Microwave quasi-optical dichroic filter based on frequency selective surface

Abstract

The invention discloses a microwave quasi-optical dichroic filter based on a frequency selective surface. The microwave quasi-optical dichroic filter comprises a first metal layer, a first dielectric substrate, a second metal layer, a bonding layer, a second dielectric substrate and a third metal layer which are sequentially arranged in the thickness direction. Through the material design of the symmetrical multi-layer structure and the metal and medium (the medium substrate and the bonding layer), compared with a pure metal material and a 3D printing material, loss optimization is achieved, and ohmic loss caused by the skin effect is effectively restrained through thinning of the metal layer; the dielectric material with low dielectric constant and low loss angle tangent is selected to control the increase of dielectric loss, and the influence of a large incident angle on the transmission performance is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the field of radio astronomy, and in particular to a microwave quasi-optical dichroic filter based on a frequency selective surface. Background Art

[0002] Currently, radio astronomy research (such as pulsar observations) has a strong demand for observations in specific, non-contiguous frequency bands. To address this issue, the radio astronomy multi-frequency receiving systems that have emerged in recent years offer effective solutions, and related research has garnered widespread attention. Contemporary multi-frequency receiving applications primarily employ three approaches: multi-frequency feed antennas, multi-feed receiving applications, and frequency selective surfaces (FSSs). These solutions offer diverse technical options for multi-frequency observations. Multi-frequency feed antennas utilize a multi-frequency feed capable of receiving signals at multiple frequencies, separating the signals and connecting them to RF receiving links at corresponding frequencies, thereby expanding the observation frequency range. Their designs are often based on traditional corrugated horn feeds and multimode horn feeds, incorporating multi-frequency receiving modifications. However, the bandwidth of each discrete frequency band received by a multi-frequency feed is relatively small, making it more suitable for satellite communication systems with smaller bandwidth requirements.

[0003] Multi-feed reception solutions achieve multi-frequency reception by deploying multiple feed antennas simultaneously near the focal point of the reflector, each equipped with an independent RF link. However, due to spatial limitations, focus offsets can occur between multiple feeds. The impact of feed defocus on system performance must be assessed and measures implemented to mitigate the impact.

[0004] FSSs utilize frequency-selective properties to alter the reception path of signals at specific frequencies, enabling simultaneous reception by multiple radio astronomy instruments. FSSs are often dichroic surfaces, capable of transmitting signals at a desired frequency while reflecting other frequencies. Alternatively, they can separate electromagnetic waves from different bands to achieve frequency duplexing, allowing spatially separated feeds to act on the same reflector antenna at different frequencies.

[0005] The FSS that the applicant knows about can be divided into pure metal FSS and 3D (three-dimensional) FSS based on its structural composition, that is, FSS using pure metal materials or 3D printed materials. However, these methods that the applicant knows about are prone to problems such as high-frequency loss, excessive impact of large incident angles on transmission, instability and low transmission efficiency. Summary of the Invention

[0006] The embodiments of the present application provide a microwave quasi-optical dichroic filter based on a frequency selective surface, thereby solving the problems of high-frequency loss, excessive transmission influence due to large incident angles, instability, and low transmission efficiency that are prone to occur in FSS in the prior art.

[0007] In order to solve the above technical problems, an embodiment of the present application provides a microwave quasi-optical dichroic filter based on a frequency selective surface, including a first metal layer, a first dielectric substrate, a second metal layer, an adhesive layer, a second dielectric substrate and a third metal layer arranged in sequence along the thickness direction.

[0008] Preferably, the second metal layer includes a metal layer body and a slot structure passing through the metal layer body.

[0009] Preferably, the slotted structure comprises a spiral slotted structure.

[0010] Preferably, the spiral slot structure includes a plurality of sub-slot bodies arranged along the circumference of the metal layer body, and the projection of the sub-slot bodies along the thickness direction is a C-shaped structure.

[0011] Preferably, the sub-trough body includes a first trough arm, which extends along a first direction and is bent to form a second trough arm; the second trough arm extends along a second direction and is bent to form a third trough arm, which extends along a third direction.

[0012] Preferably, the length of the first slot arm is 0.75-0.85 mm; and / or,

[0013] The length of the second slot arm is 0.52-0.59 mm; and / or,

[0014] The length of the third slot arm is 0.22-0.3 mm; and / or,

[0015] A width of at least one of the first slot arm, the second slot arm, and the third slot arm is 0.09-0.18 mm.

[0016] Preferably, the slotted structure comprises an annular slotted structure, and the annular slotted structure is arranged along the edge of the metal layer body.

