FSS filter

Abstract

The invention relates to the technical field of filters, in particular to an FSS (frequency selective surface) filter, the FSS filter is a multilayer FSS filter or a single-layer FSS filter, the single-layer FSS filter comprises a single-layer FSS structure and a substrate, the multilayer FSS filter is formed by superposing multiple layers of single-layer FSS filters, interlayer dielectric layers are arranged among the multiple layers of single-layer FSS structures, and the substrate is arranged between the multiple layers of single-layer FSS structures. The single layer FSS structure includes a patch or undercut of the periodic structure disposed on the substrate. The FSS filter has the advantages of high selectivity, accurate frequency control, high sensitivity and high resolution, and is suitable for high-end applications requiring efficient and accurate control.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to an FSS filter. Background Art

[0002] Filters are used to select or remove specific frequency components from a signal. Existing filters include MEMS filters, SAW filters, mechanical filters, piezoelectric filters, etc. SAW filters and piezoelectric filters have good selectivity, but are sensitive to environmental factors, especially temperature and humidity, and require compensation measures. They also require high-precision manufacturing processes and are expensive. Mechanical filters have relatively low selectivity. MEMS filters are complex to manufacture and are expensive. Summary of the invention

[0003] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and invention title of this application to avoid blurring the purpose of this section, the abstract and the invention title, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0004] The present invention provides a FSS filter with high selectivity and precise frequency control, high sensitivity and resolution, suitable for high-end applications requiring efficient and precise control.

[0005] In order to achieve the purpose of the present invention, the technical solution adopted is: a FSS filter, the FSS filter is a multi-layer FSS filter or a single-layer FSS filter, the single-layer FSS filter includes a single-layer FSS structure and a substrate, the multi-layer FSS filter is composed of multiple layers of single-layer FSS filters superimposed, an interlayer dielectric layer is arranged between the multiple layers of single-layer FSS structures, and the single-layer FSS structure includes a patch or a down-digging groove with a periodic structure arranged on the substrate.

[0006] As an optimization solution of the present invention, the patch or the undercut groove is annular, square, circular, triangular, star-shaped or hexagonal.

[0007] As an optimization solution of the present invention, the operating frequency of the patch or the lower groove in a ring shape is:

[0008]

[0009] Where: r ava is the average radius of the annular patch, defined as (rin+rout) / 2, where rin and rout are the inner and outer radii of the annulus, respectively, and ε r is the relative dielectric constant of the substrate, and C is the electromagnetic wave velocity.

[0010] As an optimization solution of the present invention, the operating frequency of the patch or the lower trench in a square shape is:

[0011]

[0012] Where: r0 is the relative dielectric constant of the substrate, and a is the side length of the square patch.

[0013] As an optimization solution of the present invention, the arrangement period p is the center spacing between adjacent square patches, p=(1+α)×a, α is the spacing coefficient, 0.1<α<0.5.

[0014] As an optimization solution of the present invention, multiple diodes are connected in series or in parallel between the patches, and the diodes are PIN diodes or varactor diodes.

[0015] As an optimization solution of the present invention, the conduction and cutoff of the diode are controlled by a control circuit, the control circuit is a microcontroller or a switch circuit, and the control circuit includes a power supply and a control signal for driving the diode.

[0016] As an optimization solution of the present invention, the plate material of the substrate is FR4, ceramic, quartz, copper, silver, aluminum, a negative refractive index metamaterial, and a ferroelectric polymer material.

[0017] As an optimized solution of the present invention, the patch is a conductive polymer film, a carbon nanotube composite material film or a metallized polymer film.

