A method for adaptive focusing scanning and resolution bandwidth dynamic regulation of radio frequency conducted emission test

Abstract

This invention relates to the field of electromagnetic compatibility testing technology, specifically to a method for adaptive focusing scanning and dynamic adjustment of resolution bandwidth in radio frequency conducted emission testing, comprising the following steps: acquiring radio frequency signals at each sampling node at a step frequency point; setting a fixed intermediate frequency as the step frequency point and configuring a corresponding local oscillator frequency point to generate a local oscillator signal at the local oscillator frequency point; performing nonlinear time-domain multiplication on the radio frequency signal and the local oscillator signal, and performing frequency decomposition through trigonometric identity transformation to obtain a mixed signal; setting the resolution bandwidth, and performing bandpass filtering on the mixed signal according to the resolution bandwidth to obtain a pure signal at the step frequency point; converting the pure signal into electromagnetic radiation intensity; determining whether the step frequency point is an interference frequency point according to interference judgment rules; if it is an interference frequency point, then using a dynamic adjustment method to adaptively reduce the resolution bandwidth; and simultaneously using a signal-to-noise ratio driven adjustment method to adjust the test duration of the step frequency point in step S1.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic compatibility testing technology, and more specifically, to a method for adaptive focusing scanning and dynamic adjustment of resolution bandwidth in radio frequency conducted emission testing. Background Technology

[0002] When electronic and electrical equipment is working normally, it will emit radio frequency electromagnetic interference signals to the external power grid or circuit system through conductor transmission links such as power lines, signal lines, and control lines. Radio frequency electromagnetic interference signals can enter the circuit through different paths such as conduction, radiation, and coupling. They can interfere with the sensitive modules of wireless communication equipment itself, such as radio frequency reception, clock, and data bus, leading to increased communication bit error rate, abnormal function, or even system crash. They can also couple into the circuits of surrounding electronic products, superimposed on the useful signal, causing distortion, causing abnormal equipment operation and malfunction. At the same time, they can also occupy wireless communication channel resources, affecting the communication quality of other devices in the same frequency band, and thus causing a series of problems such as the performance degradation of the wireless communication equipment itself and the abnormal operation of surrounding electronic products.

[0003] Therefore, in response to the various risks caused by the aforementioned electromagnetic interference, electromagnetic compatibility standards specify corresponding radiated emission limits for different frequency points. Products that exceed the limits will not be able to pass certification and be sold on the market. Therefore, in the research and development stage of wireless communication equipment (Wi-Fi / Bluetooth / cellular modules), a small shielded box pre-testing method is usually used to quickly test the radiation intensity at different frequency points and compare the radiation intensity obtained from the test at the same frequency point with the radiated emission limit, so as to promptly identify abnormal radiated emission problems in the early stages of research and development based on the test results and complete iterative rectification.

[0004] The above-mentioned small shielding box pre-testing method is as follows:

[0005] The metal enclosure structure of the shielding box is used to block external electromagnetic interference such as mobile phone signals, Wi-Fi, broadcasts, and base stations in the external environment, ensuring that only the radiation signals generated by the wireless communication device under test exist inside the shielding box.

[0006] Wireless communication equipment normally transmits electromagnetic waves such as main frequency signals, spurious signals, and harmonics within a shielded box. The built-in antenna inside the shielded box receives the electromagnetic waves transmitted by the wireless communication equipment and outputs radio frequency signals through the transmission link. Then, the radiation emission limit is used to determine whether the frequency point corresponding to the radio frequency signal is an interference frequency point.

[0007] While using a small shielded box pre-testing method for electromagnetic compatibility testing can achieve full coverage reception of signals across the entire test frequency band using a wideband test antenna, significantly improving the acquisition efficiency of multi-frequency signals, wireless communication devices generally employ wideband modulation communication mechanisms and operate at high frequencies. This results in the continuous distribution of signal energy across a wide frequency range through methods such as spread spectrum and OFDM multicarrier. Simultaneously, the nonlinear characteristics of the internal circuitry of the device generate fundamental waves, higher harmonics, and spurious radiation. These various signal components superimpose to form a continuously distributed wideband spectrum, making it impossible to directly separate and test the pure radio frequency signal corresponding to a single frequency point from the received mixed radio frequency signals. If the radiated emission limit is directly used to judge the frequency compliance of the mixed radio frequency signals, it will lead to the superposition of signals from different frequency points, and the inability to effectively eliminate out-of-band noise and spurious interference. This will not only fail to accurately identify the true radiation intensity of a single frequency point, but also easily result in false exceedances or missed detection of interference frequencies.

[0008] Meanwhile, because the test frequency band covers a wide range and there are a large number of step frequency points to be tested, if each frequency point is individually narrowband filtered, accurately sampled and signal analyzed, the hardware parameters need to be repeatedly adjusted and the test time extended point by point, which will consume a lot of test time, reduce the overall test efficiency, and cannot meet the actual engineering needs of rapid self-testing and rapid iterative rectification in the R&D stage of wireless communication equipment.

[0009] In view of this, we propose an adaptive focusing scan and dynamic adjustment method for resolution bandwidth in radio frequency conducted emission testing. Summary of the Invention

[0010] The purpose of this invention is to solve the technical problems in existing small shielded box pre-testing methods, such as misjudgment or omission of interference frequency points due to broadband signal aliasing and unreasonable bandwidth settings, and the difficulty in balancing test accuracy and efficiency.

[0011] To achieve the above objectives, the present invention provides a method for adaptive focusing scanning and dynamic adjustment of resolution bandwidth in radio frequency conducted emission testing, comprising the following steps:

[0012] Step S1: Define multiple step frequency points to form a frequency point sequence; set the test duration and sampling frequency for each step frequency point, and collect the radio frequency signal of the step frequency point according to the test duration and sampling frequency;

[0013] Step S2: Set the fixed intermediate frequency as the step frequency point, configure the corresponding local oscillator frequency point, and generate the local oscillator signal at the local oscillator frequency point;

[0014] The radio frequency signal and the local oscillator signal are multiplied in the nonlinear time domain, and the frequency is decomposed through trigonometric identity transformation to obtain a mixed signal;

[0015] Set the resolution bandwidth, perform bandpass filtering on the mixed signal according to the resolution bandwidth to obtain a clean signal with a step frequency; convert the clean signal into electromagnetic radiation intensity.

