High-isolation low-loss absorption type single-pole four-throw switch circuit and circuit optimization method

Abstract

The invention discloses a high-isolation low-loss absorption type single-pole four-throw switch circuit and a circuit optimization method, and the high-isolation low-loss absorption type single-pole four-throw switch circuit comprises four radio frequency paths which are connected in parallel on an input end common branch and have the same structure, namely a first radio frequency path, a second radio frequency path, a third radio frequency path and a fourth radio frequency path, the first radio frequency path and the second radio frequency path are symmetrically arranged relative to the input end common branch, the third radio frequency path and the fourth radio frequency path are symmetrically arranged relative to the input end common branch, each of the first radio frequency path, the second radio frequency path, the third radio frequency path and the fourth radio frequency path comprises three switch parallel branches which are connected in series, and for each radio frequency path, the switch parallel branches are connected in parallel. And the switch parallel branch which is connected in series in the middle of the three switch parallel branches is connected in series with a resonant capacitor to the ground. A resonant capacitor to the ground is introduced into a switch parallel branch, so that an isolation curve has a resonance point in a band, the isolation performance of the switch is greatly improved, and meanwhile, the loss of the switch is ensured not to deteriorate.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave and millimeter wave, and particularly to a high-isolation low-loss absorptive single-pole four-throw switch circuit and a circuit optimization method. Background Art

[0002] In modern communication fields and electronic measurement fields, absorptive single-pole four-throw switches have extensive applications. The design of an absorptive single-pole four-throw switch is a device for switching RF (radio frequency) signal paths. Its core function is to switch a common port (single-pole) to one of four selectable ports (four-throw), and at the same time, through an absorptive design, ensure that the signals of unselected ports are absorbed by the load rather than reflected, ensuring good matching of unselected ports, thereby improving system performance. Currently, it is widely used in base station antenna switching, multi-band selection, signal redundancy backup, multi-channel signal switching, beamforming networks, and multi-port calibration of vector network analyzers (VNA), and automated test equipment (ATE).

[0003] Isolation represents the signal attenuation degree between the input end and the output end of the switch in the off state, reflecting the ability of the switch to block signals. In high-frequency communication systems (such as radar and communication), to prevent signal leakage and ensure that the receiving end is not interfered, there are relatively high requirements for the isolation of the switch. Insertion loss refers to the attenuation of the signal when the switch is in the on state, and the smaller the insertion loss value, the better. In the signal chain, the loss needs to be minimized to maintain the signal-to-noise ratio, such as in the RF front-end or test equipment. Isolation is for the off state, and loss is for the on state. Isolation and loss together determine the signal processing ability of the switch.

[0004] The absorptive design mainly matches the unselected ports through a load. The load size is generally 50 ohms. By matching the load, reflection can be avoided, and the voltage standing wave ratio (VSWR) and signal interference can be reduced. Generally, the isolation of the switch can be improved by increasing the number of shunt-to-ground switch tubes on the branch, but usually, the loss of the switch will increase. Currently, while reducing the loss of the absorptive single-pole four-throw switch, the isolation is limited. How to further improve the isolation of the switch is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-isolation low-loss absorptive single-pole four-throw switch circuit, introducing a resonant capacitor to ground in the parallel branch of the switch, so that a resonant point appears in the isolation curve within the band, greatly improving the isolation performance of the switch, and at the same time ensuring that the loss of the switch will not deteriorate.

[0006] To achieve the above purpose, the present application provides the following solutions: On the one hand, the present invention provides a high-isolation and low-loss absorptive single-pole four-throw switch circuit, which includes four radio frequency paths with the same structure and connected in parallel on the common branch of the input end, namely: the first radio frequency path, the second radio frequency path, the third radio frequency path, and the fourth radio frequency path. Among them, the first radio frequency path and the second radio frequency path are symmetrically arranged with respect to the common branch of the input end, and the third radio frequency path and the fourth radio frequency path are symmetrically arranged with respect to the common branch of the input end. The first radio frequency path, the second radio frequency path, the third radio frequency path, and the fourth radio frequency path each include three series-connected switch parallel branches, and for each radio frequency path, a resonant capacitor to ground is connected in series on the middle switch parallel branch among the three switch parallel branches.

