CN107689785A - A kind of switch filter - Google Patents

Abstract

The invention discloses a switch filter, which includes a switch resonator, N first switch resonators and M second switch resonators; the switch resonator performs first-stage processing and output to the received electromagnetic wave signal through resonance, The switched resonator has two resonant frequencies, and realizes the switching and transmission of electromagnetic wave signals at the two resonant frequencies, wherein the two resonant frequencies are recorded as the first resonant frequency and the second resonant frequency; The first resonant frequency performs p+1-th stage processing on the received electromagnetic wave signal and outputs it; the qth second switch resonator is used to perform q+1-th stage processing on the received electromagnetic wave signal by resonating at the second resonant frequency and output it. The design method of switching filters in different frequency bands sharing the first-stage switching resonator can greatly reduce the size of the switching filter, simplify its structure and reduce the insertion loss.

Description

a switch filter

technical field

The invention belongs to the technical field of filters, and more specifically relates to a single-pole double-throw asymmetric switch filter.

Background technique

In the post-stage of a traditional broadband radio frequency antenna, in order to realize the time division multiplexing of the antenna, it is often necessary to connect a single-pole multi-throw radio frequency switch first, and cascade a bandpass filter after the switch. In order to improve the integration of the system, reduce the size and the overall insertion loss, people design the switch and the filter as a whole, which is the switching filter.

Traditional switching filters working in different frequency bands are generally composed of two single-pole single-throw switching filters. Compared with the cascaded RF switch and band-pass filter, the switching filter of different frequency bands composed of this structure The design improves the integration of the system and reduces the overall volume and insertion loss. However, this switching filter using two single-pole single-throw switches needs to design a corresponding isolation structure between the two single-pole single-throw switching filters, so the degree of miniaturization of the system is not enough.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a switching filter, the purpose of which is to solve the problems in the prior art by combining two single-pole single-throw switching filters with a specific structure for improving isolation. The switching filter causes a technical problem of large size of the switching filter.

To achieve the above object, the present invention provides a switching filter, comprising:

One switching resonator, N first switching resonators and M second switching resonators; the switcher has two output terminals and one input terminal, the first switching resonator has one input terminal and one output terminal, and the second switching resonator has two output terminals and one input terminal. The second switching resonator is provided with an input end and an output end;

The N first switching resonators are denoted as the first first switching resonator, the second first switching resonator, ... and the Nth first switching resonator; the M second switching resonators are denoted as the first the second switched resonator, the 2nd second switched resonator, ... and the Mth second switched resonator;

The first output terminal of the switching resonator is coupled and connected to the input terminal of the first first switching resonator, the second output terminal of the switching resonator is coupled and connected to the input terminal of the first second switching resonator, and the i-th first switching resonator The output terminal is coupled and connected to the input terminal of the i+1 first switching resonator, and the output terminal of the j second switching resonator is coupled and connected to the input terminal of the j+1 second switching resonator; wherein, 1≤i≤ N-1, 1≤j≤M-1;

The switched resonator performs first-level processing and output on the received electromagnetic wave signal through resonance. The switched resonator has two resonant frequencies to realize switching and transmission of electromagnetic wave signals at the two resonant frequencies; where the two resonant frequencies are recorded as the first resonance frequency and the second resonant frequency;

The p-th first switch resonator is used to perform p+1-th stage processing on the received electromagnetic wave signal by resonating at the first resonance frequency and output it;

The qth second switching resonator is used to perform q+1-th stage processing on the received electromagnetic wave signal by resonating at the second resonant frequency and output it, wherein, 1≤p≤N, 1≤q≤M.

Preferably, the first switching resonator can also generate another frequency of resonance, denoted as the third resonance frequency, the third resonance frequency is far away from the first resonance frequency and at the same time far away from the second resonance frequency, when the first switching resonator works at the first At three resonant frequencies, signal transmission from the first switched resonator can be prevented.

Preferably, the second switching resonator can also generate resonance at another frequency, which is denoted as the fourth resonance frequency. The fourth resonance frequency is far away from the first resonance frequency and at the same time far from the second resonance frequency. When the second switching resonator works at the first At four resonant frequencies, signal transmission from the second switched resonator can be prevented.

