CN113422181B - Adjustable filtering module with ultra-wide frequency conversion range - Google Patents

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

An adjustable filter module with ultra-wide variable frequency range

technical field

The invention relates to microwave communication technology, in particular to an adjustable filter module with ultra-wide frequency conversion range.

Background technique

In wireless communication systems, filters are used to filter out the interference of clutter signals to ensure communication quality. With the rapid development of modern wireless communication technology, the system usually needs to support multiple applications in different operating frequency bands. If all filters with fixed performance are used, not only will the system cost be increased, but the system volume will also be increased. The tunable filter is an effective way to solve this problem. It can flexibly adjust the filtering performance according to the requirements of the application scene, so as to realize the miniaturization and intelligence of the system.

However, various tunable filter devices currently proposed still have shortcomings such as narrow frequency tuning range, low operating frequency, and complicated tuning methods. At the same time, there are still few filter solutions with fully adjustable center frequency and relative bandwidth that can work in the high frequency range.

Contents of the invention

The purpose of the present invention is to solve the above problems and provide an adjustable filter module with an ultra-wide frequency conversion range that can work in a high-frequency range, the central frequency and the relative bandwidth are fully adjustable.

The object of the present invention is achieved by providing an adjustable filter module with an ultra-wide frequency conversion range, which includes a digital control circuit, N adjustable filter modules and two One single-pole multi-throw switch, N adjustable filter modules connected in parallel between two single-pole multi-throw switches, forming N mutually independent filter paths, and each filter path has a different operating frequency tuning range; digital control circuit Output control signals to two single-pole multi-throw switches, select and determine the filter path corresponding to the required frequency range, and at the same time, the digital control circuit outputs control voltage to the corresponding adjustable filter module to change the working state of the varactor diode in the filter module to achieve Adjustment of filter performance.

Preferably, the operating frequency range of the N adjustable filter modules covers 2GHz-18GHz, and for the range of 2GHz-7GHz, an adjustable filter module with a first filter circuit is used, and the first filter circuit is a microstrip loaded with a varactor diode Circuit structure; for the 7GHz-18GHz range, an adjustable filter module with a second filter circuit is used, the second filter circuit includes a cascaded high-pass filter unit and a low-pass filter unit, the low-pass filter unit adopts a defect ground structure, and the high-pass The filtering unit adopts a microstrip structure.

Preferably, the first filter circuit includes two cascaded cross-shaped microstrip resonators connected between the input end and the output end, each cross-shaped microstrip resonator includes horizontal microstrip lines perpendicular to each other and vertical A microstrip line, two ends of the horizontal microstrip line are respectively loaded with a pair of varactor diodes connected in a back-to-back form, and the cathodes of the varactor diodes are connected to a DC bias through a resistor.

Preferably, the two ends of the vertical microstrip line are respectively loaded with a pair of varactor diodes connected in a back-to-back form, and the horizontal microstrip lines of the two cross-shaped microstrip resonators are connected by a pair of varactor diodes connected in a back-to-back form. The horizontal microstrip lines of each cross-shaped microstrip resonator are respectively connected to the input microstrip line and the output microstrip line through sequentially connected varactor diodes and fixed value capacitors, and the cathodes of all varactor diodes are connected to DC bias through resistors.

Preferably, the low-pass filter unit includes a microstrip transmission line arranged on the top layer of the substrate, and a plurality of defective ground units formed by etching grooves on the ground metal plane of the bottom layer of the substrate, and the multiple defective ground units are periodically arranged at fixed intervals , to form a low-pass filter response, the microstrip transmission line is located directly above the defective ground unit, 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, and the metal strip is isolated from the grounding metal plane outside the defective ground unit through the defective ground unit, and a varactor diode is loaded on each defective ground unit. The cathode of the capacitor diode is connected to the metal strip, and the anode is connected to the grounded metal plane. The top layer of the substrate is provided with a bias network, and the bias network is connected to the metal strip through a metal via to change the capacitance value of the varactor diode through the bias network, thereby adjusting The cutoff frequency of the low-pass filter unit.

Preferably, the high-pass filter unit includes a main transmission line and four resonant branches, and each resonant branch is respectively loaded with a pair of varactor diodes connected in a back-to-back form, and the cathodes of each pair of varactor diodes are connected to the bias voltage through a resistor, and adjusted The change of the bias voltage corresponds to the capacitance value of the variable capacitance diode, so as to realize the reconstruction of the cutoff frequency of the high-pass filter unit.

