can be expressed by formula (3); finally, the expanded formulas 2 and 3 can be used to optimize and enhance the gain and bandwidth of the folded transmission array, thereby achieving the advantages of wide bandwidth and high gain.

[0015] (1)

[0016] (2)

[0017] (3)

[0018] Where (x) i ,y i ) represents the coordinates of the (i,j)th element, k c It is related to the phase compensation frequency f c The corresponding free space number, F is the focal length of the transmission array; A p λ is the area of ​​the aperture, and λ is the wavelength in free space.

[0019] Furthermore, the planar integrated feed source is a magnetoelectric dipole feed source with integrated bandpass filtering function, which includes a substrate integrated waveguide coupled feeding structure, a resonant cavity structure, and a patch aperture filter structure. The above structures work together to form at least two radiation zeros in the operating frequency band to achieve out-of-band suppression and maintain a stable radiation amplitude and phase distribution in the band.

[0020] This feature directly embeds the filtering function into the feed radiation structure, enabling the feed to simultaneously perform the dual functions of "excitation + spectrum shaping". This avoids the losses and phase distortions caused by introducing additional filters at the front end of the array, improves the overall system efficiency and polarization purity, and enhances the robustness to coupling disturbances of neighboring units.

[0021] Furthermore, after the transmission metasurface absorbs the electromagnetic wave of the corresponding polarization at the bottom, it radiates a broadband circularly polarized electromagnetic wave from the top. Phase compensation is performed according to the rotation of the top patch, so that the transmitted wave forms a circularly polarized wave with a constant phase difference in space. At the same time, the bottom of the transmission metasurface reflects the non-target polarization component.

[0022] This feature integrates circular polarization generation and polarization selectivity suppression in the same unit, avoiding the cascaded structure of the traditional "linear polarization array + external polarizer", thereby reducing insertion loss, improving axial ratio stability, and significantly enhancing the system's integration and reliability.

[0023] The present invention also provides a broadband filtered feed source for the above-mentioned folded transmission array antenna, wherein the feed source adopts a magnetoelectric dipole radiation structure and is coupled and fed through a substrate integrated waveguide aperture;

[0024] The feed introduces the synergistic effect of multiple resonant cavities and radiation null points in the radiation path, enabling the feed to form bandpass radiation characteristics within the target operating frequency band and achieve radiation suppression in the out-of-band frequency band, thus achieving the unification of feed radiation and spectrum selection without adding external filters.

[0025] Furthermore, the inherent high-pass characteristics of the substrate integrated waveguide body are used to suppress out-of-band radiation below the target operating frequency band, while the resonant cavity structure located behind the feed source is used to form a radiation null point above the target operating frequency band to achieve double-sideband radiation suppression.

[0026] Furthermore, an additional waveguide back cavity is set behind the magnetoelectric dipole radiation structure to stabilize the radiation pattern of the feed over a wide frequency range and reduce frequency drift and impedance mismatch caused by electromagnetic coupling between the feed and adjacent structures.

[0027] The present invention also provides a gain bandwidth enhancement design method for the above-mentioned folded transmission array antenna. By introducing spatial phase dispersion error, the frequency response of the transmission array antenna is modeled, and the phase deviation relationship between the spatial position of the array element, the equivalent focal length and the operating frequency is quantified into design constraints.

[0028] Based on this, according to the relationship between the spatial phase dispersion error and the maximum allowable phase error of the array, the achievable design bandwidth of the transmission array antenna is determined, and the array gain is estimated by combining the aperture area and the operating wavelength, so as to achieve the coordinated optimization design of gain and bandwidth.

[0029] Furthermore, the spatial phase dispersion error is obtained by comparing the propagation path phase of the array element at different operating frequencies with the reference phase at the phase compensation frequency, and is used to characterize the effect of frequency variation on the radiation phase consistency of the transmission array.

[0030] Furthermore, the design bandwidth is determined by the functional relationship between the array's maximum spatial phase scattering error, equivalent focal length, and effective aperture size, to ensure the stability of the main lobe direction and gain of the transmission array antenna within the design bandwidth.

[0031] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0032] 1. The invention operates in the frequency band from 12.0 GHz to 18.3 GHz, covering the entire Ku band, with a 3dB bandwidth of 41.6%, exhibiting significant broadband characteristics, enabling the antenna to operate in a wider frequency range.