Preferably, the switched resonator includes a first microstrip, a first diode and a first capacitor;

The first end of the first microstrip is grounded, the middle part of the first microstrip is connected to the cathode of the first diode, the anode of the first diode is connected to one end of the first capacitor, and the other end of the first capacitor is grounded; the second end of the first microstrip serves as switch the input of the resonator;

When the diode is turned on, only the first microstrip between the non-grounded end of the first microstrip and the negative connection section of the diode constitutes a resonant circuit, so that the switching resonator works at the first resonance frequency. When the diode is cut off, all the first microstrip The strips form a resonant circuit, so that the switched resonator operates at the second resonant frequency.

Preferably, the switch filter also includes an input capacitor and an input microstrip, the first end of the input microstrip is used as the input end of the switch filter, the second end of the input microstrip is connected to one end of the input capacitor, and the other end of the input capacitor is connected to the first end of the microstrip The second end is connected, and the input capacitor, the first microstrip, the first diode and the first capacitor form an input impedance matching network and an L-shaped capacitive load resonator.

Preferably, the first switched resonator includes a second microstrip, a second diode, a second capacitor and a third capacitor;

The first end of the second microstrip is grounded, the second end of the second microstrip is connected to the cathode of the second diode, one end of the third capacitor is connected to the second end of the second microstrip, and the anode of the second diode is connected to one end of the second capacitor Connect, the other end of the second capacitor is grounded; the other end of the third capacitor is grounded; the second capacitor value is much larger than the third capacitor value;

When the second diode is turned off, the second microstrip and the third capacitor form a capacitive load resonator, working at the first resonant frequency; when the second diode is turned on, the second microstrip, the second capacitor and The third capacitor constitutes a capacitive load resonator and works at the third resonant frequency.

Preferably, the second switched resonator includes a third microstrip, a third diode, a fourth capacitor and a fifth capacitor;

The first end of the third microstrip is grounded, the second end of the third microstrip is connected to the cathode of the third diode, one end of the fifth capacitor is connected to the second end of the third microstrip, and the anode of the third diode is connected to one end of the fourth capacitor Connect, the other end of the fourth capacitor is grounded; the other end of the fifth capacitor is grounded; the fourth capacitor value is much larger than the fifth capacitor value;

When the third diode is turned off, the third microstrip and the fifth capacitor form a capacitive load resonator, working at the second resonant frequency; when the third diode is turned on, the third microstrip, the fourth capacitor and The fifth capacitor constitutes a capacitive resonator and works at the fourth resonant frequency.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

The invention provides a microstrip single-pole double-throw switch filter with small size and low loss that combines a band-pass filter and a radio frequency control switch and works in different frequency bands. By making two single-pole single-throw switching filters working in different frequency bands share the first-stage resonator with switchable frequency, it solves the need to design a corresponding isolation structure between the two switching filters in different frequency bands, resulting in system insertion loss , a technical issue where size increases affect system performance. Compared with similar designs, the variable frequency resonator used in the present invention has the advantages of small volume and low insertion loss. The invention can work between various wide-band antennas and two radio frequency transceivers of different frequency bands, can realize the time division multiplexing function between the two radio frequency transceivers, and has very wide applicability.

Description of drawings

Fig. 1 is the circuit model of the switching filter that the present invention provides;

Fig. 2 is the coupling model of off filter that the present invention provides;

Fig. 3 is the circuit model of input capacitor and switched resonator provided by the present invention;

Fig. 4 is the equivalent transmission line model of input capacitor and switched resonator provided by the present invention;

Fig. 5 is the equivalent positive and negative capacitance structures of the input capacitance and the switched resonator provided by the present invention;

FIG. 6 is a diagram of an input capacitance and a switched resonator provided by the present invention using positive and negative equivalent capacitances to construct an admittance converter and a capacitive load;

Fig. 7 is the S parameter measurement diagram when the 2.35GHz branch circuit of the switching filter embodiment provided by the present invention is working;

Fig. 8 is a measurement diagram of S parameters when the 3.5 GHz branch of the switching filter embodiment provided by the present invention is working.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The present invention provides a switching filter including a switching resonator, N first switching resonators, and M second switching resonators; wherein, the N first switching resonators are denoted as the first first switching resonator, the first switching resonator, and the second switching resonator. 2 first switching resonators, ... and the Nth first switching resonator; the M second switching resonators are denoted as the 1st second switching resonator, the 2nd second switching resonator, ... and The Mth second switched resonator.