[0017] Preferably, the metal layer body includes a first body located outside the annular groove structure and a second body located inside the annular groove structure; the width of the annular groove structure is 0.1-0.2 mm; and / or,

[0018] The width of the first body is 0.22-0.28 mm; and / or,

[0019] The width of the second body is 1.55-1.75 mm; and / or,

[0020] Along the thickness direction, the distance between the projection of the first body on the adhesive layer and the edge of the adhesive layer is 0.04-0.08 mm; and / or,

[0021] The width of the adhesive layer is 1.95-2.2 mm.

[0022] Preferably, the microwave quasi-optical dichroic filter based on the frequency selective surface meets at least one of the following conditions:

[0023] The width of the first metal layer is 1.35-1.6 mm;

[0024] The width of the second metal layer is 1.35-1.6 mm;

[0025] The thickness of at least one of the first dielectric substrate and the second dielectric substrate is 0.787 mm;

[0026] The thickness of the adhesive layer is 0.102 mm;

[0027] At least one of the first dielectric substrate and the second dielectric substrate has a dielectric constant of 2.2 and a loss tangent of 0.0009;

[0028] The dielectric constant of the adhesive layer is 3.52, and the loss tangent is 0.004.

[0029] Preferably, the equivalent circuit of the microwave quasi-optical dichroic filter based on the frequency selective surface includes: an input port, an output port, an intermediate layer resonant network, a distributed coupling network and an impedance matching network;

[0030] The input port is formed by the first metal layer, and the input port is connected to the middle layer resonant network through a first transmission line, and the first transmission line is formed by the first dielectric substrate;

[0031] The output port is formed by the third metal layer, and the output port is connected to the middle layer resonant network through a second transmission line, and the second transmission line is formed by the second dielectric substrate;

[0032] The intermediate layer resonant network includes a series resonant unit and a parallel resonant unit. The series resonant unit is connected between the input port and the second body of the second metal layer. The series resonant unit includes a series equivalent inductor L1 and an equivalent capacitor C3. The equivalent inductor L1 is formed by the first body of the second metal layer. The equivalent capacitor C3 is formed by the gap between the equivalent inductor L1 and the edge of the first body and the adhesive layer. The parallel resonant unit is connected between the second body and the output port. The parallel resonant unit includes a parallel equivalent inductor L2 and an equivalent capacitor C4. The equivalent inductor L2 is formed by the spiral slot structure of the second metal layer. The equivalent capacitor C4 is formed by the annular slot structure of the second metal layer.

[0033] The distributed coupling network includes an equivalent capacitor C1, an equivalent capacitor C2, and an equivalent capacitor C5. The equivalent capacitor C1 is formed by the edge of the first metal layer and is connected between the input port and the first transmission line. The equivalent capacitor C2 is formed by the edge of the third metal layer and is connected between the output port and the second transmission line. The equivalent capacitor C5 is formed by the gap between the slot arms of the spiral slot structure and is connected between the slot arms.

[0034] The impedance matching network includes the first transmission line Z1 and the third transmission line Z2, the input port and the output port are connected to the third transmission line Z2 through the first transmission line Z1, the second body is connected to the parallel resonance unit through the third transmission line Z2, and the third transmission line is formed by the adhesive layer.

[0035] This application achieves loss optimization compared to pure metal materials and 3D printed materials by adopting a multilayer structure of a first metal layer, a first dielectric substrate, a second metal layer, an adhesive layer, a second dielectric substrate, and a third metal layer, as well as a material design of metal plus dielectric (dielectric substrate and adhesive layer): the thinning of the metal layer effectively suppresses the ohmic loss caused by the skin effect, and the selection of dielectric materials with low dielectric constant and low loss tangent controls the increase in dielectric loss. Through the symmetrical design of the multilayer board, the performance fluctuation problem caused by sensitivity to the incident angle can be reduced under oblique incidence conditions (such as 30° oblique incidence), and the impact of large incident angles on transmission performance can be significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0037] Figure 1 Schematic diagram of the structure of a microwave quasi-optical dichroic filter based on a frequency selective surface in an embodiment of the present application;

[0038] Figure 2 This is a schematic structural diagram of the first metal layer in an embodiment of the present application;

[0039] Figure 3 This is a schematic structural diagram of the second metal layer in an embodiment of the present application;

[0040] Figure 4 This is a schematic structural diagram of the third metal layer in an embodiment of the present application;

[0041] Figure 5 Schematic diagram of the structure of the equivalent circuit of the microwave quasi-optical dichroic filter based on the frequency selective surface in the embodiment of the present application.

[0042] Figure 6This is a flow chart of simulation settings based on electromagnetic analysis software in an embodiment of the present application;

[0043] Figure 7 This is a comparison chart of the first simulation results in the embodiment of this application;

[0044] Figure 8 This is a comparison chart of the second simulation results in the embodiment of this application.

