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

Abstract

The present invention discloses a high-isolation, low-loss absorptive single-pole, four-throw switch circuit and a circuit optimization method. The circuit includes four radio frequency paths connected in parallel on a common branch at the input end and having 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 about the common branch at the input end, and the third radio frequency path and the fourth radio frequency path are symmetrically arranged about the common branch at 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 switch parallel branches connected in series, and for each radio frequency path, a resonant capacitor connected to ground is connected in series on the middle switch parallel branch of the three switch parallel branches. The introduction of the resonant capacitor connected to ground in the switch parallel branch causes a resonant point to appear within the isolation curve, greatly improving the isolation performance of the switch while ensuring that the loss of the switch does not deteriorate.

Description

Technical Field

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

[0002] Absorptive single-pole, four-throw (SPF4T) switches are widely used in modern communications and electronic measurement. These switches are designed for switching radio frequency (RF) signal paths. Their core function is to switch a common port (single-pole) to one of four selectable ports (four-throw). The absorptive design ensures that signals from the unselected ports are absorbed by the load rather than reflected, ensuring good matching at the unselected ports, thereby improving system performance. Currently, these switches are widely used in base station antenna switching, multi-band selection, signal redundancy, multi-channel signal switching, beamforming networks, and multi-port calibration of vector network analyzers (VNAs) and automated test equipment (ATE).

[0003] Isolation measures the signal attenuation between the input and output terminals when a switch is in the off state, reflecting the switch's ability to block signals. High isolation is crucial for preventing signal leakage and ensuring interference-free reception in high-frequency communication systems (such as radar and communications). Insertion loss refers to the signal attenuation when the switch is in the on state. Minimizing insertion loss is crucial in signal chains, such as RF front-ends or test equipment, to maintain signal-to-noise ratio. Isolation measures the off state, while loss measures the on state. Together, isolation and loss determine the switch's signal-handling capabilities.

[0004] Absorptive designs primarily match the unselected ports with a load. The load is typically 50 ohms. Matching the load prevents reflections, reduces the standing wave ratio (VSWR), and reduces signal interference. Generally, increasing the number of parallel grounded switches in the branch circuit can improve switch isolation, but this typically increases switch losses. Currently, while absorptive single-pole four-throw switches reduce losses, their isolation is limited. Further improving switch isolation is an urgent issue. Summary of the Invention

[0005] The present invention aims to provide a high-isolation, low-loss absorptive single-pole four-throw switch circuit. A resonant capacitor connected to ground is introduced into the parallel branch of the switch, causing a resonant point to appear within the isolation curve, thereby greatly improving the isolation performance of the switch while ensuring that the switch loss does not deteriorate.

[0006] In order to achieve the above objectives, this application provides the following solutions:

[0007] On the one hand, the present invention provides a high-isolation, low-loss absorptive single-pole four-throw switch circuit, including four radio frequency paths with identical structures connected in parallel on a common branch at the input end, namely: a first radio frequency path, a second radio frequency path, a third radio frequency path, and a fourth radio frequency path, wherein the first radio frequency path and the second radio frequency path are symmetrically arranged about the common branch at the input end, and the third radio frequency path and the fourth radio frequency path are symmetrically arranged about the common branch at the input end, and the first radio frequency path, the second radio frequency path, the third radio frequency path, and the fourth radio frequency path each include three switch parallel branches connected in series, and for each radio frequency path, a resonant capacitor connected to ground is connected in series on the middle switch parallel branch of the three switch parallel branches.

[0008] In some specific embodiments, each RF 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 input common branch; and a third microstrip line is connected in series between the third switch parallel branch and the output series switch.

[0009] In some specific embodiments, the source of the output series switch is connected in series with the fourth microstrip line and serves as the output port of the RF 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 drain of the output series switch, and the gate of the output series switch is connected to the gate resistor.