[0016] Step S3: Obtain the radiated emission limit corresponding to the step frequency point, retrieve the electromagnetic radiation intensity of the step frequency point under all sampling nodes, and determine the step frequency point as an interference frequency point according to the interference judgment rule.

[0017] If it is an interference frequency, a dynamic adjustment method is used to adaptively reduce the resolution bandwidth;

[0018] When adaptively reducing the resolution bandwidth, the test duration of the step frequency point in step S1 is adjusted simultaneously using the signal-to-noise ratio driven adjustment method.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] In this method for adaptive focusing scanning and dynamic adjustment of resolution bandwidth in radio frequency conducted emission testing, step S2 sets a fixed intermediate frequency as the step frequency point to configure the corresponding local oscillator frequency point, generates the local oscillator signal of the local oscillator frequency point, and then further mixes the local oscillator signal and the radio frequency signal to obtain a mixed signal. Finally, the pure signal in the mixed signal is separated by the resolution bandwidth, avoiding the problems of distortion of the true radiation intensity identification of a single frequency point, false over-limit, or missed judgment of interference frequency points caused by the superposition of signals of different frequency points and the inability to effectively remove out-of-band noise and spurious interference.

[0021] During the setting process, the resolution bandwidth is selected in accordance with EMC test standard requirements and takes into account measurement accuracy, interference resolution capability and test efficiency. This maximizes test efficiency while ensuring interference identification accuracy, and avoids misjudgment caused by noise introduced by excessively wide bandwidth, or the problem of test time increasing and efficiency decreasing due to excessively narrow bandwidth.

[0022] Simultaneously, in step S3, based on the electromagnetic radiation intensity corresponding to the clean signal, it is determined whether the step frequency point is an interference frequency point. Based on the determination result, the resolution bandwidth is further adaptively reduced, so that the reduced resolution bandwidth can more accurately separate the signal and noise, improve frequency resolution and measurement accuracy, and effectively eliminate false exceedances introduced by excessively wide bandwidth. Finally, through progressive verification and refined retesting from wide to narrow, the precise location of interference frequency points, the effective elimination of false exceedances, and the accurate identification of real radiation risks are achieved. While ensuring the rigor and reliability of EMC test results, the test efficiency loss caused by excessive bandwidth compression is avoided, achieving the optimal balance between interference identification accuracy and test efficiency, and adapting to the actual engineering needs of rapid self-testing and rapid iterative rectification in the R&D stage of wireless communication equipment.

[0023] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall working steps of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] refer to Figure 1 As shown, a method for adaptive focusing scanning and dynamic adjustment of resolution bandwidth in radio frequency conducted emission testing includes the following steps:

[0027] Step S1: Define the step frequency point Set step frequency Corresponding test duration and sampling frequency The number of corresponding sampling nodes is obtained. Collect step frequency points RF signal at each sampling node ;

[0028] Step S2: Set a fixed intermediate frequency Step frequency Configure the corresponding local oscillator frequency. , cost of vibration frequency Local oscillator signal ;

[0029] Nonlinear time-domain multiplication of radio frequency signals , local oscillator signal The mixed signal is obtained by frequency decomposition through trigonometric identity transformation. ;

[0030] Set resolution bandwidth According to resolution bandwidth Bandpass filtering of mixed signals Obtain the step frequency. pure signal ; Convert to pure signal electromagnetic radiation intensity ;

[0031] Step S3: Obtain the step frequency point Corresponding radiation emission limits Adjust the step frequency Electromagnetic radiation intensity at all sampling nodes Based on the interference judgment rules, determine the step frequency point. Interference frequency ;

[0032] If it is an interference frequency point In such cases, a dynamic adjustment method is used to adaptively reduce the resolution bandwidth. ;

[0033] Adaptive reduction of resolution bandwidth Simultaneously, the signal-to-noise ratio driven adjustment method is used to adjust the step frequency point in step S1. Test duration ;

[0034] In the implementation of the above embodiments, multi-point continuous sampling tests are performed in step S1 to avoid the problems of incomplete radiated signal feature acquisition and measurement data distortion caused by random noise and transient interference in single-point sampling. At the same time, it provides comprehensive and continuous multi-node data support for subsequent compliance judgment, effectively reducing misjudgment or omission of interference frequency points caused by abnormal data at a single point; and step S2 uses a fixed intermediate frequency. It enables a constant frequency local oscillator signal to be output after mixing at all step frequency points within the entire test frequency band. This eliminates the need to adjust the hardware parameters and filtering characteristics of the intermediate frequency link with frequency switching, thereby improving the consistency, stability and testing efficiency of signal processing. It effectively avoids hardware adaptation errors and parameter calibration deviations caused by frequent adjustment of the intermediate frequency, ensuring that subsequent signal processing stages such as filtering, amplification and detection always work at the optimal fixed frequency point, and finally lays a reliable data foundation for the interference frequency point determination in step S3.

[0035] The dynamic adjustment method in step S3 is used to record the radiation emission limits. < Electromagnetic radiation intensity The number of excessive Based on the quantity exceeding the standard Make dynamic adjustments;

[0036] Signal-to-noise ratio driven adjustment method: By sequentially extracting electromagnetic radiation intensity according to the number of sampling points from few to many, multiple sets of standard radiation intensity sequences and original radiation intensity sequences with increasing lengths are formed.

[0037] The signal-to-noise ratio (SNR) between the standard radiation intensity sequence and the original radiation intensity sequence is used to determine whether the comparison is valid based on the interference judgment rules according to the SNR; then the test duration is adjusted again. ;

[0038] The resolution bandwidth is adaptively reduced in step S3. Test duration This allows for the gradual reduction of bandwidth to improve frequency resolution and noise suppression capabilities after initial detection of interference risks. This effectively eliminates false exceedances caused by excessively wide bandwidth. At the same time, signal-to-noise ratio-driven duration adjustment avoids excessively prolonged test time. While accurately identifying real interference frequencies and ensuring rigorous and reliable EMC test results, it also improves test efficiency, achieving the optimal balance between interference identification accuracy and test efficiency. This effectively reduces the risk of test rework caused by false exceedances and meets the engineering needs of rapid self-testing and rapid iterative rectification during the R&D phase of wireless communication equipment.