[0033] 2. This invention maintains high gain within the operating frequency band, with a peak gain of 22.64 dBic, demonstrating the advantage of high gain and enabling the antenna to have a longer propagation range.

[0034] 3. This invention changes the propagation path of electromagnetic waves through a folding mechanism, and the cross-section is 1 / 3 of that of a traditional transmission array. It has the advantage of low cross-section, which greatly reduces the footprint of the antenna and is conducive to integration.

[0035] 4. This invention achieves out-of-band rejection levels of 38.1 dB and 44.3 dB, and has good filtering characteristics, enabling the antenna to radiate normally within the operating frequency band and not participate in radiation outside the operating frequency band.

[0036] The technical solution of this invention solves a technical problem that people have long desired to solve but have been unable to achieve:

[0037] The technical solution of this invention solves the problem of multi-functional integration of filtering, broadband, and high gain in folded transmission arrays. Specifically, it designs a broadband filtered circularly polarized folded transmission array antenna. This antenna achieves 41.6% usable bandwidth, has superior double-sideband suppression filtering capabilities (38.1 dB, 44.3 dB), maintains circularly polarized radiation within the usable bandwidth, has a peak gain of 22.64 dBic, and its profile is only 1 / 3 that of a traditional transmission array, exhibiting significant advantages in broadband, high gain, circular polarization, filtering, and low profile. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the working principle of the folded transmission array proposed in (a) of the present invention, and a three-dimensional exploded view (b).

[0039] Figure 2 This is a structural diagram of the filter feed antenna provided in an embodiment of the present invention;

[0040] Figure 3 These are the simulated reflection coefficients and gains of the feed source provided in the embodiments of the present invention;

[0041] Figure 4 These are the simulation results of (a) the geometric parameters of the SIW-Mini-SMP transition structure and (b) the S-parameters provided in the embodiments of the present invention;

[0042] Figure 5 Here are (a) a three-dimensional structural schematic diagram of the cross-polarization conversion unit and (b) the reflection coefficients at different incident angles provided in this embodiment of the invention;

[0043] Figure 6 The embodiments of the present invention provide (a) a unit structure of a transmission metasurface, (b) a top view, and (c) a bottom view;

[0044] Figure 7 The simulated transmission and reflection coefficients of the transmission unit provided in this embodiment of the invention are (a) x-polarized incident and (b) y-polarized incident.

[0045] Figure 8 The simulation results of a broadband, high-gain, circularly polarized filtered folded transmission array antenna provided by the embodiments of the present invention (a) S-parameters (b) can achieve gain, axial ratio and aperture efficiency;

[0046] Figure 9 This is a three-dimensional radiation pattern at a typical frequency provided in the embodiments of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] like Figure 1 As shown, this embodiment of the invention provides a broadband, high-gain, circularly polarized filtered folded transmission array antenna. The device includes: a planar integrated feed antenna, a SIW-Mini-SMP transition structure, a reflective cross-polarization converter RCPC, and a transmission metasurface TMMS capable of effectively generating circularly polarized electromagnetic waves.

[0049] The feed antenna serves as the feed source for the entire antenna array and has filtering characteristics; the SIW-Mini-SMP transition structure serves as the connection between the feed source and the test equipment; the TMMS function is to convert x-polarized waves into right-hand circularly polarized RHCP waves and suppress the passage of y-polarized waves; while the RCPC realizes the mutual conversion between x- and y-polarized waves.

