Plane near-field measurement distance calibration method based on calibration antenna phase error analysis

Abstract

The invention discloses a plane near-field measurement distance calibration method based on calibration antenna phase error analysis, and belongs to the field of antenna near-field measurement. The method comprises the following steps: performing planar near-field measurement by using a calibration antenna and a probe antenna; the measured antenna and the probe antenna are used for plane near-field measurement; simulating data of the calibration antenna when the sampling surface has different offsets; the real position of the sampling plane is corrected by using simulation and actual measurement data of the calibration antenna, the simulation plane corresponding to the minimum phase error of the two is the corrected real position of the sampling plane, and the purpose of correcting the real position of the sampling plane of the tested antenna is achieved. The method is high in correction precision, low in cost and suitable for correction of planar near-field measurement of various small and medium-sized antennas.

Description

Technical Field

[0001] The invention belongs to the field of antenna near-field measurement, and in particular relates to a planar near-field measurement distance calibration method based on calibration antenna phase error analysis. Background Art

[0002] In the planar near field measurement of antennas, in order to accurately measure the planar near field of the antenna, it is usually hoped to avoid or minimize the errors existing in the planar near field measurement process to improve the accuracy of the planar near field measurement of antennas. Due to many factors such as the near field test system itself and the random errors existing during the test operation in the microwave darkroom, there may be a certain difference between the test near field and the true value. The main sources of error are: system errors such as system equipment and environmental errors, probe parameter errors, test equipment errors, and parameter errors such as probe position, scanning surface truncation, data point sampling interval, and antenna alignment.

[0003] However, in the actual near-field measurement process, it is difficult to align the antenna under test with the probe antenna. On the one hand, during multiple planar near-field measurements of the antenna under test, due to the placement of the antenna, its actual position may be offset, making it difficult to ensure that the relative position of the antenna under test and the probe antenna remains unchanged; on the other hand, when using the probe antenna to measure the near field of a certain sampling plane, the position of the antenna under test needs to be accurately placed to ensure that the distance between the antenna under test and the probe antenna is the distance set by the experimental plan; due to the error in measuring the distance between the antenna and the probe antenna, it is difficult to ensure that the placement position of the antenna under test is consistent with the theoretically set position, which may lead to a deviation between the measured near field on the sampling plane and the near field on the set actual sampling plane.

[0004] At present, the commonly used method to improve antenna alignment is to use laser interferometer to accurately measure the distance between the probe antenna and the antenna under test, and to align the center of the antenna under test with the center of the probe antenna, so as to minimize the parameter error caused by the distance measurement during the planar near-field test of the antenna under test. However, since laser interferometers are relatively expensive, the equipment is large and precise, and it is cumbersome to use when performing distance measurement operations, most microwave darkrooms for planar near-field measurements do not have this hardware facility.

[0005] Therefore, with regard to the parameter error of alignment between the antenna under test and the probe antenna, the traditional laser ranging method has the disadvantages of cumbersome operation and high cost. It is difficult to measure the distance between the antenna under test and the probe antenna simply and accurately. Therefore, it is necessary to improve the problem of cumbersome operation. Summary of the invention

[0006] In response to the need for improvement of the existing traditional distance measurement method using laser interferometer, the present invention proposes a planar near-field measurement distance calibration method based on calibration antenna phase error analysis. The method of the present invention utilizes the sensitivity of the calibration antenna's near field to phase, takes the calibration antenna's simulated planar near-field phase as a reference, and accurately determines the true distance between the calibration antenna and the probe antenna by comparing the phase error between the calibration antenna's measured planar near field and the simulated planar near field, thereby achieving calibration of the calibration antenna to the actual measured antenna distance.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] The planar near-field measurement distance calibration method based on calibration antenna phase error analysis includes the following steps:

[0009] Step 1: According to the planar near-field measurement scheme of the antenna under test, the distance between the antenna under test and the probe antenna is set to L1, and the set of sampling points on the near-field sampling plane is P = {P n |n=1,2,...,N}, where P n (x n ,y n ,z n ) is set to E(x n ,y n ,z n ), the total number of points on the sampling surface is N, n represents the nth sampling point, (x n ,y n ,z n ) represents the position of the nth sampling point in the Cartesian coordinate system.

