Apparatus and method for evaluating phase measurement error of a spherical near-field antenna when eccentric

Abstract

The application provides an evaluation device and method for phase measurement error of a spherical near-field antenna when the antenna is installed eccentrically, which can evaluate the phase measurement error of a to-be-measured antenna in a certain direction, a certain section and a certain angle range of a space under different eccentric distances of the antenna in a field. The device comprises a spherical near-field scanning ring 7, a low-frequency probe array 8, a high-frequency probe array 9, a spherical near-field test azimuth turntable 11 and an adapter tool 12. The two half rings of the spherical near-field scanning ring 7 are respectively arranged with the low-frequency probe array 8 and the high-frequency probe array 9. The spherical near-field test azimuth turntable 11 is located on the central axis of the spherical near-field scanning ring. The azimuth turntable 11 is connected with the adapter tool 12. The tool main body structure 1 and the counterweight 6 are connected with the turntable flange 3 and are installed on the adapter tool 12. The to-be-measured antenna 10 is installed on the antenna installation hole 2 of the test tool.

Description

Technical Field

[0001] This invention belongs to the field of near-field antenna measurement technology, and particularly relates to a device and method for evaluating phase measurement error when a spherical near-field antenna is eccentric. Background Technology

[0002] To meet the need for rapid testing of antenna radiation performance across the entire space, multi-probe electrically scanned spherical near-field measurement systems have emerged in recent years. These systems can rapidly acquire three-dimensional spatial data to obtain information such as amplitude, phase pattern, and polarization across the entire space.

[0003] In aerospace applications, spherical near-field testing is used not only to test the radiation performance of individual antennas but also to test the radiation performance of antennas mounted on a celestial plate, in order to examine the impact of the celestial environment on antenna radiation performance. Because it can acquire radiation information across the entire space in a single measurement, spherical near-field testing can be applied to antenna pattern testing for target localization using phase. However, since phase measurement is sensitive to many factors such as the measurement site environment, the stability of the test system, and the accuracy of model fabrication, accurate measurement of the phase pattern is more difficult than that of the amplitude pattern.

[0004] In spherical near-field antenna testing, the antenna under test (DUT) is typically placed at the center of the test area. This minimizes the radius of the smallest sphere surrounding the DUT with the center as its center, resulting in the highest testing accuracy. According to the mode expansion theory of spherical near-field, the smaller the smallest sphere surrounding the DUT, the fewer spherical wave modes are required for the radiation field, leading to higher testing accuracy. This is because environmental interference is generally composed of higher-order modes. The further the DUT deviates from the center, the more higher-order modes from the anechoic environment become during mode expansion. These higher-order modes cannot be eliminated through mode filtering post-processing, increasing the influence of the anechoic environment on the phase test results.

[0005] When testing an antenna under test (DUT) using a spherical near-field test, the general principle for DUT setup dictates that the DUT should be placed at the center of the testing platform, on the rotation axis. However, while this is feasible for testing the radiation performance of a single antenna, it's not possible to center all antennas when testing multiple antennas with the radiating carrier as the radiation boundary. In test scenarios involving multiple DUTs mounted on a large radiating carrier, such as a satellite radiation model, the multiple wide-beam antennas are easily affected by the surrounding environment. Testing with the radiating carrier present is necessary, making it impossible to center all antennas. This results in some or all antennas deviating from the center. During phase measurements, it was found that when the DUT deviates from the center, the phase measurement error increases with the eccentricity.

[0006] In practical engineering applications, there are generally certain requirements for the amplitude and phase measurement accuracy of the test site. The accuracy of spherical near-field phase measurement is related to many factors, one of which is the measurement error introduced by antenna eccentricity. This is because the antenna phase measurement result is directly related to the antenna's position in the field; the phase measured at different positions will introduce phase deviations introduced by the eccentricity. To clearly understand the accuracy of the measured phase data, it is necessary to evaluate the phase measurement error of the spherical near-field eccentrically mounted antenna. This helps testers understand the accuracy of the phase measurement data and is of great significance in engineering applications.

[0007] Currently, my country has not conducted research on the assessment of phase measurement errors when spherical near-field antennas are eccentric. Summary of the Invention

[0008] This invention proposes an evaluation device and method for phase measurement error when a spherical near-field antenna is eccentrically mounted. It can evaluate the phase measurement error of the antenna under test in a certain direction, a certain sectional area and a certain angular domain in space under different eccentric distances in the field.