[0010] 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 at the input end, the drain of the first switch and the drain of the second switch are connected in parallel at the same point, one end of the first microstrip line is connected in parallel between the drain of the first switch and the drain of 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.

[0011] 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 whose drains are connected in parallel at the same point, the sources of the first parallel-to-ground switch and the second parallel switch are respectively connected in series with a resonant capacitor to ground, the gates of the first parallel-to-ground switch and the second parallel switch are respectively connected to a gate resistor, and one end of the second microstrip line and the other end of the first microstrip line are connected in parallel between the drain of the first parallel-to-ground switch and the drain of the second parallel switch.

[0012] 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 whose drains are 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, and the other end of the second microstrip line and one end of the third microstrip line are both connected in parallel between the drain of the third parallel-to-ground switch and the drain of the fourth parallel switch.

[0013] In some specific embodiments, the common branch at the input end includes a fifth microstrip line and a sixth microstrip line, one end of the fifth microstrip line is connected to the RF input end, and the other end is connected in parallel between the first RF path and the second RF path, and one end of the sixth microstrip line 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.

[0014] In some specific embodiments, the sixth microstrip line is shorter than the fifth microstrip line.

[0015] In a second aspect, the present application provides a circuit optimization method, comprising the following steps:

[0016] S1. Construct the basic circuit topology of the absorptive single-pole four-throw switch circuit;

[0017] The basic topology of the circuit includes four RF paths with the same structure connected in parallel on the common branch at the input end, namely: a first RF path, a second RF path, a third RF path, and a fourth RF path. Among them, the first RF path and the second RF path are symmetrically arranged about the common branch at the input end, and the third RF path and the fourth RF path are symmetrically arranged about the common branch at the input end. The first RF path, the second RF path, the third RF path, and the fourth RF path all include three switch parallel branches connected in series.

[0018] S2. Disposing a resonant capacitor connected in series to ground on each of the three parallel branches of the switch in the basic circuit topology structure to obtain a first circuit structure;

[0019] Simulating the first circuit structure within a set frequency range, and selecting the first radio frequency path as a test path to obtain a test curve of the first circuit structure;

[0020] S3. Disposing a resonant capacitor connected in series to ground only on each switch parallel branch of the basic circuit topology structure, thereby obtaining a second circuit structure, a third circuit structure, and a fourth circuit structure;

[0021] Simulating the second circuit structure, the third circuit structure, and the fourth circuit structure within the set frequency range, selecting the first radio frequency path as the test path, and obtaining test curves corresponding to each circuit structure, a test curve for the third circuit structure, and a test curve for the fourth circuit structure;

[0022] S4. Compare the test curves corresponding to the various circuit structures in sequence, select the circuit structure with the best test curve, and obtain a high-isolation, low-loss absorptive single-pole four-throw switch circuit according to the first aspect. First test curve, second test curve, third test curve, and fourth test curve;

[0023] In some specific implementation schemes, the test curves include an isolation curve, an insertion loss curve, and an input-output standing wave curve; the screening of the optimal test curve is as follows: a curve that meets a preset threshold is screened out from the input-output standing wave curves of each circuit structure, and then a change trend of each isolation curve in each circuit structure that meets the preset threshold is analyzed. When the change trend meets the preset conditions, the test curve with the smallest insertion loss is further screened out from the circuit structure that meets the preset conditions, and a test curve is obtained in which the isolation curve meets the preset conditions and the insertion loss is the smallest.

