A multi-modal switchable bandpass filter

Abstract

The application relates to a miniaturized multi-mode switchable band-pass filter and belongs to the field of microwave electromagnetic structures. A filter metal microstrip transmission line part, an integrated "door" type artificial surface plasmon transmission part and a lumped part are arranged on the front surface of a dielectric substrate, the back surface of the dielectric substrate is provided with a ground plane, three variable capacitance diodes CAP, four groups of choke inductors, a group of DC blocking capacitors, a feeding circuit and a feeder; the metal rectangular microstrip transmission line part is composed of a metal rectangular microstrip, a microstrip transmission line part DC blocking capacitor and a metal rectangular bypass microstrip structure; each "door" type artificial surface plasmon lumped part is reversely connected with a variable capacitance diode CAP. Based on the "door" type artificial surface plasmon transmission part and lumped part structure, the optical dispersion characteristics of the artificial surface plasmon unit are changed by loading the variable capacitance diode CAP, and multi-mode real-time switching control of the band-pass filter among the ultra-wideband, wideband, narrowband and stopband is realized.

Description

Technical Field

[0001] This invention relates to a multimode switchable bandpass filter based on artificial surface plasmons, belonging to the field of microwave electromagnetic structures. Background Technology

[0002] With the development of terahertz (THz) communication, millimeter-wave (mmWave) and metasurface radar, SPP-like structures and artificial surface plasmons (Spoof SPPs) are showing significant potential in the fields of radar and wireless communication. As a crucial component of the microwave and RF transceiver systems of radar, bandpass filters require continuous iterative upgrades in structure and function. The high cutoff frequency and slow-wave characteristics exhibited by Spoof SPPs in optical dispersion are highly favored by researchers. Developing ultra-compact filters using the slow-wave characteristics of Spoof SPPs has become one of the key research projects in the front-end of radar systems. When the slow wave characteristics of the traditional SSPP structure are converted into transmission characteristics, it only has low-pass performance and no band-pass effect. To make it have a band-pass effect, it needs to be combined with other structures. Usually, it is combined with a substrate integrated waveguide structure with high-pass characteristics or a resonant ring is embedded between SSPP units to achieve a band-pass effect. However, once these structural combinations are determined, they are physically immutable structures, and their filtering performance indicators are also locked. If the filtering performance indicators need to be changed, a new hardware structure combination needs to be designed.

[0003] With ongoing research into SSPP structures, it has been discovered that loading nonlinear devices inside SSPP cells can effectively alter the equivalent impedance of the SSPP surface, thereby adjusting the optical dispersion characteristics of the SSPP cells. This provides a basis for developing bandpass filters based on SSPP structures to achieve multimode switching. Currently, a small number of small tunable bandpass filters based on SSPP structures have been put into experimental use. For the RF front-end of S-band and C-band radars, developing bandpass filters based on SSPP structures and varactor diodes (CAPs) to possess dynamic adjustment characteristics from stopband, narrowband, broadband, to ultra-wideband presents challenges at every step, from theoretical design calculations and structural fabrication to practical engineering applications. To fully demonstrate the enormous application potential of SSPPs in radar and wireless communication, it is essential to design a multimode switchable bandpass filter based on SSPPs with strong dynamic adjustment characteristics and good engineering implementation for radar RF front-ends. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-mode switchable bandpass filter based on artificial surface plasmons (SSPPs) for radar radio frequency front-ends. This filter allows for real-time switching between four functional modes—stopband, narrowband, wideband, and ultra-wideband—without altering the filter hardware structure in the S and C bands. It improves filter bank space utilization while also featuring miniaturization, high out-of-band suppression, and significantly reduced manufacturing costs, highlighting its energy-saving characteristics and spectrum reuse advantages. This adds a new filter to the application of SSPPs in radar. It utilizes a traditional SSPP structure to excite the SSPP fundamental mode through incident electromagnetic waves, achieving strong field confinement of the incident signal. By loading a varactor diode (CAP) inside the SSPP unit, the equivalent impedance of the SSPP surface is effectively changed, enabling continuous adjustment of the SSPP unit's optical dispersion characteristics. This allows for continuous adjustment of the filter's transmission characteristic curve, ultimately achieving the invention's objective of multi-mode switching for SSPP-based bandpass filters.