[0018] The present invention has positive effects: 1) the present invention can achieve high selectivity for specific frequencies by accurately designing the FSS structure;

[0019] 2) The FSS structure of the present invention is very compact and is suitable for the miniaturization requirements of modern wireless communication equipment; through the multi-layer FSS structure design, a wide-band filtering function can be achieved;

[0020] 3) The present invention has high selectivity and precise frequency control, high sensitivity and resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] Figure 1 A schematic diagram of a frequency selective surface structure of the present invention in the form of a ring;

[0023] Figure 2 is a schematic diagram of a square frequency selective surface structure of the present invention;

[0024] Figure 3 It is a schematic diagram of the working process of an embodiment of the FSS filter of the present invention;

[0025] Figure 4 is a frequency response curve of an embodiment of the FSS filter of the present invention;

[0026] Figure 5 It is a block diagram of an application scenario of the FSS filter of the present invention. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0030] Secondly, the present invention is described in detail with reference to the schematic diagram. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0031] Frequency Selective Surface (FSS) is a planar electromagnetic wave filter that selectively reflects or transmits electromagnetic waves according to frequency. FSS is usually composed of periodically arranged metal or conductive patterns, which are placed on a dielectric substrate. The working principle of FSS filter is that when electromagnetic waves encounter the pattern layer, the frequency whose wavelength matches the pattern size will be subject to specific phase delay and amplitude change, resulting in reflection or transmission behavior. Through the shape, size, spacing of the pattern and the properties of the dielectric substrate, a bandpass or bandstop effect can be achieved for a specific frequency range, thereby realizing the filtering function.

[0032] Example 1

[0033] Reference Figure 1 and Figure 2This embodiment provides an FSS filter, which is a multi-layer FSS filter or a single-layer FSS filter. The single-layer FSS filter includes a single-layer FSS structure and a substrate. The multi-layer FSS filter is composed of multiple layers of single-layer FSS filters stacked together. An interlayer dielectric layer is arranged between the multiple layers of single-layer FSS structures. The single-layer FSS structure includes a patch or a groove with a periodic structure arranged on the substrate.

[0034] The patch or the undercut groove is in the shape of a ring, square, circle, triangle, star or hexagon.

[0035] Multilayer structures can provide more complex frequency selective characteristics and provide bandwidth and performance. Single-layer FSS structures can be FSS patterns of the same or different shapes and sizes. The interlayer dielectric layer can be the same or different material as the substrate.

[0036] Furthermore, the multi-layer FSS structure is precisely aligned through alignment technology, and then bonded together using adhesives or lamination processes. Lamination is performed under high temperature and high pressure to firmly combine the multi-layer structure to form an integrated FSS filter.

[0037] The advantages of multilayer FSS filters include:

[0038] 1) Broadband characteristics: The multi-layer FSS structure can achieve a wider operating frequency band and more complex frequency response characteristics, which is suitable for applications that require wide frequency band operation.

[0039] 2) Multi-band selection: Through multi-layer design, selective filtering of multiple frequency bands can be achieved, which is suitable for multi-band communication systems and complex radar systems.

[0040] 3) High-performance filtering: The multi-layer structure can provide higher filtering accuracy and better ability to suppress out-of-band signals, improving system performance.

[0041] 4) Flexible design: The multi-layer design allows the use of different FSS patterns and dielectric materials in different layers to achieve more flexible electrical property adjustment.

[0042] 5) Higher Q value The multilayer structure can achieve a higher quality factor (Q value), which is beneficial to improving the selectivity of the filter and reducing losses.

[0043] 6) Composite functions: Multi-layer FSS can realize the integration of multiple functions, such as having both reflection and transmission properties, or combining with absorbing materials to achieve more complex electromagnetic properties.

[0044] Among them: Single-layer FSS filters are suitable for simple frequency selective applications, such as basic wireless communication antennas, single-band radar systems, basic stealth technology, etc. Multi-layer FSS filters are suitable for complex multi-band communication systems, high-performance radar systems, satellite communications, complex stealth technology and other occasions that require multi-band selectivity and high-performance filtering.

[0045] As an example, Figure 1 As shown, the operating frequency of the patch or the lower groove is a ring:

[0046]

[0047] Where: r ava is the average radius of the annular patch, defined as (rin+rout) / 2, where rin and rout are the inner and outer radii of the annulus, respectively, and ε r is the relative dielectric constant of the substrate, and C is the electromagnetic wave velocity. The ring patch is a resonant structure. When the wavelength of the electromagnetic wave matches the size of the ring patch, resonance occurs. This resonant frequency is the operating frequency of the ring patch, which determines the behavior of the FSS filter near this frequency.

[0048] like Figure 2 As shown, the operating frequency of the patch or the lower trench is square:

[0049]

[0050] Where: r0 is the relative dielectric constant of the substrate, and a is the side length of the square patch.