[0024] The present invention has the beneficial effects:

[0025] By increasing the number of switching transistors in the parallel switch, isolation is increased. Resonant capacitors connected in parallel to ground are introduced at appropriate locations in the parallel branches of the switches, creating a resonant point within the isolation curve. This significantly improves the isolation performance of the switches while ensuring that switch losses are minimized. The output switches of the first, second, third, and fourth RF paths are all connected in parallel with 50-ohm resistors to implement an absorptive function. Switching between these paths is accomplished by switching different control voltages. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a topological structure of a high-isolation, low-loss absorptive single-pole four-throw switch circuit provided by an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the circuit structure of one of the radio frequency paths provided in an embodiment of the present invention;

[0028] Figure 3 A schematic diagram of the basic topology of a circuit provided in an embodiment of the present invention;

[0029] Figure 4 A schematic diagram of a first circuit structure provided by an embodiment of the present invention;

[0030] Figure 5 Based on Figure 4 The circuit structure is simulated, and the isolation curves of RFC-RF2, RFC-RF3 and RFC-RF4 are simulated when the RFC-RF1 path is opened;

[0031] Figure 6 Based on Figure 4The circuit structure is simulated, and the insertion loss dB(S(2,1)) curve of RFC-RF1 is shown when the RFC-RF1 path is opened.

[0032] Figure 7 A schematic diagram of a fifth circuit structure provided in an embodiment of the present invention;

[0033] Figure 8 Based on Figure 7 The circuit structure is simulated, and the isolation curves of RFC-RF2, RFC-RF3 and RFC-RF4 are simulated when the RFC-RF1 path is opened;

[0034] Figure 9 A schematic diagram of a second circuit structure provided by an embodiment of the present invention;

[0035] Figure 10 Based on Figure 9 The circuit structure is simulated, and the isolation curves of RFC-RF2, RFC-RF3 and RFC-RF4 are simulated when the RFC-RF1 path is opened;

[0036] Figure 11 Based on Figure 9 The circuit structure is simulated, and the insertion loss curve of RFC-RF1 is shown when the RFC-RF1 path is opened;

[0037] Figure 12 Based on the third circuit structure, simulation curves of the isolation of RFC-RF2, RFC-RF3, and RFC-RF4 are simulated when the RFC-RF1 path is open;

[0038] Figure 13 The insertion loss curve of RFC-RF1 is simulated based on the third circuit structure when the RFC-RF1 path is opened;

[0039] Figure 14 Based on the fourth circuit structure, the isolation simulation curves of RFC-RF2, RFC-RF3, and RFC-RF4 are simulated when the RFC-RF1 path is opened. DETAILED DESCRIPTION

[0040] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only 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 is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] Unless otherwise specifically stated, the relative arrangement of components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention.

[0042] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0043] Additionally, descriptions of well-known structures, functions, and configurations may be omitted for clarity and conciseness. Those skilled 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.

[0044] Technologies, methods and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods and equipment should be considered part of the authorization specification.

[0045] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0046] Example 1

[0047] like Figure 1 As shown, this embodiment provides a high-isolation, low-loss absorptive single-pole four-throw switch circuit, including four RF paths connected in parallel on a common branch at the input end and having identical structures, namely: a first RF path RF-RF1, a second RF path RF-RF2, a third RF path RF-RF3, and a fourth RF path RF-RF4. The first RF path RF-RF1 and the second RF path RF-RF2 are symmetrically arranged about the common branch at the input end, and the third RF path RF-RF3 and the fourth RF path RF-RF4 are symmetrically arranged about the common branch at the input end. 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 each include three switch parallel branches connected in series, and for each RF path, a resonant capacitor connected to ground is connected in series to the middle switch parallel branch of the three switch parallel branches.

[0048] Specifically, if Figure 2 As shown, each RF path also 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 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.

[0049] For each RF path, the source of the output series switch M5 is connected in series with the fourth microstrip line TL4, serving as the output port of the RF path. The output ports of the four RF paths are RF1, RF2, RF3, and RF4, respectively. The drain of the output series switch M5 is connected in series with the third microstrip line TL3. An absorptive resistor R1 is connected in parallel between the source and drain of the output series switch M5. The gate of the output series switch M5 is connected to a gate resistor Rg, which is then connected to a control voltage to achieve switching. The control voltage for each RF path is different. The absorptive resistor R1 is a 50-ohm resistor connected in parallel to achieve the absorptive function. Each RF path switches the RF path by switching different control voltages.

