阅读说明：本技术 高选择性电可重构siw带通滤波器及其制备方法 (High-selectivity electrically-reconfigurable SIW band-pass filter and preparation method thereof ) 是由 张金玲 孙曼 郑占奇 朱雄志 于 2021-09-07 设计创作，主要内容包括：本发明涉及一种高选择性电可重构SIW带通滤波器及其制备方法,其包括：SIW腔体；梳状谐振腔,在所述SIW腔体上表面至少设置两个,并耦合连接；馈电面,设置在所述SIW腔体外部,经高阻抗微电线与所述梳状谐振腔连接；所述高阻抗微电线设置在所述SIW腔体上表面开设的缝隙中,作为偏置线；偏置电路,设置在所述高阻抗微电线与所述梳状谐振腔连接处；“缝合”电容,跨接在具有高磁场强度的所述缝隙与所述高阻抗微电线之间,避免由于所述缝隙破坏所述SIW腔体上表面完整性而造成对所述滤波器性能的影响。本发明能提高可重构滤波器的通带选择性。(The invention relates to a high-selectivity electrically reconfigurable SIW band-pass filter and a preparation method thereof, wherein the preparation method comprises the following steps: a SIW chamber; at least two comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity and are coupled; the feeding surface is arranged outside the SIW cavity and is connected with the comb-shaped resonant cavity through a high-impedance micro-wire; the high-impedance micro-wire is arranged in a gap formed in the upper surface of the SIW cavity and used as a bias wire; the bias circuit is arranged at the joint of the high-impedance micro-wire and the comb-shaped resonant cavity; and the 'stitching' capacitor is bridged between the gap with high magnetic field strength and the high-impedance micro-wire, so that the influence on the performance of the filter caused by the fact that the integrity of the upper surface of the SIW cavity is damaged by the gap is avoided. The invention can improve the passband selectivity of the reconfigurable filter.)

1. A highly selective electrically reconfigurable SIW bandpass filter, comprising:

a SIW chamber;

at least two comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity and are coupled;

the feeding surface is arranged outside the SIW cavity and is connected with the comb-shaped resonant cavity through a high-impedance micro-wire; the high-impedance micro-wire is arranged in a gap formed in the upper surface of the SIW cavity and used as a bias wire;

the bias circuit is arranged at the joint of the high-impedance micro-wire and the comb-shaped resonant cavity;

and the 'stitching' capacitor is bridged between the gap with high magnetic field strength and the high-impedance micro-wire, so that the influence on the performance of the filter caused by the fact that the integrity of the upper surface of the SIW cavity is damaged by the gap is avoided.

2. The filter of claim 1, wherein each of the comb resonators comprises:

the SIW resonant cavity is enclosed by a square gap;

the inner conductor is embedded in the center of the SIW resonant cavity; the bottom of the inner conductor is short-circuited, is directly connected with the lower surface of the SIW cavity, has an open circuit at the top and is isolated from the upper surface of the SIW cavity through the square gap;

the inner conductor and the SIW resonant cavity jointly form a parallel resonator.

3. The filter of claim 1, wherein the coupling between the comb resonators is an electromagnetic hybrid coupling comprising:

the magnetic coupling path is a main coupling path with fixed strength and is realized by windowing the side wall of the comb-shaped resonant cavity in coupling connection;

an electric coupling path, which is a secondary coupling path with adjustable strength and loads a first variable capacitance diode C on a coplanar waveguide connecting two inner conductors_BWBy controlling the first varactor C_BWThe size of the capacitance value of the hybrid coupling coefficient is adjusted.

4. The filter of claim 2, further comprising a second varactor diode C_fAnd the tuning device is arranged on the square gap and used for tuning the central frequency of the parallel resonator.

5. The filter of claim 1, wherein an input terminal and an output terminal of the filter are respectively disposed on the SIW cavity at two ends of the comb resonator;

the input end and the output end are fed through the coplanar waveguide of which the tail end of the SIW cavity is connected with the metal column, and a third variable capacitance diode C is loaded on the coplanar waveguide_QeRealize the adjustment of the input or output coupling strength and control the third variable capacitance diode C_QeThe magnitude of the external Q value is adjusted.

