On-line measurement system and method for thermal impedance of microwave plasma light source

Abstract

The present application belongs to the technical field of microwave energy, and particularly relates to a kind of hot impedance on-line measurement system and method of microwave plasma light source;The present application includes: microwave driving source, double directional coupler and microwave plasma light source connected in turn;The output end of emission module is connected with broadband power amplifier, PA isolator, the coupling input end of double directional coupler in turn;Broadband power amplifier is configured to amplify sweep frequency detection signal to preset power, and then inject into the main transmission link through coupling input end;Measuring attenuator component is used to connect the coupling output end of the double directional coupler and the receiving channel of the multi-channel frequency selection receiver, and the coupling signal emitted by the double directional coupler is attenuated to obtain an attenuated signal;Data processing unit, connected to the data port of the vector network analyzer, is used to calculate the thermal impedance.The present application truly reflects the nonlinear impedance characteristics of plasma after ionization.

Description

Technical Field

[0001] This invention belongs to the field of microwave energy technology, specifically relating to an online measurement system and method for the thermal impedance of a microwave plasma source. Background Technology

[0002] In the design and industrial applications of microwave plasma sources, to optimize the conversion efficiency of microwave energy to plasma and design impedance networks with high matching degrees, it is essential to obtain the thermal impedance and scattering parameters (S-parameters) of the source under actual operating conditions. However, traditional vector network analyzers (VNAs) can only measure the S-parameters of the source in its "cold" state when it is not ignited. Once high-power microwaves are injected, the plasma ignites, and enters a stable discharge state (hot state), its equivalent impedance changes drastically, leading to significant differences between the thermal S-parameters, hot-state impedance, and cold-state impedance. Cold-state measurements cannot accurately reflect its operating characteristics. Furthermore, if measurements are attempted directly while the source is operating, the high-power main microwave signal (drive signal) maintaining the plasma discharge will backflow into the VNA, easily causing receiver saturation or even burnout. Simultaneously, the noise of the main signal will overwhelm the VNA's own test signal. Existing online monitoring technologies mostly employ scalar measurements, which cannot obtain phase information of complex impedances, and their power is limited, making them unsuitable for high-power industrial environments. Therefore, how to safely, in real time and accurately measure the thermal S-parameters and thermal impedance of a high-power microwave plasma source online without interfering with the normal discharge of the plasma has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] To address the aforementioned problem of safely, in real-time, and accurately measuring the thermal S-parameters and thermal impedance of a high-power microwave plasma source online without interfering with normal plasma discharge, this invention employs an online thermal impedance measurement system for microwave plasma sources. The invention proposes the following specific solutions:

[0004] In a first aspect, the present invention proposes an online measurement system for the thermal impedance of a microwave plasma source, the system comprising:

[0005] The main transmission link includes a microwave drive source, a dual directional coupler, and a microwave plasma source connected in sequence; the microwave drive source is configured to output a drive signal.

[0006] The vector network analyzer includes an internally interconnected transmitter module, receiver module, and multi-channel frequency-selective receiver. The output of the transmitter module is sequentially connected to a broadband power amplifier and a PA isolator, and then connected to the coupling input of the dual directional coupler. The transmitter module is configured to output a swept-frequency detection signal. The swept-frequency detection signal is sequentially amplified by the broadband power amplifier and the PA isolator before reaching the main transmission link, where it coexists with the drive signal on the main transmission link.

[0007] A measurement attenuator assembly is connected to the coupling output of the dual directional coupler and the receiving channel of the multi-channel frequency-selective receiver; it is used to attenuate the coupling signal emitted by the dual directional coupler to obtain an attenuated signal; the multi-channel frequency-selective receiver reconstructs the attenuated signal to obtain a reconstructed signal;

[0008] The data processing unit is connected to the data port of the vector network analyzer; it is configured to receive the reconstructed signal, calculate the uncorrected thermal S-parameters based on the reconstructed signal, further calculate the thermal S-parameters by combining the system error coefficients obtained by the online thermal impedance measurement system under cold conditions, and then calculate the thermal impedance based on the thermal S-parameters.