[0050] More specifically, the four RF paths have the same structure. 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 common branch at the input end, 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, and the gates of the first switch M1 and the second switch M2 are respectively connected to gate resistors Rg.

[0051] The second switch parallel branch includes a first parallel-to-ground switch M3 and a second parallel-to-ground switch M3, symmetrically arranged with their drains connected in parallel at the same point. A resonant capacitor C1 is connected in series to the source of each of the first and second parallel switches M3. The gates of the first and second parallel switches M3 are connected to gate resistors Rg, respectively. 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 and second parallel switches M3. The introduction of resonant capacitor C1 changes the shape of the isolation curve, forming a resonant point within the isolation curve and improving intra-band isolation.

[0052] The third switch parallel branch includes a third parallel-to-ground switch M4 and a fourth parallel-to-ground switch M4, which are symmetrically arranged and whose drains are 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, and the gates of the third parallel-to-ground switch M4 and the fourth parallel-to-ground switch M4 are respectively connected to gate resistors 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.

[0053] In some specific embodiments, the input common branch includes a fifth microstrip line TL5 and a sixth microstrip line TL6, one end of the fifth microstrip line TL5 is connected to the RF input terminal RF, 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 of the first switch and the source of the second switch of the first RF path, and 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.

[0054] The sixth microstrip line TL6 is shorter than the fifth microstrip line TL5. Microstrip line TL4 is typically a quarter wavelength long, while TL6 is typically shorter to ensure amplitude and phase consistency from RFC to the four ports RF1, RF2, RF3, and RF4. The sizes of the switches M1, M2, M3, M4, and M5 are inconsistent, and the lengths of the microstrip lines TL5, TL1, TL2, TL3, and TL4 are also inconsistent. These adjustments need to be made based on performance indicators. Typically, microstrip lines TL1 and TL2 are longer.

[0055] Example 2

[0056] This embodiment provides a design process for designing Embodiment 1 and a circuit optimization method, including the following steps:

[0057] S1. Construct the basic circuit topology of the absorptive single-pole four-throw switch circuit;

[0058] like Figure 3 As shown, the basic topology of the circuit includes four RF paths with the same structure connected in parallel on the common branch at the input end, namely: a first RF path, a second RF path, a third RF path, and a fourth RF path. Among them, the first RF path and the second RF path are symmetrically arranged with respect to the common branch at the input end, and the third RF path and the fourth RF path are symmetrically arranged with respect to the common branch at the input end. The first RF path, the second RF path, the third RF path, and the fourth RF path all include three parallel branches of switches connected in series.

[0059] like Figure 3As shown, the isolation can be further improved by simply increasing the number of parallel switches in the switch branch, but the loss will also increase. Therefore, considering that the circuit needs to meet the requirements of high isolation and low loss, it is desired to increase the number of switches without increasing the insertion loss. This can be achieved by introducing a resonant capacitor into the circuit. However, the size and connection position of the resonant capacitor need to be debugged and determined. The specific process is as follows:

[0060] S21. Dispose a resonant capacitor connected in series with the switch tube to ground on each of the three switch parallel branches of the basic circuit topology structure to obtain a first circuit structure.

[0061] Simulating within a set frequency range and selecting a first radio frequency path as a test path to obtain a test curve of the first circuit structure;

[0062] S22. Disposing a resonant capacitor connected in series to ground on two of the parallel branches of the switches in the basic circuit topology structure to obtain three circuit structures: a fifth circuit structure, a sixth circuit structure, and a seventh circuit structure;

[0063] S23, only on each switch parallel branch of the basic circuit topology structure, a resonant capacitor connected in series to the ground is provided, thereby obtaining a second circuit structure, a third circuit structure, and a fourth circuit structure;

[0064] Seven circuit structures are simulated within a set frequency range, and the first RF path is selected as the test path to obtain test curves corresponding to each circuit structure. The test curves include isolation curves and insertion loss curves.

