CN113422181B - Adjustable filtering module with ultra-wide frequency conversion range - Google Patents
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- CN113422181B CN113422181B CN202110498584.XA CN202110498584A CN113422181B CN 113422181 B CN113422181 B CN 113422181B CN 202110498584 A CN202110498584 A CN 202110498584A CN 113422181 B CN113422181 B CN 113422181B
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- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
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- H01P1/20—Frequency-selective devices, e.g. filters
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P1/00—Auxiliary devices
- H01P1/20—Frequency-selective devices, e.g. filters
- H01P1/201—Filters for transverse electromagnetic waves
- H01P1/203—Strip line filters
- H01P1/20309—Strip line filters with dielectric resonator
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Abstract
The invention discloses an adjustable filter module with an ultra-wide frequency conversion range, which comprises a digital control circuit and N independent adjustable filter modules, wherein the N adjustable filter modules are connected to two single-pole multi-throw switches in parallel to form N mutually independent filter paths, each filter path has different working frequency tuning ranges, the digital control circuit outputs control signals to the two single-pole multi-throw switches, the filter path corresponding to a required frequency range is selected and determined, and meanwhile, the digital control circuit outputs control voltage to the corresponding adjustable filter module to change the working state of a variable capacitance diode in the filter module and realize the adjustment of the filter performance. The adjustable filtering module can realize flexible control on the center frequency and the relative bandwidth of the filter in the ultra-wide frequency range of 2-18 GHz.
Description
Technical Field
The invention relates to a microwave communication technology, in particular to an adjustable filtering module with an ultra-wide frequency conversion range.
Background
In a wireless communication system, a filter is used to filter interference of a clutter signal, thereby ensuring communication quality. With the rapid development of modern wireless communication technology, a system generally needs to support multiple applications in different operating frequency bands, and if filters with fixed performance are used, not only the system cost is increased, but also the system volume is increased. The adjustable filter is an effective way for solving the problem, and can flexibly adjust the filtering performance according to the application scene requirements, thereby realizing the miniaturization and the intellectualization of the system.
However, the various tunable filters proposed at present still have the disadvantages of narrow frequency tuning range, low operating frequency, complex tuning mode, and the like. At the same time, there are still fewer filter schemes with fully adjustable center frequency and relative bandwidth that can operate in the high frequency range.
Disclosure of Invention
The present invention is directed to solve the above problems, and provides an adjustable filter module with an ultra-wide frequency conversion range, which can operate in a high frequency range, and has a fully adjustable center frequency and a fully adjustable relative bandwidth.
The invention aims to realize the purpose, and provides an adjustable filtering module with an ultra-wide frequency conversion range, which comprises a digital control circuit, N adjustable filtering modules and two single-pole multi-throw switches respectively connected with a signal input end and an output end, wherein the N adjustable filtering modules are connected between the two single-pole multi-throw switches in parallel to form N mutually independent filtering paths, and each filtering path has different working frequency tuning ranges; the digital control circuit outputs control signals to the two single-pole multi-throw switches, selects a filtering channel corresponding to a determined required frequency range, and outputs control voltage to the corresponding adjustable filtering module through the digital control circuit so as to change the working state of a variable capacitance diode in the filtering module and realize the adjustment of filtering performance.
Preferably, the working frequency range of the N adjustable filter modules covers 2GHz-18GHz, and for the range of 2GHz-7GHz, the adjustable filter modules with the first filter circuit are adopted, wherein the first filter circuit is a microstrip circuit structure loaded with a varactor diode; for the range of 7GHz-18GHz, an adjustable filter module with a second filter circuit is adopted, the second filter circuit comprises a high-pass filter unit and a low-pass filter unit which are cascaded, the low-pass filter unit adopts a defected ground structure, and the high-pass filter unit adopts a microstrip structure.
Preferably, the first filter circuit comprises two cascaded cross-shaped microstrip resonators connected between the input end and the output end, each cross-shaped microstrip resonator comprises a horizontal microstrip line and a vertical microstrip line which are perpendicular to each other, a pair of back-to-back connected varactors is loaded at two ends of the horizontal microstrip line respectively, and a cathode of each varactor is connected to the direct current bias through a resistor.