[0009] The method for calculating thermal S-parameters is as follows: ;

[0010] in, For the uncorrected thermal S-parameter, For directional error, For source matching error, The first parameter of the reflection tracking error is... The second parameter of the reflection tracking error. For thermal S-parameters.

[0011] Secondly, the present invention provides an online method for measuring the thermal impedance of a microwave plasma source, based on the aforementioned online measurement system for the thermal impedance of a microwave plasma source, the method comprising:

[0012] With the microwave drive source stopped outputting drive signals, open-circuit calibrators, short-circuit calibrators, and matched load calibrators are sequentially connected to the reference plane at the main path output end of the dual directional coupler. The vector network analyzer is controlled to output a sweep frequency detection signal to obtain the corresponding first measurement complex value, second measurement complex value, and third measurement complex value. By constructing and solving the linear error matrix equation, the system error coefficients, including directional error, source matching error, and reflection tracking error, are calculated.

[0013] The microwave drive source is turned on, and its output drive signal is transmitted to the microwave plasma source through the main transmission link to break down and maintain the stable plasma discharge inside the microwave plasma source.

[0014] While the microwave plasma source is in the discharge working state, the vector network analyzer is controlled to output a sweep frequency detection signal. The sweep frequency detection signal is sequentially transformed into an amplified sweep frequency detection signal through a broadband power amplifier and a PA isolator and then reaches the main transmission link, where it coexists with the drive signal on the main transmission link.

[0015] The incident coupling signal and the reflected coupling signal are extracted from the main transmission link using the dual directional coupler. The incident coupling signal is attenuated by a first measurement attenuator and then input into the first receiving channel of the vector network analyzer. The reflected coupling signal is attenuated by a second measurement attenuator and then input into the second receiving channel of the vector network analyzer. The vector network analyzer performs narrowband frequency selective reception at the swept frequency detection signal to obtain the original incident wave complex level and the original reflected wave complex level.

[0016] The data processing unit receives the original incident wave complex level and the original reflected wave complex level; and calculates the uncorrected thermal S-parameters based on the original incident wave complex level and the original reflected wave complex level. It further calculates the thermal S-parameters by combining the system error coefficients obtained by the online thermal impedance measurement system under cold conditions, and then calculates the thermal impedance based on the thermal S-parameters.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) This invention outputs a drive signal from the microwave drive source in the main transmission link to keep the microwave plasma source in a stable discharge state; at the same time, it uses the transmit module of the vector network analyzer to output a swept frequency detection signal, which is injected into the coupling input of the dual directional coupler via a broadband power amplifier and a PA isolator, thus realizing the coexistence of the swept frequency detection signal and the drive signal in the main transmission link. This method directly measures the source when it is in a high-power operating state (hot state), which truly reflects the nonlinear impedance characteristics after plasma ionization and effectively solves the problem of distortion of cold state measurement data caused by the huge impedance difference between the "hot state" and the "cold state" in the prior art.

[0019] (2) This invention obtains an attenuated signal by measuring the attenuator assembly to attenuate the coupled signal output by the dual directional coupler, thereby suppressing the power of the mixed wave containing the drive signal and the sweep frequency probe signal to the safe operating level of the multi-channel selective receiver. Combined with the multi-channel selective receiver to reconstruct the attenuated signal, this not only prevents the high-power drive signal from backflowing and causing saturation or burnout of the vector network analyzer, but also utilizes the frequency characteristics of the sweep frequency probe signal to effectively filter out the main signal noise in the data processing unit, ensuring the acquisition of high signal-to-noise ratio original incident wave complex level and original reflected wave complex level.