[0050] The filtered feed antenna designed in this invention is as follows: Figure 2 As shown in (a), Figure 2Images (b) and (c) depict the top and bottom views of the feed source, respectively, and specify the relevant geometric details. The specific parameter is W. a1 = 16.2 mm, W a2 = 14.8mm, W a3 = 3.2 mm, W a4 = 2.25 mm, L a1 = 2.34 mm, L a2 = 4.15 mm, L d1 = 0.96 mm, L d2 mm = 0.3, L d3 = 1.2 mm, L d4 = 1.72 mm, L s1 = 2.1 mm, W s1 = 0.3 mm, D a = 0.5 mm, W b1 = 20 mm, W b2 = 14 mm, W b3 = 7.9 mm, W b4 = 9.8 mm, W d1 = 1.2 mm, W d2 = 1.2 mm, W d3 = 1.2 mm, W d4 = 1.2 mm, L s2 = 7.45 mm, W s2 = 0.61 mm, L b3 = 1.36 mm, D b = 0.75mm. To achieve broadband and stable radiation characteristics, this invention employs a magnetoelectric dipole as the feed source. The substrate integrated waveguide aperture (length L) S2 , width W S2 The waveguide is the feeding section, which performs coupling feeding; four rectangular patches with metal through-holes are the radiating section; the bandpass filter structure includes the waveguide itself, the resonant SIW back cavity in substrate 4, and the openings (L in length) on the magnetoelectric dipole patch. S1 , width W S1 The inherent high-pass characteristics of the waveguide are used to suppress the lower sideband of the Ku band. The resonant SIW back cavity in substrate 4 and the openings on the magnetoelectric dipole patch generate radiation nulls Hnull_1 and Hnull_2 in the upper sideband, respectively. In addition, an additional SIW back cavity is designed on substrate 3 to enhance the gain stability of the feed source and reduce the frequency shift and impedance mismatch caused by the mutual coupling between the feed source and surrounding adjacent components.

[0051] The broadband, high-gain, circularly polarized filtered folded transmission array antenna provided in this embodiment of the invention adopts a planar integrated architecture, which includes, from bottom to top, a planar integrated feed antenna, a SIW-Mini-SMP transition structure, a reflective cross-polarization converter (RCPC), and a transmission metasurface (TMMS). Each layer is isolated by a dielectric layer and an air layer to form a folded electromagnetic propagation path, thereby achieving broadband, high-gain, and high-quality circularly polarized radiation while maintaining a compact overall structure.

[0052] The feed antenna adopts a magnetoelectric dipole structure, which is coupled and fed through a substrate integrated waveguide aperture. The SIW waveguide aperture (length L) is set in substrate 4. s2 Width W s2 As the energy input port, the feed source is connected to the external test equipment through the SIW-Mini-SMP transition structure to achieve low reflection and high stability. Four rectangular patches with metal through holes constitute the magnetoelectric dipole radiation unit, realizing the coordinated excitation of electric dipole and magnetic dipole modes, thereby obtaining stable, wideband linear polarization radiation.

[0053] A bandpass filter is simultaneously introduced inside the feed source. The inherent high-pass characteristics of the waveguide are used to suppress low-frequency stray radiation below the Ku band; the resonant SIW back cavity in substrate 4 and the opening (L) on the magnetoelectric dipole patch are also included. s1 W s1 Two radiation nulls, Hnull1 and Hnull2, are generated in the upper sideband, respectively, thereby forming a bandpass radiation response, achieving band-selective radiation and improving out-of-band suppression capability. The additional SIW back cavity introduced in substrate 3 is used to isolate the electromagnetic coupling between the feed and the upper metasurface and reflective structure, stabilize the feed input impedance and radiation characteristics, and reduce frequency shift caused by environmental disturbances.

[0054] The linearly polarized electromagnetic wave radiated from the feed propagates upwards and first enters the RCPC layer. The RCPC is a reflective cross-polarization converter, whose function is to realize the mutual conversion between x-polarization and y-polarization components during reflection and to introduce controllable phase modulation, so that the reflected wave completes polarization state rotation in the propagation path. The reflected wave then re-enters the TMMS layer through a folded path.

[0055] TMMS is a transmission-type anisotropic metasurface whose unit cell structure selectively transmits the x-polarization component and suppresses the y-polarization component. Simultaneously, it applies a 90° phase difference to the orthogonal components during transmission, thereby converting the incident linearly polarized wave into a right-hand circularly polarized (RHCP) wave and radiating it into free space. The RCPC and TMMS work together to enable the feed radiation to complete the conversion process from linear polarization to cross-polarization to circular polarization after passing through a folded path, while simultaneously achieving multifunctional integration of filtering, polarization control, and beamforming.