Preferably, a pair of back-to-back connected varactor diodes is loaded at two ends of the vertical microstrip line respectively, the horizontal microstrip lines of the two cross microstrip resonators are connected through a pair of back-to-back connected varactor diodes, the horizontal microstrip lines of the two cross microstrip resonators are connected to the input microstrip line and the output microstrip line through the varactor diodes and the constant value capacitors which are connected in sequence, and cathodes of all the varactor diodes are connected with the direct current bias through resistors.
Preferably, the low-pass filter unit includes a microstrip transmission line disposed on a top layer of the substrate, and a plurality of defected ground units formed by etching grooves on a ground metal plane of a bottom layer of the substrate, the plurality of defected ground units are periodically arranged at a fixed pitch to form a low-pass filter response, the microstrip transmission line is disposed right above the defected ground units, and one end of the microstrip transmission line is connected to the high-pass filter unit.
Preferably, a metal strip is formed on the inner side of each defective ground unit, the metal strip is isolated from a ground metal plane on the outer side of the defective ground unit through the defective ground unit, a varactor diode is loaded on each defective ground unit, a cathode of the varactor diode is connected with the metal strip, an anode of the varactor diode is connected with the ground metal plane, a bias network is arranged on the top layer of the substrate, and the bias network is connected with the metal strip through a metal through hole so as to change a capacitance value of the varactor diode through the bias network, thereby adjusting a cut-off frequency of the low-pass filter unit.
Preferably, the high-pass filter unit comprises a main transmission line and four resonance branches, each resonance branch is loaded with a pair of varactor diodes connected in a back-to-back manner, the cathode of each pair of varactor diodes is connected with a bias voltage through a resistor, and the capacitance value of the corresponding varactor diode is changed by adjusting the bias voltage, so that the reconstruction of the cut-off frequency of the high-pass filter unit is realized.
Preferably, the main transmission line comprises a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line and a fifth microstrip line which are connected in sequence, the first microstrip line is connected with the microstrip transmission line of the low-pass filter unit through a constant-value capacitor, the first microstrip line is connected with the second microstrip line through a first varactor diode, the second microstrip line is connected with the third microstrip line through a second varactor diode, and the first varactor diode and the second varactor diode form a back-to-back connection mode; a constant value capacitor is respectively connected between the third microstrip line and the fourth microstrip line, between the fourth microstrip line and the fifth microstrip line and between the fifth microstrip line and the output microstrip line; the first microstrip line, the third microstrip line, the fourth microstrip line and the fifth microstrip line are respectively connected with one resonance stub and are all connected with a grounding resistor, and the second microstrip line is connected with a bias voltage through a resistor.
The significant advancement of the invention is at least reflected in:
the tunable filter module with the ultra-wide frequency conversion range utilizes a varactor tuning and switching method to realize flexible control of the center frequency and the relative bandwidth of the filter in the ultra-wide frequency range of 2-18 GHz. The filter comprises a variable capacitance diode loading microstrip circuit, a variable capacitance diode loading defect ground circuit, a single-pole multi-throw switch, a plurality of adjustable filter modules and a filter, wherein the variable capacitance diode loading microstrip circuit and the variable capacitance diode loading defect ground circuit are respectively used for realizing independent adjustable filter modules in low-frequency and high-frequency ranges, and the single-pole multi-throw switch is used for connecting the adjustable filter modules in parallel to realize effective expansion of the frequency conversion range of the filter.
Drawings
Fig. 1 is a circuit topology structure diagram of an adjustable filter module according to an embodiment of the invention;
FIG. 2 is a circuit diagram of a first filter circuit according to an embodiment of the present invention;
FIG. 3 is a circuit diagram of a second filter circuit according to an embodiment of the present invention;
fig. 4 is a simulation curve diagram of S21 parameters of the tunable filter module according to the embodiment of the present invention;
fig. 5 is a simulation graph of S11 parameters of the adjustable filter module according to the embodiment of the invention.
Detailed Description
The present invention is further illustrated in the following description with reference to the drawings, and it should be noted that the embodiments of the present invention are not limited to the examples provided.