Preferably, the main transmission line includes a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line and a fifth microstrip line connected in sequence, and the first microstrip line passes a fixed value The capacitor is connected to the microstrip transmission line of the low-pass filter unit, the first microstrip line and the second microstrip line are connected through the first varactor diode, and the second microstrip line and the third microstrip line are connected through the second varactor Diode connection, the first varactor diode and the second varactor diode form a back-to-back connection form; 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 A fixed-value capacitor is respectively connected between the strip 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 a resonant branch nodes, and are connected to a grounding resistor, and the second microstrip line is connected to the bias voltage through the resistor.

Significant progress of the present invention is at least reflected in:

An adjustable filter module with an ultra-wide variable frequency range is provided, which realizes flexible control of the center frequency and relative bandwidth of the filter in the ultra-wide frequency range of 2-18 GHz by using the varactor diode tuning and switching methods. Among them, the varactor diode is used to load the microstrip circuit and the varactor diode is used to load the defective ground circuit to realize independent adjustable filter modules in the low frequency and high frequency ranges, and then use single-pole multi-throw switches to connect multiple adjustable filter modules in parallel to realize filtering Effective extension of the inverter frequency range.

Description of drawings

Fig. 1 is the circuit topological structure diagram of the adjustable filter module of the embodiment of the present invention;

Fig. 2 is the circuit structural diagram of the first filtering circuit of the embodiment of the present invention;

Fig. 3 is the circuit structural diagram of the second filtering circuit of the embodiment of the present invention;

Fig. 4 is the S21 parameter simulation graph of the adjustable filter module of the embodiment of the present invention;

FIG. 5 is a simulation curve diagram of the S11 parameter of the adjustable filter module according to the embodiment of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that the embodiments of the present invention are not limited to the provided examples.

Referring to Fig. 1, it is a circuit topology diagram of an adjustable filter module of an embodiment, the adjustable filter module of the present embodiment comprises a digital control circuit, N adjustable filter modules and respectively connected signal input terminals (port 1 ) and two SPMT switches at the output terminal (port 2), N adjustable filter modules are connected in parallel between the two SPMT switches to form N mutually independent filter paths, and each filter path has Different operating frequency tuning ranges; the digital control circuit outputs control signals to two single-pole multi-throw switches to select and determine the filter path corresponding to the required frequency range, and at the same time, the digital control circuit outputs control voltage to the corresponding adjustable filter module to change the filter. The working state of the varactor diode in the module realizes the adjustment of the filtering performance. In the solution of this embodiment, N adjustable filter modules with different operating frequency ranges are connected in parallel by using a single-pole multi-throw switch, which effectively expands the operating frequency tuning range of the adjustable filter module and realizes continuous adjustment of an ultra-wide frequency range. Significantly enhanced the flexibility of adjustment. The single-pole multi-throw switch is controlled by the digital control circuit to connect to the corresponding filter path, and the filter performance adjustment of the adjustable filter module is realized, which enhances the quickness of adjustment.

As a preference, the operating frequency range of the N adjustable filter modules covers 2GHz-18GHz, and for the range of 2GHz-7GHz, an adjustable filter module with a first filter circuit is used, and the first filter circuit is a loaded varactor diode Microstrip circuit structure; for the 7GHz-18GHz range, an adjustable filter module with a second filter circuit is used, and the second filter circuit includes a cascaded high-pass filter unit and a low-pass filter unit, and the low-pass filter unit adopts a defect ground Structure, the high-pass filter unit adopts microstrip structure. In this embodiment, the diode-loaded microstrip circuit and the defective ground circuit are respectively used to achieve the required adjustable filtering performance in the low frequency range and high frequency range, which specifically solves the problem of large circuit size in the low frequency range and high frequency range. The technical problem of large insertion loss.

Referring to Fig. 2, as a kind of preference, described first filter circuit adopts 50 ohm microstrip transmission line as input (Port1) and output (Port2), and two mutually cascaded cross-shaped A microstrip resonator, each cross-shaped microstrip resonator includes a horizontal microstrip line and a vertical microstrip line perpendicular to each other, and a pair of varactor diodes connected back-to-back are respectively loaded on both ends of the horizontal microstrip line. Specifically, varactor diodes C4, C5, C6, and C7 are respectively loaded at the ends of the horizontal microstrip line of the two cross-shaped microstrip resonators, and the cathodes of the varactor diodes C4 and C5 are respectively connected to the same DC bias through resistors. Set (DC Bias), the cathodes of varactor diodes C6 and C7 are respectively connected to the same DC bias through resistors. Therefore, the capacitance values of the varactor diodes C4 , C5 , C6 , and C7 loaded on the cross-shaped microstrip resonator can be changed through the DC bias, thereby realizing the adjustment of the center frequency of the first filter circuit.

