Three-band reconfigurable filter with wide tuning range

Abstract

The invention relates to the technical field of radio frequency front ends, in particular to a three-band reconfigurable filter with a wide tuning range, which structurally consists of three parts and comprises a pair of UIR uniform impedance resonators which are positioned at the top of a dielectric substrate and above a feeder line, are mutually coupled and are provided with upward openings, and variable capacitance diodes Cv2 are loaded at the coupling parts of the resonators; the UIR uniform impedance resonator is located at the top of the dielectric substrate and below the feeder line and shares the same grounding through hole, and a variable capacitance diode Cv3 is loaded on the resonator; the SIR stepped impedance resonators are located at the top of the dielectric substrate and below the feeder line, the coupling ends of the SIR stepped impedance resonators are high-impedance microstrip ports, and variable capacitance diodes Cv1 are loaded on the SIR stepped impedance resonators. The first stray passband is controlled to be far away from the target passband, the coupling coefficient is adjusted according to a theoretical calculation result, and finally, parameter scanning and continuous simulation optimization are performed through electromagnetic simulation software, so that three-band reconfiguration within a wide tuning range is realized.

Description

Technical Field

[0001] The invention relates to the technical field of radio frequency front-end technology, and in particular to a three-band reconfigurable filter with a wide tuning range. Background Art

[0002] Multi-frequency microwave bandpass filters at home and abroad have developed from single reconfigurable bandpass filters and multi-frequency bandpass filter technology to a multi-frequency reconfigurable bandpass filter technology that combines the two, and are developing towards miniaturized, high-performance, easy-to-design, highly flexible, and highly adaptable multi-frequency reconfigurable bandpass filters and even multi-band fully adjustable bandpass filters.

[0003] At present, the common multi-frequency reconfigurable bandpass filter technologies mainly include: changing the resonant frequency and resonance form of the resonator, loading variable reactance elements, introducing defective structures, etc. By changing the resonant frequency and resonance form of the resonator, the filter passband can be tuned independently, but the bandwidth is constant; by loading variable reactance elements, the first and third passbands of the filter can be tuned independently, but the center frequency of the second passband is fixed; by introducing defective structures, the filter can be controlled to switch between single, dual or triple bandpass characteristics, but only switching between functions is achieved.

[0004] Due to the above reasons, the existing multi-frequency reconfigurable bandpass filters only realize switching between single-band and multi-band or between other functions, and the reconfigurable flexibility and independence are insufficient. Summary of the invention

[0005] The object of the present invention is to provide a three-band reconfigurable filter with a wide tuning range, aiming to solve the technical problem that the existing multi-frequency reconfigurable bandpass filters have insufficient flexibility and independence in reconfiguration.

[0006] To achieve the above object, the present invention provides a three-band reconfigurable filter with a wide tuning range, comprising three groups of multi-mode resonators, wherein the first resonator is a pair of mutually coupled SIR step impedance resonators, located below the feed line, with the coupling end at a high impedance microstrip port and loaded with a varactor diode C v1 The second resonator is a pair of mutually coupled UIR uniform impedance resonators with openings facing upwards, located above the feeder, and a variable capacitance diode C is loaded at the coupling point. v2 The third resonator is a UIR uniform impedance resonator sharing the same ground via, located below the feed line and loaded with a varactor diode C v3 .

[0007] Among them, three groups of multi-mode resonators are connected in parallel using a parallel resonator method, and each passband of the three-band reconfigurable filter with a wide tuning range is generated by only one mode of one of the multi-mode resonators, and its first spurious passband is designed to be far away from the target passband.

[0008] Each pair of varactor diodes is provided with a corresponding bias circuit, and its capacitance value is controlled by changing the bias voltage.

[0009] The present invention provides a three-band reconfigurable filter with a wide tuning range. The structure consists of three parts, including a pair of mutually coupled UIR uniform impedance resonators with openings facing upwards, located on the top of the dielectric substrate and above the feeder. The resonator coupling is loaded with a variable capacitance diode C v2 ; The UIR uniform impedance resonator located on the top of the dielectric substrate, below the feeder, and sharing the same ground via, the varactor diode C v3 Loaded on the resonator; located on the top of the dielectric substrate, below the feeder, a pair of mutually coupled SIR step impedance resonators, the coupling end is a high impedance microstrip port, and is loaded with a varactor diode C v1 In the present invention, the first stray passband is controlled to be away from the target passband, the coupling coefficient is adjusted according to the theoretical calculation result, and finally the parameter scanning is continuously simulated and optimized through electromagnetic simulation software to achieve the three-band reconfiguration with a wide tuning range. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 It is a structural schematic diagram of a three-band reconfigurable filter with a wide tuning range of the present invention.