Referring to fig. 1, a circuit topology structure diagram of an adjustable filter module according to an embodiment is shown, where the adjustable filter module according to this embodiment includes a digital control circuit, N adjustable filter modules, and two single-pole multi-throw switches respectively connected to a signal input end (port 1) and an output end (port 2), where the N adjustable filter modules are connected in parallel between the two single-pole multi-throw switches to form N independent filter paths, and each filter path has a different tuning range of operating frequency; the digital control circuit outputs control signals to the two single-pole multi-throw switches, selects a filtering channel corresponding to a determined required frequency range, and outputs control voltage to the corresponding adjustable filtering module through the digital control circuit so as to change the working state of a variable capacitance diode in the filtering module and realize the adjustment of filtering performance. In the scheme of the embodiment, the single-pole multi-throw switch is used for connecting N adjustable filtering modules with different working frequency ranges in parallel, so that the working frequency tuning range of the adjustable filtering module is effectively expanded, the continuous adjustment of the ultra-wide frequency range is realized, and the adjustment flexibility is obviously enhanced. The digital control circuit controls the single-pole multi-throw switch to be connected with the corresponding filtering channel, the filtering performance of the adjustable filtering module is adjusted, and the adjustment rapidity is enhanced.
Preferably, the working frequency range of the N adjustable filter modules covers 2GHz-18GHz, and for the range of 2GHz-7GHz, the adjustable filter modules with the first filter circuit are adopted, wherein the first filter circuit is a microstrip circuit structure loaded with varactor diodes; for the range of 7GHz-18GHz, an adjustable filter module with a second filter circuit is adopted, the second filter circuit comprises a high-pass filter unit and a low-pass filter unit which are cascaded, the low-pass filter unit adopts a defected ground structure, and the high-pass filter unit adopts a microstrip structure. In the embodiment, the diode loading microstrip circuit and the defected ground circuit are respectively adopted to realize the required adjustable filtering performance in the low-frequency range and the high-frequency range, and the technical problems of large circuit size in the low-frequency range and large insertion loss in the high-frequency range are pertinently solved.
As shown in fig. 2, as a preferred embodiment, the first filter circuit uses a 50 ohm microstrip transmission line as an input (Port 1) and an output (Port 2), two cross microstrip resonators cascaded with each other are connected between the input and the output, each cross microstrip resonator includes a horizontal microstrip line and a vertical microstrip line perpendicular to each other, and a pair of varactor diodes connected in a back-to-back manner are loaded at two ends of the horizontal microstrip line respectively. Specifically, varactor diodes C4, C5, C6, and C7 are respectively loaded at end positions of horizontal microstrip lines of the two cross-shaped microstrip resonators, cathodes of the varactor diodes C4 and C5 are respectively connected to the same direct current Bias (DC Bias) through resistors, and cathodes of the varactor diodes C6 and C7 are respectively connected to the same direct current Bias through resistors. Therefore, the capacitance values of the variable capacitance diodes C4, C5, C6 and C7 loaded on the cross-shaped microstrip resonator can be changed through direct current bias, and therefore the adjustment of the center frequency of the first filter circuit is achieved.
As a further preference, two ends of the vertical microstrip line are respectively loaded with a pair of varactor diodes connected in a back-to-back manner, specifically, varactor diodes C9 and C11 are respectively loaded on short stubs in the vertical microstrip line of the two cross-shaped microstrip resonators, varactor diodes C8 and C10 are respectively loaded on long stubs in the vertical microstrip line, cathodes of the varactor diodes C9 and C11 are respectively connected with the same dc bias through resistors, and cathodes of the varactor diodes C8 and C10 are respectively connected with the same dc bias through resistors. It will be appreciated that the vertical microstrip lines of a cruciform microstrip resonator are used to create transmission zeros, where the short leg creates a high frequency zero and the long leg creates a low frequency zero. Furthermore, the horizontal microstrip lines of the two cross-shaped microstrip resonators are connected through a pair of variable capacitance diodes C3 connected in a back-to-back mode, the horizontal microstrip line of one cross-shaped microstrip resonator is connected to the input microstrip line through the variable capacitance diodes C1 and the constant value capacitor which are connected in sequence, the horizontal microstrip line of the other cross-shaped microstrip resonator is connected to the output microstrip line through the variable capacitance diodes C2 and the constant value capacitor which are connected in sequence, and cathodes of the variable capacitance diodes C1, C2 and C3 are all connected with direct current bias through resistors. In the scheme of the embodiment, the variable capacitance diodes C1-C3 are used as coupling capacitors and mainly used for adjusting in-band echo, and the variable capacitance diodes C8-C11 loaded on the branch nodes and the variable capacitance diodes C1-C3 connected to the horizontal microstrip line are matched together to have the function of adjusting the bandwidth of a filter passband, so that the out-of-band rejection performance of the filter is also improved. It should be noted that, in the above varactors C1-C11, varactors C1 and C3 each include one varactor; varactor diode C2, C4, C5, C6, C7, C8, C9, C10, C11 all include the diode that a pair of back-to-back form is connected, and connection structure is: the anode of one diode is connected to the corresponding microstrip line, and the anode of the other diode is grounded.
