Reverberation chamber method calibration method and calibration system

Abstract

The invention discloses a reverberation chamber calibration method and calibration system, and belongs to the technical field of automotive electronic EMC testing, and the method comprises the steps: obtaining normalized field intensity data through a probe method under the condition of no load of a reverberation chamber, and storing the normalized field intensity data for later use; s21 data are collected through a network division method and stored for standby application; under the reverberation chamber loading condition, S21 data are collected through a network division method; on the basis of the S21 data under the no-load condition and in combination with the S21 data under the loading condition, the reverberation chamber loading coefficient under each test frequency point is calculated; and calculating the input power of the reverberation chamber under the target field intensity under each test frequency point by combining the loading coefficient of the reverberation chamber based on the normalized field intensity data obtained by the probe method. According to the invention, the testing operation steps are simplified, and the testing time is greatly reduced, so that the working efficiency can be remarkably improved, and the quick calibration of the reverberation room site can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of automotive electronic EMC testing, and in particular to a reverberation chamber calibration method and a calibration system. Background Art

[0002] In today's automotive industry, the widespread use of electronic systems has made automotive parts face a complex electromagnetic environment. Ensuring the normal operation of automotive parts in the radiated electromagnetic field is an important part of ensuring the overall safety and reliability of the vehicle. As a commonly used testing facility, the reverberation chamber can provide a relatively uniform electromagnetic field environment. The reverberation chamber is a new type of electromagnetic environment simulation platform that can generate a spatially statistically uniform electromagnetic environment inside a closed cavity, which is more suitable for simulating the electromagnetic environment of the cavity. At present, many car manufacturers have added reverberation chamber tests to the test standards formulated.

[0003] In the traditional reverberation chamber field calibration, the cubic area in the reverberation chamber is generally used as the working area, and the field uniformity statistics of the eight vertex positions of the working area are used to evaluate the field uniformity. That is, the field uniformity can be expressed by the standard deviation of the maximum values ​​of the field strength in three mutually perpendicular directions measured at the eight vertex positions of the working area under N stirring paddle positions. According to the conventional probe method and receiving antenna measurement method, the sampling position point is first fixed, that is, the position of the field strength probe and the receiving antenna is fixed, and then the stirrer is rotated. For each stirrer position, the software obtains the receiving antenna energy reading of the EMI receiver. The number of test frequency points, the time to move the field strength probe and the receiving antenna, the stirring paddle rotation time, and the reading time of the field strength probe and the EMI receiver all affect the calibration efficiency. Summary of the invention

[0004] The technical solution of the present invention aims at the technical problem that the existing technical solutions are too single, and provides a solution that is significantly different from the existing technology. It mainly provides a reverberation chamber calibration method and a calibration system to solve the technical problem of low efficiency of the traditional reverberation chamber field calibration method proposed in the above background technology.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] A reverberation chamber calibration method comprises the following steps:

[0007] S1, when the reverberation chamber is unloaded, the normalized field strength data is obtained by the probe method and stored for future use; the S21 data is collected by the network method and stored for future use;

[0008] S2, when the reverberation chamber is loaded, the S21 data is collected by the grid method;

[0009] S3, based on the S21 data obtained by S1 and combined with the S21 data obtained by S2, calculate the reverberation chamber loading coefficient at each test frequency point;

[0010] S4. Based on the normalized field strength data obtained in S1 and combined with the reverberation chamber loading coefficient obtained in S3, the reverberation chamber input power at the target field strength at each test frequency point is calculated.

[0011] Furthermore, in step S1, the signal source fixes the signal power output to -20dBm.

[0012] Furthermore, in step S1, the field intensity probe collects the input power of the reverberation chamber, the field intensity, and the average power of the receiving antenna at each sampling position and at each position where the stirrer stops.

[0013] Furthermore, in S1, the network division method is that the host computer controls the network analyzer to perform S21 frequency sweep test to collect S21 data within different frequency ranges and at different angles of the stirrer.

[0014] Furthermore, in step S2, the loading condition is: placing the product to be tested, the wiring harness, and the support body in the working area.

[0015] Furthermore, in step S2, the host computer controls the operation of the network analyzer in the same manner as in step S1.

[0016] Further, in step S3, the calculation formula of the reverberation chamber loading coefficient is CLF=CCF / ACF, wherein CCF is the square of the absolute value of the S21 data modulus obtained when the reverberation chamber is loaded in step S2; ACF is the square of the absolute value of the S21 data modulus obtained when the reverberation chamber is unloaded in step S1.

