RCS test calibration method under far-field condition

Abstract

The invention provides an RCS (radar cross section) test calibration method under a far field condition, and belongs to the technical field of radar cross section test. According to the method, based on the SOL calibration technology, the RC S test calibration method under the far-field condition is designed according to the characteristics of an RCS test system under the far-field condition, system errors can be accurately separated by using the SOL calibration technology, and in the far-field RCS test, internal errors of test equipment and additional errors caused by mismatching of the equipment can be remarkably reduced; in addition, environmental errors generated in air transmission can be compensated on the basis that a high-power power amplifier is not used, and the dynamic range and sensitivity of measurement are improved. And meanwhile, a background noise vector cancellation and time domain gating method is combined, so that useful signals of the to-be-detected target can be well extracted from a plurality of interference signals, and accurate evaluation on the RCS of the to-be-detected target is completed.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar cross section measurement, and particularly relates to an RCS test calibration method under far-field conditions. Background Art

[0002] The radar cross section (RCS) is an important indicator characterizing the electromagnetic stealth performance of modern equipment. In the fields of aerospace, satellite navigation, space communication, etc., the RCS measurement of targets has become an essential and important task for accurately evaluating and designing relevant important components.

[0003] Currently, there are mainly two methods for target RCS measurement. One is to perform near-field measurement. By measuring the electromagnetic scattering characteristics of the target to be measured in the near-field region, and then using the near-to-far field transformation algorithm to convert the electromagnetic scattering characteristics under near-field conditions into the RCS value of the target to be measured under far-field conditions. However, this method will have a certain impact on the target RCS measurement result due to the errors existing in the near-to-far field transformation algorithm itself. Another method is to perform far-field measurement on the target to be measured to obtain the RCS of the target. For far-field RCS measurement, due to the need to meet far-field conditions, the test site must have a sufficient test distance, which makes the electromagnetic wave need to transmit a long distance in the air. During this long-distance transmission process, the electromagnetic wave is greatly affected by the environment, and is also interfered by multipath effects such as ground reflection waves and measurement errors caused by air loss. Therefore, compared with communication systems or conventional antenna measurements, RCS measurement faces more severe challenges of broadband dynamic errors. Currently, for air transmission loss, it is mainly through the use of high-power power amplifiers to offset the influence introduced by air loss (Xu Xiaojian. New Technologies for Radar Target Scattering Characteristics Measurement and Processing [M]. Beijing: National Defense Industry Press, 2017.). The existing domestic technologies cannot meet the current technical requirements.

[0004] Therefore, how to use effective calibration techniques to separate and offset the attenuation introduced by air loss, improve the accuracy of far-field RCS measurement, and make its error meet the requirements of far-field measurement has become an urgent problem to be solved. Summary of the Invention

[0005] Aiming at the problems existing in the background art, the purpose of the present invention is to provide an RCS test calibration method under far-field conditions. This method is based on the SOL calibration technology. According to the characteristics of the RCS test system under far-field conditions, an RCS test calibration method for far-field conditions is designed, which improves the accuracy of RCS measurement after calibration using the method of the present invention.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A method for calibrating RCS testing under far - field conditions includes the following steps:

[0008] Step 1. Set up and adjust the testing system to meet the far - field testing conditions;

[0009] Step 2. Ensure that there are no sundries in the testing area of the antenna orientation, and perform load calibration on the testing system;

[0010] Step 3. Place the low - scattering platform at a suitable position, and then place the target to be measured on the low - scattering platform so that the center height of the target to be measured is flush with the height of the transmitting antenna. Place a metal plate at a certain distance in the direction close to the antenna from the target to be measured. Then perform short - circuit calibration on the testing system;

[0011] Step 4. Move the metal plate λ / 4 distance away from the antenna, and then perform open - circuit calibration on the testing system, thus completing the entire RCS testing calibration.

[0012] Further, the testing system described in Step 1 includes: a vector network analyzer, a transmitting antenna, a receiving antenna, a low - scattering platform, an absorbing material, a metal calibration plate with scales, and a computer;

[0013] Among them, one port of the vector network analyzer is connected to the transmitting antenna, and the other port is connected to the receiving antenna; the transmitting antenna and the receiving antenna are of the same height and placed side by side, and their radiation ports are symmetric about the target to be measured; the low - scattering platform is horizontally placed in front of the radiation port of the transmitting antenna, and the target to be measured is placed on it; the computer is connected to the vector network analyzer and controls the vector network analyzer to realize the testing, reading, and storage of electromagnetic data; the absorbing material is placed between the transmitting antenna and the receiving antenna to reduce the mutual coupling interference between the transmitting antenna and the receiving antenna.