[0007] In some specific embodiments, each radio frequency path further includes a first switch parallel branch, a second switch parallel branch, and a third switch parallel branch connected in series, and an output series switch connected in series with the third switch parallel branch. A first microstrip line is connected in series between the first switch parallel branch and the second switch parallel branch, a second microstrip line is connected in series between the second switch parallel branch and the third switch parallel branch, the first switch parallel branch is connected in parallel to the common branch of the input end, and a third microstrip line is connected in series between the third switch parallel branch and the output series switch.

[0008] In some specific embodiments, the source of the output series switch is connected in series with a fourth microstrip line to serve as the output port of the radio frequency path. The drain of the output series switch is connected in series with the third microstrip line. An absorptive resistor is connected in parallel between the source and the drain of the output series switch, and the gate of the output series switch is connected to a gate resistor.

[0009] In some specific embodiments, the first switch parallel branch includes a first switch and a second switch that are symmetrically arranged and connected in parallel at the same point. The source of the first switch is connected in parallel to the common branch of the input end. The drains of the first switch and the second switch are connected in parallel at the same point. One end of the first microstrip line is connected in parallel between the drains of the first switch and the second switch. The source of the second switch is grounded, and the gates of the first switch and the second switch are respectively connected to gate resistors.

[0010] In some specific embodiments, the second switch parallel branch includes a first parallel-to-ground switch and a second parallel-to-ground switch that are symmetrically arranged and have their drains connected in parallel at the same point. Resonant capacitors to ground are respectively connected in series to the sources of the first parallel-to-ground switch and the second parallel switch. The gates of the first parallel-to-ground switch and the second parallel switch are respectively connected to gate resistors. One end of the second microstrip line and the other end of the first microstrip line are connected in parallel between the drains of the first parallel-to-ground switch and the second parallel switch.

[0011] In some specific embodiments, the third switch parallel branch includes a third parallel-to-ground switch and a fourth parallel-to-ground switch that are symmetrically arranged and have their drains paralleled at the same point. The sources of the third parallel-to-ground switch and the fourth parallel switch are grounded, and the gates of the third parallel-to-ground switch and the fourth parallel switch are respectively connected to gate resistors. The other end of the second microstrip line and one end of the third microstrip line are both paralleled between the drains of the third parallel-to-ground switch and the fourth parallel switch.

[0012] In some specific embodiments, the input common branch includes a fifth microstrip line and a sixth microstrip line. One end of the fifth microstrip line is connected to the RF input terminal, and the other end is paralleled between the first RF path and the second RF path. One end of the sixth microstrip line is paralleled between the first RF path and the second RF path, and the other end is paralleled between the third RF path and the fourth RF path.

[0013] In some specific embodiments, the length of the sixth microstrip line is less than that of the fifth microstrip line.

[0014] In a second aspect, the present application provides a circuit optimization method, including the following steps: S1. Construct the basic circuit topology of an absorptive single-pole four-throw switch circuit; The basic circuit topology includes four RF paths that are paralleled on the input common branch and have the same structure, namely: the first RF path, the second RF path, the third RF path, and the fourth RF path. Among them, the first RF path and the second RF path are symmetrically arranged with respect to the input common branch, the third RF path and the fourth RF path are symmetrically arranged with respect to the input common branch, and the first RF path, the second RF path, the third RF path, and the fourth RF path each include three series-connected switch parallel branches.

[0015] S2. Respectively set series-to-ground resonant capacitors on the three switch parallel branches of the basic circuit topology to obtain a first circuit structure; Simulate the first circuit structure within a set frequency range, and select the first RF path as the test path to obtain the test curve of the first circuit structure; S3. Only set series-to-ground resonant capacitors on each switch parallel branch of the basic circuit topology respectively to obtain a second circuit structure, a third circuit structure, and a fourth circuit structure; Respectively simulate the second circuit structure, the third circuit structure, and the fourth circuit structure within the set frequency range, and select the first RF path as the test path to respectively obtain the test curves corresponding to each circuit structure; the test curve of the third circuit structure and the test curve of the fourth circuit structure; S4. Compare the test curves corresponding to each circuit structure in sequence, and screen out the circuit structure corresponding to the optimal test curve to obtain a high-isolation and low-loss absorptive single-pole four-throw switch circuit in the first aspect. The first test curve, the second test curve, the third test curve, and the fourth test curve; In some specific implementation manners, the test curves include isolation curves, insertion loss curves, and input-output standing wave curves; the screening of the optimal test curve is as follows: screen out the curves that meet the preset threshold from the input-output standing wave curves of each circuit structure, and then analyze the change trends of the isolation curves in each circuit structure that meets the preset threshold. When the change trend meets the preset conditions, continue to screen out the test curve with the minimum insertion loss from the circuit structures that meet the preset conditions to obtain the test curve when the isolation curve meets the preset conditions and the insertion loss is the smallest.