[0020] (3) This invention utilizes a data processing unit to receive the reconstructed signal and combines it with the system error coefficients measured by the open-circuit calibrator, short-circuit calibrator, and matched load calibrator under cold conditions. A standard linear error matrix equation is then constructed to calculate the precise thermal S-parameters and thermal impedance. This precise calculation based on real thermal data provides a crucial basis for designing a high-matching impedance network, thereby maximizing the energy conversion efficiency of the driving signal to the microwave plasma light source and optimizing the overall system performance. Attached Figure Description

[0021] Figure 1 This is a structural diagram of an online thermal impedance measurement system for a microwave plasma source according to an embodiment of the present invention;

[0022] Figure 2 This is a microwave network micro-signal flow diagram of an online thermal impedance measurement system for a microwave plasma source according to an embodiment of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] In some embodiments, such as Figure 1 This invention presents a structural diagram of an online thermal impedance measurement system for a microwave plasma source, the system comprising:

[0025] The main transmission link includes a microwave driver, a dual-directional coupler, and a microwave plasma source connected in sequence. The microwave driver is configured to output a drive signal. The drive signal output by the microwave driver is input to the coaxial resonant cavity of the microwave plasma source via the dual-directional coupler. The coaxial resonant cavity couples microwave energy to the discharge lamp inside it, causing the gas inside the discharge lamp to ionize and form a high-density plasma.

[0026] The vector network analyzer includes an internally interconnected transmitter module, receiver module, and multi-channel frequency-selective receiver. The output of the transmitter module is connected in sequence to a broadband power amplifier and a PA isolator, and then to the coupling input of a dual directional coupler. The transmitter module is configured to output a swept-frequency detection signal. The swept-frequency detection signal is amplified by passing through a broadband power amplifier and a PA isolator in sequence and then reaches the main transmission link, where it coexists with the drive signal in the main transmission link.

[0027] A measurement attenuator assembly is provided, connecting the coupling output of a dual directional coupler and the receiving channel of a multi-channel selective receiver; it is used to attenuate the coupling signal emitted by the dual directional coupler to obtain an attenuated signal; the multi-channel selective receiver reconstructs the attenuated signal to obtain a reconstructed signal; the measurement attenuator assembly includes a first measurement attenuator and a second measurement attenuator; the output of a microwave drive source is connected to the first input of the dual directional coupler, and the first output of the dual directional coupler is connected to the input of a microwave plasma source; the first coupling output of the dual directional coupler is connected to the first receiving channel of the multi-channel selective receiver via the first measurement attenuator, and the second coupling output of the dual directional coupler is connected to the second receiving channel of the multi-channel selective receiver via the second measurement attenuator.

[0028] The data processing unit is connected to the data port of the vector network analyzer; it is configured to receive the reconstructed signal, calculate the uncorrected thermal S-parameters based on the reconstructed signal, further calculate the thermal S-parameters by combining the system error coefficients obtained by the online thermal impedance measurement system under cold conditions, and then calculate the thermal impedance based on the thermal S-parameters.

[0029] The method for calculating thermal S-parameters is as follows: ;

[0030] in, For the uncorrected thermal S-parameter, For directional error, For source matching error, The first parameter of the reflection tracking error is... The second parameter of the reflection tracking error. For thermal S-parameters; This represents the reflection tracking error.

[0031] Calculate thermal impedance The method is as follows:

[0032] ;

[0033] in, Thermal impedance (unit: Ω); The characteristic impedance of the main transmission link is typically 50 Ω in standard high-power coaxial systems (such as the DIN 47223 interface).

[0034] It is understandable that the system error coefficients include directional error, source matching error, and reflection tracking error.

[0035] Understandably, the driving signal is microwave energy, used to excite and maintain the microwave plasma source into a stable plasma discharge working state. While the microwave plasma source is discharging, a sweep frequency detection signal is generated by a vector network analyzer. The sweep frequency detection signal is amplified by a broadband power amplifier and then converted into an amplified sweep frequency detection signal by a PA isolator. It is then injected into the main transmission link and input to the input port of the microwave plasma source through a dual directional coupler set on the main transmission link.