[0017] Further, in step S4, the calculation method is a forward power calculation formula of the reverberation chamber.

[0018] The present invention also provides a reverberation chamber calibration system, comprising a reverberation chamber, a network analyzer and a host computer, wherein a working area is provided in the reverberation chamber, and a stirrer and a field strength probe are provided in the working area; a transmitting antenna is provided outside the working area, and a receiving antenna is provided in the working area; a transmitting energy port of the network analyzer is connected to the transmitting antenna, and a receiving energy port of the network analyzer is connected to the receiving antenna; the host computer is communicatively connected to the network analyzer; and the reverberation chamber calibration system implements the above-mentioned reverberation chamber calibration method.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Compared with the traditional reverberation chamber site calibration method, the present invention performs S21 frequency sweep test through the network analyzer method, which can obtain the parameters of the entire frequency band to be calibrated at one time, collect the data of S21 under no-load and loaded conditions, and obtain the loading coefficient CLF, which simplifies the test operation steps and greatly reduces the test time, thereby significantly improving work efficiency and realizing rapid calibration of the reverberation chamber site.

[0021] (2) The present invention uses the probe method to obtain the normalized field strength data of the reverberation chamber when the reverberation chamber is unloaded, and uses the grid method to collect S21 data. When the test system remains unchanged, the reverberation chamber does not undergo major changes within the calibration date. The stability of the normalized field strength data and S21 data of the reverberation chamber obtained above is good and can be used for a long time. The subsequent calibration process only needs to perform a loading test once by the grid method, which is more convenient to use.

[0022] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural block diagram of the reverberation chamber calibration system of the present invention;

[0024] Figure 2 This is a result diagram of the step of deriving the reverberation chamber loading coefficient in the present invention.

[0025] Figure numerals: 1. Reverberation chamber; 2. Transmitting antenna; 3. Working area; 4. Receiving antenna; 5. Host computer; 6. Network analyzer. DETAILED DESCRIPTION

[0026] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings, but the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the content disclosed in the present invention more thorough and comprehensive.

[0027] Example 1: Please refer to the attached Figure 1A reverberation chamber calibration system includes a reverberation chamber 1, a working area 3 is provided in the reverberation chamber 1, a stirrer and a field strength probe (not shown in the figure) are provided in the working area 3, and the field strength probe has a radio frequency output interface, and is connected to an external power meter, spectrum analyzer and other equipment to read data in real time; a transmitting antenna 2 is provided outside the working area 3, and a receiving antenna 4 is provided in the working area 3; a No. 1 transmitting energy port of a network analyzer 6 is connected to the transmitting antenna 2, and a No. 2 receiving energy port of the network analyzer 6 is connected to the receiving antenna 4; a host computer 5 is connected to the network analyzer 6 for controlling the network analyzer 6. The reverberation chamber calibration system implements the following reverberation chamber calibration method.

[0028] A reverberation chamber calibration method comprises the following steps:

[0029] Step 1: When the reverberation chamber is unloaded, obtain normalized field strength data through the probe method;

[0030] Specifically include:

[0031] (1) Except for the antenna, stirrer, and field strength probe, the reverberation chamber is emptied, and the signal source is set to output a fixed signal power of -20 dBm (ensuring that the energy value received by the receiver exceeds the noise floor by at least 20 dB). The signal is sent to the transmitting antenna through the power amplifier. The electromagnetic wave energy is continuously reflected in the working area of ​​the reverberation chamber to produce a uniform field.

[0032] (2) First, fix the sampling point of the probe. At each sampling position, the probe rotates the stirrer 360° according to the corresponding number of steps to complete a stirring cycle. At each position where the stirrer stops, the software collects the input power of the reverberation chamber, the field strength, and the average power of the receiving antenna;

[0033] (3) Perform the same test on the remaining 7 test locations;

[0034] (4) The data obtained from the above test include the maximum field strength values ​​of the three axes X, Y, and Z when the stirrer rotates one circle at each position of the field strength probe. According to the standard requirements, the normalized field strength of the input power of the reverberation chamber is calculated and the calculation results are stored. The calculation formula is:

[0035]

[0036] Among them, Ex, Ey, and Ez are the values ​​after the input power of the reverberation chamber is normalized by the maximum field strength values ​​in three directions; Emaxx, Emaxy, and Emaxz are the maximum field strength values ​​of the three axial directions of the field strength probe when the stirrer rotates one circle; Pinput is the input power of the reverberation chamber.