[0051] The square patch is a planar resonator. The operating frequency of the square patch affects the overall performance of the FSS filter. Under resonant conditions, the square patch can be regarded as a combination of an inductor and a capacitor. The inductor comes from the current distribution at the edge of the patch, while the capacitor is formed by the space between the patch and the ground layer or the adjacent patch. When the frequency of the electromagnetic wave matches the natural frequency of the patch, the patch will show a strong response to the electromagnetic wave of a specific frequency, such as reflection or absorption. The side length a is usually 10% to 50% of the operating wavelength.

[0052] The arrangement period p is the center spacing between adjacent square patches, p = (1 + α) × a, α is the spacing coefficient, 0.1 < α < 0.5. As an independent resonant mode design, the choice of p is usually slightly larger than the unit size to avoid coupling effects between units. As a coupled mode resonator design, the choice of p should be determined by the coupled resonant mode and the wavelength at its frequency. The calculation formula for the center spacing p of the coupled mode resonator is:

[0053]

[0054] Where β is the scaling factor (0.5≤β≤1), c is the speed of light, and f r is the resonant frequency of the coupled mode, ε r is the relative dielectric constant of the medium.

[0055] Among them, the multi-layer FSS resonates at different frequencies, thus having an FSS filter with multi-band characteristics, that is, having specific passbands or stopbands at multiple frequency points or bands. Improve the selectivity of the filter. Patches of different shapes and structures have different responses to vertically and horizontally polarized electromagnetic waves, and can be used to create filters sensitive to specific polarizations. Patch layout can help reduce the sidelobe level and increase the ratio of the main lobe to the sidelobe, thereby obtaining a sharper filter rectangular coefficient and improving frequency selectivity. By arranging patches in the center, four corners and all around, the mechanical and electrical stability of the structure can be improved. It can provide additional resonance points or help control edge effects, help control the edge response of the entire structure, reduce unnecessary radiation or absorption, and thus improve overall performance.

[0056] Furthermore, in the FSS filter, adding diodes for dynamic tuning and control can achieve selective transmission or reflection at different frequencies, thereby dynamically adjusting the frequency response of the FSS. This capability enables the FSS to adaptively adjust its performance in different working environments to meet specific frequency selection requirements. Specifically, adding diodes between the FSS patches can achieve the following functions:

[0057] Tunable FSS: By inserting a diode into the FSS structure, the resonant frequency of the FSS can be dynamically adjusted. The state of the diode (on or off) changes the capacitance or inductance between the patches, thus changing the resonant characteristics of the FSS. Commonly used diode types include PIN diodes and varactor diodes.

[0058] Switching function: The switching function of FSS is realized by controlling whether the diode is turned on or off. For example, when the diode is turned on, FSS reflects electromagnetic waves of certain frequencies, and when the diode is turned off, it allows electromagnetic waves of these frequencies to pass through.

[0059] Smart FSS: By integrating multiple diodes in the FSS and controlling them independently, a smart FSS system can be realized. This system can dynamically adjust its frequency response characteristics according to external signals or environmental changes for frequency selective shielding, absorption or transmission.

[0060] Specifically, choose the right diode: PIN diode or varactor diode according to application requirements. Among them, PIN diode is suitable for fast switching applications, while varactor diode is suitable for fine tuning.

[0061] Then design the circuit: design the circuit between the FSS patches and integrate the diode. Consider the diode's operating voltage, current, power consumption and other parameters.

[0062] Control circuit: used to control the on and off state of the diode. It can be implemented using a microcontroller, a switch circuit, etc.

[0063] Simulation and testing: The design can be simulated through electromagnetic simulation software to verify its performance. Finally, testing and debugging are carried out.

[0064] Furthermore, through reasonable design and control, the diodes in the FSS can be used to realize multiple functions to improve the flexibility and adaptability of the FSS.

[0065] Add the physical connection design of the diode to FSS (Frequency Selective Surface). Here are several common physical connection schemes and steps:

[0066] Series connection: Connect diodes in series between the patches of the FSS. This connection method is usually used to control the conduction and cutoff between patches. When implementing, first determine the layout of the FSS patches. In the gap between each adjacent patch, insert a diode to make it electrically connected to the patch. Make sure that the positive and negative poles of the diode are correctly connected so that the expected conduction or cutoff effect can be achieved.