[0039] The working principle of steps S1-S3 above is explained in more detail below:

[0040] Step S1: Obtain the built-in antenna's reception and transmission data, located in the test frequency band. ( The starting frequency of the test band. The end frequency of the test band, such as the start frequency. Termination frequency Multi-frequency mixed radio frequency signals within )

[0041] Define test frequency band ( The starting frequency of the test band. The end frequency of the test band, such as the start frequency. Termination frequency All test frequencies within the range are step frequencies, forming a frequency sequence. ;

[0042] Set frequency sequence Inner step frequency ( The duration of the test and sampling frequency (The minimum sampling frequency that the corresponding hardware device can achieve) forms Each sampling node uses an internal antenna to collect step frequency points at each sampling node. Corresponding radio frequency signal (in The next step frequency point of the sampling node (radio frequency signal);

[0043] The above radio frequency signals Specifically, the antenna built into the shielded box (such as a biconical antenna, a log-periodic antenna, or other broadband test antennas) is based on the principle of electromagnetic induction and antenna radiation reciprocity. It converts the electromagnetic waves radiated and propagated by wireless communication devices in space into high-frequency radio frequency voltage signals output from the antenna port through the coupling effect between the antenna element and the electromagnetic field in space.

[0044] When an antenna is placed in an alternating electromagnetic field radiated by a wireless communication device, the antenna element will induce an alternating induced electromotive force corresponding to the frequency and amplitude of the electromagnetic field, thereby generating a time-varying electromotive force at the antenna port (the time range corresponds to the test duration). The high-frequency voltage signal fully carries the wireless communication device at the stepped frequency point. The radiation intensity, phase, and modulation information at the location provide the raw test signal for subsequent superheterodyne frequency conversion, filtering, and amplitude detection; radio frequency signal. The specific expression is:

[0045] ;

[0046] in:

[0047] Radio frequency signal amplitude (RF signal) The instantaneous amplitude peak directly corresponds to the step frequency. (electromagnetic radiation intensity).

[0048] Cosine function (describing radio frequency signals) The sinusoidal oscillation characteristics conform to the alternating characteristics of electromagnetic waves.

[0049] The pi coefficient is used to determine the step frequency. Convert to angular frequency ω= Adapted to cosine function (radian input)

[0050] The sampling times for the time variable (corresponding to the multiple sampling nodes set in step S1, with the time range being the test duration) Used to capture radio frequency signals (instantaneous fluctuations)

[0051] The initial phase of the radio frequency signal (RF signal) exist The initial phase at time step is the step frequency. (functions)

[0052] Radio frequency signals from wireless communication devices are acquired using a built-in antenna. While shielding effectively isolates external electromagnetic interference and background radiation noise from the test environment, significantly reducing the impact of environmental noise on signal acquisition, the electromagnetic radiation signals of wireless communication devices (Wi-Fi / Bluetooth / cellular modules, etc.) operate at high frequencies ranging from hundreds of MHz to GHz. These signals highly overlap with the core frequency band of electromagnetic compatibility testing, generating multiple electromagnetic signals including the fundamental frequency, higher harmonics, and spurious radiation. Furthermore, the shielded enclosure still contains various internal noise sources such as instrument background noise, thermal noise from the RF link itself, parasitic radiation from internal circuits, resonance interference within the shielded enclosure cavity, and cable coupling crosstalk. Therefore, the RF signal... It includes a large amount of noise interference;

[0053] In this example, step S1 involves setting the test duration. and sampling frequency able to test duration The system continuously acquires radio frequency signals from multiple points to avoid incomplete acquisition of radiation signal characteristics and distortion of measurement data caused by random noise and transient interference in single-point acquisition. This further enables subsequent steps, such as S3.1, to determine the step frequency point. Is it an interference frequency? In this case, it is important to avoid abnormal fluctuations in data from a single point due to noise interference, and to prevent effective signals from being overwhelmed by noise, thus avoiding misjudging false exceedances caused by noise as interference frequencies. Interference frequencies may occur due to insufficient signal acquisition. Cases of missed judgment.

[0054] Simultaneously, the step frequency point was tested using the antenna built into the shielded box. Corresponding radio frequency signal During the process, wireless communication devices (Wi-Fi / Bluetooth / cellular modules) generally adopt broadband modulation communication mechanisms to achieve high speed, high anti-interference, and multi-user access capabilities. Furthermore, their operating frequencies are in the high-frequency range of hundreds of MHz to GHz. During data transmission, they distribute signal energy evenly over a wide frequency range through methods such as spread spectrum, OFDM multicarrier, and higher-order modulation, rather than concentrating it at a single frequency point. In addition, the nonlinear characteristics of the internal RF power amplifier, clock circuit, and digital logic circuits continuously generate fundamental waves, higher-order harmonics, and spurious radiation outside the operating frequency. These components superimpose to form a continuously distributed broadband spectrum, thus affecting the RF signal. For high-frequency broadband signals, their spectral energy is not discrete spikes, but continuously covers the test frequency band in step S1. Taking Wi-Fi 2.4GHz signal as an example, its single channel bandwidth reaches 20MHz / 40MHz, and the energy is continuously distributed throughout the entire channel bandwidth. At this time, the built-in antenna acts as a broadband receiving device throughout the entire test duration. The internal system indiscriminately couples and picks up all electromagnetic radiation components present in space, and cannot selectively receive only stepped frequency points. Ultimately, this resulted in the signal transmission link operating in the test frequency band. All of them exhibit significant and continuous signal components;

[0055] Based on the characteristics of the aforementioned wireless communication device, step S2 in this example is used to process the radio frequency signal. The mixing, bandpass filtering, and detection processes are performed to obtain the step frequency. Corresponding electromagnetic radiation intensity The specific work steps are as follows:

[0056] Step S2.1: Set the step frequency. Corresponding to fixed intermediate frequency Frequency synthesis is performed based on the superheterodyne frequency transformation principle to obtain a frequency based on a fixed intermediate frequency. Step frequency Synchronous configuration of the corresponding local oscillator frequency point =Step frequency + Fixed intermediate frequency (i.e., configuring the local oscillation frequency) During the process, fixed intermediate frequency The frequency remains unchanged, while the local oscillator frequency remains the same. With step frequency (Synchronous changes)

[0057] Then, a high-precision frequency synthesizer can be used to generate the frequency point of the local oscillation. Matching with radio frequency signals Synchronized local oscillator signal The specific expression is:

[0058] ;

[0059] in:

[0060] The amplitude of the local oscillator signal (set to a constant value by the hardware circuit);

