Method for testing field performance of anechoic chamber

Abstract

The invention discloses an anechoic chamber site performance test method, and relates to the field of anechoic chamber site performance test, and the method comprises the following steps: obtaining frequency response data between receiving and transmitting antennas in an anechoic chamber site; frequency response data between the receiving antenna and the transmitting antenna are converted into a time domain through inverse discrete Fourier transform; obtaining the response of the linear propagation signal between the receiving and transmitting antennas in the time domain; obtaining a response of a reflected wave signal from the anechoic chamber in a time domain; converting the response of a linear propagation signal between receiving and transmitting antennas in a time domain into a frequency domain through discrete Fourier transform to obtain first frequency domain data; converting the response of the reflected wave signal from the anechoic chamber in the time domain to the frequency domain through discrete Fourier transform to obtain second frequency domain data; and testing the field performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data. According to the method, the hardware investment cost for darkroom site verification is reduced.

Description

Technical Field

[0001] The invention relates to the field of anechoic chamber site performance testing, and in particular to a anechoic chamber site performance testing method. Background Art

[0002] Verification of the performance of the anechoic chamber site is an important prerequisite for using the chamber to conduct electromagnetic compatibility testing of products. Among them, the SVSWR test is the main means to measure the radiated emission (RE) performance of the EMC chamber (electromagnetic compatibility chamber) above 1GHz. The physical meaning of SVSWR is the characteristics of the spatial standing wave formed by electromagnetic waves in the quiet zone (QZ) of the anechoic chamber test. At present, there are three main methods for measuring SVSWR, CISPR Spatial Sampling measurement method (spatial sampling method), ANSI TD-SVSWR measurement method (time domain measurement method), and Mode Filtering measurement method (mode filtering method). Among them, the Spatial Sampling measurement method described in the standard CISPR 16-1-4 is widely used. This method places the receiving antenna at a fixed distance of 3 meters from the front of the quiet zone, and ensures that the lobe of the receiving antenna can cover the range of the measurement quiet zone according to the standard requirements. The omni-directional antenna is arranged at 4 specified positions on the edge of the quiet zone. The SVSWR is obtained by moving the receiving antenna at different distances along the axis, and the response between the two antennas is measured to obtain the maximum value of the spatial standing wave. The sampling position intervals of the spatial standing wave of the CISPR method are 6 fixed distances, namely 0cm, 2cm, 10cm, 18cm, 30cm, and 40cm. The purpose is to change the phase relationship between the direct wave and the reflected wave by changing the distance between the transmitting and receiving antennas, so as to sample the spatial standing wave. However, in such a wide frequency range of 1GHz-18GHz, using only these 6 distances cannot fully meet the sampling of all wavelengths. In addition, the frequency step in the CISPR method is 50MHz, and the relatively wide frequency step may cause the frequency points with poor SVSWR to be ignored.

[0003] In view of the above situations that may affect the measurement results, the ANSI time domain method and the Mode Filtering measurement method have proposed improvement plans from different technical perspectives. The Mode Filtering measurement method requires that the transmitting antenna be placed at the edge of the QZ, and then the cylindrical antenna measurement is performed by rotating the turntable. The transmitting antenna is converted to the center of its turntable through mathematical transformation, and then the cylindrical mode coefficient of the antenna is calculated. This method can more accurately obtain the spatial standing wave distribution in the QZ through dense spatial sampling, and does not require the test antenna to have a short ring-down time. However, this method has not yet formed an international standard, so it cannot be used as the basis for industry-recognized darkroom performance verification.

[0004] TD-SVSWR was proposed to overcome the limitations of the spatial sampling measurement method. This is achieved by using broadband antennas and time domain transformation to distinguish between direct waves between transmitting and receiving antennas and multipath reflected signals in the darkroom. This method is in contrast to the previous technology that relied on the spatial movement measurement results of the transmitting antenna. The physical meaning of this method is clear, that is, the direct waves between the antennas and the reflected waves of the site are distinguished in the time domain, and then they are intercepted through the time domain gate to calculate the ratio of the reflected wave to the direct wave. On the other hand, there is no need to move the position of the transmitting antenna during the measurement process, so it has a higher measurement efficiency. This method is also an effective method to verify the radiation emission performance of the darkroom site in addition to the CISPR method.