[0010] Step 2: Use the calibration horn antenna to perform planar near-field measurement, set the actual distance between the calibration horn antenna and the probe antenna to L2, and obtain the calibration antenna planar near-field E1(x n ,y n ,z n ); Due to the inevitable measurement error, there is a certain error between the set distance L1 and the actual distance L2. Therefore, when measuring, the sampling point P n The real position is P n (x n +Δx,y n +Δy,z n +Δz), the plane near field at the corresponding sampling point is E(x n +Δx,y n +Δy,z n +Δz), where Δx, Δy and Δz are respectively n The deviation between the actual position of a point and its ideal position on the x, y, and z axes in the Cartesian coordinate system.

[0011] Step 3: Place the antenna under test at the location of the calibration horn antenna, ensuring that the center of the aperture plane of the antenna under test coincides with the center of the aperture plane of the calibration horn antenna. At this time, the distance error between the antenna under test and the probe antenna and the distance error between the calibration horn antenna and the probe antenna is much smaller than the actual distance and the set distance, which has little effect on the measurement result, so this error is ignored. Since the sampling surface size and sampling interval in steps 2 and 3 are the same, the sampling point P is n The actual position of the electric field at is consistent with that in step 2, which is P n (x n +Δx,y n +Δy,z n +Δz), the antenna under test corresponds to the sampling point P n The plane near field is E2(x n ,y n , z n ).

[0012] Step 4: Simulate the calibration horn antenna and set S Δx ={Δx1, Δx2, ... Δx N1},S Δy ={Δy1, Δy2, ... Δy N2},S Δz ={Δz1, Δz2, ... Δz N3} are the sets of deviations on the x, y, and z axes in the Cartesian coordinate system, and the near field of the plane under different errors is obtained by simulation. In the formula, 1≤i≤N1, 1≤j≤N2, 1≤k≤N3.

[0013] Step 5: Compare and calibrate the planar near field E1(x n ,y n , z n ) and simulated planar near field The average phase error is:

[0014]

[0015] The sampling point (x n +Δx i ,y n +Δy j , z n +Δz k ) is the actual position of the sampling plane, and the planar near field E2(x n ,y n , z n ) is corrected to the true position corresponding to (x n +Δxi ,y n +Δy j , z n +Δz k ).

[0016] The planar near-field measurement distance calibration method based on calibration antenna phase error analysis proposed in the present invention utilizes the sensitivity of the calibration antenna's near field to phase, takes the calibration antenna's simulated planar near-field phase as a reference, and compares the phase error between the calibration antenna's measured planar near field and the simulated planar near field, so as to accurately calibrate the position of the antenna under test. Compared with the traditional method of using laser ranging for calibration, the method of the present invention has the advantages of simple operation and low cost, a wider range of application, and can better meet the needs of calibrating the antenna under test in antenna measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the planar near-field measurement in a microwave darkroom for calibrating the horn antenna;

[0018] Figure 2 This is a schematic diagram of the planar near-field measurement of the antenna under test in a microwave darkroom;

[0019] Figure 3 Flowchart of the algorithm for calibrating the minimum phase error of the horn antenna.

[0020] Figure 4 Schematic diagram of the calibration horn antenna structure in the embodiment.

[0021] Figure 5 The results of the near-field phase of the plane without noise and the near-field phase of the plane after noise at different signal-to-noise ratios are shown in Figure 2.

[0022] Explanation of the accompanying figures: 1. Probe antenna, 2. Sampling plane, 3. Calibration horn antenna, 4. Wooden bracket, 5. Foam A, 6. Foam B, 7. Antenna under test. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with the accompanying drawings and corresponding microwave darkroom planar near-field measurement correction examples, which are intended to explain the present invention rather than to limit it.

[0024] The planar near-field measurement distance calibration method based on calibration antenna phase error analysis includes the following steps:

[0025] Step 1: According to the planar near-field measurement scheme of the antenna under test, determine the distance between the antenna under test and the probe, that is, the distance between the antenna under test and the sampling plane. The distance is the set distance L1. The set of near-field sampling points is P = {P n |n=1,2,...,N},set the position on the sampling surface to P n (xn ,y n , z n ) is E(x n ,y n , z n ).

[0026] One point to be explained here is the preparation work before planar near-field measurement. In theory, when the antenna is measuring the planar near-field, the antenna and the probe are both in an ideal environment with a relative dielectric constant of 1.0. In actual planar near-field measurement, the probe antenna is in the air with a relative dielectric constant of approximately 1.0, and the antenna to be measured is placed on a bracket. In order to reduce the influence of the bracket on the antenna, foam is used as the bracket for the calibration horn antenna and the antenna to be measured.