[0061] This is the initial phase of the local oscillator signal;

[0062] In step S2.1, the frequency sequence is set. All step frequency points correspond to fixed intermediate frequencies Used for gradually switching step frequency points At that time, all were at a fixed intermediate frequency. As the target frequency for downconversion, it passes through the local oscillating frequency. =Step frequency + Fixed intermediate frequency The frequency mapping relationship ensures that each different step frequency point can output a fixed intermediate frequency with the same frequency after subsequent mixing. This eliminates the need to adjust the fixed intermediate frequency as the step frequency changes. It always operates at the optimal fixed frequency point designed for it;

[0063] High-precision frequency synthesizer generates native frequency point Corresponding local oscillator signal The working principle is as follows: establish the local oscillator frequency. With local oscillator signal A strict, stable, and repeatable mapping relationship between them is established, and then based on the local oscillator frequency... The corresponding values ​​generate the corresponding sinusoidal local oscillator signal, thus obtaining the local oscillator signal. .

[0064] Step S2.1 Radio frequency signal , local oscillator signal A nonlinear time-domain multiplication operation is performed, and frequency decomposition is carried out through trigonometric identities to finally obtain the mixed signal. ,Right now:

[0065] Added step frequency Local oscillator frequency Get and frequency points ;

[0066] This vibration frequency point Subtract step frequency Obtain the difference frequency point ;

[0067] radio frequency signals , local oscillator signal Multiplication in the time domain, based on trigonometric identity decomposition, yields the sum and frequency points. Difference frequency point Corresponding frequency components Difference frequency component Mixed signals ;

[0068] The specific working principle of step S2.1 above is as follows:

[0069] Nonlinear time-domain multiplication of radio frequency signals , local oscillator signal :

[0070] = ;

[0071] Frequency decomposition using trigonometric identities:

[0072] Using the core trigonometric identity transformation formula make , After substituting, we obtain the mixed signal:

[0073] ;

[0074] The above middle For sum-frequency components , Difference frequency component .

[0075] At this point, although a mixed signal is obtained through step S2.1 However, the difference frequency point was not specified. Any filtering and interference separation processing is performed, therefore the mixed signal This includes not only frequency points Difference frequency point Corresponding sum frequency components Difference frequency component It also includes broadband noise, shielded box multipath reflection interference, and circuit spurious coupling components. If the mixed signal is directly judged at this point... Is it an interference frequency? This will result in excessively high noise floor, distorted signal amplitude measurement, and insufficient frequency resolution, failing to meet the requirements of EMC testing for accurate identification and precise quantification of interference signals. Therefore, step S2.2 is used for bandpass filtering of mixed signals. : Set resolution bandwidth The intermediate frequency is fixed in step S2.1 Generate the corresponding passband range centered on the target area. Through passband range From mixed signal Selecting difference frequency points Nearby, within the passable zone Pure signal within This filters out all out-of-band spurious interference, including broadband noise, shielded box multipath reflections, parasitic coupling, power supply ripple, and local oscillator leakage, preventing weak radiated signals from being overwhelmed by noise, solving the problem of indispensable radio frequency interference, and ensuring a clean signal. Able to reflect step frequency Features;

[0076] The local oscillator frequency in step S2.2 above Subtract step frequency Obtain the difference frequency point Based on the superheterodyne frequency transformation principle in step S2.1, the difference frequency point For fixed intermediate frequency And benefiting from the local oscillator frequency It will change with the step frequency. Based on the relationship of the superheterodyne frequency transformation principle, dynamic tracking and adjustment are performed, therefore the intermediate frequency is fixed. The frequency remained constant throughout the full-band test, meaning that the step frequency was adjusted only afterward. During the process, it is only necessary to synchronously track and change the local oscillator frequency. This ensures that the difference frequency remains constant at the difference frequency point. No need to generate passband range in step S2.2 Any redesign, hardware module switching, or parameter calibration of the required center frequency will directly allow all subsequent signal processing stages, such as filtering, amplification, detection, and amplitude detection, to operate at a uniform and stable fixed intermediate frequency. This approach not only fundamentally ensures the consistency of each step frequency point across the entire test band and the repeatability of the test process, but also effectively avoids the problems caused by frequent adjustments to the fixed intermediate frequency. This introduces hardware compatibility errors and parameter calibration deviations, while ensuring that each processing stage always operates at a fixed intermediate frequency. This further improves the accuracy and efficiency of signal processing, and also reduces the complexity of hardware debugging and testing operations, as well as reducing errors introduced by human operation, such as:

[0077] The test frequency band is 30MHz-6GHz, with a fixed intermediate frequency. When set to 400MHz, at the step frequency point The corresponding local oscillator frequency is 30MHz. The fixed intermediate frequency is 430MHz, and the difference between the two is 400MHz. When the frequency step point... When switching to 6GHz, the local oscillator frequency will be simultaneously adjusted. The frequency was adjusted to 6.4GHz, and the difference between the two remained at a fixed intermediate frequency of 400MHz. At this time, the center frequency of the filter passband in step S2.3 was always fixed at 400MHz. There was no need to redesign the filter circuit, switch the amplification module, or calibrate the detection parameters. In the full-band test from 30MHz to 6GHz, the filtering, amplification and other links all operated at the optimal working frequency of 400MHz, which ensured the consistency of the radiation intensity measurement results at different frequency points, and also made the test operation simpler and the test data more comparable.

[0078] The following is an example of bandpass filtering in step S2.2:

[0079] Differential frequency point after mixing =10.7MHz, set resolution bandwidth =100kHz, with 10.7MHz as the center, the passband range is 10.65MHz~10.75MHz;

[0080] Bandpass filtering only allows the difference frequency component within the passband range of 10.65MHz to 10.75MHz. Through low-frequency noise below 10.65MHz and difference frequency components above 10.75MHz. If this is the case, it is determined that both high-frequency spurious signals and multipath reflection interference from the shielding box have been filtered out, thus achieving the filtering of the difference frequency component. Precise screening.