[0005] The arrangement of TD-SVSWR measurement is similar to that of CISPR method, with the following differences in measurement arrangement and parameter settings.

[0006] a) The transmitting antenna of the TD-SVSWR measurement method completes the measurement at a fixed position, and there is no need to move the antenna to measure the spatial standing wave.

[0007] b) Since there is a transformation from time domain to frequency domain during the measurement process, in order to prevent the truncation effect caused by Fourier transform, it is necessary to set the measurement bandwidth of the vector network analyzer (VNA) to be larger than the actual frequency band range required. The start frequency is generally set to 500MHz, and the end frequency is generally the upper limit frequency to be measured plus 10% of the measurement bandwidth. If you need to measure 1GHz-6GHz, you need to set the measurement end frequency to 6.5GHz, and if you need to measure 1GHz-18GHz, the end frequency is 19.7GHz.

[0008] c) The frequency step of the measurement point should not exceed 1.5MHz. When the measurement start and end frequencies are 500MHz-19.7GHz, the standard recommends a frequency step of 1.2MHz, i.e. 16001 frequency points.

[0009] d) Lower IF bandwidth and / or higher output power or preamplifier may be required to improve signal-to-noise ratio. A signal-to-system noise ratio of at least 20 dB should be achieved.

[0010] e) Before measurement, the VNA needs to be calibrated with two ports.

[0011] The time domain waveform of the antenna response is obtained by using the time domain option of the vector network analyzer. The direct wave response between the antennas can be clearly distinguished from the time domain waveform, that is, the largest peak in the waveform is the direct response between the antennas. After determining the time when the direct wave reaches the receiving antenna, the bandpass mode of the vector network analyzer can be used to select the appropriate time gate, extract the direct wave response, and convert it to the frequency domain, recorded as Then the direct response is filtered out using the band-stop mode, and only the reflected wave is extracted, which is transformed into the frequency domain and recorded as The SVSWR calculation method is as follows:

[0012]

[0013] After obtaining the SVSWR value initially, a series of data post-processing is required, which includes the following steps.

[0014] Sliding average processing. Set the sliding average window width to 120MHz, and smooth the SVSWR data in the entire measurement frequency band. The processed data is recorded as For the design of the sliding average window width, the standard principle is to select the smallest possible sliding window while ensuring that there are enough independent data points for the average calculation.

[0015] After the sliding average processing, the standard deviation of each set of sliding average data is calculated and recorded as In order to match the "under-sampling" measurement value of the CISPR method, the TD-SVSWR method adds a coverage factor after obtaining the standard deviation of the moving average data. The final calculation result of TD-SVSWR is: We assume that the measurement results are normally distributed, and add a coverage factor indicating a 75% one-sided confidence interval. b =0.676, in principle, an expression of measurement result plus expanded uncertainty is constructed, which enables the time domain measurement method to achieve a certain degree of consistency in measurement results with the CISPR method, which is a theoretically under-sampling method.

[0016] From the above process, we can see that the hardware basis of the TD-SVSWR measurement method is to have a VNA with a time domain option. From confirming the peak position of the direct wave between antennas to setting the time gate to select the signal, the time domain measurement function based on the VNA is required. However, the VNA of a general testing laboratory may not have a time domain option function. If the measurement method of this standard is to be adopted, it will undoubtedly require an increase in hardware cost investment. Summary of the invention

[0017] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for testing the field performance of an anechoic chamber, which solves the problem that ordinary vector network analyzers cannot perform anechoic chamber field performance testing through the existing TD-SVSWR measurement method.

