A Wide-Angle Stable Tunable Frequency-Dual-Polarized Frequency Selective Surface Element and Selective Surface

Abstract

An adjustable-frequency dual-polarized frequency selective surface unit with wide-angle stability of the present invention includes a dielectric layer, a top layer and a bottom layer providing a varactor diode feeding network; a top layer closely attached to the dielectric layer and disposed above the dielectric layer; a bottom layer closely attached to the dielectric layer and disposed below the dielectric layer; a metal via is provided at the center of the dielectric layer; the top layer includes a first metal patch and a varactor diode group; the bottom layer includes a second metal patch; the center point of the first metal patch is connected to the center point of the second metal patch through the metal via; the varactor diode group is respectively connected to the first metal patch and the second metal patch; by adopting an integrated structure design method of the feeding network and the FSS unit, an adjustable-frequency FSS with a low profile, polarization insensitivity and high angle stability is proposed. This structure can maintain a stable transmission response when the incident angles of TE and TM polarizations vary from 0° to 70°, and the experimental results are in good agreement with the simulation results.

Description

Technical Field

[0001] The present invention belongs to the field of fully automated products, and relates to a frequency tunable dual-polarized frequency selective surface unit with wide-angle stability and a selective surface. Background Art

[0002] A frequency selective surface (FSS) is an infinite array formed by periodically arranging patch or aperture units, which acts as a spatial filter. Due to its excellent filtering performance, it has been widely used in absorbers, radar stealth, communication, electromagnetic compatibility and other fields.

[0003] In recent years, with the increasing development of multi-functional and multi-standard communication systems, the research on FSS with frequency tunable function has become a hot topic. According to different regulation methods, frequency tunable FSS can be divided into mechanical regulation, magnetic regulation, microcomputer regulation and voltage regulation types. Among them, FSS with mechanical regulation and magnetic regulation has the disadvantages of slow adjustment speed and narrow frequency modulation range; FSS with microcomputer regulation requires complex manufacturing methods. Voltage regulation usually adds active components such as PIN diodes or varactor diodes to the FSS, and realizes the adjustable function of frequency characteristics by adjusting its bias voltage. This voltage-regulated FSS has the advantages of simple preparation, low cost and fast response speed, and is widely used in multi-functional and multi-standard communication systems. However, this tunable FSS containing active components needs to set up a feeding network, and the introduction of the feeding network will affect the electromagnetic performance of the initial FSS. On the other hand, the test results of currently designed tunable FSS show that the above FSS performs unsatisfactorily in terms of angular stability - at the same bias voltage, the resonant frequency of the FSS changes unstably with the incident wave angle, which will restrict the application of frequency tunable FSS in conformal radar radomes and other structures. Therefore, further research needs to be carried out to obtain a frequency tunable FSS with high angular stability.

[0004] Compared with passive FSS, the analysis of the angular stability of frequency tunable FSS is more difficult. The reason is that once the passive FSS is manufactured, its transmission response is fixed; while the transmission response of the frequency tunable FSS will change with the change of the bias voltage of the varactor diode. For the same bias voltage, the resonant frequency and insertion loss of the frequency tunable FSS will change with the incident angle and polarization mode. The insertion loss is caused by the large junction capacitance of the varactor diode and the non-negligible parasitic resistance inside. Therefore, it is necessary to consider the influence of the incident angle and polarization mode on the offset of the resonant frequency of the frequency tunable FSS and the corresponding insertion loss under different bias voltages.

[0005] At present, tunable FSS with high angular stability mainly adopts 3D structures or multi-layer structures. Professor Shen Zhongxiang from Nanyang Technological University proposed a 3D band-pass tunable FSS with an angular stability of 60°, but this structure is a polarization-sensitive structure; then a dual-polarized second-order tunable FSS based on the cascading of three-layer structures was proposed. The simulation results show that this structure can produce a stable response when the incident angle is 0° - 60°, but no experimental verification was provided. Moreover, the tunable FSS composed of 3D structures or multi-layer structures introduces more manufacturing errors and has a higher profile, making it difficult to be used in conformal structures such as radomes.