As a further preference, the two ends of the vertical microstrip line are respectively loaded with a pair of varactor diodes connected in a back-to-back form. Specifically, the short branches in the vertical microstrip line of the two cross-shaped microstrip resonators are respectively loaded with varactors. Diodes C9 and C11, varactor diodes C8 and C10 are respectively loaded on the long branches in the vertical microstrip line, the cathodes of varactor diodes C9 and C11 are respectively connected to the same DC bias through resistors, and the cathodes of varactor diodes C8 and C10 Connect to the same DC bias through resistors respectively. It can be understood that the vertical microstrip lines of the cross-shaped microstrip resonator are used to generate transmission zeros, wherein the short legs generate high-frequency nulls, and the long legs generate low-frequency zeros. Further, the horizontal microstrip lines of two cross-shaped microstrip resonators are connected through a pair of back-to-back varactor diodes C3, and the horizontal microstrip lines of one cross-shaped microstrip resonator are connected through sequentially connected varactors The diode C1 and the fixed value capacitor are connected to the input microstrip line, and the horizontal microstrip line of another cross-shaped microstrip resonator is connected to the output microstrip line through the sequentially connected varactor diode C2 and the fixed value capacitor, and the varactor diode C1 , The cathodes of C2 and C3 are connected to DC bias through resistors. In the solution of this embodiment, the varactor diodes C1-C3 are mainly used as coupling capacitors to adjust the in-band echo, through the varactor diodes C8-C11 loaded on the branch and the varactor diode C1 connected to the horizontal microstrip line The combination of -C3 has the function of adjusting the bandwidth of the filter passband, and also improves the out-of-band rejection performance of the filter. It should be noted that among the above varactor diodes C1-C11, varactor diodes C1 and C3 both include a varactor diode; varactor diodes C2, C4, C5, C6, C7, C8, C9, C10, and C11 all include a varactor diode. For diodes connected in back-to-back form, and the connection structure is: the anode of one of the diodes is connected to the corresponding microstrip line, and the anode of the other diode is grounded.

As preferably, referring to shown in Fig. 3, among Fig. 3 (a) figure is the second filter circuit structure schematic diagram, among Fig. 3 (b) figure is the circuit structure schematic diagram that the low-pass filter unit is arranged on the bottom of the substrate, the low-pass filter unit Including a plurality of defective ground units formed by etching grooves on the ground metal plane at the bottom of the substrate, the defective ground units will have a disturbing effect on the current on the ground metal plane, thereby generating an attenuation pole; multiple defective ground units can be used to fix The intervals are arranged periodically to form a low-pass filter response, and the microstrip transmission line arranged on the top layer of the substrate is directly above the defect ground unit, and one end of the microstrip transmission line is connected to the high-pass filter unit. Furthermore, a metal strip is formed inside each defective ground unit, and the metal strip is isolated from the ground metal plane outside the defective ground unit through the defective ground unit, and each defective ground unit is loaded with a varactor diode, The cathode of the varactor diode is connected to the metal strip, the anode is connected to the ground metal plane, and the top layer of the substrate is provided with a bias network. The bias network is connected to the metal strip through a metal via to change the varactor loaded on the defective ground unit through the bias network. The capacitance value of the diode, thereby adjusting the cut-off frequency of the low-pass filter unit. As a specific example, varactor diodes CV11, CV12, CV13, CV14, CV15, CV16, CV17, CV18, and CV19 are respectively loaded on the defective ground unit, and the metal strips inside each defective ground unit are connected to metal vias through resistance. Then connect another resistor set on the top layer of the substrate through the metal through hole and then connect to the bias voltage V1. By adjusting the bias voltage V1, the capacitance value of the varactor diode on the defective ground unit can be changed, thereby effectively changing the low-pass filter. The unit's cutoff frequency.