[0016] The beneficial effects of the present invention are as follows: By increasing the number of switching tubes of the parallel switch, the isolation degree is increased, and a resonant capacitor connected to the ground is introduced at a suitable position in the switch parallel branch, so that a resonant point appears in the isolation curve within the band, greatly improving the isolation performance of the switch, and at the same time ensuring that the loss of the switch will not deteriorate. The output switches of the first RF path, the second RF path, the third RF path, and the fourth RF path are all connected in parallel with a 50-ohm resistor to achieve an absorptive function, and the switch path is switched by switching different control voltages. Description of the Drawings

[0017] Figure 1 Schematic diagram of the topological structure of the high-isolation and low-loss absorptive single-pole four-throw switch circuit provided by the embodiment of the present invention; Figure 2 Schematic diagram of the circuit structure of one of the RF paths provided by the embodiment of the present invention; Figure 3 Schematic diagram of the basic topological structure of the circuit provided by the embodiment of the present invention; Figure 4 Schematic diagram of the first circuit structure provided by the embodiment of the present invention; Figure 5 Based on Figure 4 of the circuit structure, simulation curves of the isolation degrees of RFC-RF2, RFC-RF3, and RFC-RF4 when the RFC-RF1 path is opened; Figure 6 Based on Figure 4 of the circuit structure, schematic diagram of the insertion loss dB(S(2,1)) curve of RFC-RF1 when the RFC-RF1 path is opened; Figure 7 Schematic diagram of the fifth circuit structure provided by the embodiment of the present invention; Figure 8For the circuit structure based on Figure 7 simulate the isolation degree simulation curves of RFC-RF2, RFC-RF3, and RFC-RF4 when the RFC-RF1 path is open; Figure 9 This is the schematic diagram of the second circuit structure provided by the embodiment of the present invention; Figure 10 For the circuit structure based on Figure 9 simulate the isolation degree simulation curves of RFC-RF2, RFC-RF3, and RFC-RF4 when the RFC-RF1 path is open; Figure 11 For the circuit structure based on Figure 9 simulate the schematic diagram of the insertion loss curve of RFC-RF1 when the RFC-RF1 path is open; Figure 12 For the third circuit structure, simulate the isolation degree simulation curves of RFC-RF2, RFC-RF3, and RFC-RF4 when the RFC-RF1 path is open; Figure 13 For the third circuit structure, simulate the schematic diagram of the insertion loss curve of RFC-RF1 when the RFC-RF1 path is open; Figure 14 For the fourth circuit structure, simulate the isolation degree simulation curves of RFC-RF2, RFC-RF3, and RFC-RF4 when the RFC-RF1 path is open. Specific embodiments

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0019] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0020] At the same time, it should be understood that for the convenience of description, the dimensions of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0021] In addition, descriptions of well-known structures, functions, and configurations may be omitted for clarity and conciseness. Those of ordinary skill in the art will recognize that various changes and modifications can be made to the examples described herein without departing from the spirit and scope of the present disclosure.

[0022] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be considered as part of the authorization specification.

