Reconfigurable tri-band band-pass filter based on parallel resonators

Abstract

The invention relates to the technical field of radio frequency front ends, in particular to a reconfigurable three-band band-pass filter based on parallel resonators, which is designed based on a parallel resonator method, and specifically comprises the following steps: firstly, respectively coupling a pair of UIR resonators and a pair of SIR resonators together to form three pass bands of the filter; then, a variable capacitance diode and a fixed capacitor are loaded, the first passband center frequency can be tuned by adjusting the bias voltage 3, the second passband frequency and the third passband frequency can be tuned by adjusting the bias voltage 1 and the bias voltage 2, and meanwhile, a blocking capacitor and an inductor are loaded to be grounded to improve the adjustment independence of the center frequency of each passband, so that the three-band center frequency of the band-pass filter can be independently reconstructed.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency front-end technology, and in particular to a reconfigurable three-band bandpass filter based on parallel resonators. Background Art

[0002] With the promotion of 5G and future communication standards, spectrum resources are becoming increasingly scarce, which has increased the demand for multi-band and multi-functional filters. These filters can quickly switch between different frequency bands to meet the needs of multiple communication standards.

[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] However, the existing multi-frequency reconfigurable bandpass filters realize switching between single-band and multi-band or 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 reconfigurable three-band bandpass filter based on parallel resonators, aiming to solve the technical problem that the existing multi-frequency reconfigurable bandpass filters have insufficient reconfigurable flexibility and independence.

[0006] To achieve the above-mentioned purpose, the present invention provides a reconfigurable three-band bandpass filter based on a parallel resonator, comprising two pairs of resonators coupled respectively, wherein the first resonator is a pair of half-wavelength SIR step impedance resonators coupled to each other and opened outward, and varactor diodes are loaded in the middle and at the openings respectively; the second resonator is two UIR uniform impedance resonators coupled to each other at one end, and varactor diodes are loaded at the coupling end; the UIR uniform impedance resonators are arranged on both sides of the SIR step impedance resonator.

[0007] The high impedance microstrip line port of the SIR resonator is loaded with a varactor diode C v1 , the middle of the SIR resonator low impedance line is loaded with a varactor diode C v2 , the UIR resonator port is loaded with a varactor diode C v3 .

[0008] The first passband resonance frequency is changed by changing the bias voltage 3 of the UIR resonator, and the second and third passband resonance frequencies are changed by changing the bias voltages 1 and 2 of the SIR resonator.

[0009] Among them, the loaded DC blocking capacitor, fixed capacitor and inductor in the structure are grounded.

[0010] The present invention provides a reconfigurable three-band bandpass filter based on a parallel resonator. The three-band reconfigurable bandpass filter is designed based on a parallel resonator method. Specifically, a pair of UIR resonators and a pair of SIR resonators are coupled together to form three passbands of the filter, and then a varactor diode and a fixed capacitor are loaded. The first passband center frequency can be tuned by adjusting a bias voltage 3, and the second and third passband frequencies can be tuned by adjusting bias voltages 1 and 2. At the same time, a DC blocking capacitor and an inductor grounding are loaded to improve the independence of adjusting the center frequency of each passband, so as to realize that the three-band center frequency of the bandpass filter can be independently reconstructed. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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.

[0012] Figure 1 It is a structural schematic diagram of a reconfigurable three-band bandpass filter based on parallel resonators of the present invention.

[0013] Figure 2 It is a structural schematic diagram of the triple-frequency reconfigurable filter resonator structure of the present invention.

[0014] Figure 3 It is a schematic diagram of an equivalent circuit of a UIR structure loaded with a varactor diode according to the present invention.

[0015] Figure 4 It is a schematic diagram of the structure of the SIR multi-mode resonator loaded with a varactor diode according to the present invention.

[0016] Figure 5 Schematic diagram of the even and odd mode equivalent circuit of the SIR structure loaded with a varactor diode according to the present invention, (a) odd mode; (b) even mode.

[0017] Figure 6 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 .

[0018] Figure 7 In the specific embodiment of the present invention, under different C2 conditions, the variable capacitance diode Cv2 Schematic diagram of the impact on f2 and f3.