[0009] The present invention is achieved through the following technical solution.

[0010] A test fixture for measuring phase measurement error when a spherical near-field antenna is eccentrically mounted includes: a main fixture structure 1, antenna mounting holes 2, a turntable connecting flange 3, and a counterweight 6; the main fixture structure is a cuboid frame structure with a flat upper surface and several antenna mounting holes to be tested; the surfaces of the several antenna mounting holes are arranged in a straight line at equal intervals, and the main fixture structure and the turntable connecting flange are located directly below the first antenna mounting hole, that is, slightly to the left of the center of the long side of the entire fixture, with the antenna mounting hole on the right side; the counterweight is located on the left side of the main fixture structure.

[0011] An evaluation device based on the aforementioned test fixture includes: a spherical near-field scanning ring 7, a low-frequency probe array 8, a high-frequency probe array 9, a spherical near-field test azimuth turntable 11, and a transition fixture 12. The low-frequency probe array 8 and the high-frequency probe array 9 are respectively arranged in the two half-rings of the spherical near-field scanning ring 7. The spherical near-field test azimuth turntable 11 is located on the central axis of the circular surface of the spherical near-field scanning ring. The azimuth turntable 11 is connected to the transition fixture 12. The main structure 1 of the fixture and the counterweight 6 are installed together on the transition fixture 12 using the turntable connecting flange 3. The antenna under test 10 is installed on the antenna mounting hole 2 on the test fixture.

[0012] The beneficial effects of this invention are:

[0013] 1. In the near field of the spherical surface to be evaluated, the present invention uses a test fixture to achieve different positions at the same height of the antenna installation site. After performing full-space phase pattern test and spatial position test on the antenna, the measured data is analyzed and calculated to evaluate the phase test error of the antenna under different eccentric distances at the site.

[0014] 2. This invention utilizes a cuboid test fixture to install the antenna under test, enabling testing of the antenna at the center of the site and at different eccentric distances, and achieving approximately the same radiation boundary at different mounting hole positions, thereby reducing the impact introduced by differences in radiation boundary.

[0015] 3. The evaluation device proposed in this invention uses an optical aiming measurement device to accurately measure the spatial position of the antenna under test when it is installed in different hole positions on the test fixture, thereby reducing the calculation error introduced by the actual position deviation of the antenna when calculating the spatial phase difference;

[0016] 4. The installation method proposed in this invention uses the phase of the antenna installed at the center of the site as a reference, which can ensure that the reference data is minimally affected by eccentricity. By using all the phase data collected in the region of interest for error evaluation, the evaluation accuracy can be improved.

[0017] 5. The evaluation method proposed in this invention addresses the phase measurement error caused by antenna eccentricity in a spherical near-field measurement system by using phase measurement data of the antenna under test in the spherical near-field, which is more relevant to application scenarios. Attached Figure Description

[0018] Figure 1 A top view of the test fixture used for verification testing;

[0019] Figure 2 This is the front view of the test fixture used for verification testing;

[0020] Figure 3 A schematic diagram of the test fixture used for near-field testing of the antenna under test on a multi-probe spherical surface.

[0021] Figure 4 This is a schematic diagram for calculating the theoretical phase difference between two positions in a spherical near-field coordinate system.

[0022] Figure 5 The phase measurement error is the variation of the four cross-sections obtained from the eccentricity measurement of the antenna under test with the elevation angle.

[0023] Among them, 1-Main structure of the tooling (top view), 2-Antenna mounting hole, 3-Connecting flange to the turntable (front view), 4-Main structure of the tooling (front view), 5-Connecting flange to the turntable (side view), 6-Counterweight, 7-Spherical near-field scanning ring, 8-Low-frequency probe array, 9-High-frequency probe array, 10-Antenna under test, 11-Azimuth turntable, 12-Transfer tooling. Detailed Implementation

[0024] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the drawings are merely exemplary and are intended to illustrate the principles and spirit of the present invention, and are not intended to limit the scope of the present invention.