Preferably, referring to fig. 3, (a) of fig. 3 is a schematic diagram of a second filter circuit structure, and (b) of fig. 3 is a schematic diagram of a circuit structure of a low-pass filter unit disposed at a bottom layer of a substrate, where the low-pass filter unit includes a plurality of defected ground units formed by etching grooves on a ground metal plane of the bottom layer of the substrate, and the defected ground units may generate a disturbing effect on a current on the ground metal plane, thereby generating an attenuation pole; the plurality of defected ground units are periodically arranged at fixed intervals to form low-pass filtering response, a microstrip transmission line arranged on the top layer of the substrate is arranged right above the defected ground units, and one end of the microstrip transmission line is connected with the high-pass filtering unit. Furthermore, a metal strip is formed on the inner side of each defective ground unit, the metal strip is isolated from a ground metal plane on the outer side of the defective ground unit through the defective ground unit, a varactor diode is loaded on each defective ground unit, the cathode of the varactor diode is connected with the metal strip, the anode of the varactor diode is connected with the ground metal plane, a bias network is arranged on the top layer of the substrate, the bias network is connected with the metal strip through a metal through hole, so that the capacitance value of the varactor diode loaded on the defective ground unit is changed through the bias network, and the cut-off frequency of the low-pass filter unit is adjusted. Specifically, varactors CV11, CV12, CV13, CV14, CV15, CV16, CV17, CV18 and CV19 are loaded on the defective ground cells respectively, a metal strip inside each defective ground cell is connected with a metal through hole through a resistor, then is connected with another resistor arranged on the top layer of the substrate through the metal through hole and then is connected with a bias voltage V1, and the capacitance value of the varactor on the defective ground cell is controlled and changed by adjusting the bias voltage V1, so that the cut-off frequency of the low-pass filter cell is effectively changed.
Referring to fig. 3 (c), a schematic diagram of a circuit structure of a high-pass filter unit is shown, as a further preferred, the high-pass filter unit includes a main transmission line and four resonance stubs disposed on a top metal layer of a substrate, and the four resonance stubs may generate four transmission zeros to improve the selectivity and out-of-band rejection characteristics of the filter; each resonance branch section is loaded with a pair of variable capacitance diodes connected in a back-to-back mode, the anode of one variable capacitance diode in the variable capacitance diodes connected in the back-to-back mode is connected with the main transmission line, the anode of the other variable capacitance diode is grounded through being connected to the metal through hole, the cathode of each pair of variable capacitance diodes is connected with a bias voltage through a resistor R, the capacitance value of the corresponding variable capacitance diode is changed through adjusting the bias voltage, and the reconstruction of the cut-off frequency of the high-pass filter unit is realized. Specifically, the varactors loaded on the resonance stub are specifically varactors CV211 and CV212 on the first resonance stub, varactors CV311 and CV312 on the second resonance stub, varactors CV411 and CV412 on the third resonance stub, and varactors CV511 and CV512 on the fourth resonance stub, wherein the varactors on the first resonance stub are controlled by a bias voltage V2, the varactors on the second resonance stub are controlled by a bias voltage V3, the varactors on the third resonance stub are controlled by a bias voltage V4, and the varactors on the fourth resonance stub are controlled by a bias voltage V5. Furthermore, the main transmission line comprises a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line and a fifth microstrip line which are connected in sequence, the first microstrip line is connected with the microstrip transmission line of the low-pass filter unit through a constant value capacitor CF11, the first microstrip line is connected with the second microstrip line through a varactor CV611, the second microstrip line is connected with the third microstrip line through a varactor CV612, and the cathode of the varactor CV611 and the cathode of the varactor CV612 are both connected with the second microstrip line; a constant value capacitor CF12 is connected between the third microstrip line and the fourth microstrip line, a constant value capacitor CF13 is connected between the fourth microstrip line and the fifth microstrip line, and a constant value capacitor CF14 is connected between the fifth microstrip line and the output microstrip line; the first microstrip line, the third microstrip line, the fourth microstrip line and the fifth microstrip line are respectively connected with one resonance stub, the first microstrip line, the third microstrip line, the fourth microstrip line and the fifth microstrip line are respectively connected with a grounding resistor, and the second microstrip line is connected with a bias voltage V6 through a resistor. It will be appreciated that varactor diodes CV611 and CV612 function to achieve matching during tuning of the high-pass filter unit, and have capacitance values controlled by bias voltage V6, and ground resistance functions to provide dc ground for the varactor diode pairs.