[0036] For example, the main transmission link adopts a DIN 47223 type high-power coaxial link system, and specific values ​​are set for the main transmission link and the measurement attenuator components. For instance, the microwave driver power is 200W, the broadband power amplifier output is 10W-20W, and it is recommended to maintain a power difference of more than 30dB between the drive signal and the swept-frequency detection signal. Simultaneously, the coupling degree of the dual directional coupler is specified as -20dB, the insertion loss as less than 0.2dB, the attenuation value of the measurement attenuator components is -30dB, and the system center frequency, swept-frequency bandwidth, and DIN 47223 type or N type coaxial interface standard are specified. The data processing unit runs a Python / MATLAB data correction script. After calculating the error coefficients, the data processing unit corrects the real-time acquired signals and dynamically plots and continuously monitors and displays the calculated thermal S-parameters and thermal impedance.

[0037] For example, in the system architecture, no isolation device is placed between the microwave driver and the dual directional coupler in the main transmission link. This is to avoid the approximately 0.2dB insertion loss introduced by the isolator, and because the microwave driver itself has sufficient standing wave tolerance, no additional isolation protection is required.

[0038] For example, a strict frequency separation strategy is employed to ensure the safety and accuracy of the measurement. The operating frequency of the drive signal output by the microwave driver is set to f0, f0 = 440MHz; the frequency fs of the sweep probe signal output by the vector network analyzer is set to 400MHz to 480MHz. Considering that the signal bandwidth of the microwave driver in continuous wave mode is approximately 40MHz, the system controls the frequency of the sweep probe signal to avoid the ±5MHz strong interference region centered on the frequency of the drive signal, in order to prevent the energy of the drive signal from overwhelming the test signal.

[0039] In some embodiments, the measurement attenuator assembly includes a first measurement attenuator and a second measurement attenuator; the output of the microwave drive source is connected to the first input of a dual directional coupler, and the first output of the dual directional coupler is connected to the input of a microwave plasma source; the first coupling output of the dual directional coupler is connected to the first receiving channel of a multi-channel frequency-selective receiver via the first measurement attenuator, and the second coupling output of the dual directional coupler is connected to the second receiving channel of the multi-channel frequency-selective receiver via the second measurement attenuator; the first measurement attenuator is configured to perform power attenuation on the incident wave signal in the coupled signal to obtain an attenuated incident wave signal, and reconstruct the attenuated incident wave signal in the multi-channel frequency-selective receiver to obtain the original incident wave complex level; the original incident wave complex level is used as an absolute reference quantity characterizing the amplitude and phase of the incident wave at the input port of the microwave plasma source; the second measurement attenuator is configured to perform power attenuation on the reflected wave signal in the coupled signal to obtain an attenuated reflected wave signal, and reconstruct the attenuated reflected wave signal in the multi-channel frequency-selective receiver to obtain the original reflected wave complex level; the original reflected wave complex level is used as a response quantity characterizing the amplitude and phase of the reflected wave at the input port of the microwave plasma source.

[0040] In some embodiments, the reconstructed signal includes the original incident wave complex level and the original reflected wave complex level; the data processing unit also calculates the uncorrected thermal S-parameters based on the reconstructed signal. According to the uncorrected thermal S-parameters of the original data Calculate the thermal S-parameters and, based on these parameters, calculate the hot-state impedance; uncorrected thermal S-parameters. This is the ratio of the original reflected wave complex level to the original incident wave complex level; in some embodiments, the power level of the swept-frequency detection signal is at least 30 dB lower than the power level of the drive signal.

[0041] In some embodiments, the online thermal impedance measurement system obtains the system error coefficient in the cold state by: turning off the microwave drive source, and sequentially connecting a reflection coefficient of [missing information] to the reference surface at the first output end of the dual directional coupler. Open circuit calibration components Short-circuit calibration components and The matching load calibration component is used, and the transmitting module outputs a swept-frequency detection signal; then, the vector network analyzer measures the first complex value under the swept-frequency detection signal. Second measurement complex value and the third measurement complex value ;

[0042] Constructing the standard linear error matrix equation ;

[0043] Unknown vector for: intermediate variables for: ;

[0044] ;

[0045] The data processing unit runs a matrix inversion algorithm to calculate the directional error. : ; and source matching error : The reflection tracking error is obtained using algebraic mapping relationships. : ;

[0046] in, As the first intermediate variable, As the second intermediate variable, As the third intermediate variable, The first parameter of the reflection tracking error is... Let A be the second parameter of the reflection tracking error, and let B be the first matrix and B be the second matrix.