[0005] The present invention achieves the above-mentioned objective through the following technical solution: A miniaturized multimode switchable bandpass filter includes a filter, a dielectric substrate, an artificial surface plasmon unit structure, and varactor diodes (CAPs). The filter is disposed on the dielectric substrate. The filter is characterized by: filter metal microstrip transmission lines located at both ends of the filter on the front side of the dielectric substrate; periodic units on the front side of the dielectric substrate integrating gate-type artificial surface plasmon transmission sections and gate-type artificial surface plasmon lumped sections; and a ground plane, three varactor diodes (CAPs), four sets of choke inductors, one set of DC blocking capacitors, a power supply circuit, and a power supply line disposed on the back side of the dielectric substrate. The filter metal microstrip transmission line portion located at both ends of the filter on the front side of the dielectric substrate consists of a metal rectangular microstrip, a DC blocking capacitor, and a rectangular bypass microstrip structure. The characteristic impedance of the metal rectangular microstrip is 50Ω. The DC blocking capacitor is located at the inner end of the metal rectangular microstrip, and the rectangular bypass microstrip structure is located between the DC blocking capacitor and the "gate"-shaped artificial surface plasmon transmission portion. The "gate"-shaped artificial surface plasmon transmission section consists of two mirror-symmetrical inverted "L"-shaped vertical metal microstrips and a "gate"-shaped artificial surface plasmon composed of a bottom-connected metal microstrip. There are three "gate"-shaped artificial surface plasmon lumped units. Each "gate"-shaped artificial surface plasmon lumped unit has a varactor diode CAP connected in reverse on its inner side. The varactor diode CAP is connected to the bias circuit through a feed line.

[0006] Furthermore, the "gate"-shaped artificial surface plasmon unit structure is divided into two types. One type consists of a "gate"-shaped artificial surface plasmon transmission section composed of two mirror-symmetrical inverted "L"-shaped vertical metal microstrips and a metal microstrip connected to the bottom of the inverted "L"-shaped vertical metal microstrips. The other type consists of a "gate"-shaped artificial surface plasmon lumped section composed of two mirror-symmetrical inverted "L"-shaped vertical metal microstrips and a varactor diode CAP loaded inside them. Both structures exhibit strong near-field confinement capabilities, effectively suppressing crosstalk and harmonic components between units.

[0007] Furthermore, the filter metal microstrip transmission line section achieves good transmission characteristics through the "gate"-shaped artificial surface plasmon transmission section composed of the bottom of the inverted "L"-shaped vertical metal microstrip connected to the metal microstrip. At the same time, it exhibits high-frequency cutoff characteristics in optical features, realizing the direct conversion of incident electromagnetic waves into Zenneck waves, effectively filtering the harmonic components of Zenneck waves, and suppressing higher-order harmonic components.

[0008] Furthermore, the "gate"-shaped artificial surface plasmon lumped portion, consisting of two mirror-symmetrical inverted "L"-shaped vertical microstrips and a varactor diode CAP loaded inside them, controls the equivalent capacitance of the varactor diode CAP by applying a negative voltage. The value of the equivalent capacitance of the varactor diode CAP decreases as the absolute value of the applied negative voltage increases, and the two are inversely proportional.

[0009] Furthermore, in the "gate"-shaped artificial surface plasmon lumped section, when no negative voltage is applied to the feed circuit across the varactor diode CAP, the electrical characteristics of the varactor diode CAP exhibit a high capacitance value, and the filter exhibits ultra-wideband characteristics. When a negative voltage is applied to the feed circuit across the varactor diode CAP, as the absolute value of the negative voltage across the two ends increases from zero to the clamping voltage region of the varactor diode CAP, the equivalent capacitance value of the varactor diode CAP gradually decreases, and the passband characteristics of the bandpass filter change sequentially from achieving ultra-wideband to wideband, narrowband, and bandstop states.

[0010] Furthermore, after the power supply circuit across the varactor diode CAP is energized, the optical dispersion characteristics of the unit of the "gate" type artificial surface plasmon lumped part also change. As the absolute value of the negative voltage applied across the varactor diode CAP increases, the equivalent capacitance value of the varactor diode CAP gradually decreases. At the same time, the low cutoff frequency of the "gate" type artificial surface plasmon lumped part increases.

[0011] Furthermore, the power supply circuit connected to the two ends of the varactor diode CAP of the "gate"-shaped artificial surface plasmon lumped section is characterized by being composed of two sets of choke inductors and corresponding metal rectangular microstrips with connection functions. It has the function of suppressing the symmetric current generated by high-frequency signals and the function of protecting the power supply that provides negative voltage to the two ends of the varactor diode CAP.