[0023] In all examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0024] Embodiment 1 As Figure 1 shown, this embodiment provides a high-isolation low-loss absorptive single-pole four-throw switch circuit, including four RF paths with the same structure connected in parallel on the input common branch, namely: the first RF path RF-RF1, the second RF path RF-RF2, the third RF path RF-RF3, and the fourth RF path RF-RF4. Among them, the first RF path RF-RF1 and the second RF path RF-RF2 are symmetrically arranged with respect to the input common branch, and the third RF path RF-RF3 and the fourth RF path RF-RF4 are symmetrically arranged with respect to the input common branch. Each of the first RF path RF-RF1, the second RF path RF-RF2, the third RF path RF-RF3, and the fourth RF path RF-RF4 includes three series-connected switch parallel branches, and for each RF path, a resonant capacitor to ground is connected in series on the middle switch parallel branch among the three switch parallel branches.

[0025] Specifically, as Figure 2 shown, each RF path further includes a series-connected first switch parallel branch, a second switch parallel branch, and a third switch parallel branch, and an output series switch M5 connected in series with the third switch parallel branch. A first microstrip line TL1 is connected in series between the first switch parallel branch and the second switch parallel branch, a second microstrip line TL2 is connected in series between the second switch parallel branch and the third switch parallel branch, the first switch parallel branch is connected in parallel to the input common branch, and a third microstrip line TL3 is connected in series between the third switch parallel branch and the output series switch.

[0026] Among them, for each RF path, the source of the output series switch M5 is connected in series with the fourth microstrip line TL4 and then used as the output port of the RF path. The output ports of the four RF paths are RF1, RF2, RF3, and RF4 in sequence. The drain of the output series switch M5 is connected in series with the third microstrip line TL3. An absorption resistor R1 is connected in parallel between the source and the drain of the output series switch M5. The gate of the output series switch M5 is connected to the gate resistor Rg and then connected to a control voltage to achieve switch switching, and the control voltages of each RF path are different. The absorption resistor R1 is a 50-ohm resistor in parallel to achieve the absorption function. Each RF path realizes the switching of the RF path by switching different control voltages.

[0027] More specifically, the structures of the four RF paths are the same. Taking the first RF path RF-RF1 as an example, the first switch parallel branch includes a first switch M1 and a second switch M2 that are symmetrically arranged and connected in parallel at the same point. The source of the first switch M1 is connected in parallel to the input common branch. The drain of the first switch M1 and the drain of the second switch M2 are connected in parallel at the same point. One end of the first microstrip line TL1 is connected in parallel between the drain of the first switch M1 and the drain of the second switch M2. The source of the second switch M2 is grounded. The gates of the first switch M1 and the second switch M2 are respectively connected to the gate resistor Rg.

[0028] The second switch parallel branch includes a first parallel-to-ground switch M3 and a second parallel-to-ground switch M3 that are symmetrically arranged and have their drains connected in parallel at the same point. Resonant capacitors C1 to ground are respectively connected in series to the sources of the first parallel-to-ground switch M3 and the second parallel switch M3. The gates of the first parallel-to-ground switch M3 and the second parallel switch M3 are respectively connected to the gate resistor Rg. One end of the second microstrip line TL2 and the other end of the first microstrip line TL1 are connected in parallel between the drains of the first parallel-to-ground switch M3 and the second parallel switch M3. By introducing the resonant capacitor C1, the shape of the isolation curve can be changed, a resonant point can be formed in the isolation curve, and the in-band isolation can be improved.

[0029] The third switch parallel branch includes a third parallel-to-ground switch M4 and a fourth parallel-to-ground switch M4 that are symmetrically arranged and have their drains connected in parallel at the same point. The sources of the third parallel-to-ground switch M4 and the fourth parallel-to-ground switch M4 are grounded. The gates of the third parallel-to-ground switch M4 and the fourth parallel-to-ground switch M4 are respectively connected to the gate resistor Rg. The other end of the second microstrip line TL2 and one end of the third microstrip line TL3 are both connected in parallel between the drains of the third parallel-to-ground switch M4 and the fourth parallel-to-ground switch M4. The other end of the third microstrip line TL3 is connected to the drain of the output series switch M5.

[0030] In some specific embodiments, a fifth microstrip line TL5 and a sixth microstrip line TL6 are included on the input common branch. One end of the fifth microstrip line TL5 is connected to the RF input terminal, and the other end is connected in parallel between the first RF path and the second RF path. Specifically, the microstrip line TL5 is connected in parallel between the source electrodes of the first switch and the second switch in the first RF path. One end of the sixth microstrip line TL6 is connected in parallel between the first RF path and the second RF path, and the other end is connected in parallel between the third RF path and the fourth RF path.