[0081] Furthermore, considering the filtering process for the corresponding step frequency points of the wireless communication device, since the radio frequency signal of the wireless communication device is a high-frequency broadband signal, its spectral energy is continuously distributed throughout the entire test frequency band, and the mixed signal after mixing... It contains a large amount of out-of-band interference such as broadband noise, shielded box multipath reflection, and circuit stray coupling. Therefore, step S2.2 involves resolution bandwidth. For mixed signals During the filtering process, if the resolution bandwidth is... When the passband is set too narrow, the signal frequency details become more refined and the amplitude changes become more subtle, thus requiring an increase in the number of sampling nodes in step S1. This is used to more accurately capture signal characteristics within a narrow band and ensure filtering and measurement accuracy, thus more completely restoring signal amplitude and frequency information; while due to the sampling frequency in step S1 The sampling frequency is set based on the minimum hardware sampling frequency. If it is necessary to increase the number of sampling nodes, then... At this time, a fixed sampling frequency is required. Extend the single-frequency data acquisition time, i.e., increase the test duration. While increasing the test duration Afterwards, it will lead to a significant increase in the processing time of a single frequency point, a significant increase in the overall test cycle, a sharp drop in test efficiency, and an inability to meet the actual test requirements of wide-band multi-step frequency point rapid scanning.

[0082] Therefore, when setting the resolution bandwidth in step S2.2, it should be done in accordance with the EMC testing standards such as CISPR and GB / T. That is, under the premise of ensuring measurement accuracy and interference resolution capability, the maximum resolution bandwidth that meets the standard requirements should be selected as the resolution bandwidth used for current filtering. ;

[0083] Step S2.3: Detection and processing of the clean signal Convert to pure signal Step frequency Corresponding electromagnetic radiation intensity ;

[0084] ;

[0085] in:

[0086] This is the antenna frequency response factor (used to convert the voltage signal at the antenna port into spatial radiation field strength).

[0087] The intermediate frequency link gain (the total gain of intermediate frequency circuits such as mixers, filters, and amplifiers, used to compensate for signal amplification / attenuation in the link);

[0088] This is the cable loss compensation value (used to compensate for signal attenuation caused by the cable, to avoid low field strength measurement values, and to ensure measurement accuracy).

[0089] Step frequency Electromagnetic radiation intensity at different sampling nodes Significant fluctuations and differences can occur due to factors such as instantaneous signal amplitude fluctuations, channel noise fluctuations, dynamic changes in circuit operating status, environmental reflections and multipath effects, and the noise inherent in the measurement system itself. This is further influenced by the resolution bandwidth in step S2.2. The standard bandwidth selected to balance measurement accuracy, interference resolution, and testing efficiency only reflects the overall radiation characteristics within the frequency band and cannot completely eliminate intensity differences at each sampling time. Therefore, to avoid missing out on non-compliant points and causing misjudgments due to using only partial sampling data or average values, step S3 is used to determine the step frequency point. Is it an interference frequency? If it is determined to be an interference frequency point If necessary, the resolution bandwidth in step S2.2 will be adjusted synchronously. and the test duration in step S1 Its more detailed working principle is as follows:

[0090] Step S3.1 Obtain the step frequency point Corresponding radiation emission limits And adjust the step frequency. In step S2.3 Electromagnetic radiation intensity corresponding to each sampling node ;

[0091] Compare the radiation emission limits one by one and all electromagnetic radiation intensity Determine the step frequency point Whether each radiation intensity is compliant, if any electromagnetic radiation intensity exceeds the radiation emission limit. When the step frequency is determined, the step frequency is then determined. Interference frequency This allows for the comprehensive, accurate, and complete identification of step frequency points. Is it an interference frequency point with excessive radiation? This ensures that the electromagnetic compatibility assessment results are rigorous and reliable, and effectively prevents interference risks and test failures caused by undetected local radiation exceeding the standard.

[0092] Furthermore, due to the resolution bandwidth in step S2.2 While it can improve testing efficiency, the wide filter passband may introduce additional broadband noise and aliasing of adjacent frequency components. This could lead to some radiation intensity exceeding the limit not being caused by actual interference signals from the equipment, but by false exceedances due to insufficient measurement resolution. Therefore, step S3.1 uses radiated emission limits. Determine the step frequency Interference frequency If so, it is determined that it may be due to resolution bandwidth. Setting the frequency too wide can lead to insufficient measurement accuracy, inadequate frequency resolution, or insufficient noise suppression. To ensure accuracy at interfering frequencies... Accurate identification is based on the fact that the electromagnetic radiation intensity does not meet the radiation emission limits. The number of adaptive reduction resolution bandwidth For resolution bandwidth ( For adaptive adjustment coefficients, The quantity of electromagnetic radiation intensity. The quantity exceeding the standard (i.e., electromagnetic radiation intensity > radiation emission limit) The more (number) that is, the higher the resolution of the loan. The greater the reduction, the higher the resolution bandwidth. Minimum resolution bandwidth ;

[0093] Minimum resolution bandwidth For resolution bandwidth The physical lower limit, to avoid the impact of resolution bandwidth Adaptive reduction to resolution bandwidth Excessive compression can lead to a surge in measurement time, excessively high noise floor, and failure of signal amplitude statistics. At the same time, it is necessary to ensure that the test configuration strictly meets the mandatory requirements of the electromagnetic compatibility test standards for receiver resolution capabilities, and to guarantee the legality, consistency, and comparability of the measurement results. Specifically, it can be set according to the mandatory provisions of the test standards. Specifically, according to general electromagnetic compatibility test standards such as CISPR16-1-1 and GB / T6113, the legal resolution bandwidth level and minimum allowable resolution bandwidth that the receiver must use are clearly specified for different test frequency bands.

[0094] The standard, based on the spectral characteristics of electromagnetic interference, measurement repeatability, receiver hardware capabilities, and consistency with global laboratory comparisons, imposes mandatory minimum resolution constraints on different frequency bands, prohibiting unlimited bandwidth reduction. Before testing begins, based on the current test frequency band range, the standard-permitted minimum resolution bandwidth is determined by referring to a table using the frequency band-bandwidth mapping relationship specified in the standard, and this minimum resolution bandwidth is used as the minimum resolution bandwidth. ;

[0095] In subsequent iterations of adaptively reducing resolution bandwidth, all calculation results are based on the minimum resolution bandwidth. To lower the endpoint, when the calculated resolution bandwidth... Minimum resolution bandwidth At that time, directly lock the minimum resolution bandwidth. And terminate the bandwidth reduction, so that the entire adaptive control process can be stably converged and executed in a closed loop under standard constraints;

[0096] Repeat steps S1-S2.3, and then proceed based on the current step frequency. Corresponding multiple electromagnetic radiation intensities and radiation emission limits Compare them until the resolution bandwidth is reached. Minimum resolution bandwidth This ensures that the final judgment is true and reliable.