[0012] Furthermore, the power supply that provides a negative voltage across the varactor diode CAP is characterized by being able to provide a voltage range of 0V to 30V, and having a reverse connection with the positive and negative terminals of the varactor diode CAP.

[0013] Furthermore, the line length of the metal rectangular microstrip is selected to be between 1.5 and 2 times the wavelength corresponding to the center frequency point of the selected frequency band.

[0014] Furthermore, the value of the DC blocking capacitor CAP between the metal rectangular microstrip and the rectangular bypass microstrip structure is determined based on the maximum applied voltage.

[0015] The advantages of this invention compared to the prior art are: The multimode switchable bandpass filter proposed in this invention, based on artificial surface plasmons (ASPs), utilizes a metal ground plane located at the lower end of a dielectric substrate. It employs two types of ASP unit structures: a gate-type ASP transmission section and a gate-type ASP lumped section. By combining this with a varactor diode (CAP)-type nonlinear device, the optical dispersion characteristics of the ASP units are altered, allowing them to transition from the fast-light region to the slow-light region at a low cutoff frequency. This transforms a filter that originally only had low-pass performance into a multimode reconfigurable bandpass filter. Furthermore, by changing the negative voltage applied across the varactor diode (CAP) and controlling its equivalent capacitance, the frequency at which the ASP units exit the fast-light region is altered. Ultimately, this achieves bandwidth control of the bandpass filter formed by cascading these ASPs and enables multimode control of the bandpass filter, allowing it to switch in real-time between ultra-wideband, wideband, narrowband, and stopband. This multimode switchable bandpass filter requires no changes to the filter hardware structure. It is not only compact and durable with flexible multimode switching, but also greatly reduces manufacturing costs while improving space utilization. It makes up for the shortcomings of existing technologies and adds a multimode switchable bandpass filter based on artificial surface plasmons with strong dynamic adjustment characteristics and good engineering implementation effect to the field of microwave electromagnetic structures. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the main structure of a multimode switchable bandpass filter; Figure 2 This is a side view schematic diagram of a multimode switchable bandpass filter. Figure 3 This is a schematic diagram of the rear view structure of a multimode switchable bandpass filter; Figure 4 This is a schematic diagram of the main structure of the transmission section unit of a multimode switchable bandpass filter; Figure 5 This is a schematic diagram of the front view structure of the lumped unit of a multimode switchable bandpass filter; Figure 6 Comparison of optical dispersion curves for different structural parameters of the transmission section unit of a multimode switchable bandpass filter; Figure 7 This is a comparison of the dispersion curves of the lumped unit of a multimode switchable bandpass filter in terms of optical characteristics after changing the voltage across the varactor diode CAP. Figures 8-11 This is a comparison of the return loss and transmission coefficient curves of a multimode switchable bandpass filter as the bias voltage across the varactor diode CAP is changed.

[0017] In the figure: 1. Dielectric substrate, 2. Filter metal microstrip transmission line section, 3. "Gate" type artificial surface plasmon transmission section, 4. "Gate" type artificial surface plasmon lumped section, 5. Surface metal, 6. Dielectric, 7. Bottom metal; 100. Ground; 101. Varactor diode CAP; 102. Choke inductor; 103. Power supply circuit. 200. Metal rectangular microstrip; 201. DC blocking capacitor for microstrip transmission line; 202. Rectangular bypass microstrip structure. Detailed Implementation