[0019] Figure 8 These are the electric field diagrams of the resonator at different frequencies in a specific embodiment of the present invention, (a) 2.24 GHz; (b) 3.5 GHz; (c) 5.07 GHz.

[0020] Fig. 9 Schematic diagram of a simulation model of a three-band reconfigurable filter according to a specific embodiment of the present invention, (a) top layer; (b) bottom layer.

[0021] Fig.10 It is a topological structure diagram of a three-band reconfigurable filter according to a specific embodiment of the present invention.

[0022] Fig.11 Schematic diagram of the influence of the resonator coupling length and coupling distance on the coupling coefficient k1 in a specific embodiment of the present invention, (a) the influence of the coupling length on the coupling coefficient k1; (b) the influence of the coupling distance on the coupling coefficient k1.

[0023] Fig.12 Schematic diagram of the variation curves of coupling coefficients k2 and k3 with SIR coupling distance g6 in a specific embodiment of the present invention, (a) the variation curve of k2 with g6; (b) the variation curve of k3 with g6.

[0024] Fig.13 Simulated S-parameter diagram of a triple-band reconfigurable filter in a specific embodiment of the present invention.

[0025] Fig.14 The S parameter simulation and measurement comparison diagram of the three-band reconfigurable filter of the specific embodiment of the present invention is shown in (a) v3 ; (b) Adjust C v1 ; (c) Regulation C v2 . DETAILED DESCRIPTION

[0026] 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.

[0027] The following is an explanation of some of the English term abbreviations that appear in this application:

[0028] SIR: stepped-impedance resonator, stepped impedance resonator.

[0029] UIR: uniform-impedance resonator, uniform impedance resonator.

[0030] See also Figures 1 to 5 The present invention provides a reconfigurable three-band bandpass filter based on parallel resonators, including two pairs of resonators coupled respectively, the first resonator is a pair of half-wavelength SIR step impedance resonators coupled to each other and opened outward, and varactor diodes are loaded in the middle and at the opening respectively; the second resonator is two UIR uniform impedance resonators coupled to each other at one end, and a varactor diode is loaded at the coupling end; the UIR uniform impedance resonators are arranged on both sides of the SIR step impedance resonator.

[0031] The following is further described in conjunction with specific embodiments and structures:

[0032] The filter structure is as follows Figure 1 As shown in the figure, the structure consists of two parts: ① Located on the top of the dielectric substrate, a pair of mutually coupled half-wavelength SIR step impedance resonators with openings facing outwards, with varactor diodes loaded in the middle and at the openings of the resonator. ② Located on the top of the dielectric substrate and on both sides of the SIR resonator, C v1 , C v2 and C v3 There are three different varactor diodes, which are loaded at the SIR high impedance microstrip line port, the middle of the SIR resonator low impedance line and the UIR resonator port respectively.

[0033] The structure of the resonator is as follows Figure 2 As shown, Figure 2 The pink area in the middle is a pair of UIR structures loaded with varactor diodes. This structure is used to design the first passband of the filter. Its center frequency is f1, θ1 is the equivalent electrical length of the resonator length L1+L2+L3, and Y1 is its characteristic admittance. in Direction, its input admittance is:

[0034] Y in =Y1jtanθ1+j2πf1C v3

[0035] Let its imaginary part be 0, and the resonant frequency f1 can be calculated as:

[0036]

[0037] According to the formula, when the physical length of the resonator and the dielectric substrate are determined, θ1 is fixed and the resonant frequency f1 of the resonator is only affected by C v3 Therefore, changing the bias voltage 3 will change the resonant frequency of the first passband, thereby achieving the purpose of independently tuning the center frequency of the first passband. Figure 3 Schematic diagram of the equivalent circuit of the UIR structure loaded with a varactor diode.