[0097] Step S3.2 is used to adaptively reduce the resolution bandwidth in step S3.1. For resolution bandwidth Simultaneously, the signal-to-noise ratio driven adjustment method is used to adjust the step frequency point in step S1. Test duration Specifically:

[0098] Adjust the step frequency In step S2.3 Electromagnetic radiation intensity corresponding to each sampling node ;

[0099] Enter the step frequency again The radio frequency signal in step S1 Step S2.3: Acquire radio frequency signal correspond Electromagnetic radiation intensity at each sampling node (i.e., the original electromagnetic radiation intensity that has not been screened in steps S2.1-S2.3).

[0100] Electromagnetic radiation intensity was extracted in ascending order of the number of sampling points. Electromagnetic radiation intensity This results in multiple sets of standard radiation intensity sequences and original radiation intensity sequences with increasing lengths:

[0101] The m-th standard radiation intensity sequence is: ;

[0102] The m-th group of original radiation intensity sequences ;

[0103] Calculate the signal-to-noise ratio for each sequence as the number of sampling points increases from 1 to p. Specifically, the m-th group of standard radiation intensity sequence Original radiation intensity sequence The signal-to-noise ratio between them is:

[0104] ;

[0105] in:

[0106] Standard radiation intensity sequence Original radiation intensity sequence Number of sampling points;

[0107] Standard radiation intensity sequence The mean;

[0108] Original radiation intensity sequence The standard deviation.

[0109] The signal-to-noise ratio driven adjustment method in step S3.2 above is used for quantization resolution bandwidth. For pure signals The filtering effect is used to accurately evaluate the frequency domain interference suppression capability under different bandwidths; while using resolution bandwidth During the filtering process, due to resolution bandwidth It can only filter out out-of-band spurious interference in the frequency domain, but cannot eliminate non-frequency selective noise such as random noise in the time domain (e.g., receiver thermal noise, ambient electromagnetic background noise) and transient interference (e.g., equipment switching transients, external pulse interference). Relying solely on a single statistical analysis with a fixed number of sampling points is insufficient to fully offset the random fluctuations of noise, and cannot guarantee the stability and reliability of signal amplitude measurement. Therefore, it is necessary to adjust the step frequency in step S1. Test duration By optimizing the sampling duration, the shortcomings of time-domain statistical accuracy are compensated for, achieving dual optimization of frequency-domain filtering and time-domain statistics;

[0110] And further adjustments to the test duration During the process, the duration of the test directly determines the number of sampling points, which in turn directly affects the completeness and statistical sufficiency of the acquisition of the time-domain characteristics of the electromagnetic radiation signal: the fewer the sampling points, the greater the disturbance of random noise to the time-domain statistics (such as mean and amplitude distribution), and the more significant the fluctuation of the measurement results; the more sampling points, the more sufficient the statistical averaging cancellation effect of random noise, and the closer the measurement results are to the true signal value. Therefore, it is necessary to calculate the standard radiation intensity sequence corresponding to different numbers of sampling points. Original radiation intensity sequence Signal-to-noise ratio between Through signal-to-noise ratio This visually demonstrates the improvement in time-domain statistical accuracy under different sampling durations, specifically using a standard radiation intensity sequence. As a reference for the clean signal after filtering and detection, the original radiation intensity sequence For noisy measured signals, the higher the signal-to-noise ratio, the lower the proportion of noise in the measured signal and the more reliable the statistical results.

[0111] Furthermore, when different numbers of sampling points correspond to standard radiation intensity sequences Original radiation intensity sequence Signal-to-noise ratio between With the number of sampling points When the value increases gradually, it indicates that although the resolution bandwidth is used... It can filter out some out-of-band noise and suppress interference in the frequency domain. However, due to the insufficient number of sampling points p, the time-domain characteristics of the electromagnetic radiation signal are not fully collected and statistically analyzed. The statistical average suppression effect of random noise and spurious interference has not yet reached its optimal level, and the statistical results of the signal amplitude still fluctuate significantly. The measurement reliability still has room for improvement. Further optimization is needed by extending the test duration and increasing the number of sampling points. To understand the above reasons in more detail, we will take the EMC conducted emission pre-test of a consumer Bluetooth speaker as an example and select a step frequency point. (Bluetooth operating frequency band), preset resolution bandwidth (Complies with CISPR 16-1-1 bandwidth requirements for frequency bands above 1 GHz);

[0112] Initial testing phase (insufficient sampling points): Initially set the test duration. The corresponding number of sampling points (sampling rate) At this time, although Out-of-band interference beyond 2.4GHz±0.5MHz has been filtered out, but random noise in the time domain, such as receiver thermal noise and ambient WiFi co-channel interference, has not been fully statistically analyzed: the calculated signal-to-noise ratio The measured signal amplitude fluctuated significantly between 45dBμV and 53dBμV, and the deviation of the results of repeated measurements reached 8dB, which completely failed to meet the requirements of EMC testing for measurement repeatability and posed a serious risk of false exceedance.

[0113] Duration Adjustment and Signal-to-Noise Ratio Verification Phase: Based on signal-to-noise ratio driven logic, the test duration is gradually extended: when When the number of sampling points m=500, the signal-to-noise ratio increases to 28dB, and the signal amplitude fluctuation narrows to 49dBμV-51dBμV; when When the number of sampling points m=1000, the signal-to-noise ratio stabilizes at 33dB, the signal amplitude fluctuation is only ±0.5dB, and the measurement results are completely converged. This process intuitively demonstrates that as the number of sampling points increases, time-domain random noise is canceled out by the average of multiple samplings, the signal-to-noise ratio continues to improve, and the stability and reliability of the signal amplitude statistical results are greatly enhanced, completely solving the measurement fluctuation problem caused by fixed short duration.

[0114] Convergence Termination Judgment: When the duration is extended to 20ms (number of sampling points m=2000), the signal-to-noise ratio only increases by 0.3dB, indicating that the time domain statistics have reached the optimal level. At this point, the duration adjustment is terminated, and 10ms is taken as the final test duration for this frequency point. This ensures measurement accuracy and avoids the waste of test time caused by invalid sampling, achieving a perfect balance between accuracy and efficiency.