[0018] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: A method for testing the performance of an anechoic chamber is provided, which comprises the following steps: S1. Obtain the frequency response data between the transmitting and receiving antennas in the anechoic chamber through a vector network analyzer; S2, converting the frequency response data between the transmitting and receiving antennas into the time domain through inverse discrete Fourier transform to obtain time domain data; S3, select a time window, intercept the time domain data through the time domain gate bandpass mode, and obtain the response of the linear propagation signal between the transmitting and receiving antennas in the time domain; select a time window, intercept the time domain data through the time domain gate bandstop mode, and obtain the response of the reflected wave signal from the radio darkroom in the time domain; S4, converting the response of the linear propagation signal between the transmitting and receiving antennas in the time domain into the frequency domain by discrete Fourier transform, and obtaining first frequency domain data; converting the response of the reflected wave signal from the radio wave darkroom in the time domain into the frequency domain by discrete Fourier transform, and obtaining second frequency domain data; S5. Test the performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data.

[0019] Furthermore, in step S2, the frequency response data between the transmitting and receiving antennas is converted to the time domain by inverse discrete Fourier transform as follows:

[0020] in The frequency response data between the transmitting and receiving antennas measured by the vector network analyzer is k individual data; For the Time domain data corresponding to a time series; is the total number of frequency response data between the transmitting and receiving antennas in a single time series; e is a natural constant; j is the imaginary unit; π is the circumference of a circle; n Represents the index of the frequency response data between the transmitting and receiving antennas in a single time series; , is the time interval, , is the lower frequency limit of the measurement bandwidth; the time series range is , is the upper frequency limit of the measurement bandwidth.

[0021] Furthermore, the expression for intercepting the time domain data by the time domain gate bandpass mode in step S3 is:

[0022] in is the response of the linear propagation signal between the transmitting and receiving antennas in the time domain; Represents the time domain gate function, which includes rectangular window, Hanning window and Hamming window.

[0023] Furthermore, in step S4, the expression for converting the response of the linear propagation signal between the transmitting and receiving antennas in the time domain into the frequency domain by discrete Fourier transform is:

[0024] in is the first frequency domain data.

[0025] Furthermore, the specific method for testing the performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data in step S5 includes the following sub-steps: S5-1. Calculating the site voltage standing wave ratio according to the first frequency domain data and the second frequency domain data ; S5-2, set the moving average window to 120 MHz and perform The data is moved averaged and the moving average data is specified as , and calculate the standard deviation of each group of data in the sliding average window; the standard deviation of the standard deviation of all groups is recorded as ; S5-3, according to and Calculate the time domain site VSWR ; S5-4, the time domain site voltage standing wave ratio As the result of the anechoic chamber field performance test.

[0026] Furthermore, in step S5-1, the site voltage standing wave ratio is calculated The expression is:

[0027]

[0028] in is the intermediate parameter; is the second frequency domain data; Represents a logarithmic function.

[0029] Furthermore, in step S5-3, the time domain site voltage standing wave ratio is calculated The expression is:

[0030] in is a constant.

[0031] Further, The value of is 0.676.

[0032] A computer device is provided, comprising a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes a method for testing field performance of an anechoic chamber.

[0033] A computer-readable storage medium is provided, which stores a computer program. When the computer program is executed by a processor, the processor executes a method for testing field performance of an anechoic chamber.

[0034] The beneficial effects of the present invention are as follows: the method uses an ordinary (without time domain measurement function) vector network analyzer to perform anechoic chamber field performance test based on the TD-SVSWR measurement method, thereby avoiding the increase of hardware costs and being able to quickly implement anechoic chamber field performance test. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram of the process of this method; Figure 2 This is a schematic diagram of the frequency response data between the transmitting and receiving antennas measured by a vector network analyzer; Figure 3 A schematic diagram of converting the frequency response data between the transmitting and receiving antennas into the time domain through inverse discrete Fourier transform; Figure 4 Schematic diagram for selecting appropriate time domain gate width according to impulse response; Figure 5 The passband mode and stopband mode data are converted to the frequency domain after being intercepted by the time domain gate; Figure 6 This is a schematic diagram of the automatic measurement system interface; Figure 7 is the impulse response characteristics of different antennas; Figure 8 To set the time domain gate for measurement; Fig. 9 Schematic diagram of the test site layout and the shortest path for reflected wave propagation; Fig.10 This is the result without using sliding average; Fig.11 This is the result after using sliding average. DETAILED DESCRIPTION