[0018] The following detailed description of a specific embodiment of a multimode switchable bandpass filter according to the present invention, with reference to the accompanying drawings, is provided (see attached figures). Figures 1-11 ): (See) Figure 1 A multimode switchable bandpass filter includes a filter, a dielectric substrate 1, an artificial surface plasmon structure, and a varactor diode CAP101. The filter is disposed on the dielectric substrate 1. Its features include: on the front side of the dielectric substrate 1, at both ends of the filter, filter microstrip transmission line portions 2 are disposed, each consisting of a pair of metal rectangular microstrips 200, a pair of microstrip transmission line portion DC blocking capacitors 201, and a pair of rectangular bypass microstrip structures; on the back side of the dielectric substrate 1, a ground plane 100, three varactor diodes CAP101, four sets of choke inductors 102, a set of DC blocking capacitors, a power supply circuit 103, and a power supply line are disposed. The filter microstrip transmission line 2 is connected to multiple repeating metal structures on its side, integrating a rectangular metal bypass microstrip structure, a "gate"-shaped artificial surface plasmon transmission section 3, and a "gate"-shaped artificial surface plasmon lumped section 4. The "gate"-shaped artificial surface plasmon transmission section 3 consists of a pair of mirror-symmetrical inverted "L"-shaped vertical metal microstrips and a "gate"-shaped artificial surface plasmon composed of a bottom-connected metal microstrip. There are three "gate"-shaped artificial surface plasmon lumped sections 4. Based on three "gate"-shaped artificial surface plasmons, the lumped part 4 of each "gate"-shaped artificial surface plasmon mainly consists of: two mirror-symmetrical inverted "L"-shaped vertical metal microstrips and varactor diodes CAP101 loaded inside them forming a "gate"-shaped artificial surface plasmon, three varactor diodes CAP101, and a cathode / anode bias feed interface; the feed circuit 103 consists of four sets of metal microstrip feed lines and four sets of choke inductors 102 loaded between the metal microstrip feed lines; The characteristic impedance of the transmission section of the metal rectangular microstrip 200 is 50Ω. The DC blocking capacitor 201 of the microstrip transmission line section is located at the inner end of the transmission section of the metal rectangular microstrip 200. The metal rectangular bypass microstrip structure is located between the DC blocking capacitor 201 of the microstrip transmission line section and the "gate" type artificial surface plasmon transmission section 3. A varactor diode CAP101 is connected in reverse phase inside each "gate" type artificial surface plasmon lumped unit 4. The varactor diode CAP101 is connected to the bias circuit through the feed lines on both sides.

[0019] (See) Figure 2 ), Figure 2 This is a side view schematic diagram of a multimode switchable bandpass filter, which has a three-layer structure of surface metal 5, dielectric 6, and bottom metal 7. The thickness of surface metal 5 and bottom metal 7 is usually 1 ounce, or 0.035 mm. Dielectric 6 is usually made of a material with a dielectric constant between 1 and 6.

[0020] (See) Figure 3 ), Figure 3 This is a schematic diagram of the rear view structure of a multimode switchable bandpass filter. The reverse side of the dielectric substrate 1 is a metal ground plane 100. The linewidth of the metal rectangular microstrip 200 is determined by calculation to achieve 50Ω impedance matching, depending on the selected dielectric material. The linewidth of the metal rectangular microstrip 200 is chosen to be between 1.5 and 2 times the wavelength corresponding to the center frequency of the selected frequency band, which provides good transmission effect. The value of the DC blocking capacitor 201 in the microstrip transmission line section between the metal rectangular microstrip 200 and the rectangular bypass microstrip structure is determined based on the maximum applied voltage. Taking a single case as an example: using Rogers Ro4350B board as the dielectric substrate 1, and selecting the S and C bands, the linewidth of its metal rectangular microstrip 200... w mGiven a diameter of 1.08 mm and a line length of 4 mm, the DC blocking capacitor 201 in the microstrip transmission line section is set to 8-12 pF. The DC blocking capacitor 201 in the microstrip transmission line section is connected to the rectangular bypass microstrip structure via a radius of... w m The circular metal transition is 2 / 2. The bottom connecting line of the rectangular bypass microstrip structure has a line width of 0.1mm. The length and width of the rectangle are 8mm and 1mm respectively.

[0021] (See) Figure 4 ), Figure 4 This is a schematic diagram of the structure of the three-unit plasmon transport section of the "gate"-shaped artificial surface of the present invention, showing the lengths of the "L"-shaped vertical microstrips on both sides of the three-unit plasmon transport section of the "gate"-shaped artificial surface. l 3 is 15mm, width b The length of the transverse microstrips is 0.5 mm. a It is 0.6mm wide. d The length of the bottom microstrip of the three units in the "gate"-shaped artificial surface plasmon transport section is 0.85 mm. l 2 is 5mm, width w 1 represents 0.1 mm.