[0031] Among them, the length of the sixth microstrip line TL6 is less than that of the fifth microstrip line TL5. The length of the microstrip line TL4 is generally a quarter wavelength, and the length of TL6 is generally shorter to ensure the amplitude and phase consistency of the four ports from RFC to RF1, RF2, RF3, and RF4. The sizes of the switching transistors M1, M2, M3, M4, and M5 are different, and the lengths of the microstrip lines TL5, TL1, TL2, TL3, and TL4 are also different, and need to be adjusted according to the index performance. Usually, the lengths of the microstrip lines TL1 and TL2 are longer.

[0032] Embodiment 2 This embodiment provides a design process for designing Embodiment 1 and provides a circuit optimization method, including the following steps: S1. Construct the basic circuit topology of the absorptive single-pole four-throw switch circuit; As Figure 3 shown, the basic circuit topology includes four RF paths with the same structure connected in parallel on the input common branch, namely: the first RF path, the second RF path, the third RF path, and the fourth RF path. Among them, the first RF path and the second RF path are symmetrically arranged with respect to the input common branch, and the third RF path and the fourth RF path are symmetrically arranged with respect to the input common branch. The first RF path, the second RF path, the third RF path, and the fourth RF path each include three series-connected switch parallel branches.

[0033] As Figure 3 shown, the isolation can be further improved only by increasing the number of parallel switching transistors in the switch branch, but the loss will also increase at this time. Therefore, considering that the circuit needs to meet the conditions of high isolation and low loss, in order to ensure that the insertion loss does not increase after increasing the number of switching transistors, it is achieved by introducing a resonant capacitor into the circuit. However, the size and connection position of the selected resonant capacitor need to be debugged and determined. The specific process is as follows: S21. Set a resonant capacitor connected in series to ground with the switching transistor on each of the three switch parallel branches of the basic circuit topology to obtain the first circuit structure; Perform simulation within the set frequency range and select the first RF path as the test path to obtain the test curve of the first circuit structure; S22. Resonant capacitors connected in series to ground are set on two of the switch parallel branches of the basic circuit topology to obtain three circuit structures: the fifth circuit structure, the sixth circuit structure, and the seventh circuit structure; S23. Resonant capacitors connected in series to ground are respectively set only on each switch parallel branch of the basic circuit topology to obtain the second circuit structure, the third circuit structure, and the fourth circuit structure; The seven circuit structures are respectively simulated within a set frequency range, and the first RF path is selected as the test path to obtain the test curves corresponding to each circuit structure; the test curves include isolation curves and insertion loss curves; S3. The test curves corresponding to each circuit structure are compared in sequence, and the circuit structure corresponding to the optimal test curve is selected to obtain a high-isolation and low-loss absorptive single-pole four-throw switch circuit for Embodiment 1.

[0034] The test curves include isolation curves, insertion loss curves, and input / output standing wave curves; the screening of the optimal test curve is as follows: on the premise of ensuring good input / output standing waves, analyze the change trends of the isolation curves in each circuit structure. When the change trends meet the preset conditions, then continue to screen out the test curve with the minimum insertion loss from the circuit structures that meet the preset conditions to obtain the test curve when the isolation curve meets the preset conditions and the insertion loss is the smallest.

[0035] As Figure 4 shown, in the first circuit structure, in order to further improve the isolation of each RF path of the switch, an attempt is made to introduce a resonant point on the isolation curve. By adding resonant capacitors C2, C1, and C3 at the second switch M2, the switches M3 and M4 connected to ground in the three parallel branches respectively, and then adjusting the values of C1, C2, and C3, a better isolation simulation test is obtained, and the test results are as Figures 5 - 6 shown. From Figure 5 the isolation simulation results, it can be seen that near 10 GHz, a resonant point appears on the isolation calculation curve, and the isolation performance in this frequency band is better, but the isolation deteriorates near 4 GHz. Therefore, the effect of adding resonant capacitors C1, C2, and C3 at the three switches connected to ground is average.