The first output terminal of the switching resonator is coupled and connected to the input terminal of the first first switching resonator, the second output terminal of the switching resonator is coupled and connected to the input terminal of the first second switching resonator, and the i-th first switching resonator The output terminal is coupled and connected to the input terminal of the i+1 first switching resonator, and the output terminal of the j second switching resonator is coupled and connected to the input terminal of the j+1 second switching resonator; wherein, 1≤i≤ N-1, 1≤j≤M-1.

The electromagnetic wave signal is transmitted into the switching resonator through the input capacitor, and the switching resonator realizes the first-stage filtering and output of the electromagnetic wave signal through resonance. The switching resonator has two resonance frequencies, which are recorded as the first resonance frequency and the second resonance frequency. When the switching resonance When the switch works at the first resonant frequency, it can output an electromagnetic wave signal with a frequency of the first resonant frequency; when the switcher works at the second resonant frequency, it can output an electromagnetic wave signal with a frequency of the second resonant frequency, thereby realizing two frequency electromagnetic waves Signal transmission: the first first switching resonator resonates at the first resonant frequency, and is used to receive the electromagnetic wave signal output by the switching resonator, and perform second-stage filtering and output, and the s first switching resonator resonates at the first The resonant frequency is used to receive the electromagnetic wave signal output by the s-1th first switching resonator, perform s+1 stage filtering and output the electromagnetic wave signal; where 2≤s≤N. Similarly, the first second switching resonator resonates at the second resonant frequency, and is used to receive the electromagnetic wave signal output by the switching resonator, and perform second-stage filtering and output through resonance. The t-th second switching resonator also resonates at the second resonance frequency, and is used to receive the electromagnetic wave signal output by the t-1-th first switching resonator, and perform t+1 stage filtering through resonance and output a corresponding signal, 2≤t≤M.

The switching filter provided by the present invention comprises a switching resonator and N first switching resonators to form a first filter, a switching resonator and M second switching resonators to form a second filter, and the switching filter is expected to output electromagnetic waves When the signal frequency is the first resonant frequency, the filter output of the electromagnetic wave signal is realized by the first filter, and the second filter is cut off. When the switching filter is expected to output the electromagnetic wave signal frequency as the second resonant frequency, the electromagnetic wave signal is realized by the second filter The filter rate output, the first filter cutoff. The purpose is to reduce system insertion loss and reduce the size of the switching filter by making two switching filters working in different frequency bands share a switching resonator. In addition, multiple resonators are used to form a filter to improve the frequency selectivity of the filter.

The invention provides a design example of a single-pole double-throw small-size low-insertion-loss asymmetric switch filter working at 2.35GHz and 3.5GHz. It is input from a common port, and the two frequency bands are output from independent output ports. Through the voltage control port provided by itself, the corresponding control voltage is provided for the PIN diode, and the working status of the two corresponding frequency bands of the switching filter can be switched.

First, by selecting the length of the two transmission lines of the L-shaped microstrip line and matching the capacitance of the capacitive load, the low-frequency resonant frequency of the switchable frequency resonator discussed above is 2.35GHz, and the high-frequency frequency is 3.5GHz. In order to further simplify the structure of the system, an admittance converter composed of capacitors is designed and constructed between the input end and the first-stage resonator for matching the input impedance. Through calculation, the admittance converter can be connected in parallel to The capacitance of the negative capacitance of the ground is equal to the capacitive load value of the L-shaped capacitive load resonator, thereby canceling these two capacitances. Therefore, an input matching network and an L-shaped capacitive load resonator can be formed by using a series input coupling capacitor and an L-shaped microstrip line. Then add two other capacitive load resonators corresponding to the frequency of the branch to each branch for interdigital coupling design, so as to form a switching filter corresponding to the frequency band in each branch.

Fig. 1 is the circuit model of the switching filter embodiment that the present invention provides, and switching filter comprises a switching resonator, 2 first switching resonators, 2 second switching resonators, an input capacitor C1, an input microstrip , an output capacitor C12 and an output microstrip. The switched resonator is composed of an L-shaped terminal short-circuited microstrip line and a control circuit arranged at the corner of the L-shaped microstrip line. The L-shaped terminal short-circuited microstrip line is the first microstrip , the control circuit includes a high-frequency PIN diode D3 and a first capacitor C7 connected in series, wherein the high-frequency PIN diode D3 is the first diode, and the function of the first capacitor C7 is to block direct current, so that it is convenient for the first diode Provide the corresponding bias. The corner of the L-shaped microstrip line is connected to the cathode of the high-frequency PIN diode D3, the anode of the high-frequency PIN diode D3 is connected to one end of the first capacitor C7, and the other end of the first capacitor C7 is grounded. Capacitive load resonator composed of control circuit and L-terminated microstrip line.