[0056] With the above structural configuration, the present invention achieves unified integration of broadband filtering, high-gain radiation and high-purity circular polarization output without adding the complex feed network of traditional phased arrays. The structure is compact, easy to process and integrate, and suitable for satellite communication, radar and high-speed wireless communication application scenarios with high requirements for bandwidth, polarization quality and system stability.

[0057] Figure 3 The simulated reflection coefficient and achieved gain of the proposed filtered feed are shown. The feed's S11 remains less than -15 dB in the Ku band, and the achieved gain level is approximately 7.6 dBi. Furthermore, two distinct radiation nulls are observed at 20 GHz and 21.4 GHz.

[0058] The SIW-Mini-SMP transition structure designed in this invention is as follows: Figure 4 As shown in (a), this structure is a broadband, low insertion loss band-ground coplanar waveguide (GCPW) to SIW transition structure, comprising a Mini-SMP connector, a GCPW excitation section, a transition section, and an SIW waveguide section. The Mini-SMP connector is model GPPO-JHD12 to ensure impedance matching and external connectivity; the center conductor of the GCPW is chamfered to improve matching efficiency; the transition section from GCPW to SIW is a quadrilateral transition structure, which further improves matching efficiency compared to a triangular transition structure.

[0059] Figure 4 Figure (b) shows the simulated S-parameters. The adapter achieves a reflection coefficient of less than -20 dB in the Ku band, and a forward transmission coefficient greater than -0.7 dB across the entire 12–18 GHz frequency range, indicating that the structure has a minimal impact on the transmission array efficiency. Therefore, the proposed Mini-SMP connection GCPW to SIW conversion adapter meets the design requirements.

[0060] The cross-polarization conversion unit (RCPC) designed in this invention is as follows: Figure 5 As shown in (a), the specific parameters are P2 = 5.4 mm, L a = 4.18 mm, L b = 2.93 mm, W a = 0.89 mm, W b = 0.89 mm, W d = 0.84 mm. This cell consists of a double-sided copper-clad dielectric substrate, with F4B as the dielectric material. The top layer of the cell is a set of arrow patterns placed diagonally, and the bottom layer is a metal ground. Figure 5(b) The cross-polarization reflection coefficients of this unit at different incident angles are given. In the Ku band, the reflection amplitude at vertical incidence exceeds -0.37 dB, indicating good conversion efficiency. Furthermore, the incident angle has little effect on the amplitude and phase, and the phase stability is very good.

[0061] The Transmission Unit (TMMS) structure designed in this invention is as follows: Figure 6 As shown in (a), the specific parameter is W. u1 = 5.12mm, W u2 = 4.64 mm, L1 = 3.98 mm, L2 = 3.1 mm, S u = 0.33 mm, X u = 0.84 mm, Y u =1.08 mm, D1= 0.4 mm, D2 = 0.8 mm, P1 = 8.1 mm, W d1 = 4.95 mm, W d2 = 4.95 mm, θ d = 60° mm, X d = 0.64 mm, R d = 0.94 mm, and S d = 0.85 mm. This cell consists of a horseshoe-shaped patch at the bottom, metallized vias, a metal ground plane, an asymmetric H-shaped aperture patch at the top, and two dielectric substrates. The horseshoe-shaped patch at the bottom includes a notch with a notch of θ. d The annular aperture can absorb x-polarized waves and reflect y-polarized waves. For example... Figure 6 As shown in Figures (b) and (c), one end of the top H-shaped aperture is extended to L1 to broaden the circular polarization bandwidth. The bottom and top patches are connected by metal vias passing through the circular holes in the metal ground plane. The dielectric substrate between the patches is 1.542 mm thick F4B, and there is a 0.1 mm thin film between the two dielectric substrates, made of Rogers RO4450F. It should be noted that the feed positions of the top and bottom patches are offset in this invention to improve impedance matching, thereby increasing the cell bandwidth. The simulation results of the cell are as follows: Figure 7 As shown. The transmission coefficient T of x-polarization to RHCP over the entire Ku band. rcp-x Above -1 dB, while the cross-polarized transmission coefficient T lcp-x Below -10 dB, for y-polarized incident light, the reflection coefficient R y-y It is approximately 0.1 dB.