[0014] Further, the metal calibration plate with scales includes a horizontal distance scale platform and a metal plate vertically placed on the horizontal distance scale platform.

[0015] Further, the size of the metal plate should be such that it completely blocks the target to be measured in the vertical plane, which is used to improve the dynamic range of the system and reduce the influence on RCS testing introduced by the attenuation of electromagnetic waves due to long - distance propagation.

[0016] Further, the vertical distance between the radiation ports of the transmitting antenna and the receiving antenna and the target to be measured is greater than the induction field area of the antenna to ensure that the main lobe of the antenna can completely cover the target to be measured, that is, it satisfies greater than or equal to where D 1 = max{antenna aperture, maximum size of the target to be measured}, and λ represents the wavelength corresponding to the measured frequency.

[0017] Further, the far-field test conditions are as follows: the distance between the transceiver antenna and the target under test is greater than or equal to 2D 2 2 / λ; where D 2 = the maximum lateral dimension of the target under test, and λ represents the wavelength corresponding to the test frequency.

[0018] Further, the test system further includes a turntable and a motor control module. The turntable is disposed below the low-scattering placement table and is used to rotate the target under test; the motor control module is connected to the computer and the turntable. The computer sends relevant control signals to the motor control module, and the motor control module controls the turntable to rotate at a constant speed under the drive of the control signals.

[0019] The present invention also provides an RCS test method, including the following steps:

[0020] S1. Calibrate according to the above calibration method;

[0021] S2. Without placing the target under test, conduct a test to obtain environmental background signal data;

[0022] S3. Place the target under test on the low-scattering placement table and conduct a test to obtain the signal data of the target under test;

[0023] S4. Vectorially subtract the signal data of the target under test and the environmental background data to reduce the influence of background noise, and process through the time-domain gating method to obtain the time-domain effective data of the target sample;

[0024] S5. Calculate the RCS value of the target sample using the time-domain effective data of the target sample processed in S4.

[0025] The mechanism of the present invention is as follows:

[0026] The present invention introduces a SOL calibration technique different from the traditional one. The test without placing any items is used as Load calibration, the test with a metal plate placed is used as Short calibration, and then the metal plate is moved a certain distance as Open calibration. That is, by using the SOL calibration technique combined with the experimental environment, the adjustment of the system error model can be carried out, partially compensating for the errors caused by environmental factors, realizing the decoupling processing of environmental parameters and system errors. At the same time, the air loss from the antenna radiation end face to the metal reflection face is suppressed through calibration; compared with the traditional calibration method, the dependence on high-power broadband power amplifiers is reduced.

[0027] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0028] The present invention provides a method for calibrating RCS testing under far-field conditions. By using SOL calibration technology, it can accurately separate system errors (including reflection errors, transmission errors, etc.). In far-field RCS testing, it can significantly reduce the internal errors of testing equipment and additional errors caused by equipment mismatch. In addition, it can also compensate for environmental errors generated during air transmission without using a high-power power amplifier, improving the measurement dynamic range and sensitivity. At the same time, combined with background noise vector cancellation and time-domain gating methods, it can extract useful signals of the target to be measured from many interfering signals well and complete the accurate evaluation of the RCS of the target to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of the RCS testing system under far-field conditions in the present invention.

[0030] Figure 2 It is a schematic structural diagram of the system when placing a metal plate for SOL calibration in the present invention.

[0031] Figure 3 It is a schematic diagram of the principle of the time-domain gating algorithm in the present invention.

[0032] Figure 4 It is a comparison diagram of time-domain signals for RCS testing of the object to be measured using the designed calibration technology in the present invention.

[0033] Among them, 1 is a computer, 2 is a motor control module, 3 is a low-scattering placement table, 4 is the target to be measured, 5 is a metal calibration plate with scales, 6 is a turntable, 7 is a vector network analyzer, 8 is a transmitting antenna, 9 is an absorbing material, and 10 is a receiving antenna. SPECIFIC EMBODIMENTS

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the drawings.