The resonant frequency of the switched resonator can be switched between 2.35GHz and 3.5GHz:

When the PIN diode is off, the switched resonator can be regarded as a long-terminal short-circuit microstrip line. The reason is that when the PIN diode is off, it can be equivalent to a capacitor with a very small capacitance (0.15pf), which is for The AC signal impedance is very large. For the convenience of understanding, from an approximate point of view, the control circuit can be regarded as an open circuit. Therefore, the electrical length of the long-terminal short-circuit microstrip line at this time can be regarded as the length of the L-shaped terminal short-circuit microstrip line. total length. At this time, the resonant frequency of the entire resonator is at a lower frequency, that is, it works at 2.35 GHz.

When the PIN diode is turned on, the switched resonator can be regarded as a short-circuited microstrip line with a short electrical length. The reason is that when the PIN diode is turned on, it can be equivalent to a small on-resistance (1.5Ω ), and compared with the latter section of the L-terminated short-circuited microstrip line, its impedance is much smaller than the latter section of the microstrip line, so it can be approximated that the signal basically does not pass through the latter section of the L-terminated short-circuited microstrip line. Therefore, at this time, the electrical length of the short-circuited microstrip line with shorter electrical length can be regarded as the electrical length of the previous segment of the L-shaped short-circuited microstrip line. At this time, the resonant frequency of the resonator is at a higher frequency, that is, it works at 3.5 GHz.

The first first switched resonator includes a second microstrip, a second diode D2, a second capacitor C5 and a third capacitor C6. Wherein, the first end of the second microstrip is grounded, the second end of the second microstrip is connected to the cathode of the second diode D2, the anode of the second diode D2 is connected to one end of the second capacitor C5, and the other end of the second capacitor C5 is grounded ; One end of the third capacitor C6 is connected to the second end of the second microstrip, and the other end of the third capacitor C6 is grounded; the value of the second capacitor C5 is much larger than the value of the third capacitor C6.

When the second diode D2 is cut off, the second microstrip and the third capacitor C6 form a capacitive resonator, working at the first resonance frequency (2.35GHz); when the second diode D2 is turned on, the second microstrip The band, the third capacitor C6 and the second capacitor C5 form a resonator. Since the diode D2 is followed by a larger capacitor C5, the value of the capacitive load is greatly increased, and the resonant frequency changes greatly, and it works at the third resonant frequency. , without specific design, the third resonant frequency is far away from the first resonant frequency and away from the second resonant frequency (3.5 GHz), so as to suppress the passage of the electromagnetic wave signal at the second resonant frequency.

The second first switched resonator has the same structure as the first switched resonator, consisting of a second microstrip, a second diode D1, a second capacitor C4 and a third capacitor C3, and works at the first resonance frequency or the third resonant frequency.

The first and second switched resonators include a third microstrip, a third diode D4, a fourth capacitor C8 and a fifth capacitor C9;

The first end of the third microstrip is grounded, the second end of the third microstrip is connected to the cathode of the third diode D4, the anode of the third diode D4 is connected to one end of the fourth capacitor C8, and the other end of the fourth capacitor C8 is grounded; One end of the fifth capacitor C9 is connected to the second end of the third microstrip, and the other end of the fifth capacitor C9 is grounded; the resistance value of the fourth capacitor C8 is much greater than the value of the fifth capacitor C9;

When the third diode D4 is turned off, the third microstrip and the fifth capacitor C9 form a resonator, working at the second resonant frequency; when the third diode D4 is turned on, the third microstrip, the fourth capacitor C8 And the fifth capacitor C9 constitutes a capacitive resonator, wherein since the capacitance of the fourth capacitor C8 is much larger than that of C9, its resonant frequency changes greatly and works at the fourth resonant frequency.

The structure of the second second switching resonator is the same as that of the first second switching resonator, and the second second switching resonator includes a third microstrip, a third diode D5, a fourth capacitor C10 and a first Five capacitors C11. The second second switched resonator works at the second resonant frequency or the fourth resonant frequency.

In the switching filter provided by the present invention, the electromagnetic wave signal is input from Port1, and there are two paths through which the electromagnetic wave signal can pass, respectively Port1→Port2 and Port1→Port3. Each path passes through three capacitively loaded resonators.