[0022] (See) Figure 5 ), Figure 5 This is a schematic diagram of the structure of the 4-unit "gate" type artificial surface plasmon lumped section of the present invention. The parameters of the "L"-shaped vertical metal microstrip and the bottom metal microstrip are the same as those of the 3-unit "gate" type artificial surface plasmon transmission section. A varactor diode CAP101 is loaded at a position 2mm away from the bottom metal microstrip. The power supply circuit 103 is mainly a rectangular metal microstrip. Two choke inductors 102 are loaded on each power supply circuit. Inductors of size 0603 are selected. During installation, sufficient pad space needs to be reserved for the choke inductors 102.

[0023] A miniaturized multimode switchable bandpass filter based on artificial surface plasmons is composed of four main parts: a surface metal transmission structure, a transmission section, a lumped section, and a feed circuit 103. Its overall length is... p 1 is 55mm, width p 2 is 25mm; the thickness of its surface metal 5 and bottom metal 7 is... t p All are 0.035mm thick. Taking Rogers RO4350B (with a dielectric constant of 3.66) as an example, the dielectric substrate 1 has a thickness of... t s =0.508mm.

[0024] (See) Figure 6 ), Figure 6The dispersive characteristics of a radio frequency (RF) signal incident from a 50Ω impedance-matched port and passing through a three-element "gate"-shaped artificial surface plasmon resonance (ASPR) transmission section are illustrated. The optical axis is represented by a solid circle, and the RF signal by a diamond-shaped solid line. It is evident that the RF signal corresponding to the diamond-shaped solid line is below the optical axis in all phases at each frequency point. This means that the dispersive performance of the three-element "gate"-shaped ASPR transmission section at this size is within the slow-wave region, while also exhibiting high-frequency cutoff characteristics. This demonstrates that the three-element "gate"-shaped ASPR transmission section, as the preferred embodiment of this invention, possesses excellent transmission characteristics and the outstanding advantage of high-frequency cutoff, effectively filtering out high-frequency signals. Specifically, its high cutoff frequency approaches 2.57 GHz, slightly higher than the high cutoff frequency of the four-element "gate"-shaped ASPR lumped section with a varactor diode CAP101. This means that the "gate"-shaped ASPR transmission unit under these parameters can effectively transmit signals within the 0-2.57 GHz frequency band, while exhibiting a cutoff state for signals above 2.57 GHz.

[0025] When the radio frequency signal passes through the gate-type artificial surface plasmon transmission section 3 and reaches the gate-type artificial surface plasmon lumped section 4, the original narrowband microstrip connection line at the bottom of the gate-type artificial surface plasmon lumped section 4 is replaced by a varactor diode CAP101. Therefore, the transmission of the radio frequency signal at this point will be affected by the varactor diode CAP101, thereby changing the dispersion characteristics of the radio frequency signal.

[0026] (See) Figure 7 ), Figure 7 The dispersive characteristics of the varactor diode CAP101 under different equivalent capacitances at different voltages are shown in the "gate"-shaped artificial surface plasmon lumped part 4. Figure 7 In the diagram, the solid circle represents the optical axis, and the solid diamond, dashed diamond, solid equilateral triangle, and solid inverted triangle represent the dispersion characteristic curves of the varactor diode CAP101 under different voltages for four states with different equivalent capacitances. The equivalent capacitances of the varactor diode CAP101 corresponding to these four states are 0.35pF, 1.03pF, 2.1pF, and 3.2pF, respectively. Specifically: 1) When the equivalent resistance of the varactor diode CAP101 is 0.35pF, the dispersion curve of the 4-unit plasmon lumped section of the "gate" type artificial surface is in the 0-2.73GHz frequency range, which is above the light source. This frequency range is in the fast light region, and the radio frequency signal cannot propagate on the 4-unit plasmon lumped section of the "gate" type artificial surface. When the dispersion curve enters the slow light region from the fast light region at the 2.73GHz frequency point, the radio frequency signal can be transmitted, and its corresponding high cutoff frequency approaches 2.75GHz infinitely.

[0027] 2) When the equivalent resistance of the varactor diode CAP101 is 1.03pF, the dispersion curve of the 4-unit plasmon lumped section of the "gate" type artificial surface is above the light source in the 0-2.22GHz frequency range. This frequency range is in the fast light region, and the radio frequency signal cannot propagate on the 4-unit plasmon lumped section of the "gate" type artificial surface. When the dispersion curve enters the slow light region from the fast light region at the 2.22GHz frequency point, the radio frequency signal can be transmitted, and its corresponding high cutoff frequency approaches 2.75GHz infinitely.