[0012] Figure 2 It is a structural schematic diagram of the wide tuning range three-frequency reconfigurable BPF resonator of the present invention.

[0013] Figure 3 Schematic diagram of the equivalent circuit of odd and even modes of the resonator in each path of a specific embodiment of the present invention, (a) path 1; (b) path 2; (c) path 3.

[0014] Figure 4 is the parameter C in the specific embodiment of the present invention v1 , C v2 and C v3 Schematic diagram of the impact on each resonant frequency, (a) C v1 ; (b) C v2 ; (c) C v3 .

[0015] Figure 5 It is a schematic diagram of the influence of the capacitor loading position on the third passband resonant frequency in a specific embodiment of the present invention.

[0016] Figure 6 Schematic diagram of the electric field of the resonator at different frequencies in a specific embodiment of the present invention, (a) 2.4 GHz; (b) 3.5 GHz; (c) 5 GHz; (d) 6.5 GHz.

[0017] Figure 7 Schematic diagram of a simulation model of a three-band reconfigurable BPF with a wide tuning range according to a specific embodiment of the present invention, (a) top layer; (b) bottom layer.

[0018] Figure 8 It is a topology diagram of a three-band reconfigurable BPF with wide tuning range according to a specific embodiment of the present invention.

[0019] Fig. 9 Schematic diagram of the influence of relevant parameters of a specific embodiment of the present invention on the coupling coefficient and, (a) the influence of g1 on the coupling coefficient; (b) the influence of g3 on the coupling coefficient; (c) the influence of g3 on the coupling coefficient; (d) the influence of g3 on the coupling coefficient.

[0020] Fig.10 It is a comparison diagram of S parameters of filters with and without matching branches in a specific embodiment of the present invention.

[0021] Fig.11 The following is a comparison diagram of simulation and actual measurement of a specific embodiment of the present invention. (a) Fixed C v2 and C v3 , key C v1 ; (b) Fixed C v1 and C v3 , key C v2 ; (c) Fixed C v1 and C v2 , key C v3 . DETAILED DESCRIPTION

[0022] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0023] The following is an explanation of some of the English term abbreviations that appear in this application:

[0024] SIR: stepped-impedance resonator, stepped impedance resonator.

[0025] UIR: uniform-impedance resonator, uniform impedance resonator.

[0026] BPF: Band-Pass Filter, band-pass filter.

[0027] See also Figures 1 to 6 The present invention provides a three-band reconfigurable filter with a wide tuning range, comprising three groups of multi-mode resonators, wherein the first resonator is a pair of mutually coupled SIR step impedance resonators, located below the feed line, the coupling end is a high impedance microstrip port, and is loaded with a varactor diode C v1 The second resonator is a pair of mutually coupled UIR uniform impedance resonators with openings facing upwards, located above the feeder, and a variable capacitance diode C is loaded at the coupling point. v2 The third resonator is a UIR uniform impedance resonator sharing the same ground via, located below the feed line and loaded with a varactor diode C v3 .

[0028] Three groups of multi-mode resonators are connected in parallel using a parallel resonator method. Each passband of the three-band reconfigurable filter with a wide tuning range is generated by only one mode of one of the multi-mode resonators, and its first spurious passband is designed to be far away from the target passband.

[0029] Each pair of varactor diodes is provided with a corresponding bias circuit, and its capacitance value is controlled by changing the bias voltage.

[0030] The following is a description of the specific embodiments and structures. Figure 2 This is the structure diagram of the resonator loaded with a varactor diode of a wide tuning range three-band reconfigurable filter. As can be seen from the figure, the resonator is composed of three groups of independent resonators in parallel, so it has three independent resonant paths. v1 , C v2 and C v3 Loaded on paths 1, 2 and 3 respectively. 11 , Y 12 , Y2, and Y3 are the characteristic admittances of each microstrip line segment, θ 11 ,θ 12 ,θ2,θ 31 ,θ 32 are the electrical lengths of each microstrip line segment. Since the three pairs of resonators are symmetrical structures, their equivalent models can be obtained through odd-even mode analysis, such as Figure 3 shown.