6. The filter of claim 5, wherein the bias circuit and the bias line are disposed at both the input end and the output end, and the adjustment of the lengths of the bias lines at both sides introduces an independently controllable transmission zero at both sides of the passband, thereby improving the passband selectivity of the filter.

7. A method for preparing a high-selectivity electrically reconfigurable SIW band-pass filter is characterized by comprising the following steps:

at least two coupled comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity, each comb-shaped resonant cavity comprises a square gap formed in the upper surface of the SIW cavity, an inner conductor is arranged at the center of each square gap, and the inner conductors and the square gaps form a parallel resonator;

a gap is formed in the upper surface of the cavity and used for accommodating a high-impedance micro wire, and a feeding surface is arranged outside the SIW cavity through the high-impedance micro wire;

a bias circuit is arranged at the joint of the high-impedance micro-wire and the comb-shaped resonant cavity;

a "stitched" capacitor is bridged between the gap with high magnetic field strength and the high impedance micro-wire, avoiding the impact on the filter performance caused by the gap damaging the integrity of the upper surface of the SIW cavity.

8. The method of claim 7, wherein the coupled comb resonator comprises:

windowing the side wall of the comb-shaped resonant cavity connected in a coupling manner to realize magnetic coupling;

loading a first varactor C on a coplanar waveguide connecting two of said inner conductors_BWRealizing electric coupling by controlling the first varactor diode C_BWThe size of the capacitance value of the hybrid coupling coefficient is adjusted.

9. The method according to claim 7, wherein an input terminal and an output terminal of the filter are respectively disposed on the SIW cavity at both ends of the comb resonator;

the input end and the output end are fed through the coplanar waveguide of which the tail end of the SIW cavity is connected with the metal column, and a second variable capacitance diode C is loaded on the coplanar waveguide_QeFor coupling input or outputAdjustment of the combined strength to control the first varactor C_QeThe magnitude of the external Q value is adjusted.

10. The method according to claim 7, wherein the bias circuit and the bias line are disposed at the input end and the output end, and the adjustment of the lengths of the bias lines at both sides introduces an independently controllable transmission zero at both sides of the passband, thereby improving the passband selectivity of the filter.

Technical Field

The invention relates to the technical field of communication circuit design, in particular to a high-selectivity electrically reconfigurable SIW band-pass filter and a preparation method thereof.

Background

In modern communication systems, increasingly higher requirements are placed on integration and miniaturization of wireless communication devices. At present, a plurality of communication systems such as GSM, CDMA, LTE and the like coexist, and different index requirements are provided for filters working under different systems. The traditional solution uses a radio frequency switch to select a filter with a corresponding performance index, resulting in a large communication system size and high cost. Compared with the mode switching of the combination of the non-tunable filter and the radio frequency switch, the mode switching of the communication mode by adopting the tunable filter becomes a future development trend. In recent years, research on tunable filters mainly focuses on planar filters realized based on microstrip structures, and the planar filters have the advantages of low cost, simplicity in manufacturing, low difficulty in loading tuning elements and the like, but the planar filters with microstrip structures cannot meet the requirements of power capacity of modern communication systems. In a modern mobile wireless communication base station system, an applied filter is generally a metal cavity filter or a dielectric cavity filter, and the cavity filter is difficult to form an adjustable filter in a mode of loading a tuning element due to the structural limitation and the working principle of the cavity filter. The tuning of such filters is generally realized by tuning screws on a physical structure, and then controlled by using a stepping motor, and the mechanical tuning mode has low speed and high processing cost, and is difficult to apply to a communication system.