[0028] 3) When the equivalent resistance of the varactor diode CAP101 is 2.1pF, the dispersion curve of the "gate" type artificial surface plasmon lumped unit is in the 0-1.72GHz frequency range, which is above the light source. This frequency range is in the fast light region, and the radio frequency signal cannot propagate on the 4-unit of the "gate" type artificial surface plasmon lumped unit. When the dispersion curve enters the slow light region from the fast light region at the 1.72GHz frequency point, the radio frequency signal can be transmitted, and its corresponding high cutoff frequency approaches 2.75GHz infinitely.

[0029] 4) When the equivalent resistance of the varactor diode CAP101 is 3.2pF, the dispersion curve of the 4-unit plasmon lumped section of the "gate" type artificial surface is above the light source in the 0-1.41GHz frequency range. This frequency range is in the fast light region, and the radio frequency signal cannot propagate on the 4-unit plasmon lumped section of the "gate" type artificial surface. When the dispersion curve enters the slow light region from the fast light region at the 1.41GHz frequency point, the radio frequency signal can be transmitted, and its corresponding high cutoff frequency approaches 2.75GHz infinitely.

[0030] Analysis of the dispersion characteristics of the four-unit lumped plasmon polariton section of the "gate"-shaped artificial surface in this invention reveals that when the four-unit lumped plasmon polariton section and the three-unit lumped plasmon polariton transmission section of the "gate"-shaped artificial surface (hereinafter referred to as the lumped unit and transmission unit), when the equivalent capacitance of the varactor diode CAP101 is 0.35pF, electromagnetic wave signals in the 0-2.57GHz frequency band can pass through the transmission unit, but since these signals are within the 0-2.73GHz frequency band, they cannot pass through the lumped unit. Radio frequency signals above 2.57GHz are suppressed by the transmission unit. Therefore, the cascaded structure exhibits a band-stop state across the entire frequency band. When the equivalent capacitance of the varactor diode CAP101 is 1.03pF, signals in the 0-2.57GHz frequency band can pass through the transmission unit, but signals in the 0-2.22GHz frequency band cannot pass through the lumped unit. Radio frequency signals above 2.57GHz are suppressed by the transmission unit. Therefore, in the full frequency band... Signals in the 2.22-2.57GHz frequency band can pass through a cascaded structure. When the equivalent capacitance of the varactor diode CAP101 is 2.1pF, signals in the 0-2.57GHz frequency band can pass through the transmission unit, but signals in the 0-1.72GHz frequency band cannot pass through the lumped unit, and radio frequency signals exceeding 2.57GHz will be suppressed by the transmission unit. Therefore, signals in the 1.72-2.57GHz frequency band can pass through a cascaded structure. When the equivalent capacitance of the varactor diode CAP101 is 3.2pF, signals in the 0-2.57GHz frequency band can pass through the transmission unit, but signals in the 0-1.41GHz frequency band cannot pass through the lumped unit, and radio frequency signals exceeding 2.57GHz will be suppressed by the transmission unit. Therefore, signals in the 1.41-2.57GHz frequency band can pass through a structure cascaded from a 4-unit lumped section of a gate-type artificial surface plasmon polariton and a 3-unit transmission section of a gate-type artificial surface plasmon polariton.

[0031] (See) Figure 8 , Figure 9 , Figure 10 and Figure 11 ), Figures 8-11 This is a comparison of return loss and transmission characteristic curves for the lumped part of a multimode switchable bandpass filter of the present invention, with the bias voltage across the varactor diode CAP101 at 23.5V, 5.4V, 1.6V and 0V respectively.

[0032] (See) Figure 8When the bias voltage across the varactor diode CAP101 is 23.5V, the equivalent capacitance of the varactor diode CAP101 is 0.35pF. At this time, the 3rd unit of the "gate" type artificial surface plasmon transmission section exhibits a transmission state for signals from 0 to 2.57GHz and a blocking state for radio frequency signals exceeding 2.57GHz; while the 4th unit of the "gate" type artificial surface plasmon lumped section exhibits a blocking state for signals from 0 to 2.73GHz. Therefore, signals in the S and C bands cannot pass through the filter surface. Let the stopband state be mode 1.