[0006] Therefore, the problems existing in the current tunable FSS include: on the one hand, the introduction of the feeding network affects the electromagnetic performance of the initial FSS; on the other hand, the controllable FSS structure has a relatively thick profile and poor performance in terms of angular stability - showing an unstable transmission response with the change of the incident wave angle and polarization mode. Summary of the Invention

[0007] In order to solve the problem that the additional feeding network has an adverse effect on the electromagnetic characteristics of the initial FSS structure, the technical solution adopted in the present invention is: an integrated structure design method of the feeding network and the FSS unit, a wide-angle stable tunable dual-polarized frequency selective surface unit, including a dielectric layer, a top layer and a bottom layer providing a varactor diode feeding network;

[0008] A top layer closely attached to the dielectric layer and disposed above the dielectric layer;

[0009] A bottom layer closely attached to the dielectric layer and disposed below the dielectric layer;

[0010] A metal via is provided at the center of the dielectric layer;

[0011] The top layer includes a first metal patch and a varactor diode group;

[0012] The bottom layer includes a second metal patch;

[0013] The center point of the first metal patch is connected to the center point of the second metal patch through the metal via

[0014] The varactor diode group is respectively connected to the first metal patch and the second metal patch.

[0015] Further, the varactor diode group includes 4 varactor diodes.

[0016] Further, the first metal patch includes a square ring and a curved cross structure with 4 bridge arms;

[0017] One end of each of the curved bridge arms is connected to the middle point of the first metal patch;

[0018] The square ring and the bent cross structure with four arms are symmetric about the center point;

[0019] After the previous bent arm rotates 90 degrees clockwise or counterclockwise around the center point, it coincides with the next bent arm;

[0020] The square ring is connected to the cathode of the varactor diode;

[0021] The arms of the bent cross structure are connected to the anode of the varactor diode.

[0022] Furthermore, the periodic dimensions of the dielectric layer, the first metal patch, and the second metal patch are equal.

[0023] Furthermore, the second metal patch includes four bent dipoles;

[0024] The bent dipoles are cross-connected through the midpoint;

[0025] After the previous bent dipole rotates 90 degrees clockwise or counterclockwise, it coincides with the next bent dipole;

[0026] The four bent dipoles are symmetric about the center point;

[0027] The second metal patch is connected to the anodes of multiple varactor diodes.

[0028] Furthermore, the dielectric layer has only one layer.

[0029] Furthermore, the thicknesses of the first metal patch and the second metal patch are both 0.035 mm.

[0030] A wide-angle stable tunable frequency double-polarized frequency selective surface includes a plurality of the above-mentioned frequency selective surface unit structures.

[0031] A wide-angle stable tunable frequency double-polarized frequency selective surface unit and surface provided by the present invention adopt an integrated structure design method of a feeding network and an FSS unit, and propose a tunable FSS with a low profile, polarization insensitivity, and high angle stability. This structure can maintain a stable transmission response when the incident angles of TE and TM polarizations vary from 0° to 70°, and the experimental results are in good agreement with the simulation results. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 (a) is a 3D schematic diagram of the tunable frequency selective surface; (b) is a top layer schematic diagram of the tunable frequency selective surface; (c) is a middle layer schematic diagram of the tunable frequency selective surface; (d) is a bottom layer schematic diagram of the tunable frequency selective surface;

[0034] Figure 2 is (a) the simulated transmission coefficient of the tunable FSS when the TE polarized wave is incident with a capacitance value of 0.33 pF, (b) the simulated transmission coefficient of the tunable FSS when the TM polarized wave is incident with a capacitance value of 0.33 pF, (c) the simulated transmission coefficient of the tunable FSS when the TE polarized wave is incident with a capacitance value of 0.21 pF, (d) the simulated transmission coefficient of the tunable FSS when the TM polarized wave is incident with a capacitance value of 0.21 pF;

[0035] Figure 3 (a) is the top layer diagram of the fabricated sample, (b) is the bottom layer diagram of the fabricated sample;

[0036] Figure 4 is a schematic diagram of the test device;

[0037] Figure 5 (a) is the simulated result diagram of the transmission coefficient under the condition of normal incidence, (b) is the measured result diagram of the corresponding transmission coefficient;

[0038] Figure 6 (a) is the measured transmission coefficient of the TE polarized wave when the tunable frequency selective surface is obliquely incident at 10 V voltage, (b) is the measured transmission coefficient of the TM polarized wave when the tunable frequency selective surface is obliquely incident at 10 V voltage, (c) is the measured transmission coefficient of the TE polarized wave when the tunable frequency selective surface is obliquely incident at 20 V voltage, (d) is the measured transmission coefficient of the TM polarized wave when the tunable frequency selective surface is obliquely incident at 20 V voltage. Specific embodiments

[0039] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine with the embodiments to detail the present invention.