[0038] Figure 2The middle blue area is the SIR multi-mode resonator structure loaded with a varactor diode, which is used to design the second and third passbands of the filter. Figure 4 As shown, a single resonator is also symmetrical about the central vertical plane. Therefore, according to the odd-even mode analysis method, its odd-mode equivalent circuit model and even-mode equivalent circuit model can be obtained, where θ2 and θ3 are the equivalent electrical lengths of the high impedance line length L4+L5+L6 and the low impedance line length L7 of the SIR multimode resonator, respectively, and Y2 and Y3 are the characteristic admittances of the high and low impedance microstrip lines of the SIR multimode resonator, respectively.

[0039] The odd and even mode equivalent circuits of the SIR structure loaded with a varactor diode are as follows: Figure 5 As shown in the figure, when odd-mode excitation is applied, the symmetry plane is equivalent to a short-circuit surface. in Looking in the direction, its odd-mode input admittance is:

[0040]

[0041] in,

[0042] When even-mode excitation is applied, the symmetry plane is equivalent to an open surface. in Looking from the direction, its even-mode input admittance is:

[0043]

[0044] in,

[0045] Let the imaginary part of the input admittance be 0, and we can get:

[0046]

[0047] From the above formula, it can be concluded that when the physical length of the resonator and the dielectric substrate are determined, the odd-mode resonant frequency of the resonator is only affected by C v1 The even-mode resonant frequency of the resonator is only affected by C v2 By changing the external bias voltage 1, 2, C v1 , C v2 The size of the filter can be adjusted independently to control the second and third passbands.

[0048] Furthermore, Figure 6 The resonator model is built in the electromagnetic simulation software for eigenmode simulation, and the scanning parameter C v1 , C v2 and C v3 As a result, it can be seen that C v1 Only affects the second passband center frequency, C v2 Only affects the third passband center frequency, Cv3 It almost only affects the center frequency of the first passband. The three passband center frequencies of the filter can be tuned independently, which verifies the correctness of the theory.

[0049] In addition to two types of varactor diodes, the SIR resonator is also loaded with a DC blocking capacitor C1 and a fixed capacitor C2. Figure 7 The results show that the capacitance of the variable capacitance diode C v2 The influence of f2 and f3. It can be seen that f2 is almost not affected by the fixed capacitor C2 and the variable capacitance diode C v2 This is consistent with the previous formula derivation. v2 In series state, C2 plays the role of limiting the total capacitance of the two. For the third center frequency f3, it can be seen from the figure that for a fixed C v2 , as C2 increases, f3 decreases continuously; for C v2 In the entire capacitance range, as C2 increases, the adjustable range of f3 becomes larger. However, due to the process limitations of the varactor diode used, the minimum capacitance that can be achieved is limited. Therefore, the value of the fixed capacitor C2 cannot be increased blindly. The filter indicators and the capacitance range of the varactor diode must be considered comprehensively.

[0050] Figure 8 The electric field diagram of the filter structure composed of a UIR resonator and a SIR resonator in parallel is shown. When the frequency is at the center frequency of the first passband (2.24 GHz), the resonance position is mainly located at the open end of the UIR resonator, as shown in Figure 8 (a) shows that when the frequency is at the center frequency of the second passband (3.5 GHz), the resonance position is mainly located at the high impedance microstrip arm of the SIR resonator, as shown in Figure 8 (b) When the frequency is at the third passband center frequency (5.07 GHz), the resonance position is mainly located near the connection between the high impedance microstrip line of the SIR resonator and C1 and the coupling between the low impedance lines, as shown in Figure 8 (c) It can be seen that the SIR resonator and the UIR resonator have little influence on each other.

[0051] The three-frequency independent reconfigurable bandpass filter of the present invention is designed by connecting the above-mentioned UIR resonator and SIR multimode resonator in parallel, and the center frequency reconstruction range is 2.2GHz-2.7GHz, 3.43GHz-3.53GHz and 5GHz-5.08GHz, and the bandwidth of each passband is 100MHz, 250MHz and 150MHz respectively. The varactor diode model used is SMV1413-079LF (C v3 )、SMV1430-040LF(C v1 ) and SMV1405-040LF(C v2 ). Fig. 9 is a simulation model of a reconfigurable three-band bandpass filter based on parallel resonators according to the present invention, Fig. 9 (a) shows the top layer 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 pink part is the two fixed capacitors C1 and C2. Fig. 9 (b) shows the bottom layer structure, which has eight rectangular slots. The six rectangular slots in the middle are used to introduce DC bias lines from the outside, and the two rectangular slots on the sides are used to strengthen the coupling excitation of the feed to the UIR resonator.