[0045] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0046] The embodiments of the present application provide a microwave quasi-optical dichroic filter based on a frequency selective surface, thereby solving the problems of high-frequency loss, excessive transmission influence due to large incident angles, instability, and low transmission efficiency that are prone to occur in FSS in the prior art.

[0047] To better understand the above technical solutions, exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numbers in different drawings represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of devices consistent with certain aspects of the present application, as detailed in the appended claims.

[0048] As a spatial filter, FSS is widely used in various fields of communication. The FSS commonly used in millimeter wave and submillimeter wave bands known to the applicant can be divided into pure metal FSS and 3D FSS based on the structural composition. However, the high conductivity of metal leads to a significant skin effect at high frequencies, and the current is concentrated on the surface of the conductor, which increases the effective resistance, resulting in a large ohmic loss, reducing the transmission efficiency of FSS. Especially in the millimeter wave or terahertz frequency band, the loss is aggravated, limiting its performance in high-frequency applications. Metal FSS usually relies on the resonance mechanism, resulting in a narrow working bandwidth, which is difficult to meet broadband requirements. In addition, it is sensitive to the incident angle, and its transmission performance varies significantly with the incident angle of the electromagnetic wave, which is very restrictive in practical applications.

[0049] However, FSS based on 3D printing technology also has some shortcomings and deficiencies. For example, most 3D printing materials (such as PLA (polylactic acid), ABS (acrylonitrile-butadiene-styrene copolymer), photosensitive resin, etc.) are inherently non-conductive. Although conductivity can be enhanced by electroplating or adding conductive fillers (such as carbon nanotubes, metal particles), this will significantly increase the complexity of the process and may cause surface unevenness, affecting electromagnetic performance; for example, the dielectric constant and loss tangent of 3D printing materials are different from those of traditional microwave materials (such as PTFE (polytetrafluoroethylene) and ceramics), especially in the millimeter wave or terahertz frequency bands, which may lead to signal attenuation and reduced efficiency; in addition, some 3D printing materials are prone to deformation or aging in high-temperature environments, limiting their application in extreme scenarios such as aerospace.

[0050] Based on this, the present application provides an innovative design of a microwave quasi-optical dichroic filter based on frequency selective surface technology, which aims to solve the key technology of frequency band analysis in multi-band microwave quasi-optical receiving systems. The device realizes efficient frequency division processing of K-band (18-26GHz) and Q-band (34-50GHz) electromagnetic waves through an innovative periodic resonant unit structure design. This design is particularly suitable for quasi-optical systems such as radio astronomy receivers and multi-band communication systems that need to process multiple frequency band signals at the same time. Its angular stability, low insertion loss and high stopband suppression characteristics are significant. Compared with traditional metal mesh filters, this design effectively expands the operating bandwidth through multi-layer dielectric loading technology. In addition, the present application achieves a compact structure by integrating the feed horns of three bands into a single Dewar, and realizes precise control of the electromagnetic wave path through multi-stage FSS filters.

[0051] This embodiment provides a microwave quasi-optical dichroic filter based on a frequency selective surface, such as Figure 1 As shown, the structure includes a first metal layer 101, a first dielectric substrate 102, a second metal layer 20, an adhesive layer 40, a second dielectric substrate 302, and a third metal layer 302, which are sequentially arranged along the thickness direction. In this embodiment, the structure is symmetrical along the thickness direction with the second metal layer 20 and the adhesive layer 40 as the center. That is, the first dielectric substrate 102 and the first metal layer 101 are disposed on one side of the second metal layer 20 and the adhesive layer 40 in the thickness direction, and the second dielectric substrate 302 and the third metal layer 301 are disposed on the other side.

[0052] The first metal layer 101 is a metal patch, such as Figure 2 As shown, the first metal layer 101 is attached to the first dielectric substrate 102, and the second metal layer 20 is also a metal patch, as shown in FIG. Figure 4 As shown, the second metal layer 20 is attached to the second dielectric substrate 302 .

[0053] In this embodiment, by adopting a multilayer structure comprising a first metal layer 101, a first dielectric substrate 102, a second metal layer 20, an adhesive layer 40, a second dielectric substrate 302, and a third metal layer 302, and a metal-plus-dielectric (dielectric substrate and adhesive layer) material design, loss optimization is achieved compared to pure metal materials and 3D-printed materials. The thinning of the metal layer effectively suppresses ohmic losses caused by the skin effect, and the selection of dielectric materials with low dielectric constants and low loss tangents controls the increase in dielectric losses. The symmetrical design of the multilayer board reduces performance fluctuations due to incident angle sensitivity under oblique incidence conditions (e.g., 30° oblique incidence), significantly reducing the impact of high incident angles on transmission performance.