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. The following description of at least one exemplary embodiment is actually illustrative only and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0041] It should be noted that the terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly dictates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of the stated features, steps, operations, devices, components, and / or combinations thereof.

[0042] Unless otherwise specifically stated, the relative arrangements of the components and steps, numerical expressions and values set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the authorized specification. In all the examples shown and discussed here, any specific values should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, further discussion thereof is not required in subsequent drawings.

[0043] In the description of the present invention, it should be understood that orientation terms such as "front, rear, upper, lower, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom", etc. generally indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Without contrary description, these orientation terms do not indicate and imply that the devices or elements referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of the present invention. The orientation terms "inside, outside" refer to the inside and outside relative to the contour of each component itself.

[0044] For ease of description, spatial relative terms such as "above", "over", "on the upper surface", "upper", etc. can be used here to describe the spatial positional relationship between a device or feature shown in the figure and other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figure for the device. For example, if the device in the figure is inverted, a device described as "above" or "over" other devices or structures will then be positioned "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both the orientations of "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and corresponding interpretations will be made for the spatial relative descriptions used here.

[0045] In addition, it should be noted that the use of terms such as "first" and "second" to define components is only for the convenience of differentiating the corresponding components. Without additional statements, the above terms have no special meanings, and thus should not be construed as limiting the protection scope of the present invention.

[0046] Figure 1 (a) is a 3D schematic diagram of the tunable frequency selective surface; (b) is a top layer schematic diagram of the tunable frequency selective surface; (c) is a middle layer schematic diagram of the tunable frequency selective surface; (d) is a bottom layer schematic diagram of the tunable frequency selective surface;

[0047] A wide-angle stable tunable dual-polarization frequency selective surface unit includes a dielectric layer, a top layer and a bottom layer providing a varactor diode feed network;

[0048] The top layer is in close contact with the dielectric layer and is disposed above the dielectric layer; the selective surface has a low profile and there is only one dielectric layer;

[0049] The bottom layer is in close contact with the dielectric layer and is the bottom layer disposed below the dielectric layer;

[0050] A metal via is provided at the center of the dielectric layer;

[0051] The top layer includes a first metal patch and a varactor diode group; the varactor diode group includes 4 varactor diodes;

[0052] The bottom layer includes a second metal patch;

[0053] The center point of the first metal patch is connected to the center point of the second metal patch through the metal via;

[0054] The varactor diode group is respectively connected to the first metal patch and the second metal patch.

[0055] The first metal patch includes a square loop and a bent cross structure with 4 arms disposed inside the square loop;

[0056] One end of each of the bent arms is connected to the middle point of the first metal patch;

[0057] The square loop and the bent cross structure with 4 arms are symmetric about the center point;

[0058] The previous bent arm coincides with the next bent arm after rotating 90 degrees clockwise or counterclockwise around the center point;

[0059] The square loop is connected to the cathode of the varactor diode;

[0060] The arms of the bent cross structure are connected to the anode of the varactor diode. The bent cross structure includes a first side, a first bend, a second bend, a third bend, a fourth bend, and a fifth bend;

[0061] The first side, the first bend, the second bend, the third bend, the fourth bend, and the fifth bend are connected end to end in sequence;

[0062] When the first side, the first bend, the second bend, the third bend, the fourth bend, and the fifth bend are connected, they form a 90-degree angle;

[0063] The length l1 of the first side is 0.8 mm, the length l2 of the first bend is 0.55 mm, the length l3 of the third bend is 1.3 mm; the length l4 of the fifth bend is 1.2 mm;

[0064] The widths of the first side, the first bend, the second bend, the third bend, the fourth bend, and the fifth bend are all w1 = 0.3 mm;

[0065] The distance g from the fifth bend to the inner border of the square frame is 0.35 mm;

[0066] The width of the square frame is d = 1.4 mm;

[0067] The dielectric layer, the first metal patch, and the second metal patch are all square, and the side length of the square is 10 mm.