[0036] As Figure 7 shown, in the fifth circuit structure, in order to improve the isolation, continue to consider using resonant capacitors only in two switch branches. An attempt is made to place the two resonant capacitors C1 and C3 at the switch transistors M3 and M4, and adjust the values of C2 and C3. As Figure 8 shown, a better simulation result under the fifth circuit structure is obtained. The isolation performance of the fifth circuit structure is slightly improved. The effect achieved by introducing capacitors on both switch branches is only slightly improved. Consider using only one resonant capacitor to achieve the best effect.

[0037] In the second circuit structure, the third circuit structure, and the fourth circuit structure, series resonance capacitors are respectively connected in series on one switch parallel branch, and the values of C1, C3, and C2 are respectively adjusted. Taking the second circuit structure as an example, as Figure 9 shown, in the second circuit structure, only the capacitor C2 is connected in series on the second switch M2 of the first switch parallel branch, and then the value of C2 is adjusted so that the current circuit performance can be optimized. As Figures 10 - 14 shown, a schematic diagram of the comparison of the isolation curves and insertion loss curves of the second circuit structure, the third circuit structure, and the fourth circuit structure is obtained; According to the comparison results, it can be seen that when the series resonance capacitor C2 is connected in series on the second switch M2, the isolation simulation curve (such as Figure 10 ) is similar to the isolation curve when the series resonance capacitor C1 is connected in series on the shunt-to-ground switch M3 of the second parallel branch (such as Figure 12 ). From Figure 11 and Figure 13 's insertion loss curves, it can be known that the insertion loss of the second circuit structure will increase at about 10.5 GHz. If the series resonance capacitor C3 is connected in series on the third shunt-to-ground switch M4 of the third switch parallel branch to obtain the fourth circuit structure, at this time, as Figure 14 shown, the resonance point of the isolation curve at this time is at about 8 GHz. At this time, the isolation curve deteriorates at high frequencies, the operating frequency band of the switch becomes narrower, and the isolation is poor at 4 GHz.

[0038] Therefore, through comprehensive comparison and analysis of all situations, connecting a series resonance capacitor C1 to the ground at the switch tube M3 of the second switch parallel branch can achieve the best effect. Finally, the feasibility of this circuit structure is verified through chip test.

[0039] It can be understood that by adding a shunt-to-ground switch tube in each RF path and introducing a series-to-ground resonance capacitor C1 between the second parallel switch branch and the ground, a resonance point appears in the isolation curve within the band, greatly improving the isolation performance of the switch and ensuring that the loss of the switch will not deteriorate. The output switches of the first RF path, the second RF path, the third RF path, and the fourth RF path are all connected in parallel with a 50-ohm resistor to achieve an absorption function. The circuit has ultra-high isolation while satisfying good input and output standing waves, and realizes the single-pole four-throw function by switching different control voltages to switch the switch path. The circuit structure is compact.

[0040] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments within the spirit and principle of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A high isolation and low loss absorptive single-pole four-throw switch circuit, characterized in that It includes four radio frequency paths connected in parallel on the common input branch and having the same structure, namely: the first radio frequency path, the second radio frequency path, the third radio frequency path, and the fourth radio frequency path. Among them, the first radio frequency path and the second radio frequency path are symmetrically arranged with respect to the common input branch, and the third radio frequency path and the fourth radio frequency path are symmetrically arranged with respect to the common input branch. The first radio frequency path, the second radio frequency path, the third radio frequency path, and the fourth radio frequency path all include three series-connected switch parallel branches, and for each radio frequency path, a resonant capacitor to ground is connected in series on the middle switch parallel branch among the three switch parallel branches.

2. The absorptive single-pole four-throw switch circuit with high isolation and low loss according to claim 1, characterized in that Each radio frequency path further includes a series-connected first switch parallel branch, a second switch parallel branch, and a third switch parallel branch, and an output series switch connected in series with the third switch parallel branch. A first microstrip line is connected in series between the first switch parallel branch and the second switch parallel branch, a second microstrip line is connected in series between the second switch parallel branch and the third switch parallel branch, the first switch parallel branch is connected in parallel to the common input branch, and a third microstrip line is connected in series between the third switch parallel branch and the output series switch.