[0054] In some specific embodiments, the overall width of the microwave quasi-optical dichroic filter is 130 mm. It should be understood that in one embodiment, the projection of the microwave quasi-optical dichroic filter in the thickness direction is a square, and the overall width is the width of the square. In another embodiment, the projection of the microwave quasi-optical dichroic filter in the thickness direction is a rectangle, and the overall width is the width of the facet. This embodiment uses the above method as an example for the convenience of illustration, and it should be understood that this example should not be construed as limiting the embodiments of this application.

[0055] In this embodiment, by introducing the composite resonant structure of the second metal layer, the electromagnetic wave resonance characteristics of the FSS can be determined. The use of a centrally symmetrical structure can reduce the incident angle sensitivity and support consistent polarization performance under oblique incidence.

[0056] like Figure 2 As shown, in some specific embodiments, the width PU of the first metal layer 101 is 1.55-1.75 mm.

[0057] like Figure 4 As shown, in some specific embodiments, the width PB of the second metal layer 20 is 1.35-1.6 mm.

[0058] In this embodiment, the substantially symmetrical width design of the first metal layer 101 and the second metal layer 20 can reduce thermal stress deformation and ensure the reliability of the filter in low-temperature cooling environments (such as radio astronomy receivers). Slight differences in width can adjust the multi-layer capacitance distribution and optimize passband and stopband performance.

[0059] In some specific embodiments, at least one of the first dielectric substrate 102 and the second dielectric substrate 302 has a dielectric constant of 2.2, a loss tangent of 0.0009, and a thickness of 0.787. In this embodiment, the first dielectric substrate 102 and the second dielectric substrate 302 can be made of Rogers 5880 (i.e., microwave plate material manufactured by Rogers Corporation, model RO5880) to meet the requirements of the first dielectric substrate 102 and the second dielectric substrate 302 in this embodiment.

[0060] In some specific embodiments, the adhesive layer 40 has a dielectric constant of 3.52, a loss tangent of 0.004, and a thickness of 0.102 mm. In this embodiment, the adhesive layer 40 can be made of a thermosetting polymer composite material specifically for high-frequency circuits, which has low dielectric loss and forms a uniform dielectric layer during the multilayer board lamination process, thus meeting the requirements of the adhesive layer 40 in this embodiment.

[0061] In this embodiment, the use of low-loss materials for the first dielectric substrate 102, the second dielectric substrate 302 (e.g., Rogers 5880), the adhesive layer 40, and the multi-layer structure effectively reduces ohmic losses caused by the high-frequency skin effect. Simulation results show that high-frequency losses can be effectively reduced.

[0062] like Figure 1 and Figure 3 and Figure 4 As shown, in this embodiment, the second metal layer 20 includes a metal layer body and a slot structure penetrating the metal layer body. Preferably, the slot structure includes a spiral slot structure 204.

[0063] In this embodiment, by slotting the second metal layer 20, the resonance points introduced by the slots can generate transmission zeros in the stopband (e.g., 18-26 GHz), improving the stopband suppression capability. The slots also disrupt the continuous current distribution in the metal layer, stimulating multi-mode resonance, widening the passband (e.g., 34-50 GHz) or achieving multi-band response. By setting the specific slot structure in a spiral shape, a tortuous path can be added to extend the effective current length, significantly increasing the equivalent inductance, thereby achieving resonance control in a lower frequency band within a limited area.

[0064] The spiral groove structure 204 in this embodiment is described below through a specific example:

[0065] The spiral slot structure 204 includes a plurality of sub-slots arranged along the circumference of the metal layer body, and the projection of the sub-slots along the thickness direction is a C-shaped structure. In this embodiment, by setting the sub-slots with C-shaped projections, the spiral structure can be arranged symmetrically, thereby reducing the dependence on the polarization direction.

[0066] The sub-groove body includes a first groove arm, which extends along the first direction and is bent to form a second groove arm; the second groove arm extends along the second direction and is bent to form a third groove arm, and the third groove arm extends along the third direction. Through the cooperation of the first groove arm, the second groove arm and the third groove arm, a sub-groove body with a C-shaped structure projected along the thickness direction can be formed.

[0067] It should be understood that the first direction in this embodiment refers to any direction in a plane perpendicular to the thickness direction, the second direction is a direction at a certain angle to the first direction, and the third direction is a direction at a certain angle to the second direction. In a specific embodiment, the first groove wall is bent counterclockwise (such as 90 degrees) to form a second groove wall, and the second groove wall is bent counterclockwise (such as 90 degrees) to form a third groove wall.