[0036] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0037] like Figure 1 As shown, the anechoic chamber field performance test method includes the following steps: S1. Obtain the frequency response data between the transmitting and receiving antennas in the anechoic chamber through a vector network analyzer; S2, converting the frequency response data between the transmitting and receiving antennas into the time domain through inverse discrete Fourier transform to obtain time domain data; S3, select a time window, intercept the time domain data through the time domain gate bandpass mode, and obtain the response of the linear propagation signal between the transmitting and receiving antennas in the time domain; select a time window, intercept the time domain data through the time domain gate bandstop mode, and obtain the response of the reflected wave signal from the radio darkroom in the time domain; S4, converting the response of the linear propagation signal between the transmitting and receiving antennas in the time domain into the frequency domain by discrete Fourier transform, and obtaining first frequency domain data; converting the response of the reflected wave signal from the radio wave darkroom in the time domain into the frequency domain by discrete Fourier transform, and obtaining second frequency domain data; S5. Test the performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data.

[0038] In the specific implementation process, the frequency response data between the transmitting and receiving antennas measured by the vector network analyzer is as follows: Figure 2 As shown, the frequency response data between the transmitting and receiving antennas is converted to the time domain through the inverse discrete Fourier transform as shown in Figure 3 As shown, the frequency response data between the transmitting and receiving antennas is converted to the time domain through the inverse discrete Fourier transform:

[0039] in The frequency response data between the transmitting and receiving antennas measured by the vector network analyzer is k individual data; For the Time domain data corresponding to a time series; is the total number of frequency response data between the transmitting and receiving antennas in a single time series; e is a natural constant; j is the imaginary unit; π is the circumference of a circle; n Represents the index of the frequency response data between the transmitting and receiving antennas in a single time series; , is the time interval, , is the lower frequency limit of the measurement bandwidth; the time series range is , is the upper frequency limit of the measurement bandwidth.

[0040] The specific method of intercepting the time domain data by the time domain gate bandpass mode in step S3 is: like Figure 4 As shown, select an appropriate time window width and intercept the time domain data through the time domain gate bandpass mode. The expression is:

[0041] in is the response of the linear propagation signal between the transmitting and receiving antennas in the time domain; Represents the time domain gate function, which includes rectangular window, Hanning window and Hamming window. The time domain expressions of rectangular window, Hanning window and Hamming window are as follows:

[0042]

[0043]

[0044] in Represents the window function.

[0045] In step S4, the response of the linear propagation signal between the transmitting and receiving antennas in the time domain is converted to the frequency domain by discrete Fourier transform:

[0046] in is the first frequency domain data.

[0047] Frequency response data between the transmitting and receiving antennas The reflected signal level is obtained by band-stop filtering. , and then use discrete Fourier transform to obtain the frequency domain response of the reflected signal level, that is, the second frequency domain data The calculation process is consistent with the previous bandpass filtering and discrete Fourier transform. It only needs to change the window function Replace with a window function with a stop mode , the results are as follows Figure 5 shown.

[0048] The specific method for testing the performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data in step S5 includes the following sub-steps: S5-1. Calculating the site voltage standing wave ratio according to the first frequency domain data and the second frequency domain data , whose expression is:

[0049]

[0050] in is the intermediate parameter; is the second frequency domain data; represents the logarithmic function; S5-2, set the moving average window to 120 MHz and perform The data is moved averaged and the moving average data is specified as , and calculate the standard deviation of each group of data in the sliding average window; the standard deviation of the standard deviation of all groups is recorded as ; S5-3. Calculate the time domain site voltage standing wave ratio , whose expression is:

[0051] S5-4, the time domain site voltage standing wave ratio As the result of the anechoic chamber field performance test; The value of is 0.676.