[0027] Step 2: Use a calibration horn antenna to perform planar near-field measurement. Place the calibration horn antenna on a bracket in a microwave darkroom. Use a tape measure to measure to ensure that the distance between the calibration horn antenna and the probe is the set distance L1. Due to measurement errors, the actual distance between the two is L2.

[0028] When performing planar near-field measurement of the calibration horn antenna, the calibration horn antenna is placed on foam A. Both foam A and the calibration horn antenna are placed on a wooden bracket for measurement. Figure 1 As shown. Before the experiment, the position of the antenna under test needs to be drawn on foam A to ensure that the center of the aperture surface of the antenna under test can coincide with the center of the aperture surface of the calibration horn antenna. When placing foam A and the calibration horn antenna during the experiment, it is necessary to measure with a ruler to ensure that the center of the aperture surface of the calibration horn antenna coincides with the center of the probe. The distance between the calibration horn antenna and the probe antenna is measured as L1 (this distance is the set measurement distance. Due to measurement errors, the actual distance is recorded as L2).

[0029] Step 3: Place the antenna under test at the location of the calibration horn antenna, and ensure that the center of the aperture plane of the antenna under test coincides with the center of the aperture plane of the calibration horn antenna. At this time, it can be considered that the distance between the antenna under test and the probe is consistent with the distance between the calibration horn antenna and the probe, that is, the distance between the antenna under test and the probe is the measurement distance L2.

[0030] When measuring the planar near field of the antenna under test, the antenna under test is also fixed on the foam B. The foam B and the antenna under test are placed at the position of the calibration horn antenna in step 2. When placing, the center of the aperture surface of the antenna under test should be kept coincident with the center of the aperture surface of the calibration horn antenna, such as Figure 2As shown. Before the experiment, it is necessary to measure with a ruler to determine the position of foam B while ensuring that the measured antenna and the calibration horn antenna aperture surface coincide with each other, and draw the position of foam B on foam A. Then, in the actual plane near-field measurement, after the center of the calibrated horn antenna aperture surface coincides with the center of the probe in step 2, the measured antenna is placed. This ensures that the center of the measured antenna aperture surface coincides with the center of the probe, and the distance between the measured antenna and the probe is consistent with the distance between the calibration horn antenna and the probe in step 2, both of which are L2.

[0031] Step 4: Use the full-wave simulation software FEKO to simulate the calibration horn antenna and set S Δx ={Δx1, Δx2, ... Δx N1},S Δy ={Δy1, Δy2, ... Δy N2},S Δz ={Δz1, Δz2, ... Δz N3} is the set of deviations on the x, y, and z axes in the Cartesian coordinate system. FEKO is used to simulate the near-field data of the plane with different Δx, Δy, and Δz. In the formula, 1≤i≤N1, 1≤j≤N2, 1≤k≤N3.

[0032] Step 5: Compare the average phase error between the actual measured near field and the simulated near field of the calibration horn antenna by traversing Δx, Δy and Δz. The flowchart of the algorithm for calibrating the minimum phase error of the horn antenna is as follows: Figure 3 shown.

[0033]

[0034] Where N is the total number of sampling points on the sampling surface, E1(x n ,y n , z n ) is the sampling point P obtained by actual measurement n (x n ,y n , z n) electric field, The deviations Δx on the x, y, and z axes of the Cartesian coordinate system obtained by FKEO simulation are i , Δy j and Δz k The simulated electric field.

[0035] When the phase average error error is the smallest, the corresponding position (x n +Δx i ,y n +Δy j , z n +Δz k) is the real position of the sampling point in the Cartesian coordinate system after joint correction using the simulation data and the actual measurement data, that is, the planar near-field data E2(x n ,y n , z n ) corresponds to P n (x n ,y n , z n )The actual position of the sampling point is (x n +Δx i ,y n +Δy j , z n +Δz k ).

[0036] In order to illustrate the advantages of the method of the present invention, specific examples are given below.

[0037] The calibration horn antenna of this embodiment is an E-plane horn antenna with a size of 30cm×11cm×51cm. Figure 4 The working frequency band of the antenna is 2.3-2.9 GHz. In the planar near-field measurement of this implementation example, the working frequency is 2.5 GHz. The wavelength of the antenna working at this frequency is 12 cm, and the antenna feeding voltage is 1 V. The sampling plane size is 2m×2m, the sampling interval is 0.1m, and the distance between the antenna and the sampling plane is set to 1m. There are 441 sampling points in total, of which the main radiation component is E x , that is, the real position of the sampling surface of the antenna during near-field measurement is set. In this embodiment, when the method of the present invention is used, Δx in step 4 i , Δy j and Δz k The deviation range and deviation interval are as follows: Δx = {-5cm, -4cm, ...5cm}, Δy = {-5cm, -4cm, ...5cm}, Δz = {-5cm, -4.9cm, ...5cm}.