[0068] The number of sub-tanks can be selected according to actual conditions. In a specific embodiment, the total number of sub-tanks is 4. Figure 4 As shown, the four sub-trough bodies are arranged in sequence in a clockwise direction, wherein the third groove wall of any sub-trough body is embedded between the first groove wall and the third groove arm of the previous sub-trough body, thereby surrounding to form a spiral structure.

[0069] Specifically, such as Figure 3 As shown, the length L1 of the first slot arm is 0.75-0.85 mm; and / or, the length L2 of the second slot arm is 0.52-0.59 mm; and / or, the length L3 of the third slot arm is 0.22-0.3 mm; and / or, the width W2 of at least one of the first slot arm, the second slot arm and the third slot arm is 0.09-0.18 mm.

[0070] In this embodiment, the shape of the slots in the second metal layer 20 is inspired by the spiral inductor, which is equivalent to an LC (inductor and capacitor) parallel resonant circuit. Through multi-stage bending slot arms, a progressive current path can be formed to regulate the resonance intensity of different frequency bands. By setting the width of 0.09-0.18mm, it is adapted to the conventional PCB (printed circuit board) lithography process, which can save costs and improve yield.

[0071] In some specific embodiments, the slot structure includes an annular slot structure 202, which is disposed along the edge of the metal layer body. In this embodiment, the annular slot structure 202 can be used to adjust the capacitance value and optimize the LC resonant frequency.

[0072] In this embodiment, the metal layer body includes a first body 201 located outside the annular groove structure 202 and a second body 203 located inside the annular groove structure 202; the width S2 of the annular groove structure 202 is 0.1-0.2mm; and / or, the width W2 of the first body 201 is 0.22-0.28mm; and / or, the width P2 of the second body 203 is 1.55-1.75mm.

[0073] In this embodiment, by precisely controlling the width of the annular slot structure 202, the width of the first body 201, and the width of the second body 203, efficient separation of dual bands, K-band blocking and Q-band transmission can be achieved, further optimizing the electromagnetic performance and achieving low loss, wide bandwidth, and angular stability.

[0074] In a specific embodiment, along the thickness direction, a distance S1 between the projection of the first body 201 on the adhesive layer 40 and the edge of the adhesive layer 40 is 0.04-0.08 mm.

[0075] In this embodiment, by introducing a gap S1 at the edge of the second metal layer 20, which is equivalent to introducing a gap capacitor into the entire circuit, a transmission zero point can be introduced at low frequency to achieve a frequency response characteristic with rapid roll-off from the stop band to the pass band.

[0076] Figure 5 A structural schematic diagram of an equivalent circuit of a microwave quasi-optical dichroic filter based on a frequency selective surface in a specific implementation of this embodiment is shown, including: an input port, an output port, an intermediate layer resonant network and a distributed coupling network.

[0077] The input port is formed by the first metal layer 101 and represents the interface where the electromagnetic wave enters the first metal layer 101, that is, the starting port for the electromagnetic wave to enter the multilayer structure of this embodiment from free space. The input port is connected to the intermediate layer resonant network via a first transmission line. The first transmission line is formed by the first dielectric substrate 102. In a specific embodiment, the equivalent impedance of the first dielectric substrate 102 is 254Ω (calculated based on the dielectric constant and thickness of the first dielectric substrate 102).

[0078] The output port is formed by the third metal layer 302, indicating that the transmitted signal is output from the third metal layer 302 to free space. The output port is connected to the intermediate layer resonant network via a second transmission line. The second transmission line is formed by the second dielectric substrate 302. In this embodiment, the equivalent impedance of the second dielectric substrate 302 is 254Ω (calculated based on the dielectric constant and thickness of the second dielectric substrate 302).

[0079] The intermediate layer resonant network includes a series resonant unit and a parallel resonant unit. The series resonant unit is connected between the input port and the second body 203 of the second metal layer 20, and is used to form high-stop band suppression in the 18-26 GHz frequency band; the series resonant unit includes an equivalent inductor L1 and an equivalent capacitor C3 connected in series. The equivalent inductor L1 is formed by the first body 201 of the second metal layer 20, and the equivalent capacitor C3 is formed by the gap between the equivalent inductor L1 and the edge of the first body 201 and the adhesive layer 40; in this embodiment, the equivalent inductor L1 is 89.5pH, and the equivalent capacitor C3 is 28.42fF.