[0062] Furthermore, the broadband, high-gain, circularly polarized filtered folded transmission array antenna proposed in this invention employs a novel gain bandwidth enhancement method. This invention demonstrates that the constraint on the gain bandwidth of the transmission array antenna can be attributed to its inherent spatial phase dispersion error; proposes a gain prediction model for the transmission array antenna; and quantifies the trend of the transmission array gain bandwidth with changes in key parameters. This extends the traditional formula (1) for calculating the spatial phase error factor, allowing the design bandwidth to be expressed using the spatial phase dispersion error, formula (2), and formula (3) for the gain of the array antenna. Ultimately, the extended formulas 2 and 3 can be used to optimize and enhance the gain and bandwidth of the folded transmission array, thereby achieving the advantages of wide bandwidth and high gain.

[0063] (1)

[0064] (2)

[0065] (3)

[0066] Where (x) i ,y i ) represents the coordinates of the (i,j)th element, k c It is related to the phase compensation frequency f c The corresponding free space number, F is the focal length of the transmission array. A p λ is the area of ​​the aperture, and λ is the wavelength in free space.

[0067] Example 1: Overall Structure Implementation of a Folded Circularly Polarized Filtered Transmission Array Antenna

[0068] This embodiment provides a broadband, high-gain, circularly polarized folded transmission array antenna structure. From bottom to top, the antenna comprises a planar integrated feed, a reflective cross-polarization conversion layer, and a transmission metasurface radiating layer. Linearly polarized electromagnetic waves emitted by the feed first enter the reflective cross-polarization conversion layer, where they undergo conversion between orthogonal polarization components before being guided to the upper transmission metasurface radiating layer. Through this folded propagation path, the electromagnetic waves achieve a phase compensation effect equivalent to that of a long-focal-length transmission array within a finite profile height.

[0069] In this structure, the transmission-type metasurface radiation layer spatially modulates the transmission phase of the incident wave, reconstructing the original spherical wave into a circularly polarized radiation in an approximate plane wave form along the radiation direction. Since polarization conversion and phase modulation are performed separately in different functional layers, the performance degradation caused by strong polarization-phase coupling in a single-layer structure is avoided. Thus, while significantly reducing the profile height, high aperture efficiency and stable far-field gain are still maintained.

[0070] Example 2: Polarization Cooperative Working Process under Folded Propagation Path

[0071] In this embodiment, the linearly polarized electromagnetic wave radiated from the feed is incident at an angle onto the reflective cross-polarization conversion layer. This layer achieves cross-conversion of the incident polarization components through an anisotropic metallic pattern structure, causing the polarization direction of the reflected wave to rotate. The polarization-converted electromagnetic wave propagates along the folded path to the transmission metasurface radiation layer, thereby forming an equivalently extended propagation distance within a limited space.

[0072] The transmission-type metasurface radiating layer applies a differential phase response to different polarization components during transmission, causing the transmitted wave to form orthogonal electric field components with equal amplitude and a phase difference of one-quarter of a period in space. Through this polarization coordination process, the antenna can achieve stable circular polarization radiation without the need for an additional feed polarization network, while ensuring the consistency of polarization purity and radiation pattern over a wide frequency range.

[0073] Example 3: Structural Implementation of a Broadband Magnetoelectric Dipole Filter Feed

[0074] This embodiment provides a broadband filtered feed structure for a folded transmission array antenna. The feed uses a magnetoelectric dipole as the radiating element, coupled and fed through a substrate-integrated waveguide aperture. The magnetoelectric dipole is composed of multiple metal patches and through-hole structures, simultaneously exciting both electric and magnetic dipole radiation modes within the operating frequency band, thereby obtaining a wide impedance bandwidth and a stable radiation pattern.

[0075] Multiple resonant cavity structures are introduced into the radiation path of the feed source, enabling the feed source to exhibit bandpass radiation characteristics within the target operating frequency band. The high-pass characteristics of the substrate-integrated waveguide body are used to suppress out-of-band radiation below the operating frequency band, while the resonant cavities located inside or behind the feed source form radiation nulls on the high-frequency side, thereby achieving an integrated design of spectrum selection and radiation functions without the need for external filters.

