A calibration factor estimation and correction method for direct measurement of radio frequency high power calibration

Abstract

The present invention discloses a calibration factor estimation and correction method for a radio frequency high power calibration direct measurement method, comprising receiving a radio frequency high power signal, calculating an equivalent source reflection coefficient of a directional coupler to be corrected; setting a test end face between the directional coupler and a device under test DUT to detect a loss constant ka; and correcting the estimation of the calibration factor of the direct measurement method by using experimentally measured radio frequency high power standard indications and power indications of the device under test DUT. The present invention avoids the situation where the calibration factor of the direct measurement method has a large error at a higher frequency, reduces the measurement error brought about at a higher frequency, and thus improves the accuracy of high power measurement of the radio frequency directional power sensor in a higher frequency environment.

Description

Technical Field

[0001] The present invention relates to the technical field of calibration factor estimation and correction, and in particular to a calibration factor estimation and correction method for a radio frequency high-power calibration direct measurement method. Background Art

[0002] RF directional power sensors are mainly used to monitor the power level of RF signals in real time to ensure the normal operation and safety of the equipment. The sensor provides feedback to the system by measuring the strength of the RF signal in order to adjust the power output and avoid signal overload or distortion. RF directional power sensors are mainly divided into through-type power sensors and terminal power sensors, both of which are suitable for medium and high power calibration. Terminal power sensors do not require external loads, measure power at the end of the signal transmission link, and provide accurate power readings. They are suitable for the alternating comparison method and the transfer standard method in the calibration method. Through-type power sensors require external loads, measure power in real time in the signal transmission link, monitor and transfer the power level of the signal, and are suitable for the direct measurement method in the calibration method.

[0003] RF high power calibration plays a vital role in fields such as semiconductor manufacturing, medical devices, space science and radar technology. In semiconductor manufacturing, the etching process in semiconductor manufacturing relies on high-precision RF power amplifiers (i.e., RF plasma generators) to generate plasma, where the output power level reaches 10kW continuously. The entire etching process requires very high stability and accuracy of RF output power, otherwise the entire wafer will be damaged by unstable plasma, resulting in huge economic losses; in medical equipment, especially in therapeutic equipment using RF energy, too high or too low power may lead to poor treatment effects or unnecessary risks to patients. For example, a magnetic resonance imaging (MRI) scanner requires a stable RF pulse with a peak power of more than 35kW to flip the direction of hydrogen atoms, so that pathological organs with abnormal water content can be distinguished from the hydrogen atom distribution image. Excessive RF power may cause potential harm to the human body, while too low RF power will affect the quality of imaging; in space science, accurate power calibration ensures that communication signals are transmitted stably in space, making communication between the earth and satellites clear and reliable. This is crucial to the success of scientific data transmission, navigation and remote sensing missions. At the same time, accurate power levels can also optimize signal strength and coverage, reduce signal interference and loss, thereby ensuring efficient execution of tasks and data integrity; in terms of radar technology, accurate calibration improves the detection range and resolution of radar systems, enabling them to accurately identify and track targets. And through calibration, radar systems can maintain consistent performance under different environmental conditions, reduce false alarms and missed alarms, and enhance overall detection capabilities, which is particularly important for military surveillance, meteorological monitoring, and traffic management. At present, the calibration methods for directional power sensors in the calibration specifications include alternating comparison method, transfer standard method, and direct measurement method. Among them, the measurement errors of the calibration factors of the alternating comparison method and the transfer standard method are small and reasonable. However, the calibration factor error measured by the direct measurement method at higher frequencies is large and is not suitable for calibration. Therefore, when the direct measurement method is applied to RF high-power calibration, there is a problem of being affected by frequency, which leads to inaccurate RF high-power calibration results. Therefore, a calibration factor estimation and correction method for the direct measurement method of RF high-power calibration is required. Summary of the invention

[0004] The object of the present invention is to provide a calibration factor estimation and correction method for a radio frequency high power calibration direct measurement method.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] The present invention comprises the following steps:

[0007] Receive high-power radio frequency signals and calculate the equivalent source reflection coefficient of the directional coupler to be corrected;

[0008] The test end face is set between the directional coupler and the device under test DUT to detect the loss constant ka;

[0009] The estimation of the calibration factor of the direct measurement method is corrected by the experimentally measured RF high power standard indication and the power indication of the device under test DUT. The formula is expressed as:

[0010]

[0011] in, is the loss constant of the device under test DUT, is the calibration factor for the power standard, and It is the RF high power standard indication and the power indication of the device under test DUT obtained through experimental measurement. is the reflection coefficient of the “combination” of the device under test (DUT) and the power standard, is the reflection coefficient of the power standard, It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

[0012] Furthermore, the receiving of the radio frequency high-power signal and the calculation of the required equivalent source reflection coefficient of the directional coupler specifically include:

[0013] Receive high-power RF signals, measure the S parameters of the directional coupler and calculate the equivalent source-reflection coefficient of the required directional coupler:

[0014]

[0015] in, It is calculated by monitoring the equivalent source reflection coefficient determined by the directional coupler and measuring the S parameters of the directional coupler after calibration with a network analyzer.