[0067] Parallel connection: Connect diodes in parallel between the FSS patches. This method is usually used to adjust the capacitance. When implementing, first determine the layout of the FSS patches. Connect one terminal of the diode on one side of each patch, and the other end of the diode to the adjacent conductor of the patch. Make sure that all diodes are firmly connected and do not interfere with other circuit components.

[0068] Mixed connection: Mix series and parallel diodes to achieve specific circuit characteristics. When implementing, first determine which patches need series diodes and which patches need parallel diodes. Connect series or parallel diodes in the corresponding patch gaps. Finally, check all connections to ensure that they are correct.

[0069] Furthermore, in order to control the conduction and cutoff of the diode, a control circuit is designed. The control circuit usually includes a power supply and a control signal for driving the diode. When implemented, the control circuit includes a power supply and a control signal generating part. The control circuit is connected to the control end of each diode (usually the anode and cathode of a PIN diode, or the control electrode of a varactor diode). Ensure that the control signal can drive the diode correctly and that the control circuit does not interfere with other parts of the FSS.

[0070] Figure 3This is a schematic diagram of the working process of the FSS filter embodiment of the present invention. Each patch and the space around it form a resonant cavity. When the frequency of the electromagnetic wave matches the natural frequency of the resonant cavity, a strong resonance phenomenon will occur. This resonance effect determines the reflection or transmission characteristics of the FSS for a specific frequency. Due to the periodicity of the FSS structure, the incident electromagnetic wave will experience phase modulation when passing through or reflecting. This phase change leads to interference of electromagnetic waves, which in turn affects the propagation characteristics of electromagnetic waves. In the FSS structure, the gaps between the patches form inductance and capacitance effects. These inductance and capacitance effects will further affect the reflection and transmission characteristics of the electromagnetic waves. By introducing active devices such as diodes in the FSS, dynamic tuning can be achieved, allowing the FSS to adapt to different working conditions.

[0071] like Figure 4 As shown in the figure, the horizontal axis represents the frequency (in MHz), and the vertical axis represents the power attenuation amplitude (in dB). Each line corresponds to a different quality factor (Q value), from left to right, Q = 1000 and Q = 100. Among them, the quality factor is an indicator that measures the ratio of the filter bandwidth to the center frequency. The higher the value, the better the filter selectivity. The application scenarios of FSS filters are as follows: Figure 5 shown.

[0072] Furthermore, the undercut groove can be tuned to a specific frequency, so that the FSS filter can be highly reflective, highly transmissive or highly absorbing at that frequency. The length and width of the groove determine its resonant frequency, which affects the passband or stopband of the filter. The bandwidth of the FSS filter can be broadened by optimizing geometric parameters such as width, length and spacing, so that it can work effectively in a wider frequency range. The layout of the array can increase the selectivity of the FSS filter, that is, form a clear transition zone between the passband and the stopband, improve the rectangular coefficient, and reduce the sidelobe level. By optimizing the arrangement and shape, the sensitivity of the FSS filter to the angle of the incident electromagnetic wave can be reduced, and stable performance can be maintained even under oblique incidence conditions.

[0073] In terms of material selection, FR4 (glass fiber reinforced epoxy), ceramics, quartz, copper, silver, aluminum, negative refractive index metamaterials and ferroelectric polymer materials. Among them, copper, silver and aluminum have good conductivity and relatively low cost. Ferroelectric polymer materials include polyvinylidene fluoride (PVDF), barium lead titanate (PZT), etc. Ferroelectric polymer materials use high dielectric constant materials to make substrates, reduce the size of FSS units, and improve frequency selectivity. Metamaterials with negative refractive index can achieve more complex and efficient frequency selection characteristics.

[0074] FR4 has a very low loss factor, and the energy loss of the signal is small when it propagates in the medium, thus improving the integrity of the signal. It is essential for FSS filters with high efficiency and low signal attenuation. It can be used to achieve high-efficiency filtering at high frequencies. It brings advantages such as high frequency stability, low loss, and miniaturization.