Substrate Integrated Waveguides (SIWs) are new waveguide structures with low insertion loss, low radiation, high power capability, etc. Due to the substrate integration characteristic of the SIW, the difficulty of loading the tuning element by the resonant cavity formed by the SIW technology is much lower than that of the traditional cavity filter, and the possibility of realizing the electrically adjustable cavity filter is provided. The requirement of a communication system link on the selectivity of the filter is more and more strict, so that the improvement of the selectivity of the filter becomes a new research hotspot while the adjustable frequency and bandwidth performance of the SIW band-pass filter are realized. The type of tuning element of the tunable filter is a key factor affecting the performance of the tunable filter. The electric tuning elements are mainly PIN diodes, RF MEMS devices, semiconductor varactors, etc. Due to the advantages of the varactor diode in terms of cost, tuning rate and process, more and more electrically tunable filters are designed to realize continuous tuning of frequency and bandwidth by using the varactor diode as a tuning element, and research and application of the electrically tunable filter based on the varactor diode have become mainstream. Due to the relative sealing of the SIW cavity structure, however, a reasonable layout space needs to be provided for loading the varactor and its bias circuit.

At present, the common bias circuit design scheme for realizing the variable capacitance diode-based SIW reconfigurable band-pass filter mainly comprises the following steps: connecting the varactor diode with an external feed circuit by introducing a flying lead at one side of the varactor diode outside the integral structure of the SIW tunable filter; by utilizing the symmetry of the SIW structure, a Half-Mode Substrate integrated Waveguide (HMSIW) structure is adopted, and a loading space is provided for the variable capacitance diode and a bias circuit thereof at the open side of the cavity. However, the existing solutions have the following problems: 1. the space electromagnetic energy interference caused by the flying wire is difficult to control or eliminate by connecting the variable capacitance diode and an external bias circuit thereof in a flying wire introducing mode, the space electromagnetic energy interference is particularly obvious at a high frequency, and meanwhile, more uncertainty and instability are caused by the flying wire for the practical installation and use of the filter. 2. By adopting the HMSIW structure, the varactor and its bias circuit can be loaded on the open side of the cavity, but compared to the SIW structure, HMSIW will bring extra electromagnetic energy loss, sacrificing the insertion loss performance of the filter to some extent.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a high-selectivity electrically reconfigurable SIW band-pass filter and a method for manufacturing the same, which can improve the passband selectivity of the reconfigurable filter.

In order to achieve the purpose, the invention adopts the following technical scheme: a high selectivity electrically reconfigurable SIW bandpass filter comprising: a SIW chamber; at least two comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity and are coupled; the feeding surface is arranged outside the SIW cavity and is connected with the comb-shaped resonant cavity through a high-impedance micro-wire; the high-impedance micro-wire is arranged in a gap formed in the upper surface of the SIW cavity and used as a bias wire; the bias circuit is arranged at the joint of the high-impedance micro-wire and the comb-shaped resonant cavity; and the 'stitching' capacitor is bridged between the gap with high magnetic field strength and the high-impedance micro-wire, so that the influence on the performance of the filter caused by the fact that the integrity of the upper surface of the SIW cavity is damaged by the gap is avoided.

Further, each of the comb resonators includes: the SIW resonant cavity is enclosed by a square gap; the inner conductor is embedded in the center of the SIW resonant cavity; the bottom of the inner conductor is short-circuited, is directly connected with the lower surface of the SIW cavity, has an open circuit at the top and is isolated from the upper surface of the SIW cavity through the square gap; the inner conductor and the SIW resonant cavity jointly form a parallel resonator.

Further, the coupling between the comb resonators adopts electromagnetic hybrid coupling, which includes: the magnetic coupling path is a main coupling path with fixed strength and is realized by windowing the side wall of the comb-shaped resonant cavity in coupling connection; an electric coupling path, which is a secondary coupling path with adjustable strength and loads a first variable capacitance diode C on a coplanar waveguide connecting two inner conductors_BWBy controlling the first varactor C_BWThe size of the capacitance value of the hybrid coupling coefficient is adjusted.

Further, a second variable capacitance diode C is also included_fAnd the tuning device is arranged on the square gap and used for tuning the central frequency of the parallel resonator.

Further, an input end and an output end of the filter are respectively arranged at two ends of the comb-shaped resonant cavity on the SIW cavity;

the input end and the output end are fed through the coplanar waveguide of which the tail end of the SIW cavity is connected with the metal column, and a third variable capacitance diode C is loaded on the coplanar waveguide_QeRealize the adjustment of the input or output coupling strength and control the third variable capacitance diode C_QeThe magnitude of the external Q value is adjusted.