The following is a filtering performance simulation of the adjustable filtering module according to the embodiment of the present invention, and the specific adopted settings include: the thickness of the base plate adopted by the dielectric base plate is 0.254mm in the Rogers 5880,5 GHz-7GHz frequency band, and the thickness of the base plate adopted by other frequency bands is 0.508mm. The single-pole multi-throw switch is connected with the adjustable filtering module by using a coaxial transmission line, and the switch state is determined by a control signal output by the digital control circuit. The adjustable filter module with the working frequency range below 7GHz adopts a micro-strip circuit (a first filter circuit) loaded by a diode, and the adjustable filter module with the working frequency range above 7GHz adopts a defect ground circuit (a second filter circuit) loaded by the diode.
Through simulation analysis, the frequency range from 2GHz to 7GHz is divided into three sections of 2GHz to 3.5GHz,3.5GHz to 5GHz,5GHz to 7GHz for adjustment. Specifically, in a frequency band of 2GHz to 3.5GHz, the variable capacitance diode is MA46H202, the fixed value capacitor is 0603 series, the capacitance value is 8pF, and the direct current bias voltage is 100K ohms through a resistor R. MA46H201 and MA46H202 are selected as the variable capacitance diodes in the frequency band of 3.5 GHz-5 GHz, the direct current bias voltage is 100K ohms through a resistor, the variable capacitance diodes are connected in a back-to-back mode, and a defected ground low-pass filter is cascaded to suppress harmonic waves. In a frequency band from 5GHz to 7GHz, MA46H201 is selected as the variable capacitance diode, the direct current bias voltage is 100K ohm through a resistor, and the variable capacitance tube is connected in a mode of adding the variable capacitance diode to a constant value capacitor for convenient welding because the size of a circuit is reduced.
For the frequency range of 7GHz-18GHz, the frequency range is divided into five sections of 7GHz-9GHz,9GHz-11GHz, 111GHz-13.5GHz, 13.5GHz-1699 GHz, 16900 GHz-18 GHz. Specifically, the varactors CV11, CV12, CV13, CV14, CV15, CV16, CV17, CV18 and CV19 are of the type MAVR-011020-1411 from MACOM, the diodes CV211, CV212, CV311, CV312, CV411, CV412, CV511, CV512, CV611 and CV612 are of the type MAVR-000120-1411 from MACOM. The capacitors CF11, CF12, CF13 and CF14 are constant-value patch capacitors of ATC company. The resistor is a packaged type 0402 chip resistor with resistance of 100K ohm.
Fig. 4 and 5 show S-parameter response curves of the filter module according to the embodiment of the present invention at 2ghz,4ghz,7ghz,12ghz and 18GHz, where the solid line corresponds to a relative bandwidth of 30% and the dashed line corresponds to a relative bandwidth of 20%. It can be seen that by adjusting the switch state and the bias state of the varactor, the filter module can achieve continuous adjustability of the center frequency and the bandwidth within the frequency range of 2-18GHz, and the result shows that the design concept of the invention is correct and feasible.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (6)
1. A tunable filter module with an ultra-wide frequency conversion range is characterized by comprising a digital control circuit, N tunable filter modules and two single-pole multi-throw switches respectively connected with a signal input end and a signal output end, wherein the N tunable filter modules are connected between the two single-pole multi-throw switches in parallel to form N mutually independent filter paths, and each filter path has different working frequency tuning ranges; the digital control circuit outputs control signals to the two single-pole multi-throw switches, selects a filtering channel corresponding to a determined required frequency range, and outputs control voltage to the corresponding adjustable filtering module by the digital control circuit so as to change the working state of a variable capacitance diode in the filtering module and realize the adjustment of filtering performance;
the working frequency range of the N adjustable filter modules covers 2GHz-18GHz, and for the range of 2GHz-7GHz, the adjustable filter modules with first filter circuits are adopted, wherein the first filter circuits are microstrip circuit structures loaded with variable capacitance diodes; for the range of 7GHz-18GHz, an adjustable filter module with a second filter circuit is adopted, the second filter circuit comprises a high-pass filter unit and a low-pass filter unit which are cascaded, the low-pass filter unit adopts a defected ground structure, and the high-pass filter unit adopts a microstrip structure;
the first filter circuit comprises two cascaded cross-shaped microstrip resonators connected between an input end and an output end, each cross-shaped microstrip resonator comprises a horizontal microstrip line and a vertical microstrip line which are perpendicular to each other, a pair of variable capacitance diodes connected in a back-to-back mode are loaded at two ends of the horizontal microstrip line respectively, and the cathodes of the variable capacitance diodes are connected to direct current bias through resistors.