Referring to Figure 3, (c) shows a schematic diagram of the circuit structure of the high-pass filter unit. As a further preference, the high-pass filter unit includes a main transmission line arranged on the top metal layer of the substrate and four resonant branches, and the four resonant branches can be Four transmission zeros are generated to improve the selectivity and out-of-band suppression characteristics of the filter; each resonant branch is loaded with a pair of varactor diodes connected back-to-back, and one of the varactor diodes connected back-to-back The anode of the diode is connected to the main transmission line, and the anode of the other varactor diode is connected to the metal via for grounding. The cathode of each pair of varactor diodes is connected to the bias voltage through the resistor R, and the capacitance of the corresponding varactor diode is changed by adjusting the bias voltage. value to realize the reconstruction of the cutoff frequency of the high-pass filter unit. Specifically, the varactor diodes loaded on the resonant branch are specifically: the varactor diodes CV211 and CV212 on the first resonant branch, the varactor diodes CV311 and CV312 on the second resonant branch, and the varactor diodes CV312 on the third resonant branch. Varactor diodes CV411 and CV412, varactor diodes CV511 and CV512 on the fourth resonant branch, the varactor diode on the first resonant branch is controlled by bias voltage V2, and the varactor diode on the second resonant branch is biased by The varactor diode on the third resonant branch is controlled by the bias voltage V4, and the varactor diode on the fourth resonant branch is controlled by the bias voltage V5. Furthermore, the main transmission line includes a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line and a fifth microstrip line connected in sequence, and the first microstrip line passes through a fixed The value capacitor CF11 is connected to the microstrip transmission line of the low-pass filter unit, the first microstrip line and the second microstrip line are connected through a varactor diode CV611, and the second microstrip line and the third microstrip line are connected through a varactor diode CV612 is connected, the cathode of the varactor diode CV611 and the cathode of the varactor diode CV612 are connected to the second microstrip line; a fixed-value capacitor CF12 is connected between the third microstrip line and the fourth microstrip line, and the fourth microstrip line A fixed value capacitor CF13 is connected between the line and the fifth microstrip line, and a fixed value capacitor CF14 is connected between the fifth microstrip line and the output microstrip line; the first microstrip line, the third microstrip line, and the fourth microstrip line The strip line and the fifth microstrip line are respectively connected to one of the resonant branches, and the first microstrip line, the third microstrip line, the fourth microstrip line and the fifth microstrip line are all connected to a ground The second microstrip line is connected to the bias voltage V6 through the resistor. It can be understood that the function of varactor diodes CV611 and CV612 is to achieve matching during the tuning process of the high-pass filter unit, and their capacitance value is controlled by the bias voltage V6, and the function of the grounding resistor is to provide DC grounding for the varactor diode pair.

The filter performance simulation of the adjustable filter module of the embodiment of the present invention is performed below. The specific settings include: Rogers 5880 is selected as the dielectric substrate, the thickness of the substrate is 0.254mm for the 5GHz--7GHz frequency band, and the thickness of the substrate for other frequency bands is 0.508mm. The single-pole multi-throw switch is connected with the adjustable filter module through a coaxial transmission line, and the switch state is determined by the control signal output by the digital control circuit. The adjustable filter module with a working frequency range below 7GHz uses a diode-loaded microstrip circuit (first filter circuit), and the adjustable filter module with a working frequency range above 7GHz uses a diode-loaded defective ground circuit (second filter circuit).

Through simulation analysis, first divide the frequency range of 2GHz--7GHz into three sections of 2GHz--3.5GHz, 3.5GHz--5GHz, and 5GHz--7GHz for adjustment. Specifically, in the 2GHz--3.5GHz frequency band, the variable capacitance diode is selected from MA46H202, the fixed value capacitor is selected from 0603 series, the capacitance value is 8pF, and the DC bias voltage passes through the resistor R to be 100K ohms. In the 3.5GHz--5GHz frequency band varactor diodes use MA46H201 and MA46H202, the DC bias voltage through the resistance is 100K ohms, the varactors are connected back to back with a pair of varactor diodes, and a defective low-pass filter is cascaded Suppresses harmonics. In the 5GHz--7GHz frequency band, the varactor diode is MA46H201, and the DC bias voltage passes through a resistance of 100K ohms. Since the circuit size becomes smaller, for the convenience of welding, the varactor is connected with a fixed value capacitor and a varactor diode.

For the frequency range of 7GHz-18GHz, the frequency range is divided into five segments of 7GHz-9GHz, 9GHz-11GHz, 11GHz-13.5GHz, 13.5GHz-16GHz, and 16GHz-18GHz for adjustment. Specifically, the varactor diodes CV11, CV12, CV13, CV14, CV15, CV16, CV17, CV18, and CV19 use the MAVR-011020-1411 type varactor diodes from MACOM, and the diodes CV211, CV212, CV311, CV312, CV411, CV412, CV511, CV512, CV611, CV612 select the MAVR-000120-1411 model variable capacitance diode of MACOM Company for use. Capacitors CF11, CF12, CF13, and CF14 use fixed-value chip capacitors from ATC Company. The resistors are chip resistors with package type 0402, and the resistance values are all 100K ohms.