[0047] For example, if the system is a primary transmission coaxial system, the standard short-circuit-open-load-through calibration algorithm is used to calculate the system error coefficient; if the system is a primary transmission waveguide system, the triple offset short-circuit calibration algorithm is used to calculate the system error coefficient.

[0048] In some embodiments, the noise level of the microwave drive source outside its operating frequency is at least 20 dB lower than the power level of the swept-frequency probe signal. Its operating frequency is the frequency of the drive signal. This allows for effective isolation between the drive signal and the amplified swept-frequency probe signal in the frequency domain by utilizing the narrowband intermediate frequency filtering characteristics of the vector network analyzer.

[0049] In some embodiments, the measurement attenuator assembly attenuates the coupled signal emitted by the dual directional coupler to obtain an attenuated signal, including: the first coupling output terminal of the dual directional coupler outputs an incident coupled signal containing a mixed wave of the driving signal and the amplified swept-frequency probe signal; the second coupling output terminal of the dual directional coupler outputs a reflected coupled signal containing a mixed wave of the driving signal and the amplified swept-frequency probe signal; the first measurement attenuator performs a fixed amount of power attenuation on the incident coupled signal and outputs a first attenuated signal to the first receiving channel of the multi-channel selective receiver; the second measurement attenuator performs a fixed amount of power attenuation on the reflected coupled signal and outputs a second attenuated signal to the second receiving channel of the multi-channel selective receiver; wherein the power levels of the first attenuated signal and the second attenuated signal are suppressed to the safe operating level of the multi-channel selective receiver, and the energy of the driving signal after attenuation is lower than the noise floor of the swept-frequency probe signal.

[0050] In some embodiments, the dual directional coupler is used to enable the coexistence of the driving signal and the amplified swept-frequency detection signal in the main transmission link, and to directionally extract the incident coupling signal and the reflected coupling signal from the main transmission link; the dual directional coupler transmits the driving signal to the main transmission link, and reaches the microwave plasma source through the main transmission link; the first coupling output terminal extracts the forward-propagating incident coupling signal from the main transmission link with a coupling degree of -20dB, and the second coupling output terminal extracts the backward-propagating reflected coupling signal from the main transmission link with a coupling degree of -20dB.

[0051] In some embodiments, the second coupling output is closer to the input of the microwave plasma light source than the first coupling output.

[0052] like Figure 2 As shown, The original incident wave complex level measured by the multi-channel frequency-selective receiver corresponds to the reference source node of the measurement reference plane. The original complex level of the reflected wave measured by a multi-channel frequency-selective receiver; This refers to the actual physical incident wave signal that flows into the input port of the microwave plasma source through the main transmission link. This represents the actual physical reflected wave signal scattered outward from the input port of the microwave plasma source. In the system error term characterized by the directed branch, the directional error... Signal leakage and source matching error stemming from the limited isolation of the dual directional coupler The reflection tracking error originates from secondary multiple reflections caused by imperfect impedance at the ports of the main measurement link and the dual directional coupler. The product of complex frequency response amplitude attenuation and time delay originates from the test cable and attenuator assembly at the input end. Here are the thermal S-parameters; point E is the node where the original incident wave enters the reference surface of the microwave plasma source input port, point F is the node of the internal input port of the microwave plasma source; point C is the node where the original reflected wave leaves the reference surface of the microwave plasma source input port, and point D is the node of the internal output port of the microwave plasma source; wherein, the reference surface of the input port where points E and C are located is at the same physical location as the reference surface of the first output end of the dual directional coupler.

[0053] Understandably, the data processing unit uses a single-port three-term error model for calculation, eliminating the need to jointly solve cumbersome two-port eight- or twelve-term complex matrices. This simplified model supports ultra-high-speed online stripping calculations at the microsecond level, demonstrating stability not only when the load matching is excellent, but also providing superior algorithm convergence and real-time impedance tracking response when the measured plasma impedance undergoes drastic changes, adapting to the entire process of plasma monitoring from glow discharge to arc discharge.