[0025] like Figure 1 , 2 As shown, the present invention provides a test fixture for measuring phase measurement error when a spherical near-field antenna is eccentrically mounted, comprising: a main fixture structure 1, antenna mounting holes 2, a turntable connecting flange 3, and a counterweight 6; the main fixture structure is a cuboid frame structure with a flat upper surface and several antenna mounting holes to be tested; the surfaces of the several antenna mounting holes are arranged in a straight line at equal intervals, and in specific implementation, the number of mounting holes and the spacing between the holes are set according to the maximum eccentricity distance of the antenna to be tested; the main fixture structure and the turntable connecting flange are located directly below the first antenna mounting hole, that is, at a position slightly to the left of the center of the long side of the entire fixture, with the antenna mounting hole on the right side; the counterweight is located on the left side of the main fixture structure, and in specific implementation, the weight is determined according to the length of the fixture on the right side of the flange to ensure left and right weight balance at the mounting flange position.

[0026] like Figure 3 As shown, the present invention also proposes an evaluation device based on the above-mentioned test fixture, comprising: a spherical near-field scanning ring 7, a low-frequency probe array 8, a high-frequency probe array 9, a spherical near-field test azimuth turntable 11, and a transition fixture 12; the low-frequency probe array 8 and the high-frequency probe array 9 are respectively arranged in the two half-rings of the spherical near-field scanning ring 7, the spherical near-field test azimuth turntable 11 is located on the central axis of the circular surface of the spherical near-field scanning ring, the azimuth turntable 11 is connected to the transition fixture 12, the main structure 1 of the fixture and the counterweight 6 are installed together on the transition fixture 12 using the turntable connecting flange 3, and the antenna under test 10 is installed on the antenna mounting hole 2 on the test fixture.

[0027] In practice, the above-mentioned device can be used to perform full-space phase pattern testing and spatial position testing on the antenna under test at different positions at the same height of the installation site. After analyzing and calculating the measured data, the phase test error of the antenna under test at different eccentric distances in the site can be evaluated.

[0028] The present invention also proposes an installation method based on the above-mentioned evaluation device, which specifically includes the following steps:

[0029] Step 1: Prepare a rectangular test fixture. The length of the fixture is set according to the eccentricity of the phase error to be evaluated. The width of the fixture is sufficient for antenna flange installation. Multiple antenna mounting holes are arranged at 20cm intervals along the long side of the upper surface of the fixture.

[0030] Step 2: For the spherical near-field test system whose phase measurement error is to be evaluated, select the antenna to be tested according to the frequency band to be evaluated, and set up the two theodolites used for optical aiming at the measurement location on the field after calibration.

[0031] Step 3: Install the test fixture on the spherical near-field test turntable using the adapter fixture. Connect the flange of the test fixture to the adapter fixture. Add a counterweight to one end of the test fixture to keep the left and right sides of the connecting flange balanced.

[0032] Step 4: Mount the antenna under test in the mounting hole located directly above the flange of the test fixture at the center of the site, set the test frequency, use the spherical near-field test system to test the phase pattern of the antenna under test in the entire space, and then use a theodolite to measure the current spatial position of the antenna under test in the site.

[0033] Step 5: Move the antenna under test along the long side of the test fixture to another mounting hole that is off-center from the site. Repeat the antenna phase pattern measurement and spatial position measurement in Step 4. After the test is completed, remove the test fixture and the antenna under test.

[0034] like Figure 4 As shown, the present invention also proposes an evaluation method based on the above-mentioned evaluation device, which specifically includes the following steps:

[0035] Step 1: Assume the antenna under test is measured at point O (x0, y0, z0) at the center of the field and at point A (x1, y1, z1) at an off-center position. Then the baseline length is... P is any direction in space (θ) i ,φ i The unit vector in that direction is for:

[0036]

[0037] Assuming λ is the operating wavelength, then the baseline Theoretical phase difference in the P direction for:

[0038]

[0039] Step 2: Measure the phase difference using the antenna under test at the center and off-center positions of the field. After unwinding and period reduction, the theoretical phase difference is subtracted. Phase measurement error in different directions of eccentric position is obtained

[0040]

[0041] Following this procedure, phase error values ​​at different pitch angles in the 0°, 45°, 90°, and 135° sections are obtained, such as... Figure 5 As shown;

[0042] Step 3: Based on the phase measurement error The root mean square (RMS) value is used to evaluate the average phase measurement error during eccentricity measurement of a spherical near-field antenna. The RMS value of the phase measurement error in a certain elevation (θ) direction is:

[0043]

[0044] Where, N φ This indicates the number of points on the azimuth φ. If the phase measurement error represents a certain angle, then the RMS value of the phase measurement error over a certain angular domain is expressed as:

[0045]

[0046] Where, N θ Indicates the number of points on the pitch scale.