[0031] For these three resonant paths, the input admittance Y of the three paths is in1 , Y in2 and Y in3 They are:

[0032] Path 1:

[0033] Path 2: Y in2 =j2πf2C v2 +jY2tanθ2 (2)

[0034] Path 3:

[0035] Let the imaginary part of the input admittance be 0, and the center frequencies f1, f2, and f3 of the three passbands can be determined:

[0036]

[0037] It can be seen from formulas 4, 5, and 6 that after determining the physical dimensions of the dielectric substrate and the microstrip line of the resonator structure, the center frequency f1 of the first passband is only affected by the capacitance C v1 The center frequency f2 of the second passband is only affected by the capacitance C v2 The center frequency f3 of the third passband is only affected by the capacitance C v3 Therefore, by changing the external bias voltages V1, V2, and V3, C v1 , C v2 and C v3 , so the center frequencies of the three passbands can be adjusted independently.

[0038] The second is the first spurious passband control design. First determine the first spurious frequency and the center frequency, and use their ratio to determine the impedance ratio of the high-impedance and low-impedance microstrip lines, and then design their electrical lengths. Similarly, the center frequency of the second passband can be designed relatively easily. When designing the center frequency of the third passband, the influence of the capacitor loading position must be considered. Figure 5 The capacitor C is shown v3 The influence of the loading position on the resonant frequency of the third passband shows that when the capacitor moves from the ground end to the open end, the resonant frequency increases slowly, and the first spurious frequency of the resonator is greater than 8 GHz, which is far away from the three target passbands.

[0039] Figure 6The resonator electric field diagram of the resonator structure of the present invention at different frequencies is shown. When the resonant frequency is the first passband center frequency of 2.4 GHz, the SIR resonator in path one resonates, and the resonant position is mainly located on the low impedance line of the SIR resonator; when the resonant frequency is the second passband center frequency of 3.5 GHz, the UIR resonator in path two resonates, and the resonant position is mainly located on the open end of the UIR resonator; when the resonant frequency is the third passband center frequency of 5 GHz, the UIR resonator in path three resonates, and the resonant position is mainly located on the open end of the UIR resonator; when the resonant frequency is the first stray frequency of 6.5 GHz, the SIR resonator in path one resonates, and the resonant position is mainly located on the high impedance line of the SIR resonator. It can be inferred that the three paths have little influence on each other, and the first stray frequency is controlled by the resonator in path one, so it will be affected by the capacitor C v1 impact.

[0040] A three-band independent reconfigurable bandpass filter is designed by connecting the above resonators in parallel. The requirements include 2.4 GHz, 3.5 GHz and 5 GHz, and the three passband bandwidths are 130 MHz, 300 MHz and 300 MHz respectively. The varactor diode model used is SMV1234-079LF (C v1 )、SMV1405-079LF(C v2 ) and SMV1413-079LF(C v3 ), the main parameters of SMV1234-079LF are: R s 0.8Ω; L s is 0.7nH; the capacitance value ranges from 1.32 to 9.63pF. The simulation model of the filter is as follows Figure 7 shown. Figure 7 (a) is the top structure, where the brown part is the microstrip structure, the green part is the pad, the red part is the three types of varactor diodes, and the blue part is the dielectric substrate. Figure 7 (b) is the bottom layer structure, which has seven rectangular slots, three slot lines and four through holes. The five rectangular slots in the middle are used to introduce bias voltage from the outside, and the two rectangular slots on both sides are used to strengthen the coupling excitation of the UIR resonator in the feeding path 1. The three slot lines are also used to strengthen the excitation of the feeding line to the resonator. The four through holes are metalized through holes for grounding.

[0041] Then the coupling feeding coefficient is calculated and the coupling length and coupling gap are designed. The filter topology is as follows: Figure 8As shown, each resonator is a symmetrical structure, so each passband of the filter has two transmission poles. The filter indicators are determined as follows: f1 = 2.4GHz, BW1 = 130MHz; f2 = 3.5GHz, BW2 = 300MHz; f3 = 5GHz, BW3 = 300MHz. According to the coupling matrix theory and the second-order ideal coupling matrix mentioned in the first section, the coupling coefficient required for each passband can be calculated:

[0042] k1=FBW*m 12 =0.0898 (7)

[0043] k2=FBW*m 12 =0.1421 (8)

[0044] k3=FBW*m 12 =0.0994 (9)

[0045] It can be seen from the filter structure that the resonators of the first passband and the second passband are coupled through the gap, so the coupling coefficient can be adjusted by changing the coupling length and the coupling gap width. Fig. 9 The coupling coefficient of the two passbands varies with the relevant parameters. Fig. 9 It can be seen from (a) and (b) that the coupling coefficient k1 decreases with the increase of the SIR resonator coupling gap g1 and increases with the increase of the coupling length L5. Fig. 9 It can be seen from (c) and (d) that the coupling coefficient k2 decreases with the increase of the UIR resonator coupling gap g3 and increases with the coupling length L 12 By properly selecting the coupling length and coupling gap, the desired coupling coefficient can be easily achieved.