[0076] Example 4: Methods to Enhance Radiation Stability of Filtered Feed Sources

[0077] In this embodiment, an additional substrate-integrated waveguide back cavity is disposed behind the magnetoelectric dipole feed. This back cavity and the main feed structure participate in the electromagnetic resonance process together through coupling, keeping the equivalent radiation center position of the feed relatively stable over a wide frequency range. In this way, the main lobe shift phenomenon caused by frequency variation in feed radiation is effectively reduced.

[0078] Meanwhile, the cavity structure provides spatial electromagnetic isolation for the feed, reducing the coupling strength between the feed and the reflective cross-polarization conversion layer and the surrounding metal structure. This mitigates frequency drift and impedance mismatch issues, enabling the feed to maintain good return loss characteristics and radiation consistency even under broadband operating conditions.

[0079] Example 5: Implementation process of the gain-bandwidth coordinated design method

[0080] This implementation presents a gain-bandwidth enhancement design method for folded transmission array antennas. By analyzing the phase difference between the center frequency and the actual operating frequency, a method for calculating spatial phase scattering error is proposed, and the impact of spatial phase error on gain bandwidth is explained. Subsequently, by comparing the spatial phase errors under different focal ratios and array sizes, it is qualitatively demonstrated that a larger focal ratio and a smaller aperture size can result in a smaller spatial phase error, thereby achieving better gain bandwidth.

[0081] Example 6: Structural Parameter Optimization Based on Gain Prediction Model

[0082] This embodiment proposes a gain estimation method based on aperture efficiency factor and array directivity. This method enables more specific calculation of gain bandwidth and evaluates the gain variation of the transmission array under different sizes or focal diameter ratios. Specifically, this embodiment starts with directivity and aperture effects, analyzing taper efficiency, leakage efficiency, phase efficiency, and element efficiency. Among these, phase efficiency is the most relevant parameter for spatial phase dispersion error, mainly characterizing the frequency-dependent variation of the phase distribution of the transmission array aperture. By quantitatively comparing the directivity and gain variation of the transmission array under different focal diameter ratios and aperture sizes, it is confirmed that a larger focal diameter ratio and a smaller aperture size can achieve better phase efficiency, thereby obtaining a wider gain bandwidth.

[0083] Example 7: Verification of Circularly Polarized Stable Radiation in the Ku Band

[0084] This embodiment verifies the polarization performance of a folded transmission array antenna across the entire Ku-band. By adjusting the geometric parameters of the elements in the transmitting metasurface radiating layer, it maintains an axial ratio level below 3dB and gradient phase control at different frequencies, thereby maintaining a stable circularly polarized radiation state over a wide frequency range.

[0085] Experimental results show that within the designed bandwidth, the antenna's axial ratio performance and main lobe direction variation are both within a controllable range, with no obvious polarization degradation or radiation distortion. This implementation further verifies that the proposed folded transmission array can radiate circularly polarized electromagnetic waves with stable gain in the Ku band.

[0086] Example 8: Integrated Application of Folded Transmission Array in Compact Systems

[0087] This embodiment applies the folded transmission array antenna to a space-constrained communication system. By designing a folded propagation path, gain performance comparable to traditional transmission arrays is achieved without increasing the overall system height, thereby significantly improving the system's integration.

[0088] In this application scenario, the filter feed and the folded transmission array structure work together to effectively suppress out-of-band radiation interference to other modules of the system, while maintaining efficient radiation characteristics within the target frequency band. This implementation demonstrates that the technical solution has good engineering applicability and promotional value.

[0089] The overall simulation reflection coefficient of the "broadband, high-gain, circularly polarized filtered folded transmission array antenna" provided in this embodiment of the invention is as follows: Figure 8 As shown in (a), the antenna achieves an impedance bandwidth of 45.3%, maintaining complete coverage of the Ku band. In terms of filtering response, the antenna achieves a stopband reflection coefficient exceeding -3 dB. Figure 8 (b) Simulated and measured achievable gain and axial ratio results are provided, along with calculated aperture efficiency. The antenna achieves a peak achievable gain of 22.64 dBic and a maximum aperture efficiency of 35.1%. The measured 3-dB gain bandwidth and 3-dB axial ratio bandwidth are 41.6% and 51.8%, respectively. The antenna exhibits good filtering characteristics, with suppression levels of 38.1 dB and 44.3 dB for the lower and upper sidebands outside the Ku band, respectively. Figure 9 Simulated three-dimensional far-field radiation maps at several typical frequencies are shown. The antenna exhibits significant directional radiation characteristics within its operating passband, achieving efficient energy transfer. Conversely, in the stopband, the antenna's radiation capability is significantly suppressed, effectively preventing energy from radiating outwards.