[0038] The method provided by the present invention is used to determine the actual distance between the antenna and the sampling plane, that is, the offset of the antenna sampling plane on the x, y, and z axes of the Cartesian coordinate system. The results are shown in Table 1, which provides four groups of calculation examples under different position deviations. The method provided by the present invention can accurately correct the sampling plane position during the near-field measurement of the antenna plane, and the result is very consistent with the actual position set in the FKEO simulation.

[0039] In order to verify the effectiveness of the method of the present invention in the actual plane near-field measurement distance correction, Table 2 shows the comparison of the position deviation corrected by the present invention under different signal-to-noise ratios and the real position deviation set in the FEKO simulation, where the set real position deviations Δx, Δy, and Δz are all 0, and the results of the plane near-field phase without noise and the plane near-field phase after noise at different signal-to-noise ratios are shown in Figure 2. Figure 5 As shown, it can be seen from the results that under the condition of noise interference, the method provided by the present invention can still accurately correct the distance.

[0040] Table 1 Comparison of position deviation corrected by the present invention and FEKO simulation

[0041]

[0042] Table 2 Comparison of position deviation corrected by the present invention and FEKO simulation at different signal-to-noise ratios

[0043]

[0044]

[0045] It can be seen that the present invention can accurately correct the sampling surface position deviation caused by the measurement error of the antenna in the planar near-field measurement, has high calculation accuracy and low cost, and effectively solves the problem that the traditional method of using a laser interferometer to align the antenna is relatively expensive, the equipment is large and precise, and it is cumbersome to use when performing ranging operations.

[0046] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way; any non-essential additions and substitutions made by technicians in this field based on the technical features of the technical solution of the present invention belong to the protection scope of the present invention.

Claims

1. A planar near-field measurement distance calibration method based on calibration antenna phase error analysis, characterized in that: The following steps are involved: Step 1: According to the planar near-field measurement scheme of the antenna under test, the distance between the antenna under test and the probe antenna is set to L1, and the set of sampling points on the near-field sampling plane is P = {P n |n=1,2,...,N}, where P n (x n ,y n ,z n ) is set to E(x n ,y n ,z n ), the total number of points on the sampling surface is N, n represents the nth sampling point, (x n ,y n ,z n ) represents the position of the nth sampling point in the Cartesian coordinate system; Step 2: Use the calibration horn antenna to perform planar near-field measurement, set the actual distance between the calibration horn antenna and the probe antenna to L2, and obtain the calibration antenna planar near-field E1(x n ,y n ,z n ); Due to measurement error, there is an error between the set distance L1 and the actual distance L2, so when measuring, the sampling point P n The real position is P n (x n +Δx,y n +Δy,z n +Δz), the plane near field at the corresponding sampling point is E(x n +Δx,y n +Δy,z n +Δz), where Δx, Δy and Δz are the actual measurement process, n The deviation between the actual position of a point and the set position on the x, y, and z axes in the Cartesian coordinate system; Step 3: Place the antenna under test at the location of the calibration horn antenna, ensuring that the center of the aperture plane of the antenna under test coincides with the center of the aperture plane of the calibration horn antenna. Since the sampling surface size and sampling interval in steps 2 and 3 are the same, the sampling point P is n The actual position of the electric field at is consistent with that in step 2, which is P n (x n +Δx,y n +Δy,z n +Δz), the antenna under test corresponds to the sampling point P n The plane near field is E2(x n ,y n ,z n ); Step 4: Simulate the calibration horn antenna and set S Δx ={Δx1,Δx2,...Δx N1 },S Δy ={Δy1,Δy2,...Δy N2 },S Δz ={Δz1,Δz2,...Δz N3 } are the sets of deviations on the x, y, and z axes in the Cartesian coordinate system, and the near field of the plane under different errors is obtained by simulation. Where 1≤i≤N1,1≤j≤N2,1≤k≤N3; Step 5: Compare and calibrate the planar near field E1(x n ,y n ,z n ) and simulated planar near field The average phase error is: When the average phase error is the smallest, the corresponding sampling point (x n +Δx i ,y n +Δy j , z n +Δz k ) is the actual position of the sampling plane, and the planar near field E2(x n ,y n ,z n ) is corrected to (x n +Δx i ,y n +Δy j , z n +Δz k ).

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