[0047] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. An evaluation device for a test fixture based on phase measurement error when a spherical near-field antenna is eccentrically mounted, characterized in that, The test fixture includes: a main fixture structure (1), antenna mounting holes (2), a turntable connecting flange (3), and a counterweight (6); the main fixture structure is a cuboid frame structure with a flat upper surface and several antenna mounting holes to be tested; the surfaces of the several antenna mounting holes are arranged in a straight line at equal intervals, and the main fixture structure and the turntable connecting flange are located directly below the first antenna mounting hole, that is, slightly to the left of the center of the long side of the entire fixture, with the antenna mounting hole on the right side; the counterweight is located on the left side of the main fixture structure; The evaluation device includes: a spherical near-field scanning ring (7), a low-frequency probe array (8), a high-frequency probe array (9), a spherical near-field test azimuth turntable (11), and a transition fixture (12); the low-frequency probe array (8) and the high-frequency probe array (9) are respectively arranged in the two half rings of the spherical near-field scanning ring (7), the spherical near-field test azimuth turntable (11) is located on the central axis of the circular surface of the spherical near-field scanning ring, the spherical near-field test azimuth turntable (11) is connected to the transition fixture (12), the main structure (1) of the fixture and the counterweight (6) are installed together on the transition fixture (12) using the turntable connecting flange (3), and the antenna to be tested (10) is installed on the antenna mounting hole (2) on the test fixture.

2. The evaluation apparatus as described in claim 1, characterized in that, The number of antenna mounting holes and the spacing between them are set according to the maximum eccentricity distance of the antenna under test.

3. The evaluation apparatus as described in claim 1 or 2, characterized in that, The weight of the counterweight is determined based on the length of the tooling on the right side of the flange.

4. A method for installing the evaluation device according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Prepare a rectangular test fixture. The length of the fixture is set according to the eccentricity distance of the phase error to be evaluated. The width of the fixture is sufficient for antenna flange installation. Multiple antenna mounting holes are arranged along the long side of the upper surface of the fixture. Step 2: For the spherical near-field test system whose phase measurement error is to be evaluated, select the antenna to be tested according to the frequency band to be evaluated, and set up the two theodolites used for optical aiming at the measurement location on the field after calibration. Step 3: Install the test fixture on the spherical near-field test turntable using the adapter fixture. Connect the flange of the test fixture to the adapter fixture. Add a counterweight to one end of the test fixture to keep the left and right sides of the connecting flange balanced. Step 4: Mount the antenna under test in the mounting hole located directly above the flange of the test fixture at the center of the site, set the test frequency, use the spherical near-field test system to test the phase pattern of the antenna under test in the entire space, and then use a theodolite to measure the current spatial position of the antenna under test in the site. Step 5: Move the antenna under test along the long side of the test fixture to another mounting hole that is off-center from the site. Repeat the antenna phase pattern measurement and spatial position measurement in Step 4. After the test is completed, remove the test fixture and the antenna under test.

5. An installation method based on the evaluation device according to claim 4, characterized in that, Multiple antenna mounting holes are arranged at 20cm intervals along the long side of the upper surface of the fixture.

6. An evaluation method based on the evaluation apparatus of claim 4, characterized in that, Includes the following steps: Step 1: Assume the antenna under test is located at point O when measuring at the center of the field. Point A is the measurement location when the position is eccentric. The baseline length is P is any direction in space. The unit vector in this direction is for: （1） Assumption If the operating wavelength is used, then the baseline is... Theoretical phase difference in the P direction for: （2） Step 2: Measure the phase difference using the antenna under test at the center and off-center positions of the field. After unwinding and periodic removal, the theoretical phase difference is subtracted. The phase measurement error in different directions of the eccentric position is obtained. （3） Following this procedure, phase error values ​​at different pitch angles in the 0°, 45°, 90°, and 135° sections were obtained; Step 3: Based on the phase measurement error The root mean square (RMS) value is used to evaluate the average phase measurement error when measuring the eccentricity of a spherical near-field antenna. Then, at a certain elevation ( The RMS value of the phase measurement error in the direction is: （4） in, Indicates direction The number of points on it If the phase measurement error represents a certain angle, then the RMS value of the phase measurement error over a certain angular domain is expressed as: （5） in, Indicates the number of points on the pitch scale.

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