[0035] Figure 1 It is a schematic structural diagram of the RCS testing device under far-field conditions in the present invention. As Figure 1 shown, the testing system of the present invention includes a turntable 6, a motor control module 2, a vector network analyzer 7, a transmitting antenna 8, a receiving antenna 10, a low-scattering placement table 3, a turntable 6, an absorbing material 9, a metal calibration plate 5 with scales, and a computer 1;

[0036] Among them, one port of the vector network analyzer 7 is connected to the transmitting antenna 8, and the other port is connected to the receiving antenna 10; the transmitting antenna 8 and the receiving antenna 10 are placed at the same height and side by side, and their radiation ports are symmetric about the target under test 9; the low-scattering platform 3 is horizontally placed in front of the radiation port of the transmitting antenna 8, and the target under test 4 is placed thereon; the low-scattering platform 3 is arranged on the turntable 6, and the computer 1 is connected to the vector network analyzer 7 and the motor control module 2. The computer 1 controls the vector network analyzer to realize the test, reading and storage of electromagnetic data. At the same time, the computer sends relevant control signals to the motor control module, and the motor control module controls the turntable to rotate at a constant speed under the drive of the control signal; the absorbing material 9 is placed between the transmitting antenna 8 and the receiving antenna 10 to reduce the mutual coupling interference between the transmitting antenna and the receiving antenna;

[0037] The metal calibration plate with scale includes a horizontal distance scale platform and a metal plate vertically placed on the horizontal distance scale platform; the size of the metal plate should be such that it completely shields the target under test in the vertical plane, which is used to improve the dynamic range of the system and reduce the influence of the attenuation of electromagnetic waves caused by long-distance propagation on the RCS test.

[0038] Embodiment 1

[0039] A method for RCS testing under far-field conditions includes the following steps:

[0040] Step 1. Build and adjust the test system to make the test system meet the far-field test conditions;

[0041] Step 2. Perform pre-test calibration in the frequency band of 1 - 18 GHz:

[0042] Step 2.1. Ensure that there are no sundries in the test area in the direction of electromagnetic wave radiation, and perform load calibration on the test system as the Load calibration in the SOL calibration test;

[0043] Step 2.2. Place the low-scattering platform in a suitable position, and then place the target under test on the low-scattering platform so that the center height of the target under test is flush with the height of the transmitting antenna. A metal flat plate is placed at a certain distance in the direction of the target under test close to the antenna, and then the test system is calibrated for short circuit. The short circuit surface of the metal flat plate is used as the Short in the SOL calibration test;

[0044] Step 2.3. Move the metal flat plate a distance of λ / 4 in the direction away from the antenna, and then perform open-circuit calibration on the test system. The open-circuit surface after the metal flat plate is moved is used as the Open calibration in the SOL calibration test; the schematic diagram of the system structure during the calibration process is as Figure 2 shown;

[0045] Step 3. Without placing any samples to be tested, conduct a test to obtain environmental background signal data;

[0046] Step 4. Place the samples to be tested and conduct a test to obtain target signal data to be tested;

[0047] Step 5. Vectorially superimpose the original electromagnetic signal data and the environmental background data to reduce the influence of background noise, and process through the time-domain gating method to obtain the time-domain effective data of the target sample.

[0048] Figure 3 This is the schematic diagram of the time-domain gating algorithm in the present invention. Using the time-domain gating algorithm for the test signal can selectively filter out the direct coupling signal between the transmitting and receiving antennas, the interference signal generated by ground reflection at a large scale, the environmental noise interference signal, etc., which is beneficial to extracting the effective signal of the target to be tested.

[0049] Comparative Example 1

[0050] A method for RCS testing under far-field conditions includes the following steps:

[0051] Step 1. Build and adjust the test system to make the test system meet the far-field test conditions;

[0052] Step 2. Conduct pre-test calibration: Perform SOL calibration on the vector network analyzer through the standard calibration parts provided by the manufacturer within the corresponding frequency band;

[0053] Step 3. Without placing any samples to be tested, conduct a test to obtain environmental background signal data;

[0054] Step 4. Place the samples to be tested and conduct a test to obtain target signal data to be tested;

[0055] Step 5. Vectorially superimpose the original electromagnetic signal data and the environmental background data to reduce the influence of background noise, and process through the time-domain gating method to obtain the time-domain effective data of the target sample.