[0052] According to the indicators of each passband: f1 = 2.24GHz, BW1 = 100MHz; f2 = 3.5GHz, BW2 = 250MHz; f1 = 5.07GHz, BW3 = 150MHz. The ideal coupling coefficient required for each passband can be calculated, and the calculation results are as follows:

[0053] k1=k 1_12 =k 1_21 =FBW*m 12 =0.074

[0054] k3=k 3_12 =k 3_21 =FBW*m 12 =0.049

[0055] In the present invention, a pair of UIR resonators and a pair of SIR resonators are coupled together to form three passbands, and the strength of the coupling between a pair of resonators can be controlled by adjusting the coupling distance (g6 and g7) and coupling length between the resonators. Fig.11 The effect of the coupling length and coupling distance of the UIR resonator on the coupling coefficient k1. It can be seen from the figure that the larger the coupling length L3, the larger the coupling coefficient; the larger the coupling distance g7, the smaller the coupling coefficient. Reasonable selection of the values ​​of L3 and g7 can make the coupling coefficient k1 meet the required value. Fig.12 The figure shows the variation curves of coupling coefficients k2 and k3 with SIR coupling distance g6. It can be seen that the larger the coupling distance g6, the smaller the coupling coefficient k2, while the larger the coupling coefficient k3. Since there is only one adjustment parameter, coupling distance g6, it is difficult for coupling coefficients k2 and k3 to meet the ideal conditions at the same time. The present invention selects a relatively compromise number when taking the value.

[0056] Fig.13 For the filter in C v1 =0.31pF, C v2 =0.63pF, C v3=3.1pF when the simulated S parameter diagram. The filter has five transmission zeros, four of which (Tz1, Tz2, Tz3, Tz5) are introduced by source-load coupling, and one (Tz4) is introduced by cross-coupling between SIR resonators. The five transmission zeros greatly improve the frequency selectivity of the filter.

[0057] Fig.14 The following is a comparison of the simulation and actual measurement of the filter, where (a) is the S parameter comparison of the filter when Cv3 is adjusted; (b) is the S parameter comparison of the filter when Cv1 is adjusted; (c) is the S parameter comparison of the filter when Cv2 is adjusted. From the results, it can be seen that the three passband center frequencies of the filter can be independently tuned.

[0058] In a specific embodiment, the size of the entire filter is 30mm*22mm (0.36λ g *0.27λ g ), the effective area is 16.9mm*15.7mm(0.21λ g *0.19λ g ). g is the waveguide wavelength corresponding to the first center frequency.

[0059] 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 reconfigurable three-band bandpass filter based on parallel resonators, characterized in that: The invention comprises two pairs of resonators coupled respectively. The first resonator is a pair of half-wavelength SIR step impedance resonators coupled to each other and opened outward, and variable capacitance diodes are loaded in the middle and at the opening respectively. The second resonator is two UIR uniform impedance resonators coupled to each other at one end, and a variable capacitance diode is loaded at the coupling end. The UIR uniform impedance resonators are arranged on both sides of the SIR step impedance resonator.

2. The reconfigurable three-band bandpass filter based on parallel resonators according to claim 1, characterized in that: The high impedance microstrip line port of the SIR resonator is loaded with a varactor diode C v1 , the middle of the SIR resonator low impedance line is loaded with a varactor diode C v2 , the UIR resonator port is loaded with a varactor diode C v3 .

3. The reconfigurable triple-band bandpass filter based on parallel resonators according to claim 2, characterized in that: The first passband resonance frequency is changed by changing the bias voltage 3 of the UIR resonator, and the second and third passband resonance frequencies are changed by changing the bias voltages 1 and 2 of the SIR resonator.

4. The reconfigurable triple-band bandpass filter based on parallel resonators as claimed in claim 3, characterized in that: The loading blocking capacitors, fixed capacitors and inductors in the structure are grounded.

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