[0037] Step 2: When the reverberation chamber is unloaded, collect S21 data through the grid method;

[0038] Specifically include:

[0039] (1) Connect the No. 1 transmitting energy port of the network analyzer to the transmitting antenna and aim it at the stirrer to transmit energy;

[0040] (2) According to the recommended rotation steps of the stirrer required by the standard, a uniform field is formed in the reverberation chamber space through continuous reflection of energy;

[0041] (3) Connect the No. 2 receiving energy port of the network analyzer to the receiving antenna to receive the electric field value in the reverberation chamber space;

[0042] (4) The host computer controls the network analyzer to perform S21 frequency sweep test, collects S21 data within different frequency ranges and at different angles of the agitator, and saves the data in an EXCEL table.

[0043] Before using the network analyzer, a TOSM calibration is performed to ensure the accuracy of the data obtained by the network analyzer.

[0044] Step 3: Under the condition of reverberation chamber loading, collect S21 data by grid division method;

[0045] Specifically include:

[0046] (1) Place the product to be tested, wiring harness, support, etc. in the working area;

[0047] (2) The host computer controls the network analyzer in the same way as in the second step to collect S21 data under loading conditions at different frequency ranges and at different angles of the stirrer.

[0048] Step 4: If Figure 2 As shown, based on the S21 data of the reverberation chamber under no-load condition obtained in the second step, combined with the S21 data of the reverberation chamber under loaded condition obtained in the third step, the loading factor (CLF) of the reverberation chamber at each test frequency point is derived;

[0049] Specifically include:

[0050] (1) The S21 data of the reverberation chamber under no-load condition obtained in the second step is plotted into a graph, such as Figure 2 (a)

[0051] (2) The S21 data of the reverberation chamber under loading obtained in step 3 is plotted into a graph, such as Figure 2 (b)

[0052] (3) The formula for calculating the reverberation chamber loading factor is CLF = CCF / ACF; where CCF is the square of the absolute value of the S21 data modulus obtained when the reverberation chamber is loaded in the third step; ACF is the square of the absolute value of the S21 data modulus obtained when the reverberation chamber is unloaded in the second step. The test frequency data obtained by the network analyzer is calculated as above to obtain the CLF. The derived reverberation chamber loading factor is plotted into a graph, as shown in Figure 2. Figure 2 (c) as shown.

[0053] Step 5: Based on the normalized field strength data obtained in the first step and combined with the CLF obtained in the fourth step, the reverberation chamber input power at the target field strength at each test frequency point is calculated using the reverberation chamber forward power calculation formula to complete the calibration work; the reverberation chamber forward power calculation formula is:

[0054]

[0055] Among them, P Forw,Test It represents the input power of the reverberation chamber under the target field strength at each test frequency point; E Test Indicates the required field strength value in volts per meter (V / m); F CLF Represents the reverberation chamber loading factor; G RC It represents the reverberation chamber gain, that is, at each test frequency point, the normalized maximum value of the electric field measurement value of each axis of the field intensity probe at N (usually N=8) calibration positions is calculated, and the average value of the maximum value is calculated.

[0056]

[0057] e X =E X , e Y =E Y， e Z =E Z .

[0058] Using a network analyzer for quick calibration, the calibration time is about 2 hours under the same conditions as the comparative example. The network analyzer method uses the S21 frequency sweep test function to obtain the parameters of the entire frequency band to be calibrated at one time, collects the network S21 data under no-load and loaded conditions, and calculates the loading coefficient CLF through the formula, which simplifies the test operation steps and improves work efficiency.

[0059] While keeping the test system unchanged, the equipment did not undergo major changes in the reverberation chamber within the calibration date. First, when the reverberation chamber is unloaded, the normalized field strength data obtained by the probe method is very stable and can be used for a long time. Then, when the reverberation chamber is unloaded, the S21 data collected by the network method is very stable and can be used for a long time. Before each subsequent test, the product to be tested, supports, and wiring harnesses will be arranged in the test work area. The tester only needs to use a network analyzer with a stirrer to perform a loading test (to ensure that the test system (such as test equipment, test cables, etc.) is consistent, and the angle of the transmitting antenna is placed consistently), and the CLF can be calculated, thereby calculating the input power of the reverberation chamber, and the calibration of the reverberation chamber can be completed.

[0060] Embodiment 2: This embodiment differs from Embodiment 1 in that:

[0061] In the reverberation chamber calibration method, S21 data is first collected by the grid method when the reverberation chamber is unloaded; then, normalized field strength data is obtained by the probe method when the reverberation chamber is unloaded.