[0056] Figure 4 This is the time-domain signal comparison diagram of the RCS test for the target to be tested in Example 1 and Comparative Example 1. Among them, the left figure is the time-domain signal diagram of the RCS test for the target to be tested after calibrating the test system using the method of the present invention, and the right figure is the time-domain signal diagram of the RCS test for the target to be tested after calibrating the test system in Comparative Example 1. It can be seen from the figure that the target reflection signal on the left is clearly visible, while directly calibrating with the conventional standard parts, the target reflection signal will be submerged in the environmental level.

[0057] The above are only specific embodiments of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any manner.

Claims

1. A RCS test calibration method under far-field conditions, characterized in that: The following steps are involved: Step 1. Build and adjust the test system to meet the far-field test conditions; Step 2. Ensure that there is no debris in the test area where the antenna is facing, and perform load calibration on the test system; Step 3. Place the low-scattering table in a suitable position, and then place the target to be tested on the low-scattering table so that the center height of the target to be tested is flush with the height of the transmitting antenna. Place a metal plate at a certain distance from the target to be tested in the direction of the antenna, and then perform short-circuit calibration on the test system. Step 4. Move the metal plate away from the antenna by a distance of λ / 4, and then perform open-circuit calibration on the test system to complete the entire RCS test calibration.

2. The RCS test calibration method under far-field conditions as claimed in claim 1, characterized in that: The test system in step 1 includes a vector network analyzer, a transmitting antenna, a receiving antenna, a low-scattering storage table, an absorbing material, a metal calibration plate with a scale, and a computer; Among them, one port of the vector network analyzer is connected to the transmitting antenna, and the other port is connected to the receiving antenna; the transmitting antenna and the receiving antenna are placed at the same height and side by side, and the radiation ports of the two are symmetrical about the target to be measured; the low-scattering storage table is placed horizontally in front of the radiation port of the transmitting antenna, and the target to be measured is placed on it; the computer is connected to the vector network analyzer and controls the vector network analyzer to realize the testing, reading and storage of electromagnetic data; the absorbing material is placed between the transmitting antenna and the receiving antenna to reduce the mutual coupling interference between the transmitting antenna and the receiving antenna.

3. The RCS test calibration method under far-field conditions as claimed in claim 2, characterized in that: The metal calibration plate with scales comprises a horizontal distance scale platform and a metal plate vertically placed on the horizontal distance scale platform.

4. The RCS test calibration method under far-field conditions as claimed in claim 2, characterized in that: The size of the metal plate should be such that it completely blocks the object to be measured in the vertical plane.

5. The RCS test calibration method under far-field conditions as claimed in claim 1, characterized in that: The vertical distance between the transmitting antenna radiation port and the receiving antenna radiation port and the target to be measured is greater than the induction field area of ​​the antenna and satisfies the condition that it is greater than or equal to Where D1 = max{antenna aperture, maximum size of the target to be measured}, and λ represents the wavelength corresponding to the test frequency.

6. The RCS test calibration method under far-field conditions as claimed in claim 1, characterized in that: The far-field test condition is: the distance between the transceiver antenna and the target to be tested is greater than or equal to 2D2 2 / λ; where D2 = the maximum horizontal dimension of the target to be measured, and λ represents the wavelength corresponding to the test frequency.

7. The RCS test calibration method under far-field conditions as claimed in claim 2, characterized in that: The test system also includes a turntable and a motor control module. The turntable is arranged below the low-scattering storage table and is used to rotate the target to be tested. The motor control module is connected to a computer and the turntable. The computer sends relevant control signals to the motor control module. The motor control module controls the turntable to rotate at a uniform speed under the drive of the control signal.

8. A RCS testing method, characterized in that: The following steps are involved: S1. Calibrate according to the RCS test calibration method under far-field conditions according to any one of claims 1 to 7; S2. Perform the test without placing the target to be tested to obtain the environmental background signal data; S3. Place the target to be tested on a low-scattering storage table, perform a test, and obtain the target signal data to be tested; S4. Subtract the target signal data and the environmental background data by vector to reduce the influence of background noise, and obtain the effective time domain data of the target sample by time domain gating method; S5. Calculate the RCS value of the target sample using the time domain effective data of the target sample processed in S4.

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