[0080] The parallel resonant unit is connected between the second body 203 and the output port, and is used to achieve low-loss transmission in the 34-50 GHz frequency band. The parallel resonant unit includes an equivalent inductor L2 and an equivalent capacitor C4 connected in parallel. The equivalent inductor L2 is formed by the spiral slot structure 204 of the second metal layer 20, and the equivalent capacitor C4 is formed by the annular slot structure 202 of the second metal layer 20. In this embodiment, the equivalent inductor L2 is 627.8 pH, and the equivalent capacitor C4 is 71.63 fF.

[0081] The distributed coupling network includes equivalent capacitors C1, C2, and C5. Equivalent capacitor C1 is formed by the edge of the first metal layer 101 and spans between the input port and the first transmission line, adjusting impedance matching. Equivalent capacitor C2 is formed by the edge of the third metal layer 302 and spans between the output port and the second transmission line, adjusting impedance matching. Equivalent capacitor C5 is formed by the tiny gaps between the slot arms of the spiral slot structure 204 and spans between the slot arms to suppress parasitic resonances at the passband edge. In this embodiment, equivalent capacitor C1 is 5.68 fF, equivalent capacitor C2 is 7.02 fF, and equivalent capacitor C5 is 0.65 fF.

[0082] The impedance matching network includes a first transmission line Z1 and a third transmission line Z2. Specifically, the input port and the output port are connected to the third transmission line Z2 through the first transmission line Z1. Figure 5 The spatial wave impedance Z0 in the second metal layer 20 is specifically 377Ω in this embodiment. The second body 203 is connected to the parallel resonant unit via a third transmission line, wherein the third transmission line is formed by the adhesive layer 40. In this embodiment, the impedance Z2 of the third transmission line is 200Ω. The equivalent inductance L1 and the equivalent inductance L2 are controlled by the geometric dimensions of the slots in the second metal layer 20, respectively. The equivalent capacitances C1 to C5 are controlled by the slot width and gap distance. The equivalent impedance Z1 and the equivalent impedance Z2 are determined by the dielectric constant and thickness matching of the dielectric substrate. Ultimately, a two-color filtering characteristic is formed with a stopband return loss of less than 0.5dB and a passband insertion loss of less than 0.4dB.

[0083] Here, it should be understood that the equivalent inductance L1 in this embodiment corresponds to the width W2 of the first body 201 = 0.25 mm, the equivalent capacitance C3 corresponds to the gap S1 = 0.06 mm between the first body 201 and the edge, the equivalent inductance L2 corresponds to the arm length L1 = 0.8 mm of the spiral slot structure 204, and the equivalent capacitance C4 corresponds to the width S2 = 0.17 of the annular slot structure 202; the equivalent impedance Z1 and the equivalent impedance Z2 are respectively obtained by Rogers 5880 (such as Figure 1 As shown, the thickness sh1 is 0.787mm) and the semi-cured sheet (such as Figure 1 As shown, the dielectric constant of the thickness sh2 (0.102mm) is calculated.

[0084] In this embodiment, the input port and output port of the equivalent circuit are connected to the free space and the intermediate layer resonant network by the first transmission line Z1 to achieve impedance matching; the series resonant unit (equivalent inductor L1-equivalent capacitor C3) and the parallel resonant unit (equivalent inductor L2-equivalent capacitor C4) are coupled through the second body 203 to form a hybrid resonant topology; the distributed capacitors (equivalent capacitor C1, equivalent capacitor C2 and equivalent capacitor C5) are connected across the key nodes to optimize the passband flatness and edge suppression.

[0085] In this embodiment, stopband suppression (i.e., return loss <0.5dB) can be achieved through the series resonant circuit, passband transmission (i.e., insertion loss <0.4dB) can be achieved through the cooperation of the parallel resonant circuit and the equivalent capacitor, and angular stability can be achieved through the symmetrical structure, distributed coupling network and impedance matching network.

[0086] The following is a verification and explanation of the microwave quasi-optical dichroic filter based on the frequency selective surface in this embodiment by means of modeling and simulation. This embodiment uses electromagnetic analysis software to model and simulate the microwave quasi-optical dichroic filter based on the frequency selective surface in this embodiment. The specific operation process is as follows: Figure 6 As shown in the figure, the master-slave boundary conditions are used to simulate an infinite periodic surface (x and y directions), and two polarized incident waves, transverse electric (TE) and transverse magnetic (TM), are set as the excitation sources. The incident angle range is 0-30 degrees, the port size is the same as the unit period, and the frequency response of the dual-polarized incident wave is observed.

[0087] The equivalent circuit of FSS was constructed and simulated using circuit simulation software, and the final results were compared with the simulation results of electromagnetic simulation software. The comparison chart is as follows: Figure 7 and Figure 8 shown.