[0090] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A broadband, high-gain, circularly polarized filtered folded transmission array antenna, characterized in that, The antenna includes a planar integrated feed, a reflective cross-polarization conversion layer, and a transmission metasurface radiating layer arranged sequentially along the electromagnetic wave propagation path. The reflective cross-polarization conversion layer is used to realize polarization conversion between orthogonally linearly polarized electromagnetic waves, and the transmission metasurface radiation layer is used to selectively transmit and phase-modulate the incident linearly polarized wave during transmission, so that the transmitted wave forms circularly polarized radiation in space. The feed, the reflective cross-polarization conversion layer, and the transmission metasurface radiation layer form an equivalent long focal length phase compensation relationship through folded propagation paths, reducing the overall profile height and achieving high-aperture-efficiency circularly polarized transmission array radiation.

2. The antenna according to claim 1, characterized in that, The folded propagation path causes the electromagnetic wave to undergo at least one reflection polarization conversion process between the feed and the transmission metasurface radiation layer, compressing the antenna profile height to one-third of the traditional direct-fire transmission array structure while keeping the equivalent phase compensation distance unchanged.

3. The antenna according to claim 1, characterized in that, The transmission-type metasurface radiation layer modulates the spatial distribution of the transmission phase, converting the spherical wave from the feed into circularly polarized radiation in the form of an approximate plane wave in the radiation direction, thereby improving the aperture efficiency and far-field gain of the folded transmission array.

4. A broadband filtered feed for the folded transmission array antenna of claim 1, characterized in that, The feed source adopts a magnetoelectric dipole radiation structure and is coupled and fed through the substrate integrated waveguide aperture; The feed introduces the synergistic effect of multiple resonant cavities and radiation null points in the radiation path, enabling the feed to form bandpass radiation characteristics within the target operating frequency band and achieve radiation suppression in the out-of-band frequency band, thus achieving the unification of feed radiation and spectrum selection without adding external filters.

5. The feed source according to claim 4, characterized in that, The inherent high-pass characteristics of the substrate integrated waveguide body are used to suppress out-of-band radiation below the target operating frequency band, while the resonant cavity structure located behind the feed source is used to form a radiation null point above the target operating frequency band to achieve double-sideband radiation suppression.

6. The feed source according to claim 4, characterized in that, An additional waveguide back cavity is set behind the magnetoelectric dipole radiation structure to stabilize the radiation pattern of the feed over a wide frequency range and reduce frequency drift and impedance mismatch caused by electromagnetic coupling between the feed and adjacent structures.

7. A gain-bandwidth enhancement design method for the folded transmission array antenna of claim 1, characterized in that, By introducing spatial phase dispersion error to model the frequency response of the transmission array antenna, the phase deviation relationship between the spatial position of the array elements, the equivalent focal length, and the operating frequency is quantified into design constraints. Based on this, according to the relationship between the spatial phase dispersion error and the maximum allowable phase error of the array, the achievable design bandwidth of the transmission array antenna is determined, and the array gain is estimated by combining the aperture area and the operating wavelength, so as to achieve the coordinated optimization design of gain and bandwidth.

8. The method according to claim 7, characterized in that, The spatial phase dispersion error is obtained by comparing the propagation path phase of the array element at different operating frequencies with the reference phase at the phase compensation frequency, and is used to characterize the effect of frequency variation on the radiation phase consistency of the transmission array.

9. The method according to claim 7, characterized in that, The design bandwidth is determined by the functional relationship between the array's maximum spatial phase dispersion error, equivalent focal length, and effective aperture size, to ensure the stability of the main lobe direction and gain of the transmission array antenna within the design bandwidth.

10. The method according to claim 7, characterized in that, The array gain is estimated by the ratio between the aperture area and the free space wavelength, and an aperture efficiency factor is introduced to correct the polarization conversion loss and structural folding loss, thereby guiding the realization of high gain of folded transmission array antennas under broadband conditions.

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