[0033] (See) Figure 9 When the bias voltage across the varactor diode CAP101 is 5.4V, the equivalent capacitance of the varactor diode CAP101 is 1.03pF. At this time, the "gate" type artificial surface plasmon transmission unit exhibits a transmission state for signals from 0 to 2.57GHz and an impedance state for radio frequency signals exceeding 2.57GHz. Meanwhile, the "gate" type artificial surface plasmon lumped unit exhibits an impedance state for signals from 0 to 2.22GHz and a transmission state for radio frequency signals from 2.22 to 2.75GHz. Therefore, radio frequency signals in the 2.22-2.57GHz band pass through the filter surface, and the relative bandwidth percentage at this time is 12%, which belongs to the narrowband bandpass filter. Let the state at this time be mode 2.

[0034] (See) Figure 10 When the bias voltage across the varactor diode CAP101 is 1.6V, the equivalent capacitance of the varactor diode CAP101 is 2.1pF. At this time, the 3rd unit of the "gate" type artificial surface plasmon transmission section exhibits a transmission state for signals from 0 to 2.57GHz and a blocking state for radio frequency signals exceeding 2.57GHz; while the 4th unit of the "gate" type artificial surface plasmon lumped section exhibits a blocking state for signals from 0 to 1.72GHz and a transmission state for radio frequency signals from 2.22 to 2.75GHz. Therefore, radio frequency signals in the 1.72-2.57GHz frequency band pass through the filter surface, and the relative bandwidth percentage at this time is 40%, which belongs to a broadband bandpass filter. Let this state be mode 3.

[0035] (See) Figure 11When the bias voltage across the varactor diode CAP101 is 0V, the equivalent capacitance of the varactor diode CAP101 is 3.2pF. At this time, the 3rd unit of the "gate" type artificial surface plasmon transmission section exhibits a transmission state for signals from 0 to 2.57GHz and a blocking state for radio frequency signals exceeding 2.57GHz. Meanwhile, the 4th unit of the "gate" type artificial surface plasmon lumped section exhibits a blocking state for signals from 0 to 1.41GHz and a transmission state for radio frequency signals from 2.22 to 2.75GHz. Therefore, radio frequency signals in the 1.41-2.57GHz frequency band pass through the filter surface, and the relative bandwidth percentage at this time is 60%, which belongs to the ultra-wideband bandpass filter. Let the state at this time be mode 4.

[0036] This invention discloses a multimode switchable bandpass filter. By analyzing the dispersion characteristics of a cascaded structure of a three-unit "gate"-shaped artificial surface plasmon transmission section and a four-unit "gate"-shaped artificial surface plasmon lumped section, the analysis results show that this multimode switchable bandpass filter can reconstruct the center frequency in real time and switch between four different modes: stopband, narrowband, wideband, and ultra-wideband. The relative bandwidth of the ultra-wideband mode reaches 60%. When the external bias voltage across the varactor diode CAP101 is increased, the lower cutoff frequency rises while the upper cutoff frequency remains unchanged, resulting in a blue shift of the center frequency, and the wideband effect transforms into a narrowband effect. When the external bias voltage reaches 23.5V, the bandpass filter exhibits full-band bandstop characteristics, with a bandstop suppression capability of -20dB.

[0037] In the face of the severe challenge of increasingly scarce spectrum resources in current 5G communication systems, the multi-mode switchable bandpass filter of this invention demonstrates great application value and market prospects due to its outstanding energy-saving characteristics and spectrum reuse advantages.

[0038] The above description is merely a preferred embodiment of the present invention. The above examples do not limit the substantive content of the present invention in any way. Any simple modifications or variations made by those skilled in the art to the above specific embodiments based on the technical essence of the present invention after reading this specification, as well as equivalent embodiments that may be changed or modified using the disclosed technical content, shall still fall within the scope of the technical solution of the present invention and shall not depart from the essence and scope of the present invention.