[0088] Specifically, Figure 7 and Figure 8The following table shows the simulation results of FSS under TE polarization and TM polarization, respectively. The horizontal axis represents the frequency of signal transmission or reflection, and the vertical axis represents the scattering (S) parameter. The solid line represents the schematic diagram of the simulation results using electromagnetic simulation software, and the dashed line represents the schematic diagram of the simulation results using circuit simulation software. S11 represents the reflection coefficient of the input port, that is, the return loss of the input port, and S21 represents the transmission coefficient from the input port to the output port, that is, the forward transmission coefficient. The electromagnetic simulation results are modeled and simulated using a set of typical values. The specific parameters are: P = 2.1mm, P2 = 1.7mm, PU = 1.55mm, PB = 1.5mm, S1 = 0.06mm, S2 = 0.17mm, W1 = 0.15mm, W2 = 0.25mm, L1 = 0.8mm, L2 = 0.55mm, L3 = 0.26mm. This set of parameters is representative and can reflect the typical transmission characteristics of the structure within this parameter range. The specific results are as follows:

[0089] By comparing the results of circuit simulation and electromagnetic full-wave simulation, it was found that the FSS showed excellent performance consistency in large-angle oblique incidence scenarios. In terms of passband characteristics, when the operating frequency is in the range of 34-50GHz, both simulation methods verified that its insertion loss is always less than 0.4dB, showing good electromagnetic wave transmission efficiency. In terms of stopband suppression capability, the return loss in the 18-26GHz frequency band is stably controlled within the range of less than 0.5dB. It is worth noting that even under large-angle incidence conditions, the transition band slope between the passband and the stopband still maintains a steep characteristic, which fully verifies the angular stability of the FSS structure under oblique incidence conditions. This high degree of consistency between the full-wave simulation and the equivalent circuit model not only proves the effectiveness of the design method, but also provides a reliable theoretical basis for rapid parameter optimization in subsequent engineering applications.

[0090] This embodiment utilizes a low-loss dielectric material (Rogers 5880), a low-loss prepreg, and a multilayer structure (first metal layer 101, first dielectric substrate 102, second metal layer 20, adhesive layer 40, second dielectric substrate 302, and third metal layer 302) to effectively reduce ohmic losses caused by the high-frequency skin effect. Simulation results show that the insertion loss in the 34-50 GHz passband is less than 0.4 dB, and the return loss in the stopband (18-26 GHz) is less than 0.5 dB, significantly improving the high-frequency loss issues of traditional pure metal FSS.

[0091] In this embodiment, through the symmetrical design of the multi-layer structure and the optimization of the resonant structure of the second metal layer 20, the transmission characteristics of TE and TM polarizations remain highly consistent under large angle conditions, and the insertion loss difference is less than 0.1dB, which improves the angle stability and solves the performance fluctuation problem caused by sensitivity to the incident angle.

[0092] In this embodiment, the LC resonant circuit (equivalent inductance L1~L3) and gap capacitance (equivalent capacitance C3~C5) introduced by the slots in the second metal layer form an LC parallel resonant circuit and a series resonant unit, which accurately regulates the stopband suppression and passband transmission characteristics, forming a steep transition band between the stopband and the passband. At the same time, the passband range (34-50GHz) is widened through multi-stage resonant coupling, overcoming the narrow bandwidth defect of traditional FSS.

[0093] It should be understood that the distance parameters (such as length, thickness, etc.) designed in this embodiment are preferred values determined through electromagnetic simulation and experimental verification, thereby ensuring efficient transmission and suppression of electromagnetic signals in a specific frequency band. However, it should be understood that in the actual manufacturing and installation process, taking into account engineering factors such as processing tolerances, thermal deformation compensation, and installation errors, the actual acceptable parameter range includes deviations within the range of plus or minus 0.02mm. For example, "the length of the first slot arm is 0.75-0.85mm" also includes a deviation within the range of plus or minus 0.02mm, that is, "the length of the first slot arm is within the range of 0.73mm to 0.87mm." Other parameters are similar and will not be repeated here.

[0094] In addition, although the terms "first," "second," and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the exemplary embodiments.

[0095] The directional terms such as up, down, left, right, front, back, front, back, top, and bottom mentioned or possibly mentioned in this specification are defined relative to the structure shown in the drawings. They are relative concepts and may vary depending on the location and usage of the device. Therefore, these or other directional terms should not be interpreted as restrictive.

[0096] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to a fixed connection, an indirect connection via an intermediate medium, internal communication between two components, or an interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0097] In addition, the terms "comprises" and "having" and any variations thereof are intended to cover a non-exclusive inclusion. For example, a process, method, system, product or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, product or apparatus.

[0098] The above description is only a preferred embodiment of the present application and does not limit the present application in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present application, and these improvements and supplements should also be considered as the scope of protection of the present application. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present application by using the technical content disclosed above are all equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present application are still within the scope of the technical solution of the present application.