Furthermore, the input end and the output end are both provided with the bias circuit and the bias line, the lengths of the bias lines on the two sides are adjusted, and an independently controllable transmission zero is respectively introduced into the two sides of the passband, so that the passband selectivity of the filter is improved.

A method of making a highly selective electrically reconfigurable SIW bandpass filter, comprising: at least two coupled comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity, each comb-shaped resonant cavity comprises a square gap formed in the upper surface of the SIW cavity, an inner conductor is arranged at the center of each square gap, and the inner conductors and the square gaps form a parallel resonator; a gap is formed in the upper surface of the cavity and used for accommodating a high-impedance micro wire, and a feeding surface is arranged outside the SIW cavity through the high-impedance micro wire; a bias circuit is arranged at the joint of the high-impedance micro-wire and the comb-shaped resonant cavity; a "stitched" capacitor is bridged between the gap with high magnetic field strength and the high impedance micro-wire, avoiding the impact on the filter performance caused by the gap damaging the integrity of the upper surface of the SIW cavity.

Further, the coupled comb resonator comprises: windowing the side wall of the comb-shaped resonant cavity connected in a coupling manner to realize magnetic coupling; loading a first varactor C on a coplanar waveguide connecting two of said inner conductors_BWRealizing electric coupling by controlling the first varactor diode C_BWThe size of the capacitance value of the hybrid coupling coefficient is adjusted.

Further, an input end and an output end of the filter are respectively arranged at two ends of the comb-shaped resonant cavity on the SIW cavity;

the input end and the output end are fed through the coplanar waveguide of which the tail end of the SIW cavity is connected with the metal column, and a second variable capacitance diode C is loaded on the coplanar waveguide_QeRealize the adjustment of the input or output coupling strength and control the first variable capacitance diode C_QeThe magnitude of the external Q value is adjusted.

Furthermore, the input end and the output end are both provided with the bias circuit and the bias line, the lengths of the bias lines on the two sides are adjusted, and an independently controllable transmission zero is respectively introduced into the two sides of the passband, so that the passband selectivity of the filter is improved.

Due to the adoption of the technical scheme, the invention has the following advantages:

1. because the SIW electric reconfigurable filter has the problem of loading a tuning device and a bias circuit thereof due to the self-sealing property of the cavity, the invention provides a reasonable layout space for the loading of the device and the high-impedance microstrip line by opening the gap on the upper surface of the cavity, and sews a capacitor on the gap on which electromagnetic energy leaks due to the damage of the upper surface of the cavity to ensure the integrity of the cavity, so that the passband performance of the filter is not influenced by the loading of the bias circuit, meanwhile, the high-impedance microstrip line is used as a feed bias line, and the bias circuit is designed in a mode of moving the feed pad away from the cavity, thereby improving the reliability and stability of the filter in actual installation and use.

2. On the basis of not additionally introducing a trapped wave structure, the invention introduces an independently controllable transmission zero point on each side of the passband by adjusting the length of the bias line of the input/output end, thereby obviously improving the passband selectivity of the filter.

In summary, the invention enhances the reliability and stability of the reconfigurable filter without affecting the original performance of the reconfigurable filter, and simultaneously can improve the passband selectivity of the filter, thereby providing greater flexibility for the actual installation and use of the electrically reconfigurable SIW bandpass filter.