[0115] For the reasons mentioned above, step S3.2 increases the number of sampling points in the resolution bandwidth. To obtain a richer and more complete electromagnetic radiation signal, thereby improving resolution bandwidth. Adjusting the number of sampling points creates a dual constraint for identifying interference frequencies, while using a narrower resolution bandwidth. To achieve finer and deeper frequency domain filtering, and to avoid the problem of insufficient sampling points preventing the effective identification of interference frequencies, the specific working principle is as follows:

[0116] Obtain the signal-to-noise ratio of the standard radiation intensity sequence and the original radiation intensity sequence corresponding to different numbers of sampling points. ;

[0117] Calculate the signal-to-noise ratio difference corresponding to the number of adjacent sampling points. ;

[0118] If the signal-to-noise ratio difference If the value is greater than 0, then the comparison is considered valid, and the number of valid comparisons is recorded. ,in For indicator functions, i.e. When it is 1, otherwise The time is 0;

[0119] The number of calculations r and the total number of comparisons of adjacent signal-to-noise ratios The effective ratio between Set an effective percentage threshold If the effective ratio >Effective percentage threshold If so, it can be determined that the signal-to-noise ratio gradually increases as the number of sampling points increases;

[0120] Adjusted test duration ,in This is for adjusting the coefficient.

[0121] Adaptive adjustment coefficient in step S3.1 Adjustment coefficient in step S3.2 The settings can be configured using methods such as historical test data fitting and on-site interference environment calibration. Taking historical test data fitting as an example, the adaptive adjustment coefficient can be specifically set. Adjustment coefficient The working principle is as follows:

[0122] First, a large amount of historical EMC pre-test data was collected from the same frequency band, the same type of device under test, the same test standard, and the same test environment. The historical EMC pre-test data covered different interference intensities, different exceedance conditions, different signal-to-noise ratio levels, different resolution bandwidth configurations, and different test duration configurations, which constituted the data used to train the adaptive adjustment coefficients. Adjustment coefficient Standard sample library;

[0123] In the standard sample library, each set of historical data includes the actual test conditions, the number of out-of-standard points, the number of sampling points, the measurement results before and after the resolution bandwidth adjustment, the signal-to-noise ratio change before and after the test duration adjustment, and the optimal resolution bandwidth and optimal test duration that have been manually confirmed.

[0124] Based on this, the data in the standard sample library is preprocessed to remove invalid samples such as abnormal fluctuations, sudden environmental changes, and equipment malfunctions, while retaining valid, stable, and reproducible test data to ensure the accuracy of the subsequent fitting process.

[0125] Subsequently, the self-adaptive adjustment coefficient was adjusted. Establish a mapping relationship between the excess ratio and the reduction range of the optimal resolution bandwidth; and address the adjustment coefficient. A mapping relationship between the effective signal-to-noise ratio and the optimal test duration extension was established; adaptive adjustment coefficients were obtained through statistical analysis, trend fitting, and correlation calculation of a large amount of effective historical data. Adjustment coefficient The stable variation law of the interference level and signal-to-noise ratio;

[0126] During the fitting process, the optimization objectives are to reduce the resolution bandwidth to better reflect real interference and extend the test duration to precisely meet the signal-to-noise ratio convergence. The calculations are iteratively performed to ensure that the adjusted coefficient outputs maintain a high degree of consistency with the historical best results. Simultaneously, to ensure adaptive coefficient adjustment... Adjustment coefficient There will be no uncontrolled adjustment due to excessive or insufficient adjustment. Constraints will be added during the fitting process to ensure that the resolution bandwidth is never lower than the minimum resolution bandwidth specified by the standard, and to ensure that the test duration is not extended beyond the preset limit, so as to avoid excessive adjustment that leads to a decrease in test efficiency.

[0127] After fitting, a set of adaptive adjustment coefficients suitable for the current equipment type, test frequency band, and test standard is obtained. Adjustment coefficient .

[0128] In summary:

[0129] First, set the test duration using step S1. and sampling frequency This is used to set multiple sampling nodes so that the subsequent step S2 can analyze the radio frequency signal. Corresponding electromagnetic radiation intensity Afterwards, it can fully capture the dynamic changes in radiation at each step frequency point, providing comprehensive and continuous raw data support for the subsequent S3 compliance determination.

[0130] Furthermore, the electromagnetic radiation intensity is analyzed in step S2. During the process, a fixed intermediate frequency is set. Generate the corresponding local oscillator frequency. The corresponding local oscillator signal is generated by acoustic measurement using a high-precision frequency synthesizer. Then mix the radio frequency signal. With local oscillator signal The step frequency point is obtained. Mixed signals with electromagnetic radiation characteristics ;

[0131] Due to fixed intermediate frequency Irrelevant step frequency The change in frequency thus generates the native oscillating frequency in the high-precision frequency synthesizer. During the process, the high-precision frequency synthesizer can always keep the hardware parameters and filtering characteristics of the intermediate frequency link constant, without having to repeatedly adjust the circuit parameters with frequency switching, thereby improving the stability, consistency and response speed of the test system.

[0132] Step S2 sets the resolution bandwidth for coarse filtering. Through resolution bandwidth It can initially filter out out-of-band broadband noise and interference from adjacent frequencies while maintaining testing efficiency, and further extract mixed signals. Pure signals in This provides basic data for subsequent interference determination;

[0133] Step S3 further examines the clean signals from multiple sampling nodes. Determine the step frequency Is it an interference frequency? If the judgment is made, the resolution bandwidth will be adaptively adjusted again. and test duration Then determine the interference frequency again. Until resolution bandwidth Minimum resolution bandwidth If the step frequency is at this time Interference frequency This indicates the step frequency. The presence of genuine, stable, and non-negligible electromagnetic radiation exceeding the standard, rather than being caused by noise or measurement errors introduced by excessive bandwidth, allows for precise location of interfering frequencies, effective elimination of false exceedances, and accurate identification of genuine radiation risks through progressive verification and refined retesting from wide to narrow bandwidth. This enables accurate identification of frequencies with real interference problems, ensuring rigorous and reliable EMC test results, while avoiding test efficiency losses caused by excessive bandwidth compression, thus achieving the optimal balance between interference identification accuracy and test efficiency.