[0016] Furthermore, the loss constant of the device under test (DUT) The calculation formula is expressed as:

[0017]

[0018] in, It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

[0019] The beneficial effects of the present invention are:

[0020] The present invention is a calibration factor estimation and correction method for a radio frequency high-power calibration direct measurement method. Compared with the prior art, the present invention has the following technical effects:

[0021] The present invention reduces the error of radio frequency high power calibration caused by factors such as high frequency, thereby improving the accuracy of radio frequency high power calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a radio frequency high-power directional power sensor;

[0023] Figure 2 A schematic diagram of the structure of the alternating comparison method provided by an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of the structure of the transfer standard method provided by an embodiment of the present invention;

[0025] Figure 4 A schematic diagram of the structure of a direct measurement method provided by an embodiment of the present invention;

[0026] Figure 5 A connection diagram for measuring the power of a device under test (DUT) when connected to an ideal RF load (without reflection) and a reflective RF load provided in an embodiment of the present invention;

[0027] Figure 6 A schematic diagram of a flow chart of comparison of calibration methods of radio frequency directional power sensors and estimation and correction of calibration factors provided in an embodiment of the present invention; DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0029] The present invention comprises the following steps:

[0030] Receive high-power radio frequency signals and calculate the equivalent source reflection coefficient of the directional coupler to be corrected;

[0031] The test end face is set between the directional coupler and the device under test DUT to detect the loss constant ka;

[0032] The estimation of the calibration factor of the direct measurement method is corrected by the experimentally measured RF high power standard indication and the power indication of the device under test DUT. The formula is expressed as:

[0033]

[0034] in, is the loss constant of the device under test DUT, is the reflection coefficient of the “combination” of the device under test (DUT) and the power standard, is the reflection coefficient of the power standard, It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

[0035] The receiving of the radio frequency high-power signal and calculating the required equivalent source reflection coefficient of the directional coupler specifically includes:

[0036] Receive high-power RF signals, measure the S parameters of the directional coupler and calculate the equivalent source-reflection coefficient of the required directional coupler:

[0037]

[0038] in, It is calculated by monitoring the equivalent source reflection coefficient determined by the directional coupler and measuring the S parameters of the directional coupler after calibration with a network analyzer.

[0039] Loss constant of the device under test (DUT) The calculation formula is expressed as:

[0040]

[0041] in, It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

[0042] like Figure 1 As shown, directional power sensors are mainly divided into through-type power sensors and terminal power sensors. They are the most common sensor types in RF high-power measurement. Power sensors are composed of directional couplers, detectors, and metering elements. In the directional coupler, a small part of the RF high-power signal will be coupled and transmitted to the detector. In addition, symmetrical detection circuits are designed at the forward and reverse ends of the directional coupler, which can demodulate sinusoidal signals and pulse modulated signals into measurable DC signals or baseband pulse signals. At the same time, the output voltage of the detector can be indicated by a power meter, a traditional magnet and coil (analog power meter), or an A / D circuit (digital power meter). Forward power is usually the part of the power we need to pay attention to, indicating how much power is transmitted to the RF load to ensure the effective output of the signal and the normal operation of the system. Reverse power refers to the power reflected back from the load or system, so as to evaluate the matching degree and loss of the system and prevent the reflected power from damaging the equipment. In the present invention, the directional power sensor uses the through-type power sensor Bird 7020.

[0043] The calibration methods of directional power sensors listed in the existing calibration specifications are mainly divided into the alternating comparison method, the transfer standard method and the direct measurement method.