Drawings

FIG. 1 is a schematic diagram of a two-stage SIW electrically reconfigurable bandpass filter according to an embodiment of the invention;

FIG. 2 shows a loaded varactor C in an embodiment of the present invention_fThe structural schematic diagram of the comb-shaped SIW resonant cavity with the adjustable central frequency is shown;

FIG. 3 is a top view of a two-stage SIW electrically reconfigurable bandpass filter in accordance with an embodiment of the present invention;

FIG. 4 shows simulation results of S-parameters of a loaded bias circuit and an unloaded bias circuit in an embodiment of the invention;

FIG. 5 shows an embodiment of the present invention in which L is adjusted₁、L₂The length of the transmission zero point schematic diagram is introduced into two sides of a passband respectively;

FIG. 6 shows a fixed L in accordance with an embodiment of the present invention₁Length, adjustment L₂The length independently controls the transmission zero diagram of the upper stop band;

FIG. 7 shows a fixed L in accordance with an embodiment of the present invention₂Length, adjustment L₁Length independent controlAnd the transmission zero of the lower stop band is shown schematically.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular is intended to include the plural unless the context clearly dictates otherwise, and further it is to be understood that when the terms "comprises" and/"comprising" are used in this specification, they specify the presence of the stated features, steps, operations, devices, components and/or combinations thereof.

Because the SIW is a novel transmission line structure, the SIW is manufactured on a medium substrate, and the metal through hole 6 or the metal column replaces the side wall of the traditional rectangular waveguide, the SIW has the characteristics of large power capacity, low insertion loss, high quality factor and the like of the traditional rectangular waveguide, and has the advantages of small volume and easy integration with other circuits similar to planar circuits such as microstrip lines and the like.

The invention optimally designs the selectivity of the two-stage SIW electrically reconfigurable band-pass filter with the adjustable frequency range of 3-4.5 GHz and the adjustable bandwidth range of 40-260 MHz and the bias circuit 3. The high-impedance microstrip line is used as a feed bias line, the feed pad is moved away from the cavity, and meanwhile, the high-impedance microstrip line 2 is introduced to bridge a capacitor to perform 'stitching' at the position where the integrity of the surface of the cavity is damaged. The invention improves the reliability and stability of the filter when in actual installation and use under the condition of ensuring that the passband performance of the filter is not influenced by the external bias circuit 3; meanwhile, by utilizing the bias lines on the input side and the output side, on the basis of not additionally increasing a trapped wave structure, an independently controllable transmission zero point can be respectively introduced into two sides of a passband by adjusting the lengths of the bias lines on the two sides, so that the passband selectivity of the reconfigurable filter is improved.

In an embodiment of the present invention, as shown in fig. 1 and fig. 3, a high-selectivity electrically reconfigurable SIW band-pass filter is provided, and in this embodiment, a two-stage SIW electrically reconfigurable band-pass filter is taken as an example for description, and includes:

a SIW chamber;

at least two comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity and are coupled;

the feeding surface 1 is arranged outside the SIW cavity and is connected with the comb-shaped resonant cavity through a high-impedance micro wire 2; the high-impedance micro wire 2 is arranged in a gap formed in the upper surface of the SIW cavity and used as a bias wire;

the bias circuit 3 is arranged at the joint of the high-impedance micro-wire 2 and the comb-shaped resonant cavity;

"stitched" capacitor C_linkAnd the gap with high magnetic field intensity is bridged between the high-impedance micro-wire 2, so that the influence on the performance of the filter caused by the fact that the integrity of the upper surface of the SIW cavity is damaged by the gap is avoided.

In the above embodiment, as shown in fig. 2, each comb resonator comprises:

the SIW resonant cavity is enclosed by a square gap 4;

the inner conductor 5 is embedded in the center of the SIW resonant cavity; the bottom of the inner conductor 5 is short-circuited, is directly connected with the lower surface of the SIW cavity, and the top of the inner conductor is open-circuited and is isolated from the upper surface of the SIW cavity through the square gap 4;

the inner conductor 5 and the SIW resonator together form a parallel resonator.

In the above embodiments, the coupling between the comb resonators adopts electromagnetic hybrid coupling, which includes:

the magnetic coupling path is a main coupling path with fixed strength and is realized by windowing the side wall of the comb-shaped resonant cavity in coupling connection;

an electric coupling path, which is a secondary coupling path with adjustable strength and loads a first varactor diode C on a coplanar waveguide connecting two inner conductors 5_BWBy controlling the first varactor C_BWThe size of the capacitance value of (a) adjusts the size of the hybrid coupling coefficient k.