[0054] The technical solution of this invention is based on the premise that "the influence of temperature on the scattering matrix formula is not considered". Under this premise, the thermal electrical characteristics are obtained by utilizing the weak linear scattering interaction of small signal waves on the surface of plasma, a nonlinear time-varying medium.

[0055] Experimental results show that S measured using the system of this embodiment 11 and It can accurately expose the frequency points of plasma ionization impedance abrupt changes at specific power levels. By adjusting the output power and frequency of the microwave drive source through thermal impedance feedback, the center of the high-temperature plasma arc inside the bulb can be safely moved from between the breakdown electrodes to the point of strongest electric field at the conductor end inside the resonant cavity. This significantly optimizes microwave coupling efficiency while completely avoiding abnormal ablation of the high-voltage ignition electrodes.

[0056] In other embodiments, an online method for measuring the thermal impedance of a microwave plasma source is provided, based on the above-described online measurement system for the thermal impedance of a microwave plasma source. The method includes:

[0057] With the microwave drive source stopped outputting drive signals, open-circuit calibrators, short-circuit calibrators, and matched load calibrators are sequentially connected to the reference plane at the main path output end of the dual directional coupler. The vector network analyzer is controlled to output a sweep frequency detection signal to obtain the original measurement data corresponding to each set of calibrators. By constructing and solving the linear error matrix equation, the system error coefficients, including directional error, source matching error, and reflection tracking error, are calculated and stored.

[0058] Turn on the microwave drive source to output a drive signal, which is then transmitted to the microwave plasma source through the main transmission link to break down and maintain stable plasma discharge inside the microwave plasma source.

[0059] While the microwave plasma source is in the discharge working state, the control vector network analyzer outputs a sweep frequency detection signal. After being amplified by a broadband power amplifier, the sweep frequency detection signal is injected into the main transmission link in parallel through the coupling input of the dual directional coupler, so that the sweep frequency detection signal and the drive signal coexist in the main transmission link.

[0060] The incident coupling signal and the reflected coupling signal are extracted from the main transmission link using dual directional couplers. The incident coupling signal is attenuated by the power of the first measurement attenuator and then input into the first receiving channel of the vector network analyzer. The reflected coupling signal is attenuated by the power of the second measurement attenuator and then input into the second receiving channel of the vector network analyzer. The vector network analyzer performs narrowband frequency selective reception at the swept frequency detection signal to obtain the original incident wave complex level and the original reflected wave complex level.

[0061] The data processing unit receives the original incident wave complex level and the original reflected wave complex level; and calculates the thermal S-parameters based on the original incident wave complex level and the original reflected wave complex level, as well as the system error coefficients obtained by the online thermal impedance measurement system under cold conditions, and then calculates the thermal impedance based on the thermal S-parameters.

[0062] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An online measurement system for the thermal impedance of a microwave plasma source, characterized in that, The system includes: The main transmission link includes a microwave drive source, a dual directional coupler, and a microwave plasma source connected in sequence; the microwave drive source is configured to output a drive signal. The vector network analyzer includes an internally interconnected transmitter module, receiver module, and multi-channel frequency-selective receiver. The output of the transmitter module is sequentially connected to a broadband power amplifier and a PA isolator, and then connected to the coupling input of the dual directional coupler. The transmitter module is configured to output a swept-frequency detection signal. The swept-frequency detection signal is sequentially amplified by the broadband power amplifier and the PA isolator before reaching the main transmission link, where it coexists with the drive signal on the main transmission link. A measurement attenuator assembly is connected to the coupling output of the dual directional coupler and the receiving channel of the multi-channel frequency-selective receiver; it is used to attenuate the coupling signal emitted by the dual directional coupler to obtain an attenuated signal; the multi-channel frequency-selective receiver reconstructs the attenuated signal to obtain a reconstructed signal; The data processing unit is connected to the data port of the vector network analyzer; it is configured to receive the reconstructed signal, calculate the uncorrected thermal S-parameters based on the reconstructed signal, further calculate the thermal S-parameters by combining the system error coefficients obtained by the online thermal impedance measurement system under cold conditions, and then calculate the thermal impedance based on the thermal S-parameters. The method for calculating thermal S-parameters is as follows: ; in, For the uncorrected thermal S-parameter, For directional error, For source matching error, The first parameter of the reflection tracking error is... The second parameter of the reflection tracking error. For thermal S-parameters, This represents the reflection tracking error.