[0134] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for adaptive focusing scanning and resolution bandwidth dynamic regulation of radio frequency conducted emission test, characterized in that, Includes the following steps: Step S1: Define multiple step frequency points to form a frequency point sequence; set the test duration and sampling frequency for each step frequency point, and collect the radio frequency signal of the step frequency point according to the test duration and sampling frequency; Step S2: Set the fixed intermediate frequency as the step frequency point, configure the corresponding local oscillator frequency point, and generate the local oscillator signal at the local oscillator frequency point; The radio frequency signal and the local oscillator signal are multiplied in the nonlinear time domain, and the frequency is decomposed through trigonometric identity transformation to obtain a mixed signal; Set the resolution bandwidth, perform bandpass filtering on the mixed signal according to the resolution bandwidth to obtain a clean signal with a step frequency; convert the clean signal into electromagnetic radiation intensity. Step S3: Obtain the radiated emission limit corresponding to the step frequency point, retrieve the electromagnetic radiation intensity of the step frequency point under all sampling nodes, and determine the step frequency point as an interference frequency point according to the interference judgment rule. If it is an interference frequency, a dynamic adjustment method is used to adaptively reduce the resolution bandwidth; When adaptively reducing the resolution bandwidth, the test duration of the step frequency point in step S1 is adjusted simultaneously using the signal-to-noise ratio driven adjustment method.

2. The method of claim 1, wherein the method further comprises: The frequency point sequence in step S1 is: Acquire data received and transmitted via the built-in antenna, located in the test frequency band. Multi-frequency mixed radio frequency signals corresponding to different test frequencies; define the test frequency band. All test frequencies are step frequencies, forming a frequency sequence. ; Set frequency sequence Each step frequency point The test duration is Sampling frequency is Used for a test duration of Inside, a sampling frequency of is used. Real-time acquisition of step frequency points Corresponding radio frequency signal .

3. The method of claim 2, wherein: The local oscillator frequency point and the local oscillator signal corresponding to the local oscillator frequency point in step S2 are: Set step frequency Corresponding to fixed intermediate frequency Based on the superheterodyne frequency transformation principle, frequency synthesis was performed to finally obtain the local oscillator frequency. =Step frequency + Fixed intermediate frequency ; generating a local frequency point matching, with a radio frequency signal synchronized local signal .

4. The method of claim 3, wherein: Step S2 involves radio frequency signals. , local oscillator signal A nonlinear time-domain multiplication operation is performed, and frequency decomposition is carried out through trigonometric identities to finally obtain the mixed signal. Specifically, the mixed signal for: addition step frequency point local frequency point obtained sum frequency point ; local frequency point subtracted step frequency point difference frequency point ; radio frequency signals , local oscillator signal Multiplication in the time domain, based on trigonometric identity decomposition, yields the sum and frequency points. Difference frequency point Corresponding frequency components Difference frequency component Mixed signals .

5. The method of claim 4, wherein: The step S2 band-pass filters the mixed signal Is: Set resolution bandwidth With the fixed intermediate frequency Generate the corresponding passband range centered on the target area. Through passband range From mixed signal Selecting difference frequency points Nearby, within the passable zone Pure signal within .

6. The method of adaptive focusing scan and resolution bandwidth dynamic regulation for radio frequency conducted emission test according to claim 5, wherein: The step S2 detects the pure signal , converts the pure signal to a step frequency point , and obtains the corresponding electromagnetic radiation intensity , specifically: ； wherein, is an antenna frequency response factor, is an intermediate frequency link gain, is a cable loss compensation value.

7. The method of adaptive focusing scan and resolution bandwidth dynamic regulation for radio frequency conducted emission test according to claim 6, wherein: The interference judgment rule in the step S3 judges whether the step frequency point is an interference frequency point :​ Obtain step frequency Corresponding radiation emission limits And adjust the step frequency. Electromagnetic radiation intensity corresponding to multiple sampling nodes in step S2 The multiple sampling nodes are the step frequency points. In step S2, the number of samples corresponding to the acquisition of radio frequency signals is determined using the test duration and sampling frequency. Compare the radiation emission limits one by one and all electromagnetic radiation intensity Determine the step frequency point Whether each radiation intensity is compliant, if any electromagnetic radiation intensity exceeds the radiation emission limit. When the step frequency is determined, the step frequency is then determined. Interference frequency .

8. The method of adaptive focusing scan and resolution bandwidth dynamic regulation for radio frequency conducted emission test according to claim 7, wherein: The dynamic adjustment method in the step S3 is used to adaptively reduce the resolution bandwidth for the resolution bandwidth , specifically: ； wherein, is an adaptive adjustment coefficient, is an electromagnetic radiation intensity quantity, is an electromagnetic radiation intensity > radiation emission limit exceeded quantity.

9. The method of claim 7, wherein: The step S3 signal-to-noise ratio driven adjustment method is used to adjust the step S1 step frequency point The test duration is the test duration , and the specific process is as follows: Calling out step frequency In step S2, the electromagnetic radiation intensity corresponding to the plurality of sampling nodes ; Enter the step frequency again The radio frequency signal in step S1 Step S2: Acquire radio frequency signal Electromagnetic radiation intensity corresponding to multiple sampling nodes ; Electromagnetic radiation intensity was extracted sequentially from the fewest to the most numerous sampling points, forming multiple sets of standard radiation intensity sequences and the original radiation intensity sequences with increasing lengths: The signal-to-noise ratio corresponding to each group of sequences is calculated when the sampling point number is sequentially increased from 1 to p ; Calculate the signal-to-noise ratio difference value corresponding to the adjacent sampling points ; Signal-to-noise ratio difference If the difference is greater than 0, it is determined that the contrast is valid contrast and the number of valid contrasts is recorded Wherein is an indicator function, i.e. 1 if 0 if Calculate the effective number of comparisons r and the total number of adjacent signal-to-noise ratio comparisons. The effective ratio between ; Set the effective proportion threshold , if the effective proportion > the effective proportion threshold , it is judged that the signal-to-noise ratio gradually increases with the increase of the sampling point number; adjusted test duration , is an adjustment factor.

10. The method of claim 7, wherein: The m-th group of standard radiation intensity sequences in step S3 Original radiation intensity sequence The signal-to-noise ratio between them is: ； in: for the standard radiation intensity sequence , the original radiation intensity sequence number of sampling points in the mean of the standard radiation intensity sequence the mean of the standard radiation intensity sequence the standard deviation of the original intensity sequence of the original intensity sequence.

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