In the above embodiments, the filter in this embodiment further includes a second varactor diode C_fAnd the tuning circuit is arranged on the square slot 4 and used for tuning the central frequency of the parallel resonator.

The method specifically comprises the following steps: as shown in FIG. 2, the inner conductor 5 can be equivalent to an inductor L_pThe square gap 4 can be equivalent to a fixed capacitor C₀And the two resonators jointly form a parallel resonator. By loading the second varactor C in the square gap 4_fRealizing the center frequency f of the resonator₀Tuning of (3).

In the above embodiment, the SIW cavity is located at two ends of the comb-shaped resonant cavity, and the input end and the output end of the filter are respectively arranged;

the input end and the output end are fed through the coplanar waveguide with the metal column connected with the tail end of the SIW cavity, and the third variable capacitance diode C is loaded on the coplanar waveguide_QeRealize the adjustment of the input or output coupling strength and control the third variable capacitance diode C_QeThe magnitude of the external Q value is adjusted. While utilizing the first varactor C_BWA third varactor diode C_QeAnd the tuning of the bandwidth of the filter is realized.

The value of the external Q value represents the input/output coupling strength, which is the basic concept of the filter, and can be extracted through the S11 phase response of the single-end loading resonator, and the formula is:

in the above embodiment, the input end and the output end are both provided with the bias circuit 3 and the bias line, and the lengths of the bias lines on the two sides are adjusted to introduce an independently controllable transmission zero point on the two sides of the passband, so that the passband selectivity of the filter is improved.

In this embodiment, to implement the second varactor diode C_fA first variable capacitance diode C_BWA third varactor diode C_QeTuning of capacity, settingA bias circuit 3 is provided. High-impedance microstrip line and bias resistor R are realized by opening gap on surface of SIW cavity_sAnd a bypass capacitor C_bThe loading improves the reliability and stability of the reconfigurable filter, and an independently controllable transmission zero is respectively introduced into two sides of a passband by utilizing bias lines at two input/output sides, so that the passband selectivity of the reconfigurable filter is improved.

When the filter is used, firstly, a gap is formed on the upper surface of the SIW cavity, a layout space is provided for loading the high-impedance micro-wire 2 and the integrated device, and a 'stitching' capacitor C is bridged at the position where the integrity of the surface of the SIW cavity is damaged according to the influence of the width and the position of the gap and the high-impedance micro-wire 2 on the performance of the filter_linkSimulation results show that the design of the additional bias circuit 3 does not influence the pass band index of the filter. And then, by adjusting the length of the input/output bias line (equivalent to a quarter-wavelength open line), a transmission zero is respectively introduced into two sides of the passband, and simulation results show that along with the change of the length of the bias line, the independent adjustment of the transmission zeros at two sides can be realized, and the passband selectivity is further improved.

In one embodiment of the invention, a method for preparing a high selectivity electrically reconfigurable SIW band-pass filter comprises the following steps:

step 1, at least two coupled comb-shaped resonant cavities are arranged on the upper surface of the SIW cavity, each comb-shaped resonant cavity comprises a square gap formed in the upper surface of the SIW cavity, an inner conductor 5 is arranged at the center of each square gap, and the inner conductors 5 and the square gaps 4 form a parallel resonator;

step 2, forming a gap on the upper surface of the cavity for accommodating the high-impedance micro-wire 2, and arranging the feed surface 1 outside the SIW cavity through the high-impedance micro-wire 2;

step 3, arranging a bias circuit 3 at the joint of the high-impedance micro-wire 2 and the comb-shaped resonant cavity;

step 4, bridging a 'stitching' capacitor C between the gap with high magnetic field strength and the high-impedance micro-wire 2_linkAnd the influence on the performance of the filter caused by the fact that the integrity of the upper surface of the SIW cavity is damaged by the gap is avoided.

In step 1, the coupled comb-shaped resonant cavity includes the following two couplings to form an electromagnetic hybrid coupling:

windowing the side wall of the comb-shaped resonant cavity connected in a coupling way to realize magnetic coupling;

loading a first varactor C on a coplanar waveguide connecting two inner conductors 5_BWRealize electric coupling by controlling the first varactor diode C_BWThe size of the capacitance value of the hybrid coupling coefficient is adjusted.