[0065] S3. Compare the test curves corresponding to the various circuit structures in turn, select the circuit structure that best corresponds to the test curve, and obtain a high-isolation, low-loss absorptive single-pole four-throw switch circuit according to Example 1.

[0066] The test curves include isolation curve, insertion loss curve and input and output standing wave curves; the screening of the optimal test curve is: under the premise of ensuring good input and output standing waves, analyze the change trend of each isolation curve in each circuit structure. When the change trend meets the preset conditions, continue to screen out the test curve with the smallest insertion loss from the circuit structure that meets the preset conditions, and obtain the test curve with the isolation curve meeting the preset conditions and the smallest insertion loss.

[0067] like Figure 4 As 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 resonance point on the isolation curve. By adding resonant capacitors C2, C1, and C3 to the second switch M2 and the ground switches M3 and M4 in the three parallel branches, and then adjusting the values of C1, C2, and C3, a better isolation simulation test is obtained. The test results are shown in Figure 1. Figures 5 and 6As shown. Figure 5 From the isolation simulation results, we can see that a resonance point appears on the isolation calculation curve near 10 GHz. The isolation performance in this frequency band is good, but the isolation deteriorates near 4 GHz. Therefore, the effect of adding resonant capacitors C1, C2, and C3 to the three switches connected in parallel to ground is average.

[0068] like Figure 7 As shown, in the fifth circuit structure, in order to improve the isolation, we continue to consider using resonant capacitors only in the two switch branches, try to place the two resonant capacitors C1 and C3 at the switch tubes M3 and M4, and adjust the values of C2 and C3, as shown in FIG. Figure 8 As shown, the simulation results show that the fifth circuit structure has better performance, and the isolation performance of the fifth circuit structure is slightly improved. Introducing capacitors in both switch branches only slightly improves the effect. Consider using only one resonant capacitor to achieve the best effect.

[0069] In the second circuit structure, the third circuit structure and the fourth circuit structure, a resonant capacitor is connected in series with a switch parallel branch, and the values of C1, C3 and C2 are adjusted respectively. Taking the second circuit structure as an example, Figure 9 As shown, in the second circuit structure, the capacitor C2 is connected in series only to the second switch M2 of the first switch parallel branch, and then the value of C2 is adjusted to optimize the current circuit performance. Figures 10 to 14 As shown, a schematic diagram comparing the isolation curves and insertion loss curves of the second circuit structure, the third circuit structure, and the fourth circuit structure is obtained;

[0070] According to the comparison results, it can be seen that the second switch M2 is connected in series with the resonant capacitor C2, and the isolation simulation curve (such as Figure 10 ) and the isolation curve when the second parallel branch is connected in parallel to the ground switch M3 and the series resonant capacitor C1 (as shown Figure 12 ) is close, from Figure 11 and Figure 13 The insertion loss curve shows that the insertion loss of the second circuit structure increases at around 10.5GHz. If the third parallel-connected switch M4 in the third parallel branch is connected in series with the resonant capacitor C3, a fourth circuit structure is obtained. At this time, Figure 14 As shown, the resonance point of the isolation curve at this time is around 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.

[0071] Therefore, after comprehensive comparison and analysis of all situations, it was found that connecting a resonant capacitor C1 in series with the switch tube M3 of the second switch parallel branch to the ground can achieve the best effect. Finally, the feasibility of this circuit structure was verified through chip testing.

[0072] As can be understood, by adding a switch connected in parallel to ground in each RF path and introducing a resonant capacitor C1 connected in series to ground between the second parallel switch branch and ground, the isolation curve achieves a resonant point within the band, significantly improving the isolation performance of the switches while ensuring that switch losses are not degraded. The output switches of the first, second, third, and fourth RF paths are all connected in parallel with a 50-ohm resistor to achieve absorption. The circuit maintains excellent input and output standing waves while also achieving ultra-high isolation. Switching between the switch paths is accomplished by switching different control voltages, thus achieving single-pole, four-throw (SP4T) functionality. The circuit structure is compact.