[0046] The filter feed line adopts a slot-coupled feeding structure and introduces source-load coupling. In addition, a section of length L is added to the feed line. 15 The microstrip open-circuit branch with a width of W6 is used to adjust the overall matching of the filter. Fig.10 The S-parameter diagram of the filter with and without the matching branch is shown. As can be seen from the figure, the branch has a greater impact on the last two passbands, so it is necessary to reasonably select its position and length and width, which can be optimized by parameter scanning in electromagnetic simulation software.

[0047] Finally, the electromagnetic simulation software parameter scanning and other simulation optimizations are carried out. To verify the correctness of the above theoretical analysis, a filter model is built in the electromagnetic simulation software and the eigenmode simulation is performed on it. The simulation results are shown in Figure 2. Figure 4 As shown in the figure, f n-odd and f n-even are the odd and even mode resonant frequencies of the nth passband (n=1, 2, 3), and f4-odd and f 4-even is the first spurious frequency. Figure 4 It can be seen from (a) that C v1 It only affects the first passband center frequency f1 and the stray frequency f4. It can be seen that the stray frequency f4 is generated by the resonator in path 1. Figure 4 As can be seen from (b), C v2 Only affects the second passband center frequency f2. Figure 4 It can be seen from (c) that C v3 It only affects the third passband center frequency f3. It can be seen that the center frequencies of the three passbands of the filter can be adjusted independently, which verifies the correctness of the theoretical analysis.

[0048] In order to verify the feasibility of the wide tuning range three-band reconfigurable filter of the present invention, the above wide tuning range three-band independent reconfigurable BPF was processed and measured. The dielectric substrate used in the BPF is Rogers RO4350, with a relative dielectric constant of 3.66, a loss tangent of 0.004, and a substrate thickness of 0.508mm. The size of the entire filter is 30.15mm*18mm (0.37λ g *0.22λ g ), the effective area is 14.3mm*15.15mm(0.17λ g *0.18λ g ). g is the waveguide wavelength corresponding to the first center frequency.

[0049] Fig.11The simulation and actual measurement comparison of the filter is shown in Figure 12. The simulation S parameters are obtained by three-dimensional electromagnetic simulation software, and the test results are measured by KEYSIGHT E5080B network analyzer. It can be seen from Figure 12 that the three passband center frequencies of the filter can be tuned independently. The measured reconstruction range of the three passband center frequencies is 2.08~2.6GHz (22.2%), 3.17~3.82GHz (18.6%) and 5.04~5.4GHz (6.9%). The three passband bandwidths will change during the tuning process, among which the first passband bandwidth changes from 110 to 140MHz; the second passband bandwidth changes from 270 to 320MHz; and the third passband bandwidth changes from 250 to 280MHz. The minimum insertion losses in the three passbands are 3.17dB, 2.45dB, and 3.78dB, respectively. During tuning, the parasitic resistance of the varactor diode increases, resulting in a decrease in the quality factor, thereby increasing the insertion loss of the filter. The return loss of the first passband is better than 15dB, the return loss of the second passband is better than 12dB, and the return loss of the first passband is better than 10dB. The filter also has 2 to 4 transmission zeros. Even if there is no transmission zero between the passbands, the suppression between the passbands is greater than 20dB, which will not affect the frequency selectivity of the filter. The results show that the simulation and actual measurement fit well.

[0050] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A three-band reconfigurable filter with a wide tuning range, characterized in that: The first resonator is a pair of mutually coupled SIR step impedance resonators located below the feed line, with the coupling end at the high impedance microstrip port and loaded with a varactor diode C. v1 The second resonator is a pair of mutually coupled UIR uniform impedance resonators with openings facing upwards, located above the feeder, and a variable capacitance diode C is loaded at the coupling point. v2 The third resonator is a UIR uniform impedance resonator sharing the same ground via, located below the feed line and loaded with a varactor diode C v3 .

2. The three-band reconfigurable filter with a wide tuning range as claimed in claim 1, characterized in that: Three groups of multi-mode resonators are connected in parallel using a parallel resonator method. Each passband of the three-band reconfigurable filter with a wide tuning range is generated by only one mode of one of the multi-mode resonators, and its first spurious passband is designed to be far away from the target passband.

3. The three-band reconfigurable filter with a wide tuning range as claimed in claim 2, characterized in that: Each pair of varactor diodes is provided with a corresponding bias circuit, and its capacitance value is controlled by changing the bias voltage.

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