[0052] According to the above calculation process, if Figure 6 As shown, this embodiment has compiled an automatic measurement system, which realizes the automatic measurement of the time-domain site VSWR that is independent of the VNA time-domain option by remotely controlling the VNA and calculating and processing the measurement data.

[0053] In the specific implementation process, the purpose of using the time domain gate to intercept the data is to effectively distinguish the direct signal between the antennas from the reflected signal of the surrounding environment. The factors that affect the selection of the time domain gate width are mainly quantitative aspects, one is the ring down time of the antenna itself, and the other is the fastest time for the reflected electromagnetic wave to reach the receiving antenna.

[0054] Ring down time is a phenomenon caused by the structural characteristics of the antenna itself. Figure 7 It can be seen that after the antenna receives the broadband pulse signal, it will produce different degrees of oscillation after the main peak of the signal, which is the so-called ring downtime. The duration of oscillation is different for different types of antennas. In theory, the smaller the ring down time, the better. If the ring down time is too large, it will be mixed with the reflected signal, and it will be impossible to effectively distinguish the response of the direct wave and the reflected wave, thus affecting the site voltage standing wave ratio (SVSWR) result.

[0055] To obtain accurate SVSWR, we need to select an antenna with a ring down time less than a certain time. This means we need to know how much time the reflected wave that reaches the antenna in the shortest time is delayed compared to the direct wave. As long as the ring down time is less than this time, we can use the time domain gate to distinguish the direct wave from the reflected wave, such as Figure 8 shown.

[0056] In this embodiment, if Fig. 9 As shown, the straight-line distance between the antennas is d1. The height of the absorber is h1, and the height of the antenna is h2. The path of the electromagnetic wave reflected by the absorber surface to reach the receiving antenna should be the shortest of all reflected paths. The time difference between this path and the direct wave path is calculated as follows:

[0057] in , is the speed of light. When the transmitting antenna is at the front point of the quiet zone, d1 is 3m. Generally, h1 is 0.4 and h2 is 1.2m. Calculation yields It is about 1.4ns. Therefore, the ring downtime of the antenna selected for testing should be less than this value. What is calculated here is the front point position of the quiet zone. As the distance of d1 becomes longer for other test points, the distance traveled by the reflected wave also becomes longer accordingly, so the front point position is the position point with the shortest delay between the reflected wave and the direct wave path. The standard ANSI C63.25 recommends that the time domain gate setting is 2ns to the left and right of the time domain response peak as the center. According to the above calculations, in the actual test environment, the width of the time domain gate can be appropriately adjusted, and the setting of the time window width can be weighed based on the two factors of the shortest reflection path and the ring down time to ensure the accuracy of the measured data. In this embodiment, the time window width is less than the shortest path reflection time and greater than the ring down time of the antenna, and an antenna with a sufficiently short ringing time is selected, for example, less than 1ns.

[0058] like Fig.10 and Fig.11 As shown, the measurement results are processed using the above three time windows respectively, and the differences between the time windows are compared. It can be seen from the figure that the use of different types of time windows will have a certain impact on the results, but the differences between the results are not large.

[0059] In other embodiments of the present invention, a computer device is provided, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the method for testing the field performance of an anechoic chamber.

[0060] In other embodiments of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the processor executes the method for testing the field performance of an anechoic chamber.

[0061] In summary, the present invention provides a method for testing the performance of an anechoic chamber site that does not rely on the VNA time domain option, implements TD-SVSWR measurement based on frequency domain data post-processing, reduces the hardware investment cost for applying the method to verify the anechoic chamber site, develops an automated measurement system, improves measurement efficiency, clarifies the parameter setting principles that are not specifically described in the standard method, and provides users who use the method to conduct anechoic chamber site evaluation with analysis and verification results of reference value.