2. The adjustable filter module with an ultra-wide frequency conversion range according to claim 1, wherein a pair of back-to-back connected varactors is loaded at each end of the vertical microstrip line, the horizontal microstrip lines of the two cross microstrip resonators are connected by a pair of back-to-back connected varactors, the horizontal microstrip lines of the two cross microstrip resonators are connected to the input microstrip line and the output microstrip line by sequentially connected varactors and constant value capacitors, and cathodes of all varactors are connected to a dc bias by resistors.
3. The tunable filter module with an ultra-wide frequency conversion range according to claim 1, wherein the low-pass filter unit comprises a microstrip transmission line disposed on a top layer of the substrate, and a plurality of defected ground units formed by etching grooves on a ground metal plane on a bottom layer of the substrate, the plurality of defected ground units are periodically arranged at a fixed interval to form a low-pass filter response, the microstrip transmission line is disposed right above the defected ground units, and one end of the microstrip transmission line is connected to the high-pass filter unit.
4. The tunable filter module with an ultra-wide frequency conversion range according to claim 3, wherein a metal strip is formed on an inner side of each defective ground unit, the metal strip is isolated from a ground metal plane on an outer side of the defective ground unit through the defective ground unit, a varactor diode is loaded on each defective ground unit, a cathode of the varactor diode is connected to the metal strip, an anode of the varactor diode is connected to the ground metal plane, a bias network is disposed on a top layer of the substrate, and the bias network is connected to the metal strip through a metal via hole so as to change a capacitance value of the varactor diode through the bias network, thereby adjusting a cut-off frequency of the low-pass filter unit.
5. The adjustable filter module with an ultra-wide frequency conversion range according to claim 1, wherein the high-pass filter unit comprises a main transmission line and four resonance branches, each resonance branch is loaded with a pair of varactor diodes connected back to back, a cathode of each pair of varactor diodes is connected with a bias voltage through a resistor, and the reconstruction of the cut-off frequency of the high-pass filter unit is realized by adjusting the bias voltage to change the capacitance of the corresponding varactor diode.
6. The adjustable filter module with an ultra-wide frequency conversion range according to claim 5, wherein the main transmission line comprises a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line and a fifth microstrip line which are sequentially connected, the first microstrip line is connected with the microstrip transmission line of the low-pass filter unit through a constant value capacitor, the first microstrip line is connected with the second microstrip line through a first varactor diode, the second microstrip line is connected with the third microstrip line through a second varactor diode, and the first varactor diode and the second varactor diode form a back-to-back connection; a constant value capacitor is respectively connected between the third microstrip line and the fourth microstrip line, between the fourth microstrip line and the fifth microstrip line and between the fifth microstrip line and the output microstrip line; the first microstrip line, the third microstrip line, the fourth microstrip line and the fifth microstrip line are respectively connected with one resonance stub and are all connected with a grounding resistor, and the second microstrip line is connected with a bias voltage through a resistor.
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| CN1901274B (en) * | 2006-07-27 | 2010-11-03 | 上海交通大学 | Super wide band plane microstrip filter |
| CN202210797U (en) * | 2011-09-28 | 2012-05-02 | 四川九立微波有限公司 | Front end assembly of frequency-selecting receiver of multichannel microwave communication machine |
| CN104733813B (en) * | 2015-03-16 | 2017-06-06 | 华南理工大学 | A kind of broadband band-pass filter of frequency and the equal restructural of bandwidth |
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