[0068] ]>The first metal patch and the second metal patch are made of copper;

[0069] The second metal patch includes 4 bent dipoles;

[0070] The bent dipoles are cross-connected through the middle point;

[0071] The previous bent dipole coincides with the next bent dipole after rotating 90 degrees clockwise or counterclockwise;

[0072] The 4 bent dipoles are symmetric about the center point;

[0073] The second metal patch is connected to the anodes of a plurality of varactor diodes;

[0074] The bent dipole includes a second side, a sixth bend, a seventh bend, an eighth bend, and a ninth bend;

[0075] The second side, the sixth bend, the seventh bend, the eighth bend, and the ninth bend are connected end to end in sequence;

[0076] When the second side, the sixth bend, the seventh bend, the eighth bend, and the ninth bend are connected, they form 90-degree angles with each other;

[0077] The length of the second side l6 = 0.8mm, the vertical distance between the sixth bend and the seventh bend is l7 = 1.3mm, and the length of the ninth bend l5 = 1.75mm.

[0078] The length of the second side, the widths of the sixth bend, the seventh bend, the eighth bend, and the ninth bend w2 = 0.3mm;

[0079] The thickness of the dielectric layer, t = 0.5mm. The ultra-thin dielectric layer uses F4B-2, ε r = 2.65, tanδ = 0.005;

[0080] The thicknesses of the first metal patch and the second metal patch are 0.035mm.

[0081] The periodic dimensions of the dielectric layer, the first metal patch, and the second metal patch are equal. The periodic dimension is the size of one unit, and the frequency selective sample can be made several or dozens of times the size of one periodic dimension;

[0082] An adjustable frequency frequency selective surface includes a plurality of the above-mentioned selective surface unit structures.

[0083] To study the angular stability of the proposed tunable FSS at different capacitance values, the transmission coefficients of the structure when TE and TM polarized waves are incident at different angles are calculated respectively when the capacitance values are 0.33pF and 0.21pF. Figure 2(a) is the simulated transmission coefficient of the tunable FSS for TE-polarized wave incidence when the capacitance value is 0.33 pF, (b) is the simulated transmission coefficient of the tunable FSS for TM-polarized wave incidence when the capacitance value is 0.33 pF, (c) is the simulated transmission coefficient of the tunable FSS for TE-polarized wave incidence when the capacitance value is 0.21 pF, and (d) is the simulated transmission coefficient of the tunable FSS for TM-polarized wave incidence when the capacitance value is 0.21 pF;. It can be seen from the figure that the designed FSS shows a stable passband frequency response for both polarized waves within an incident angle range of up to 70°. This is because the designed FSS structure has a small cell size and an ultra-low profile. However, when the capacitance value is reduced to 0.21 pF, sharp harmonics appear outside the band in the TE response, and when the capacitance value remains unchanged, as the incident angle increases, parasitic resonances appear outside the band in the TM response. The sharp harmonics in the TE response are due to the unbalanced electric fields between the FSS cells exciting higher-order resonance modes. The parasitic resonances in the TM response are caused by the bending modes of the meandered metal patches on the one hand and the coupling of the electric field components perpendicular to the surface of the structure with the conductive metal vias on the other hand, and the coupling can be weakened by reducing the diameter of the metal vias. Considering that the sharp harmonics and parasitic resonances outside the band are far from the target frequency band, their effects can be ignored. Therefore, this structure has high angular stability.

[0084] To further verify the effectiveness of the tunable FSS structure, an FSS sample was fabricated using printed circuit boards (PCB) technology.

[0085] Figure 3 (a) is the top view of the fabricated sample, and (b) is the bottom view of the fabricated sample;

[0086] The overall size is 240 mm × 240 mm, and 20 × 20 cells are printed on both sides of a dielectric substrate with a thickness of 0.5 mm and a material of F4B-2. Integrated inductors (LQW15AN6N2B00D, 6.2 nH, Murata Inc.) are symmetrically soldered on the feed lines. These inductors exhibit high impedance characteristics at their self-resonant frequencies and can provide the function of isolating radio frequency signals throughout the tunable frequency range. Each varactor diode of this structure is connected in parallel, which has the advantages of short response time, small required voltage, and small experimental error.

[0087] In the microwave anechoic chamber, the transmission coefficient of the above-mentioned tunable FSS sample was measured using the free space measurement method.

[0088] Figure 4It is a schematic diagram of the test device. The instruments used include a vector network analyzer (Agilent N5242A), transmitting and receiving antennas (2 - 8 GHz), and a DC voltage source (HJS - 480 - 0 - 36) for powering the varactor diode. The position of the antenna is about 0.8 m away from the sample. To reduce the edge effect and improve the test accuracy, the sample is placed in the middle of the pyramidal absorber. The transmission coefficient measured by the pyramidal absorber without the sample is used as the normalization coefficient, and the time - domain gating technique is adopted to filter out the influence of diffracted waves on the measurement results.