Claims

1. A method for testing field performance of an anechoic chamber, characterized in that: The following steps are involved: S1. Obtain the frequency response data between the transmitting and receiving antennas in the anechoic chamber through a vector network analyzer; S2, converting the frequency response data between the transmitting and receiving antennas into the time domain through inverse discrete Fourier transform to obtain time domain data; S3, select a time window, intercept the time domain data through the time domain gate bandpass mode, and obtain the response of the linear propagation signal between the transmitting and receiving antennas in the time domain; select a time window, intercept the time domain data through the time domain gate bandstop mode, and obtain the response of the reflected wave signal from the radio darkroom in the time domain; S4, converting the response of the linear propagation signal between the transmitting and receiving antennas in the time domain into the frequency domain by discrete Fourier transform, and obtaining first frequency domain data; converting the response of the reflected wave signal from the radio wave darkroom in the time domain into the frequency domain by discrete Fourier transform, and obtaining second frequency domain data; S5. Test the performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data.

2. The method for testing the field performance of an anechoic chamber according to claim 1, characterized in that: In step S2, the frequency response data between the transmitting and receiving antennas is converted to the time domain through the inverse discrete Fourier transform. The expression is: in The frequency response data between the transmitting and receiving antennas measured by the vector network analyzer is k individual data; For the Time domain data corresponding to a time series; is the total number of frequency response data between the transmitting and receiving antennas in a single time series; e is a natural constant; j is the imaginary unit; π is the circumference of a circle; n Represents the index of the frequency response data between the transmitting and receiving antennas in a single time series; , is the time interval, , is the lower frequency limit of the measurement bandwidth; the time series range is , is the upper frequency limit of the measurement bandwidth.

3. The method for testing the field performance of an anechoic chamber according to claim 2, characterized in that: The expression for intercepting the time domain data by the time domain gate bandpass mode in step S3 is: in is the response of the linear propagation signal between the transmitting and receiving antennas in the time domain; Represents the time domain gate function, which includes rectangular window, Hanning window and Hamming window.

4. The method for testing the field performance of an anechoic chamber according to claim 3, characterized in that: In step S4, the response of the linear propagation signal between the transmitting and receiving antennas in the time domain is converted to the frequency domain by discrete Fourier transform: in is the first frequency domain data.

5. The method for testing the field performance of an anechoic chamber according to claim 4, characterized in that: The specific method for testing the performance of the anechoic chamber according to the first frequency domain data and the second frequency domain data in step S5 includes the following sub-steps: S5-1. Calculating the site voltage standing wave ratio according to the first frequency domain data and the second frequency domain data ; S5-2, set the moving average window to 120 MHz and perform The data is moved averaged and the moving average data is specified as , and calculate the standard deviation of each group of data in the sliding average window; the standard deviation of the standard deviation of all groups is recorded as ; S5-3, according to and Calculate the time domain site VSWR ; S5-4, the time domain site voltage standing wave ratio As the result of the anechoic chamber field performance test.

6. The method for testing the field performance of an anechoic chamber according to claim 5, characterized in that: Step S5-1 calculates the site voltage standing wave ratio The expression is: in is the intermediate parameter; is the second frequency domain data; Represents a logarithmic function.

7. The method for testing the field performance of an anechoic chamber according to claim 6, characterized in that: Step S5-3 calculates the time domain site voltage standing wave ratio The expression is: in is a constant.

8. The method for testing the field performance of an anechoic chamber according to claim 7, characterized in that: The value of is 0.

676.

9. A computer device, characterized in that: The invention comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the method for testing field performance of an anechoic chamber as claimed in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that: A computer program is stored, and when the computer program is executed by a processor, the processor executes the anechoic chamber field performance testing method described in any one of claims 1 to 8.

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