2. The online measurement system for the thermal impedance of a microwave plasma source according to claim 1, characterized in that, The measurement attenuator assembly includes a first measurement attenuator and a second measurement attenuator; The output terminal of the microwave drive source is connected to the first input terminal of the dual directional coupler, and the first output terminal of the dual directional coupler is connected to the input terminal of the microwave plasma source. The first coupling output terminal of the dual directional coupler is connected to the first receiving channel of the multi-channel frequency selective receiver via the first measurement attenuator, and the second coupling output terminal of the dual directional coupler is connected to the second receiving channel of the multi-channel frequency selective receiver via the second measurement attenuator. The first measuring attenuator is configured to attenuate the power of the incident wave signal in the coupled signal to obtain an attenuated incident wave signal, and to reconstruct the attenuated incident wave signal in the multi-channel frequency selective receiver to obtain the original incident wave complex level. The original incident wave complex level is used as an absolute reference quantity to characterize the amplitude and phase of the incident wave at the input port of the microwave plasma source; The second measuring attenuator is configured to attenuate the power of the reflected wave signal in the coupled signal to obtain an attenuated reflected wave signal, and to reconstruct the attenuated reflected wave signal in the multi-channel frequency selective receiver to obtain the original reflected wave complex level. The original reflected wave complex level is used as a response quantity characterizing the amplitude and phase of the reflected wave at the input port of the microwave plasma source.

3. The online measurement system for the thermal impedance of a microwave plasma source according to claim 2, characterized in that, The reconstructed signal includes the original incident wave complex level and the original reflected wave complex level; the data processing unit also calculates the uncorrected thermal S-parameters based on the reconstructed signal. According to the uncorrected thermal S-parameters of the original data Calculating the thermal S-parameters and, based on the thermal S-parameters, the hot-state impedance includes: Uncorrected thermal S-parameters It is the ratio of the original complex level of the reflected wave to the original complex level of the incident wave; Calculate thermal impedance The method is as follows: ； in, The thermal impedance; The characteristic impedance of the main transmission link.

4. The online measurement system for the thermal impedance of a microwave plasma source according to claim 3, characterized in that, The power level of the frequency sweep detection signal is at least 30 dB lower than the power level of the drive signal.

5. The online measurement system for the thermal impedance of a microwave plasma source according to claim 4, characterized in that, The system error coefficients include directional error, source matching error, and reflection tracking error; The system error coefficients obtained by the online thermal impedance measurement system of the microwave plasma source under cold conditions include: With the microwave drive source turned off, sequentially connect the following components with reflection coefficients to the reference plane at the first output terminal of the dual directional coupler: Open-circuit calibration component, reflection coefficient is The short-circuit calibration component and the reflection coefficient are The matching load calibration component, the transmitting module outputs a swept frequency detection signal; Then, the vector network analyzer is used to scan the frequency detection signal. Below, the first complex value of the measurement was obtained. Second measurement complex value and the third measurement complex value ; Constructing the standard linear error matrix equation ; Unknown vector for: intermediate variables for: ; The data processing unit runs a matrix inversion algorithm to calculate the directional error. : ; and source matching error : The reflection tracking error is obtained using algebraic mapping relationships. : ; in, As the first intermediate variable, As the second intermediate variable, As the third intermediate variable, The first parameter of the reflection tracking error is... Let A be the second parameter of the reflection tracking error, and let B be the first matrix and B be the second matrix.