[0089] The bias voltage across the varactor diode is adjusted from 6 V to 20 V, and a set of frequency - response data is collected for every 2 V increase. Figure 5 (a) shows the simulation results of the transmission coefficient under the condition of vertical incidence. Figure 5 (b) shows the measured results of the corresponding transmission coefficient. From Figure 5 it can be seen that when the voltage increases from 6 V to 20 V, both the simulated and measured center frequencies of the passband increase from 3 GHz to 4.53 GHz, and the agreement between the simulated center frequency and the measured center frequency is good. The simulated insertion loss changes from 6.2 dB to 2.4 dB, and the measured insertion loss changes from 7.1 dB to 2.48 dB.

[0090] Figure 6 (a) shows the measured transmission coefficient of the tunable frequency - selective surface for TE - polarized waves under the condition of oblique incidence at 10 V voltage, (b) shows the measured transmission coefficient of the tunable frequency - selective surface for TM - polarized waves under the condition of oblique incidence at 10 V voltage, (c) shows the measured transmission coefficient of the tunable frequency - selective surface for TE - polarized waves under the condition of oblique incidence at 20 V voltage, and (d) shows the measured transmission coefficient of the tunable frequency - selective surface for TM - polarized waves under the condition of oblique incidence at 20 V voltage.

[0091] When the voltage of the varactor diode is 10 V, from Figure 6 the measured results of (a) and (b), it can be seen that for both TE - and TM - polarized waves, when the incident angle increases to 70°, the resonance - frequency offset is 0.8%. When the voltage of the varactor diode is 20 V, from Figure 6 the measured results of (c) and (d), it can be seen that as the incident angle of the TE - polarized wave increases, the resonance frequency shifts to the lower frequency. When the angle increases to 70°, the resonance - frequency offset is 3.19%. For the TM - polarized wave, as the incident angle increases, the resonance frequency hardly shifts, and the insertion loss gradually decreases.

[0092] The above - mentioned measured results show that when the bias voltage of the designed tunable FSS is 10 V - 20 V, it shows a stable passband frequency response for both TE - and TM - polarized waves within a wide range of incident angles up to 70°. Therefore, a compact and low - profile unit structure can achieve good angular stability.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An adjustable-frequency dual-polarized frequency selective surface unit with wide-angle stability, characterized in that: It includes a dielectric layer, a top layer and a bottom layer that provide a varactor diode feeding network; A top layer that closely adheres to the dielectric layer and is disposed above the dielectric layer; A bottom layer that closely adheres to the dielectric layer and is disposed below the dielectric layer; A metal via is provided at the center of the dielectric layer; The top layer includes a first metal patch and a varactor diode group; The bottom layer includes a second metal patch; The center point of the first metal patch is connected to the center point of the second metal patch through the metal via The varactor diode group is respectively connected to the first metal patch and the second metal patch; The varactor diode group includes 4 varactor diodes; The first metal patch includes a square loop and a bent cross structure with 4 bridge arms; One end of each of the bent bridge arms is connected to the middle point of the first metal patch; The square loop and the bent cross structure with 4 bridge arms are symmetric about the center point; One bent bridge arm coincides with the next bent bridge arm after rotating 90 degrees clockwise or counterclockwise around the center point; The square loop is connected to the cathode of the varactor diode; The bridge arms of the bent cross structure are connected to the anodes of the varactor diodes; The second metal patch includes 4 bent dipoles; The bent dipoles are cross-connected through the middle points; One bent dipole coincides with the next bent dipole after rotating 90 degrees clockwise or counterclockwise; The 4 bent dipoles are symmetric about the center point; The second metal patch is connected to the anodes of multiple varactor diodes.

2. The tunable dual-polarization frequency selective surface unit with wide-angle stability according to claim 1, characterized in that: The periodic dimensions of the dielectric layer, the first metal patch and the second metal patch are equal.

3. The tunable frequency-diplexed frequency selective surface unit with wide-angle stability according to claim 1, wherein: There is only one layer of the dielectric layer.

4. The tunable frequency-doubling polarization frequency selective surface unit with wide-angle stability according to claim 1, characterized in that: The thicknesses of the first metal patch and the second metal patch are both 0.035 mm.

5. An adjustable-frequency dual-polarization frequency selective surface with wide-angle stability, characterized in that: It includes a plurality of frequency selective surface unit structures as described in any one of claims 1-4.

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