[0044] like Figure 2 FIG. 1 is a schematic diagram of the structure of the alternating comparison method provided by an embodiment of the present invention. The alternating comparison method is performed by comparing the result of the radio frequency high power standard and the through-type power sensor of the device under test (DUT). Figure 2 It can be seen that the whole system is composed of a signal generator, a power amplifier, a directional coupler, a power meter, a stabilizer, a high-power RF standard and a device under test (DUT). The specific experimental steps are as follows: before the signal generator and the power amplifier output RF, we need to set the signal generator, the power amplifier and the power meter to the same frequency, set the power level of the signal generator to the minimum value, and adjust the power amplifier to a stable radiation state. Then connect the high-power RF standard to the test end face for RF output. Gradually adjust the power level of the signal generator so that the high-power RF standard indication reaches the selected value, and then record the high-power RF standard indication. Then turn off the RF output of the signal generator and the power amplifier, disconnect the high-power RF standard from the test end face, and connect the device under test (DUT) to the test end face, and keep the stable radiation state for RF output again, so as to record the power indication of the device under test (DUT) again. At this point, we have obtained the high-power RF standard indication and the power indication of the device under test (DUT) that we need to measure. During the experiment, we should pay attention to selecting the power amplifiers and directional couplers of different frequency ranges according to the different frequencies set. Otherwise, it will not be conducive to obtaining accurate power measurement results and will reduce the reliability and effectiveness of the calibration.

[0045] like Figure 3 FIG. 1 is a schematic diagram of the structure of the alternating comparison method provided by an embodiment of the present invention. The transfer standard method is to calibrate the device under test DUT using a transfer standard pre-calibrated with a power standard. Figure 3 It can be seen that the required experimental equipment is the same as that of the alternating standard method. The difference is that the transfer standard method does not need to measure the power indication of the RF high power standard and the device under test DUT separately, but connects the RF high power standard and the device under test DUT together, and connects the device under test DUT to the test end face. The specific experimental steps are similar to the alternating comparison method: set the signal generator, power amplifier and power meter to the same frequency, minimum level of the signal generator and stable radiation state of the power amplifier. Then perform RF output and gradually adjust the power level of the signal generator so that the RF high power standard indication reaches the selected value, thereby simultaneously recording the RF high power standard indication and the power indication of the device under test DUT. Here we should also pay attention to selecting the power amplifier and directional coupler of different frequency ranges required according to the different frequencies set to improve the reliability and accuracy of calibration.

[0046] like Figure 4 FIG. 1 is a schematic diagram of the structure of the direct measurement method provided by an embodiment of the present invention. The direct measurement method is used to calibrate the output power of the device under test DUT. Figure 4It can be seen that the experimental equipment required is also a signal generator, power amplifier, directional coupler, power meter, stabilizer, RF high power standard and DUT, and the RF high power standard and DUT are connected together as in the transfer standard method. The difference is that the RF high power standard is connected to the test end face, and then the RF high power standard indication and the power indication of the DUT at different frequencies can be obtained by following the same experimental steps as the transfer standard method.

[0047] Receive high-power RF signals and calculate the equivalent source-reflection coefficient of the required directional coupler;

[0048] Based on the calculated equivalent source reflection coefficient of the directional coupler and the measured RF high power standard indication and the power indication of the device under test (DUT), the calibration factors of different calibration methods of the directional power sensor listed in the calibration specification are calculated and compared;

[0049] According to the calculation comparison of the calibration factors of different calibration methods of the directional power sensor listed in the calibration specification, the estimation of the calibration factor in the calibration method with larger error is corrected.

[0050] The equivalent source reflection coefficient is calculated by the reflection coefficient of the RF high power standard and the device under test DUT measured by the network analyzer, the S parameters of the required directional coupler, and the Figure 2 , 3 The calibration factors corresponding to different calibration methods are calculated and compared based on the RF high-power standard indications and the power indications of the device under test (DUT) measured by 4 different calibration methods.

[0051] Estimate the calibration factor for the alternating comparisons method:

[0052]

[0053] in, , and It is the reflection coefficient of the device under test (DUT) and the power standard and the equivalent source reflection coefficient of the directional coupler measured by the network analyzer. and It is the RF high power standard indication and the power indication of the device under test (DUT) (that is, the net absorbed power) obtained through experimental measurement. is the calibration factor for the power standard, is the calculated calibration factor of the device under test DUT. Since the alternating comparison method requires additional connections and disconnections to obtain results from the device under test DUT and the RF standard high power meter respectively, it is inefficient in operation, but this method has high measurement accuracy, small error and is more suitable for the calibration of complex equipment;

[0054] Estimate the calibration factor for the transfer standard method:

[0055]