In the above embodiment, the method further includes the step of setting the input end and the output end: the SIW cavity is positioned at two ends of the comb-shaped resonant cavity and is respectively provided with an input end and an output end of a filter;

the input end and the output end are fed through the coplanar waveguide with the metal column connected with the tail end of the SIW cavity, and a second variable capacitance diode C is loaded on the coplanar waveguide_QeRealizes the adjustment of the input or output coupling strength and controls the first variable capacitance diode C_QeThe magnitude of the external Q value is adjusted.

The input end and the output end are both provided with a bias circuit 3 and bias lines, the lengths of the bias lines on the two sides are adjusted, and an independently controllable transmission zero is respectively introduced to the two sides of a passband, so that the passband selectivity of the filter is improved. Preferably, the bias lines on both sides have a length of a quarter-wave open line.

In conclusion, when the reconfigurable SIW band-pass filter is used, the upper surface of the SIW cavity is provided with the gap and the high-impedance micro-wire 2 as a feed bias line, the bias circuit 3 of the electrically reconfigurable SIW band-pass filter is arranged in a mode that the feed pad is moved away from the cavity, and meanwhile, a 'stitching' capacitor is connected at the position where the integrity of the upper surface of the cavity is damaged. By adopting the bias circuit 3, on the basis of not additionally introducing a trapped wave structure, an independently controllable transmission zero point can be respectively introduced into two sides of a passband by adjusting the length of the bias line of the input/output end.

Example one

Taking a two-stage SIW electrically reconfigurable bandpass filter as an example, as shown in fig. 3, the reconfigurable filter adopts a Rogers TMM3 board with the thickness h of 5.08mm, the relative dielectric constant of 3.27 and the dielectric loss tangent of 0.002, the dimensional parameters are shown in table 1, the feed bias line adopts high-impedance microstrip lines, which are 0.2mm except for special indications, and the minimum gap on the surface of the filter is 0.15mm and the maximum gap is 0.3 mm.

TABLE 1 two-stage SIW electrically reconfigurable band-pass filter and bias circuit 3 parameter table thereof

Selecting a specific set of values of the varactor diode, C_f＝0.47pF、C_BW＝0.13pF、C_QeThe results of the simulation of the filter S parameters when the bias circuit 3 was loaded and when the bias circuit 3 was not loaded were compared at 0.3pF, as shown in fig. 4. As can be seen from the comparison of simulation results, the performance of the pass band of the filter is basically unchanged before and after the bias circuit 3 is loaded, and the frequency and the bandwidth are slightly shifted by tuning C_f、C_BW、C_QeThe capacitance value of the bias circuit 3 is compensated, the practicability of the design of the bias circuit 3 provided by the invention is verified, and the reliability and the stability of the filter in actual installation and use are improved under the condition that the passband performance of the filter is not influenced by the additional bias circuit 3.

As can be seen from FIG. 4, the upper stop-band rejection is slightly degraded by adjusting the length L of the bias line at the input/output end₁、L₂Introducing a transmission zero point L on each side of the pass band₁Corresponding to the controlled transmission zero point, L of the stop band₂Correspondingly controlling the transmission zero point of the upper stop band when L₁＝7mm、L₂When the thickness is 5.6mm, transmission zero points are respectively introduced at 3.34GHz and 3.74GHz, and the comparison result L is compared₁＝L_2＝The out-of-band rejection degree is obviously improved when the thickness is 4mm, and the simulation result of the S21 parameter is shown in FIG. 5. Furthermore, when L is₁While stationary, adjust L₂Length, which can realize independent adjustment of the transmission zero point of the upper stop band, as shown in fig. 6; when L is₂While stationary, adjust L₁Length, an independent adjustment of the lower stop band transmission zero can be achieved, as shown in fig. 7. The simulation results verify that the transmission zero points on two sides of the passband can be independently adjusted by using the bias line of the input/output end, and the passband selectivity is improved.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.