Claims

1. A miniaturized multimode switchable bandpass filter, comprising a filter, a dielectric substrate (1), an artificial surface plasmon structure, and a varactor diode CAP (101), wherein the filter is disposed on the dielectric substrate (1); characterized in that: The front side of the dielectric substrate (1) has filter metal microstrip transmission line portions (2) located at both ends of the bandpass filter. The periodic unit on the front side of the dielectric substrate (1) integrates a "gate" type artificial surface plasmon transmission portion (3) and a "gate" type artificial surface plasmon lumped portion (4). The back side of the dielectric substrate (1) has a ground plane (100), three varactor diodes CAP (101), four sets of choke inductors (102), a set of DC blocking capacitors, a power supply circuit (103), and a power supply line. The filter metal rectangular microstrip transmission line portion (2) located on the front side of the dielectric substrate (1) at both ends of the bandpass filter is composed of a metal rectangular microstrip (200), a microstrip transmission line portion DC blocking capacitor (201), and a metal rectangular bypass microstrip structure; the characteristic impedance of the metal rectangular microstrip (200) is 50Ω, the microstrip transmission line portion DC blocking capacitor (201) is located at the inner end of the metal rectangular microstrip (200), and the metal rectangular bypass microstrip structure is located between the microstrip transmission line portion DC blocking capacitor (201) and the "gate" type artificial surface plasmon transmission portion (3); The “gate” type artificial surface plasmon lumped section (4) has three units. Each “gate” type artificial surface plasmon lumped section (4) has a varactor diode CAP (101) connected in reverse on the inner side. The varactor diode CAP (101) is connected to the power supply circuit (103) through the metal feed lines on both sides.

2. The miniaturized multimode switchable bandpass filter according to claim 1, characterized in that: The "gate" type artificial surface plasmon unit structure is divided into two types. One type is composed of a "gate" type artificial surface plasmon transmission part (3) consisting of two mirror-symmetrical inverted "L" vertical metal microstrips and a metal microstrip connected to the bottom of the inverted "L" vertical metal microstrips. The other type is composed of a "gate" type artificial surface plasmon lumped part (4) consisting of two mirror-symmetrical inverted "L" vertical microstrips and a varactor diode CAP (101) loaded inside them.

3. The miniaturized multimodal switchable bandpass filter according to claim 1, characterized in that: The bandpass filter located on the front side of the dielectric substrate (1) has metal microstrip transmission sections at both ends. Through the "gate"-shaped artificial surface plasmon transmission section (3) composed of metal microstrips connected to the bottom of the inverted "L" vertical metal microstrips, it achieves good transmission characteristics. At the same time, it exhibits high-frequency cutoff characteristics in optical features, realizing the direct conversion of incident electromagnetic waves into Zenneck waves, effectively filtering the harmonic components of Zenneck waves, and suppressing higher harmonic components.

4. A miniaturized multimode switchable bandpass filter according to claim 1, characterized in that: The "gate"-shaped artificial surface plasmon lumped section, consisting of two mirror-symmetrical inverted "L" vertical microstrips and a varactor diode CAP (101) loaded inside them, controls the equivalent capacitance of the varactor diode CAP (101) by applying a negative voltage. The value of the equivalent capacitance of the varactor diode CAP (101) decreases as the absolute value of the applied negative voltage increases, and the two are inversely proportional.

5. A miniaturized multimode switchable bandpass filter according to claim 1, characterized in that: When the feed circuit (103) across the varactor diode CAP (101) is not negatively charged, the electrical characteristics of the varactor diode CAP (101) are that of a high-capacitance capacitor. At this time, the bandpass filter exhibits ultra-wideband filtering characteristics. When a negative voltage is applied across the varactor diode CAP (101), as the absolute value of the negative voltage increases from zero to the clamping voltage region of the varactor diode CAP (101), the equivalent capacitance of the varactor diode CAP (101) gradually decreases. The passband characteristics of the bandpass filter change from ultra-wideband to wideband, narrowband and bandstop in sequence.

6. A miniaturized multimode switchable bandpass filter according to claim 1, characterized in that: After the power supply circuit (103) across the varactor diode CAP (101) of the "gate" type artificial surface plasmon lumped part (4) is energized, the optical dispersion characteristics of its unit also change accordingly. As the absolute value of the negative voltage applied across the varactor diode CAP (101) increases, the equivalent capacitance value of the varactor diode CAP (101) gradually decreases. At the same time, the low cutoff frequency of the "gate" type artificial surface plasmon lumped part (4) increases.

7. A miniaturized multimode switchable bandpass filter according to claim 1, characterized in that: The power supply circuit (103) connected to the two ends of the varactor diode CAP (101) of the "gate" type artificial surface plasmon lumped part (4) consists of two sets of choke inductors (102) and corresponding metal rectangular microstrips (200) with connection function. It suppresses the sympathetic current generated by high frequency signals and protects the power supply that provides negative voltage to the two ends of the varactor diode CAP (101). The power supply is connected to the positive and negative terminals of the varactor diode CAP (101) in reverse connection mode, providing a voltage range of 0V to 30V.

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