3. The absorptive single-pole four-throw switch circuit with high isolation and low loss according to claim 2, characterized in that, The source of the output series switch is connected in series with a fourth microstrip line and serves as the output port of the radio frequency path. The drain of the output series switch is connected in series with the third microstrip line. An absorption resistor is connected in parallel between the source and the drain of the output series switch, and the gate of the output series switch is connected to a gate resistor.

4. The absorptive single-pole four-throw switch circuit with high isolation and low loss according to claim 2, wherein The first switch parallel branch includes a first switch and a second switch that are symmetrically arranged and connected in parallel at the same point. The source of the first switch is connected in parallel to the common input branch, the drains of the first switch and the second switch are connected in parallel at the same point, one end of the first microstrip line is connected in parallel between the drains of the first switch and the second switch, the source of the second switch is grounded, and the gates of the first switch and the second switch are respectively connected to gate resistors.

5. A high isolation and low loss absorptive single-pole four-throw switch circuit according to claim 4, characterized in that The second switch parallel branch includes a first parallel-to-ground switch and a second parallel-to-ground switch that are symmetrically arranged and have their drains connected in parallel at the same point. Resonant capacitors to ground are respectively connected in series to the sources of the first parallel-to-ground switch and the second parallel switch. The gates of the first parallel-to-ground switch and the second parallel switch are respectively connected to gate resistors. One end of the second microstrip line and the other end of the first microstrip line are connected in parallel between the drains of the first parallel-to-ground switch and the second parallel switch.

6. The high-isolation and low-loss absorptive single-pole four-throw switch circuit according to claim 5, characterized in that The third switch parallel branch includes a third parallel-to-ground switch and a fourth parallel-to-ground switch that are symmetrically arranged and have their drains connected in parallel at the same point. The sources of the third parallel-to-ground switch and the fourth parallel switch are grounded. The gates of the third parallel-to-ground switch and the fourth parallel switch are respectively connected to gate resistors. The other end of the second microstrip line and one end of the third microstrip line are both connected in parallel between the drains of the third parallel-to-ground switch and the fourth parallel switch.

7. The absorptive single-pole four-throw switch circuit with high isolation and low loss according to claim 1, characterized in that The common input branch includes a fifth microstrip line and a sixth microstrip line. One end of the fifth microstrip line is connected to the radio frequency input terminal, and the other end is connected in parallel between the first radio frequency path and the second radio frequency path. One end of the sixth microstrip line is connected in parallel between the first radio frequency path and the second radio frequency path, and the other end is connected in parallel between the third radio frequency path and the fourth radio frequency path.

8. The absorptive single-pole four-throw switch circuit with high isolation and low loss according to claim 7, characterized in that The length of the sixth microstrip line is less than that of the fifth microstrip line.

9. A circuit optimization method, characterized in that, It includes the following steps: S1. Construct the basic circuit topology of the absorptive single-pole four-throw switch circuit; S2. Set a resonant capacitor connected in series to ground on each of the three switch parallel branches of the basic circuit topology to obtain the first circuit structure; Simulate the first circuit structure within a set frequency range, and select the first RF path as the test path to obtain the test curve of the first circuit structure; S3. Only set a resonant capacitor connected in series to ground on each of the switch parallel branches of the basic circuit topology respectively to obtain the second circuit structure, the third circuit structure, and the fourth circuit structure; Simulate the second circuit structure, the third circuit structure, and the fourth circuit structure respectively within the set frequency range, and select the first RF path as the test path to obtain the test curves corresponding to each circuit structure respectively; S4. Compare the test curves corresponding to each circuit structure in sequence, screen out the circuit structure corresponding to the optimal test curve, and obtain a high-isolation low-loss absorptive single-pole four-throw switch circuit as described in claim 1.

10. A circuit optimization method according to claim 9, characterized in that, The test curves include isolation curves, insertion loss curves, and input / output standing wave curves; the screening of the optimal test curve is as follows: screen out the curves that meet the preset threshold from the input / output standing wave curves of each circuit structure, then analyze the change trends of the isolation curves in each circuit structure that meets the preset threshold. When the change trend meets the preset conditions, continue to screen out the test curve with the minimum insertion loss from the circuit structures that meet the preset conditions to obtain the test curve when the isolation curve meets the preset conditions and the insertion loss is the smallest.

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