[0073] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Based on the technical essence of the present invention and within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement of the above embodiment shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A high-isolation, low-loss absorptive single-pole four-throw switch circuit, characterized in that: The invention also includes four radio frequency paths connected in parallel on a common branch at the input end and having 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, wherein the first radio frequency path and the second radio frequency path are symmetrically arranged about the common branch at the input end, and the third radio frequency path and the fourth radio frequency path are symmetrically arranged about the common branch at the input end, and each of the first radio frequency path, the second radio frequency path, the third radio frequency path, and the fourth radio frequency path includes three switch parallel branches connected in series, and for each radio frequency path, a resonant capacitor connected to ground is connected in series to the middle switch parallel branch connected in series among the three switch parallel branches; Each RF 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 input common branch; and a third microstrip line is connected in series between the third switch parallel branch and the output series switch; The source of the output series switch is connected in series with the fourth microstrip line and serves as an 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 between the source and the drain of the output series switch. The gate of the output series switch is connected to a gate resistor. The first switch parallel branch includes a first switch and a second switch symmetrically arranged and connected at the same point, the source of the first switch is connected to the input common branch, the drain of the first switch and the drain of the second switch are connected at the same point, one end of the first microstrip line is connected between the drain of the first switch and the drain of 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; The second switch parallel branch includes a first parallel-to-ground switch and a second parallel-to-ground switch symmetrically arranged with drains connected to the same point, the sources of the first parallel-to-ground switch and the second parallel switch are respectively connected in series with a resonant capacitor to ground, the gates of the first parallel-to-ground switch and the second parallel switch are respectively connected to a gate resistor, and one end of the second microstrip line and the other end of the first microstrip line are connected between the drain of the first parallel-to-ground switch and the drain of the second parallel switch; 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 drains connected to 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 between the drain of the third parallel-to-ground switch and the drain of the fourth parallel switch.

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

3. The high isolation and low loss absorptive single-pole four-throw switch circuit according to claim 2, characterized in that: The length of the sixth microstrip line is shorter than that of the fifth microstrip line.

4. A circuit optimization method, characterized in that: The following steps are involved: S1. Construct the basic circuit topology of the absorptive single-pole four-throw switch circuit; S2. Disposing a resonant capacitor connected in series to ground on each of the three parallel branches of the switch in the basic circuit topology structure to obtain a first circuit structure; Simulating the first circuit structure within a set frequency range, and selecting the first radio frequency path as a test path to obtain a test curve of the first circuit structure; S3. Disposing a resonant capacitor connected in series to ground only on each switch parallel branch of the basic circuit topology structure, thereby obtaining a second circuit structure, a third circuit structure, and a fourth circuit structure; Simulating the second circuit structure, the third circuit structure, and the fourth circuit structure within the set frequency range, selecting the first radio frequency path as a test path, and obtaining test curves corresponding to each circuit structure; S4. Compare the test curves corresponding to the various circuit structures in sequence, select the circuit structure with the best test curve, and obtain the high-isolation, low-loss absorptive single-pole four-throw switch circuit as claimed in claim 1.

5. A circuit optimization method according to claim 4, characterized in that: The test curves include an isolation curve, an insertion loss curve, and an input / output standing wave curve. The optimal test curve is screened as follows: a curve that meets a preset threshold is screened out from the input / output standing wave curves of each circuit structure, and then a change trend of each isolation curve in each circuit structure that meets the preset threshold is analyzed. When the change trend meets the preset conditions, the test curve with the smallest insertion loss is further screened out from the circuit structure that meets the preset conditions, thereby obtaining a test curve in which the isolation curve meets the preset conditions and the insertion loss is the smallest.

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