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

Abstract

The present invention discloses a planar near-field measurement distance calibration method based on calibration antenna phase error analysis, which belongs to the field of antenna near-field measurement. The present invention first uses a calibration antenna and a probe antenna to perform planar near-field measurement; then uses the antenna under test and the probe antenna to perform planar near-field measurement; then simulates the data of the calibration antenna when there are different offsets on the sampling plane; uses the simulated and measured data of the calibration antenna to correct the true position of the sampling plane, and the simulated plane corresponding to the minimum phase error between the two is the true position of the sampling plane after correction, thereby achieving the purpose of correcting the true position of the sampling plane of the antenna under test. The present invention has high correction accuracy and low cost, and is suitable for the correction of planar near-field measurements 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] To accurately measure the antenna's planar near-field, it's often desirable to avoid or minimize errors during the measurement process, thereby improving accuracy. Due to numerous factors, including random errors in the near-field test system itself and during test operations within a microwave anechoic chamber, there may be some discrepancy between the measured near-field value and the true value. The main sources of these errors include systematic errors such as system equipment and environmental errors, probe parameter errors, and test equipment errors, as well as parameter errors such as probe position, scan plane truncation, data point sampling interval, and antenna alignment.

[0003] However, during actual near-field measurement operations, 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, its actual position may be offset due to the placement of the antenna, making it difficult to ensure that the relative positions of the antenna under test and the probe antenna remain 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 errors 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 theoretical setting, which may result in a deviation between the measured near field on the sampling plane and the near field on the set actual sampling plane.

[0004] Currently, a common method for improving antenna alignment is to use a 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. This minimizes parameter errors caused by distance measurement during planar near-field testing. However, laser interferometers are relatively expensive, large, and sophisticated, making them cumbersome to use for distance measurement. Therefore, most microwave anechoic chambers for planar near-field measurements lack this hardware.

[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] To address the need for improvements to existing methods of distance measurement using laser interferometers, this paper proposes a planar near-field distance calibration method based on phase error analysis of a calibration antenna. This method leverages the sensitivity of the calibration antenna's near-field to phase, using the simulated planar near-field phase of the calibration antenna as a reference. By comparing the phase error between the calibration antenna's measured planar near-field and the simulated planar near-field, the method accurately determines the true distance between the calibration antenna and the probe antenna, thereby calibrating the calibration antenna to the actual distance of the antenna being measured.

[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 as the electric field at the sampling point 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 true 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 error between the distance between the antenna under test and the probe antenna and the distance between the calibration horn antenna and the probe antenna is much smaller than the difference between the actual distance and the set distance, and has little effect on the measurement results, 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 is consistent with that in step 2, which is P n (x n +Δx,y n +Δy,z n +Δz), the measured antenna 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) actually measured by the horn antenna by traversing Δx, Δy and Δz. 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 surface, and the plane near field E2(x n ,y n , z n ) is corrected to the true position (x n +Δxi ,y n +Δy j , z n +Δz k ).

[0016] The proposed planar near-field distance calibration method based on calibration antenna phase error analysis leverages the sensitivity of the calibration antenna's near-field to phase. Using the simulated planar near-field phase of the calibration antenna as a reference, the method accurately corrects the position of the antenna under test by comparing the phase error between the calibration antenna's measured and simulated planar near-fields. Compared to traditional calibration methods using laser ranging, this method offers the advantages of ease of operation, low cost, and wider applicability, better meeting the need for calibrating the antenna under test during antenna measurement. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[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.

[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 with reference to the accompanying drawings and corresponding microwave darkroom planar near-field measurement correction examples, which are intended to explain rather than limit the present invention.

[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 the electric field at the sampling point E(x n ,y n , z n ).

[0026] One point worth mentioning here is the preparation required before performing a planar near-field measurement. Theoretically, when performing a planar near-field measurement, both the antenna and the probe are in an ideal environment with a relative permittivity of 1.0. However, in actual planar near-field measurements, the probe antenna is immersed in air with a relative permittivity of approximately 1.0, while the antenna under test is placed on a bracket. To minimize the bracket's effect on the antenna, foam is used as the bracket for the calibration horn antenna and the antenna under test.

[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 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 stand 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 of the antenna under test coincides with the center of the aperture of the calibration horn antenna. During the experiment, when placing foam A and the calibration horn antenna, it is necessary to use a ruler to measure to ensure that the center of the aperture 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 error, the actual distance is recorded as L2).

[0029] 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 point, the distance between the antenna under test and the probe is considered to be the same as 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] During the planar near-field measurement of the antenna under test, the antenna under test is also fixed on the foam B. Place the foam B and the antenna under test at the location of the calibration horn antenna in step 2. When placing them, the center of the aperture of the antenna under test should be kept coincident with the center of the aperture of the calibration horn antenna, as shown in the following example: Figure 2As shown. Before the experiment, you need to use a ruler to measure and determine the position of foam B while ensuring that the aperture planes of the antenna under test and the calibration horn antenna coincide. The position of foam B should be plotted on foam A. Then, during the actual planar near-field measurement, after the center of the calibration horn antenna aperture plane coincides with the center of the probe in step 2, place the antenna under test. This ensures that the center of the antenna aperture plane coincides with the center of the probe, and the distance between the antenna under test and the probe is consistent with the distance between the calibration horn antenna and the probe in step 2, both being 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 antenna operates in a frequency band of 2.3-2.9 GHz. In the planar near-field measurement of this example, the operating frequency is 2.5 GHz. The wavelength of the antenna operating at this frequency is 12 cm, and the antenna feed voltage is 1 V. The sampling plane size is 2 m × 2 m, the sampling interval is 0.1 m, and the distance between the antenna and the sampling plane is set to 1 m. There are 441 sampling points in total, of which the main radiation component is E x , that is, the actual 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 determines the true 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 examples of four groups of calculations under different position deviations. The method provided by the present invention can accurately correct the sampling plane position during antenna planar near-field measurement. The results are very consistent with the true 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 and the actual position deviation set in the FEKO simulation under different signal-to-noise ratios, where the set actual position deviations Δx, Δy, and Δz are all 0. 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 in FIG, it can be seen from the results that, in the case 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 measurement error in the planar near-field measurement of the antenna, with high calculation accuracy and low cost, and effectively solves the problems of the traditional method of using laser interferometer to align the antenna, which 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 embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with 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 or replacements made by those skilled in the art based on the technical features of the technical solution of the present invention fall within the scope of protection of the present invention.

Claims

1. A planar near-field measurement distance calibration method based on calibration antenna phase error analysis is 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 as the electric field at the sampling point 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 true 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 is consistent with that in step 2, which is P n (x n +Δx,y n +Δy,z n +Δz), the measured antenna 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 plane near field under different errors is simulated. Where 1≤i≤N1,1≤j≤N2,1≤k≤N3; Step 5: Compare and calibrate the planar near field E1 (x) actually measured by the horn antenna by traversing Δx, Δy and Δz. n ,y n ,z n ) and simulated planar near field The average phase error is: The sampling point (x n +Δx i ,y n +Δy j , z n +Δz k ) is the actual position of the sampling surface, and the plane near field E2(x n ,y n ,z n ) is corrected to the true position (x n +Δx i ,y n +Δy j , z n +Δz k ).

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