[0062] The rest is the same as the first embodiment.

[0063] Comparative example: According to the requirements of standard ISO 11452-11, the calibration content mainly includes:

[0064] (1) When the reverberation chamber is unloaded, the probe and receiving antenna are placed in different positions, and the normalized field strength data and the receiving antenna calibration coefficient ACF are obtained during one rotation of the stirrer;

[0065] (2) When the reverberation chamber is loaded (the DUT and wiring harness are placed in the working area of ​​the reverberation chamber), the receiving antenna is placed in different positions, and the calibration coefficient CCF of the receiving antenna is obtained during one rotation of the stirrer;

[0066] (3) Calculate the reverberation chamber loading factor (CLF) according to the standard requirements: CLF = CCF / ACF;

[0067] (4) Combining the normalized field strength data and the loading factor (CLF), the input power value of the reverberation chamber under the target field strength can be calculated using the standard calculation formula. According to the conventional probe method and receiving antenna measurement method, the sampling position point is first fixed, that is, the position of the field strength probe and the receiving antenna is fixed, and then the stirrer is rotated. For each stirrer position, the software obtains the receiving antenna energy reading of the EMI receiver.

[0068] Due to the signal source point frequency feed signal, field strength probe and EMI receiver point frequency reading, the time required for the software acquisition process increases. Taking ISO 11452-11:2010 standard as an example, the test frequency range is: 200MHz~6000MHz, about 175 frequency points are tested, the number of stirrer rotation steps is 12, the position of the field strength probe and the receiving antenna is 8, and the calibration time takes about 14 hours.

[0069] By comparison, it can be seen that, under the same conditions, the present invention can greatly reduce the calibration time and improve the calibration efficiency of the reverberation chamber method.

[0070] The above is an exemplary description of the present invention in combination with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A reverberation chamber calibration method, characterized in that: The steps include: S1, when the reverberation chamber is unloaded, the normalized field strength data is obtained by the probe method and stored for future use; the S21 data is collected by the network method and stored for future use; S2, when the reverberation chamber is loaded, the S21 data is collected by the grid method; S3, based on the S21 data obtained by S1 and combined with the S21 data obtained by S2, calculate the reverberation chamber loading coefficient at each test frequency point; S4. Based on the normalized field strength data obtained in S1 and combined with the reverberation chamber loading coefficient obtained in S3, the reverberation chamber input power at the target field strength at each test frequency point is calculated.

2. A reverberation chamber calibration method according to claim 1, characterized in that: In step S1, the signal source fixes the signal power output to -20dBm.

3. The reverberation chamber calibration method according to claim 1, characterized in that: In step S1, the field intensity probe collects the input power of the reverberation chamber, the field intensity, and the average power of the receiving antenna at each sampling position and at each position where the stirrer stops.

4. The reverberation chamber calibration method according to claim 1, characterized in that: In step S1, the network division method is that the host computer controls the network analyzer to perform S21 frequency sweep test to collect S21 data within different frequency ranges and at different angles of the stirrer.

5. The reverberation chamber calibration method according to claim 1, characterized in that: In step S2, the loading condition is: placing the product to be tested, the wiring harness, and the support body in the working area.

6. The reverberation chamber calibration method according to claim 1, characterized in that: In step S2, the host computer controls the operation of the network analyzer in the same manner as in step S1.

7. The reverberation chamber calibration method according to claim 1, characterized in that: In step S3, the calculation formula of the reverberation chamber loading coefficient is CLF=CCF / ACF, wherein CCF is the square of the absolute value of the S21 data modulus obtained when the reverberation chamber is loaded in step S2; ACF is the square of the absolute value of the S21 data modulus obtained when the reverberation chamber is unloaded in step S1.

8. The reverberation chamber calibration method according to claim 1, characterized in that: In step S4, the calculation method is the forward power calculation formula of the reverberation chamber.

9. A reverberation chamber calibration system, characterized in that: The invention comprises a reverberation chamber (1), a network analyzer (6) and a host computer (5); a working area (3) is provided in the reverberation chamber (1), a stirrer and a field strength probe are provided in the working area (3); a transmitting antenna (2) is provided outside the working area (3), and a receiving antenna (4) is provided in the working area (3); a transmitting energy port of the network analyzer (6) is connected to the transmitting antenna (2), and a receiving energy port of the network analyzer (6) is connected to the receiving antenna (4); the host computer (5) is connected to the network analyzer (6) in communication; and the reverberation chamber calibration system implements the reverberation chamber calibration method according to any one of claims 1 to 8.

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