Fig. 2 is a coupling model of the switching filter provided by the present invention, R1, R2, R3, R4, R5 respectively correspond to five resonators of the filter. When the corresponding 2.35GHz filter branch in Figure 1 is working, that is, D1, D2, and D3 are cut off; when D4 and D5 are turned on, the filter can be regarded as composed of input coupling capacitors, R1, R2, R3, and output coupling capacitors. , at this time, the above three resonators all resonate at 2.35GHz to form a third-order bandpass filter. When D1, D2, and D3 are turned on; when D4 and D5 are turned off, the filter is composed of input coupling capacitors, R1, R4, R5, and output coupling capacitors. At this time, because D3 is turned on, the resonance frequency of R1 is increased to 3.5 GHz, so that the three resonators all resonate at 3.5GHz to form a bandpass filter with a center frequency of 3.5GHz.

Fig. 3 is the circuit model of the input capacitor provided by the present invention and the switched resonator; Fig. 4 is the equivalent transmission line model of the input capacitor provided by the present invention and the switched resonator; The equivalent transmission line model is according to the equivalent shown in Fig. 5 , that is, between the coupling capacitor C ₁ and the short-circuited microstrip line at the terminal, two capacitors connected in parallel to the ground with the capacitance values C _R and _-CR respectively are equivalent. The equivalent is to make C ₁ , -C _R form an admittance converter, and the precondition for C _R and L-shaped microstrip line to form a resonator is to use related formulas for each branch of C ₁ , L-shaped microstrip line The electrical length of the circuit, the admittance of the L-shaped microstrip line and the relative bandwidth of the filter to be formed are carefully mathematically calculated to make it meet the requirements of the admittance converter and the resonator at the same time.

Figure 6 specifically shows the division of the actual modules of the admittance converter and the resonator after the equivalent, that is, the capacitor C ₁ and _{-CR form an admittance converter for impedance matching, and the capacitor C R connected} in parallel to the ground and the terminal The shorted microstrip line forms a capacitively loaded resonator. It is easy to know that when the diode D ₃ is cut off, the electrical length of the terminal short-circuited microstrip line is θ ₁₁ + θ ₁₂ , and the resonant frequency of the capacitive load resonator formed by it and C _R is at a low frequency of 2.35GHz; when the diode D ₃ is turned on , the electrical length of the terminal short-circuited microstrip line is approximately θ ₁₁ , and the resonator frequency of the capacitive load resonator formed by it and C _R is at a high frequency, namely 3.5GHz.

Carry out relevant tests to this embodiment, as shown in Figure 7, the S parameter measurement result when the 2.35GHz branch is turned on, S11 reflects the return loss of the 2.35GHz branch, its center frequency is at 2.34GHz, and the return loss is - 27dB, the system impedance matching performance is good. S21 reflects the insertion loss of the 2.35GHz branch, its center frequency is located at 2.35GHz, and the insertion loss is 1.3dB. S31 is the suppression situation of closing the 3.5GHz branch at this time, and the suppression is greater than 20dB in the frequency range from DC to 9GHz. As shown in Figure 8, the S parameter measurement results when the 3.5GHz branch is turned on, S11 reflects the return loss of the 3.5GHz branch, its center frequency is at 3.5GHz, the return loss is -28dB, and the system impedance matching performance is good. At this time, it can be seen from S31 that the 3.5GHz branch filter is working normally, and the insertion loss is about 134dB. From S21, it can be seen that the 2.35GHz branch filter is blocked at this time, and its suppression is higher than 20dB in 0-7GHz.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention can simplify the SPDT filter by applying the frequency variable resonator proposed by the present invention in the design of the SPDT switch filter. The overall structure of the filter makes the design of the two filters more compact, greatly reducing the overall size of the system, and eliminating the insertion loss caused by unnecessary structures.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (7)