Claims

1. A microwave quasi-optical dichroic filter based on a frequency selective surface, characterized in that: The invention comprises a first metal layer, a first dielectric substrate, a second metal layer, an adhesive layer, a second dielectric substrate and a third metal layer which are sequentially arranged along the thickness direction.

2. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 1, wherein: The second metal layer includes a metal layer body and a slot structure passing through the metal layer body.

3. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 2, wherein: The slotted structure comprises a spiral slotted structure.

4. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 3, wherein: The spiral slot structure includes a plurality of sub-slot bodies arranged along the circumference of the metal layer body, and the projection of the sub-slot bodies along the thickness direction is a C-shaped structure.

5. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 4, wherein: The sub-trough body includes a first slot arm, which extends along a first direction and is bent to form a second slot arm; the second slot arm extends along a second direction and is bent to form a third slot arm, which extends along a third direction.

6. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 5, wherein: The length of the first slot arm is 0.75-0.85 mm; and / or, The length of the second slot arm is 0.52-0.59 mm; and / or, The length of the third slot arm is 0.22-0.3 mm; and / or, A width of at least one of the first slot arm, the second slot arm, and the third slot arm is 0.09-0.18 mm.

7. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 2, wherein: The slotted structure includes an annular slotted structure, and the annular slotted structure is arranged along the edge of the metal layer body.

8. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 7, wherein: The metal layer body includes a first body located outside the annular groove structure and a second body located inside the annular groove structure; the width of the annular groove structure is 0.1-0.2 mm; and / or, The width of the first body is 0.22-0.28 mm; and / or, The width of the second body is 1.55-1.75 mm; and / or, Along the thickness direction, the distance between the projection of the first body on the adhesive layer and the edge of the adhesive layer is 0.04-0.08 mm; and / or, The width of the adhesive layer is 1.95-2.2 mm.

9. The microwave quasi-optical dichroic filter based on a frequency selective surface according to claim 1, wherein: The microwave quasi-optical dichroic filter based on the frequency selective surface meets at least one of the following conditions: The width of the first metal layer is 1.35-1.6 mm; The width of the second metal layer is 1.35-1.6 mm; The thickness of at least one of the first dielectric substrate and the second dielectric substrate is 0.787 mm; The thickness of the adhesive layer is 0.102 mm; At least one of the first dielectric substrate and the second dielectric substrate has a dielectric constant of 2.2 and a loss tangent of 0.0009; The dielectric constant of the adhesive layer is 3.52, and the loss tangent is 0.

004.

10. The microwave quasi-optical dichroic filter based on a frequency selective surface according to any one of claims 1 to 9, characterized in that: The equivalent circuit of the microwave quasi-optical dichroic filter based on the frequency selective surface includes: an input port, an output port, an intermediate layer resonant network, a distributed coupling network and an impedance matching network; The input port is formed by the first metal layer, and the input port is connected to the middle layer resonant network through a first transmission line, and the first transmission line is formed by the first dielectric substrate; The output port is formed by the third metal layer, and the output port is connected to the middle layer resonant network through a second transmission line, and the second transmission line is formed by the second dielectric substrate; The intermediate layer resonant network includes a series resonant unit and a parallel resonant unit. The series resonant unit is connected between the input port and the second body of the second metal layer. The series resonant unit includes a series equivalent inductor L1 and an equivalent capacitor C3. The equivalent inductor L1 is formed by the first body of the second metal layer. The equivalent capacitor C3 is formed by the gap between the equivalent inductor L1 and the edge of the first body and the adhesive layer. The parallel resonant unit is connected between the second body and the output port. The parallel resonant unit includes a parallel equivalent inductor L2 and an equivalent capacitor C4. The equivalent inductor L2 is formed by the spiral slot structure of the second metal layer. The equivalent capacitor C4 is formed by the annular slot structure of the second metal layer. The distributed coupling network includes an equivalent capacitor C1, an equivalent capacitor C2, and an equivalent capacitor C5. The equivalent capacitor C1 is formed by the edge of the first metal layer and is connected between the input port and the first transmission line. The equivalent capacitor C2 is formed by the edge of the third metal layer and is connected between the output port and the second transmission line. The equivalent capacitor C5 is formed by the gap between the slot arms of the spiral slot structure and is connected between the slot arms. The impedance matching network includes the first transmission line Z1 and the third transmission line Z2, the input port and the output port are connected to the third transmission line Z2 through the first transmission line Z1, the second body is connected to the parallel resonance unit through the third transmission line Z2, and the third transmission line is formed by the adhesive layer.

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