4 and 5 show the S parameter response curves of the filter module of the embodiment of the present invention at 2GHz, 4GHz, 7GHz, 12GHz and 18GHz, wherein 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 diode, the filter module can realize continuous adjustment of the center frequency and bandwidth within the frequency range of 2-18 GHz. This result shows that the design concept of the present invention is correct and feasible.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (6)

1. An adjustable filter module with an ultra-wide frequency conversion range, characterized in that the filter module includes a digital control circuit, N adjustable filter modules and two single-pole multi-throw modules connected to the signal input and output terminals respectively switch, N adjustable filter modules are connected in parallel between two single-pole multi-throw switches to form N independent filter paths, and each filter path has a different operating frequency tuning range; The multi-throw switch outputs the control signal to select and determine the filter path corresponding to the required frequency range, and at the same time, the digital control circuit outputs the control voltage to the corresponding adjustable filter module to change the working state of the varactor diode in the filter module and realize the optimization of the filter performance. adjust; The operating frequency range of the N adjustable filter modules covers 2GHz-18GHz. For the range of 2GHz-7GHz, an adjustable filter module with a first filter circuit is adopted, and the first filter circuit is a microstrip circuit structure loaded with varactor diodes; For the 7GHz-18GHz range, an adjustable filter module with a second filter circuit is used, the second filter circuit includes a cascaded high-pass filter unit and a low-pass filter unit, the low-pass filter unit adopts a defect structure, and the high-pass filter unit adopts microstrip structure; The first filtering circuit includes two cascaded cross-shaped microstrip resonators connected between the input end and the output end, each cross-shaped microstrip resonator includes horizontal microstrip lines and vertical microstrip lines perpendicular to each other , the two ends of the horizontal microstrip line are respectively loaded with a pair of varactor diodes connected in a back-to-back form, and the cathodes of the varactor diodes are connected to a DC bias through a resistor. 2. The adjustable filter module with ultra-wide frequency conversion range according to claim 1, characterized in that, a pair of varactor diodes connected in back-to-back form are respectively loaded on the two ends of the vertical microstrip line, and two cross-shaped microstrips The horizontal microstrip lines of the resonators are connected through a pair of back-to-back varactor diodes, and the horizontal microstrip lines of the two cross-shaped microstrip resonators are respectively connected to the input microstrip through sequentially connected varactor diodes and fixed-value capacitors. Stripline and output microstrip lines, the cathodes of all varactors are connected to DC bias through resistors. 3. The adjustable filter module with an ultra-wide frequency conversion range according to claim 1, wherein the low-pass filter unit includes a microstrip transmission line arranged on the top layer of the substrate, and etched on a grounded metal plane on the bottom layer of the substrate A plurality of defective ground units formed by grooves are periodically arranged at fixed intervals to form a low-pass filter response. The microstrip transmission line is located directly above the defective ground unit, and one end of the microstrip transmission line is connected to a high-pass filtering unit. 4. The adjustable filter module with an ultra-wide frequency conversion range according to claim 3, wherein a metal strip is formed on the inner side of each defective ground unit, and the metal strip and the grounded metal plane on the outside of the defective ground unit pass through the defect The ground unit is isolated, and a varactor diode is loaded on each defective ground unit. The cathode of the varactor diode is connected to the metal strip, and the anode is connected to the ground metal plane. The top layer of the substrate is provided with a bias network. The holes are connected to the metal strips to change the capacitance value of the varactor diode through the bias network, thereby adjusting the 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 includes a main transmission line and four resonant branches, and each resonant branch is respectively loaded with a pair of back-to-back Connected varactor diodes, the cathodes of each pair of varactor diodes are connected to a bias voltage through a resistor, and the capacitance value of the corresponding varactor diode is changed by adjusting the bias voltage to realize the reconstruction of the cut-off frequency of the high-pass filter unit. 6. The adjustable filter module with an ultra-wide frequency conversion range according to claim 5, wherein the main transmission line includes a first microstrip line, a second microstrip line, and a third microstrip line connected in sequence line, the fourth microstrip line and the fifth microstrip line, the first microstrip line is connected to the microstrip transmission line of the low-pass filter unit through a fixed value capacitor, and the first microstrip line and the second microstrip line are connected by the first variable The second microstrip line and the third microstrip line are connected through the second varactor diode, and the first varactor diode and the second varactor diode form a back-to-back connection form; the third microstrip line and the fourth microstrip line A constant-value capacitor is respectively connected between the strip lines, 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 1, the fourth microstrip line and the fifth microstrip line are respectively connected to one of the resonant branches, and both are connected to a grounding resistor, and the second microstrip line is connected to a bias voltage through a resistor.

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