1. A switch filter, characterized in that, comprising: One switching resonator, N first switching resonators and M second switching resonators; the switching resonator is provided with two output terminals and one input terminal, and the first switching resonator is provided with one input terminal and one output terminal, The second switching resonator has an input terminal and an output terminal; The N first switching resonators are denoted as the first first switching resonator, the second first switching resonator, ... and the Nth first switching resonator; the M second switching resonators are denoted as the first the second switched resonator, the 2nd second switched resonator, ... and the Mth second switched resonator; The first output terminal of the switching resonator is coupled and connected to the input terminal of the first first switching resonator, the second output terminal of the switching resonator is coupled and connected to the input terminal of the first second switching resonator, and the i-th first switching resonator The output terminal is coupled and connected to the input terminal of the i+1 first switching resonator, and the output terminal of the j second switching resonator is coupled and connected to the input terminal of the j+1 second switching resonator; wherein, 1≤i≤ N-1, 1≤j≤M-1; The switched resonator performs first-stage filtering and output to the electromagnetic wave signal received by the input terminal by generating resonance. The switched resonator has two resonant frequencies to realize switching and transmission of electromagnetic wave signals at two resonant frequencies; where the two resonant frequencies are recorded as a first resonant frequency and a second resonant frequency; The p-th first switching resonator is used to generate resonance with a frequency of the first resonant frequency, perform p+1-stage filtering processing on the electromagnetic wave signal received at its input end and output it through the output end; The qth second switching resonator is used to generate resonance with the frequency of the first resonance frequency, perform q+1-th stage filtering on the electromagnetic wave signal received at the input end and output it through the output end, wherein, 1≤p≤N, 1≤q ≤M. 2. The switching filter according to claim 1, wherein the first switching resonator can also produce another frequency resonance, which is denoted as the third resonance frequency, and the third resonance frequency is far away from the first resonance frequency and at the same time The second resonant frequency prevents signal transmission from the first switched resonator when the first switched resonator operates at the third resonant frequency. 3. The switching filter according to claim 1 or 2, wherein the second switching resonator can also generate another frequency resonance, which is denoted as the fourth resonance frequency, and the fourth resonance frequency is far away from the first resonance frequency Simultaneously away from the second resonant frequency, when the second switched resonator operates at the fourth resonant frequency, signal transmission from the second switched resonator can be prevented. 4. The switched filter according to any one of claims 1 to 3, wherein the switched resonator comprises a first microstrip, a first diode and a first capacitor; The first end of the first microstrip is grounded, the middle part of the first microstrip is connected to the cathode of the first diode, the anode of the first diode is connected to one end of the first capacitor, and the other end of the first capacitor is grounded; the second end of the first microstrip serves as switch the input of the resonator; When the diode is turned on, only the first microstrip between the non-grounded end of the first microstrip and the negative connection section of the diode constitutes a resonant circuit, so that the switching resonator works at the first resonance frequency. When the diode is cut off, all the first microstrip The strips form a resonant circuit, so that the switched resonator operates at the second resonant frequency. 5. The switching filter according to any one of claims 1 to 4, wherein the switching filter also includes an input capacitor and an input microstrip, the first end of the input microstrip is used as the input end of the switching filter, and the input microstrip The second end of the strip is connected to one end of the input capacitor, and the other end of the input capacitor is connected to the second end of the first microstrip. The input capacitor, the first microstrip, the first diode and the first capacitor form an input impedance matching network and an L-type capacitor. sex-loaded resonators. 6. The switched filter according to any one of claims 1 to 5, wherein the first switched resonator comprises a second microstrip, a second diode, a second capacitor and a third capacitor; The first end of the second microstrip is grounded, the second end of the second microstrip is connected to the cathode of the second diode, one end of the third capacitor is connected to the second end of the second microstrip, and the anode of the second diode is connected to one end of the second capacitor Connect, the other end of the second capacitor is grounded; the other end of the third capacitor is grounded; the second capacitor value is much larger than the third capacitor value; When the second diode is turned off, the second microstrip and the third capacitor form a capacitive load resonator, working at the first resonant frequency; when the second diode is turned on, the second microstrip, the second capacitor and The third capacitor constitutes a capacitive load resonator and works at the third resonant frequency. 7. The switched filter according to any one of claims 1 to 6, wherein the second switched resonator comprises a third microstrip, a third diode, a fourth capacitor and a fifth capacitor; The first end of the third microstrip is grounded, the second end of the third microstrip is connected to the cathode of the third diode, one end of the fifth capacitor is connected to the second end of the third microstrip, and the anode of the third diode is connected to one end of the fourth capacitor Connect, the other end of the fourth capacitor is grounded; the other end of the fifth capacitor is grounded; the fourth capacitor value is much larger than the fifth capacitor value; When the third diode is turned off, the third microstrip and the fifth capacitor form a capacitive load resonator, which works at the second resonant frequency; when the third diode is turned on, the third microstrip, the fourth capacitor and the The fifth capacitor constitutes a capacitive load resonator and works at the fourth resonant frequency.