[0075] The patch can be a conductive polymer film, a carbon nanotube composite film or a metallized polymer film. FSS filters need to be made of flexible materials to facilitate installation on non-planar or deformable surfaces. Conductive polymer films, carbon nanotube composite films or metallized polymer films have good conductivity and flexibility to ensure the stability and reliability of FSS filters. Parameters such as the bandwidth and insertion loss of the filter characterize the sensitivity of the FSS filter. In FSS filters, resolution is closely related to the bandwidth and selectivity of the filter.

[0076] Using metamaterials with negative refractive index or other unique electromagnetic properties, more complex and efficient frequency selective characteristics can be achieved. Develop flexible FSS filters for easy integration into wearable devices or curved applications. Use high dielectric constant materials to make substrates to reduce FSS unit size and improve frequency selectivity. FSS is insensitive to environmental factors.

[0077] In terms of structural design, we designed a three-dimensional FSS filter to further expand the frequency response range and function. We also developed an FSS structure that can adaptively adjust the frequency characteristics according to external environment or signal changes.

[0078] In terms of manufacturing, nanofabrication techniques are used to make more sophisticated and complex FSS structures to improve performance, and low-cost manufacturing processes, such as printed electronics, are used to reduce the cost of large-scale production.

[0079] Furthermore, we design FSS filters with integrated sensing functions that can detect environmental changes and adjust their own performance. We design composite FSS structures with both frequency selectivity and wave absorption characteristics for use in radar stealth technology. We design FSS structures that can collect environmental energy (such as solar energy and radio frequency energy) to provide additional functions. We design FSS filters for terahertz frequency band applications, which are suitable for communication technology and imaging systems. FSS filters with wider bandwidth characteristics meet the needs of higher frequencies and wider bandwidths.

[0080] Furthermore, electrically tuned FSS filters adjust the frequency response in real time by applying an electric field or voltage. FSS structures that adjust the frequency characteristics by mechanical means (such as deformation or rotation).

[0081] It should be understood that in the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but for those of ordinary skill having the benefit of this disclosure, the development effort will be a routine task of design, fabrication, and production without undue experimentation.

[0082] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A FSS filter, characterized in that: The FSS filter is a multilayer FSS filter or a single-layer FSS filter. The single-layer FSS filter includes a single-layer FSS structure and a substrate. The multilayer FSS filter is composed of multiple layers of single-layer FSS filters superimposed on each other. An interlayer dielectric layer is arranged between the multiple layers of single-layer FSS structures. The single-layer FSS structure includes patches or undercuts with a periodic structure arranged on the substrate.

2. A FSS filter according to claim 1, characterized in that: The patch or the undercut groove is in the shape of a ring, square, circle, triangle, star or hexagon.

3. A FSS filter according to claim 2, characterized in that: The operating frequency of the patch or the lower groove is a ring: Where: r ava is the average radius of the annular patch, defined as (rin+rout) / 2, where rin and rout are the inner and outer radii of the annulus, respectively, and ε r is the relative dielectric constant of the substrate, and C is the electromagnetic wave velocity.

4. A FSS filter according to claim 2, characterized in that: The operating frequency of the patch or the square groove is: Where: r0 is the relative dielectric constant of the substrate, and a is the side length of the square patch.

5. A FSS filter according to claim 4, characterized in that: The arrangement period p is the center spacing between adjacent square patches, p=(1+α)×a, α is the spacing coefficient, 0.1<α<0.

5.

6. A FSS filter according to claim 2, characterized in that: Multiple diodes are connected in series or in parallel between the patches, and the diodes are PIN diodes or varactor diodes.

7. The FSS filter according to claim 2, characterized in that: The on and off of the diode is controlled by a control circuit, wherein the control circuit is a microcontroller or a switch circuit, and the control circuit includes a power supply and a control signal for driving the diode.

8. The FSS filter according to claim 2, characterized in that: Substrate materials include FR4, ceramic, quartz, copper, silver, aluminum, negative refractive index metamaterials and ferroelectric polymers.

9. The FSS filter according to claim 2, characterized in that: The patch is a conductive polymer film, a carbon nanotube composite film or a metallized polymer film.

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