[0056] in, and They are the device under test (DUT) and the power indicated by the power standard. is the calibration factor for the power standard, The calculated calibration factor of the device under test (DUT). Compared with the alternating comparison method, the transfer standard method does not require the device under test and the RF high power standard to be connected alternately to measure their corresponding power indications respectively. Therefore, the RF high power standard indications at different frequencies can be obtained at one time. And the power indication of the device under test , short measurement time and few reconnections. However, the calibration factor of the power standard requires a calibrated high-precision transfer standard, which needs to be calibrated regularly using a reference of known accuracy (such as a standard signal source or a reference device of known accuracy). This ensures that the measurement performance of the transfer standard always remains within the specified accuracy range, ensuring that it can continue to serve as a reliable reference. And because the equivalent source reflection coefficient in this method Calibration requires disassembly of the transfer standard, so a spare transfer standard may be needed during this process;

[0057] Estimate the calibration factor for the direct measurement method:

[0058]

[0059] in, and They are the RF high power standard indication and the power indication of the device under test (DUT) obtained through experimental measurement. and They are the power standard and the calculated calibration factor of the device under test. The direct measurement method can also directly read the power indication of the device under test DUT and the RF standard high power meter at the same time, so the operation is relatively simple and the measurement time is short. However, this method is highly dependent on the measurement conditions and has a large error before being corrected.

[0060] from Figure 2 , 3 Schematic diagram of the structure of different calibration methods in 4 and Figure 5 The comparison of calibration methods for RF directional power sensors and the flow chart of estimation and correction of calibration factors can be seen. In the direct measurement method, the equivalent source reflection coefficient It is related to the device under test (DUT), and the measurement uncertainty of the standard is unknown when the device under test (DUT) is not connected, and the measurement results may be unreliable. Although the device under test (DUT) is a 2-port device without an RF load, the test end face is set between the directional coupler and the device under test (DUT) (that is, the device under test (DUT) is connected to the test end face), and the transfer standard method is still applicable. The power at the RF load port 2 can be corrected and expressed by the following formula:

[0061]

[0062] in, and They are the RF high power standard indication and the power indication of the device under test (DUT) obtained through experimental measurement. is the loss constant of the device under test DUT, is the reflection coefficient of the “combination” of the device under test (DUT) and the power standard, is the reflection coefficient of the power standard.

[0063]

[0064] It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

[0065] The comparison of the calibration factors of different calibration methods for directional power sensors listed in the calibration specification obtained by experimental calculation according to the embodiment of the present invention without correction and after correction is shown in Table 1;

[0066] Table 1 Comparison of the calibration factors of different calibration methods for directional power sensors without correction and after correction

[0067]

[0068] The present invention compares the calibration methods of directional power sensors listed in the calibration specifications from both theoretical and experimental aspects. The table lists the calibration factor results of different methods. The device under test DUT in this invention is a directional power sensor (that is, a through-type power sensor) Bird 7020. The results show that the errors of the alternating comparison method, the transfer standard method, and the correction method are all less than 1%, which is acceptable considering the uncertainty of the power sensor. At higher frequencies, the error of the original direct measurement method exceeds 3%, indicating that the scattering parameters of the device under test have an influence on the equivalent source reflection coefficient. and power standards indicate power Therefore, the original direct measurement method in the calibration specification is not suitable for calibration compared with the alternating comparison method and the transfer standard method, and the corrected direct measurement method has a smaller error and is more suitable for calibration.

[0069] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A calibration factor estimation and correction method for a radio frequency high power calibration direct measurement method, characterized in that: include: Receive high-power radio frequency signals and calculate the equivalent source reflection coefficient of the directional coupler to be corrected; The test end face is set between the directional coupler and the device under test DUT to detect the loss constant ka; The estimation of the calibration factor of the direct measurement method is corrected by the experimentally measured RF high power standard indication and the power indication of the device under test DUT. The formula is expressed as: in, is the loss constant of the device under test DUT, is the calibration factor for the power standard, and It is the RF high power standard indication and the power indication of the device under test DUT obtained through experimental measurement. is the reflection coefficient of the "combination" of the device under test (DUT) and the power standard, is the reflection coefficient of the power standard.

2. The calibration factor estimation and correction method of the radio frequency high power calibration direct measurement method according to claim 1 is characterized in that: The receiving of the radio frequency high-power signal and calculating the required equivalent source reflection coefficient of the directional coupler specifically includes: Receive high-power RF signals, measure the S parameters of the directional coupler and calculate the equivalent source-reflection coefficient of the required directional coupler: in, It is calculated by monitoring the equivalent source reflection coefficient determined by the directional coupler and measuring the S parameters of the directional coupler after calibration with a network analyzer. It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

3. The calibration factor estimation and correction method of the radio frequency high power calibration direct measurement method according to claim 1 is characterized in that: Loss constant of the device under test (DUT) The calculation formula is expressed as: in, It is the transmission coefficient of the device under test (DUT) measured by the network analyzer.

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