6. The online measurement system for the thermal impedance of a microwave plasma source according to claim 5, characterized in that, The noise level of the microwave drive source outside its operating frequency is at least 20 dB lower than the power level of the swept-frequency detection signal.

7. The online measurement system for the thermal impedance of a microwave plasma source according to claim 6, characterized in that, The measurement attenuator assembly attenuates the coupled signal emitted by the dual directional coupler to obtain an attenuated signal, including: The first coupling output terminal of the dual directional coupler outputs an incident coupling signal containing a mixed wave of the driving signal and the amplified swept-frequency detection signal; the second coupling output terminal of the dual directional coupler outputs a reflected coupling signal containing a mixed wave of the driving signal and the amplified swept-frequency detection signal; the first measuring attenuator performs a fixed amount of power attenuation on the incident coupling signal and outputs a first attenuation signal to the first receiving channel of the multi-channel frequency-selective receiver; the second measuring attenuator performs a fixed amount of power attenuation on the reflected coupling signal and outputs a second attenuation signal to the second receiving channel of the multi-channel frequency-selective receiver. The power levels of the first attenuation signal and the second attenuation signal are suppressed to the safe operating level of the multi-channel frequency selective receiver, and the energy of the drive signal after attenuation is lower than the noise floor of the frequency sweep detection signal.

8. The online measurement system for the thermal impedance of a microwave plasma source according to claim 7, characterized in that, The dual directional coupler is used to enable the coexistence of the driving signal and the amplified swept frequency detection signal in the main transmission link, and to directionally extract the incident coupling signal and the reflected coupling signal from the main transmission link. The dual directional coupler transmits the drive signal to the main transmission link, and then to the microwave plasma source through the main transmission link; The first coupling output terminal extracts the forward-propagating incident coupling signal from the main transmission link with a coupling degree of -20dB, and the second coupling output terminal extracts the backward-propagating reflected coupling signal from the main transmission link with a coupling degree of -20dB.

9. The online measurement system for the thermal impedance of a microwave plasma source according to claim 8, characterized in that, The second coupling output terminal is closer to the input terminal of the microwave plasma light source than the first coupling output terminal.

10. A method for online measurement of the thermal impedance of a microwave plasma source, based on the online measurement system for the thermal impedance of a microwave plasma source according to any one of claims 1 to 9, characterized in that, The method includes: With the microwave drive source stopped outputting drive signals, open-circuit calibrators, short-circuit calibrators, and matched load calibrators are sequentially connected to the reference plane at the main path output end of the dual directional coupler. The vector network analyzer is controlled to output a sweep frequency detection signal to obtain the corresponding first measurement complex value, second measurement complex value, and third measurement complex value. By constructing and solving the linear error matrix equation, the system error coefficients, including directional error, source matching error, and reflection tracking error, are calculated. The microwave drive source is turned on, and its output drive signal is transmitted to the microwave plasma source through the main transmission link to break down and maintain the stable plasma discharge inside the microwave plasma source. While the microwave plasma source is in the discharge working state, the vector network analyzer is controlled to output a sweep frequency detection signal. The sweep frequency detection signal is sequentially transformed into an amplified sweep frequency detection signal through a broadband power amplifier and a PA isolator and then reaches the main transmission link, where it coexists with the drive signal on the main transmission link. The incident coupling signal and the reflected coupling signal are extracted from the main transmission link using the dual directional coupler. The incident coupling signal is attenuated by a first measurement attenuator and then input into the first receiving channel of the vector network analyzer. The reflected coupling signal is attenuated by a second measurement attenuator and then input into the second receiving channel of the vector network analyzer. The vector network analyzer performs narrowband frequency selective reception at the swept frequency detection signal to obtain the original incident wave complex level and the original reflected wave complex level. The data processing unit receives the original incident wave complex level and the original reflected wave complex level; and calculates the uncorrected thermal S-parameters based on the original incident wave complex level and the original reflected wave complex level. It further calculates the thermal S-parameters by combining the system error coefficients obtained by the online thermal impedance measurement system under cold conditions, and then calculates the thermal impedance based on the thermal S-parameters.

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