Antenna circular polarization mismatch loss correction method and system for space target RCS measurement

Abstract

The invention discloses a method and system for correcting circular polarization mismatch loss of antenna for measuring RCS of space target, belonging to the field of radar communication technology, and solving the problem of how to correct circular polarization mismatch loss of antenna transceiver beam to improve the measurement accuracy of RCS of space target. The method of the invention first obtains the theoretical value of Faraday rotation angle in a frequency band based on the relationship between Faraday rotation angle, frequency and total content of ionospheric electron concentration, then obtains the circular polarization axis ratio of transceiver beam based on directional pattern test, and then uses polarization mismatch formula to process the theoretical value of Faraday rotation angle and the test value of circular polarization axis ratio to obtain the correction value of circular polarization loss. The correction method is easy to realize in engineering and can improve the measurement accuracy of RCS of space target by radar. The invention fills the blank of circular polarization mismatch loss correction of antenna transceiver beam.

Description

Technical Field

[0001] The invention belongs to the technical field of radar communication, and relates to a method and a system for correcting antenna circular polarization mismatch loss for measuring RCS of a space target. Background Art

[0002] When low-frequency electromagnetic waves such as VHF (Very high frequency) and UHF (Ultra High Frequency) pass through the ionosphere, the polarization axis rotates, resulting in inconsistency between the polarization axes of the incident wave and the reflected wave, causing polarization mismatch and, in turn, antenna gain loss. Compared with linear polarization, circularly polarized electromagnetic waves can minimize the polarization mismatch loss caused by Faraday rotation. Due to the effect of feed amplitude and phase errors, the actual radar radiates elliptically polarized waves, and there is still polarization mismatch in the transmit and receive beams.

[0003] The circular polarization mismatch loss of the antenna's transmit and receive beams is related to the circular polarization axis ratio and Faraday rotation angle of the transmit and receive beams. The circular polarization axis ratio of the antenna changes with the beam scanning angle, and the Faraday rotation angle changes with the electromagnetic concentration (TEC) of the ionosphere, that is, it changes with the weather conditions. RCS (Radar Cross Section) is the radar cross-sectional area of ​​the radar measurement object. It describes the scattering ability of the radar target to the incident electromagnetic wave. It is a reflection of the physical properties of the target such as size, shape, and material. It is an important basic information for target identification. The existence of circular polarization mismatch loss will affect the RCS measurement accuracy of space targets, and the circular polarization mismatch loss of the antenna's transmit and receive beams must be corrected.

[0004] In the prior art, the Chinese invention patent application "A Method for Identifying the RCS Measurement Accuracy of Phased Array Radar Targets" with application publication number CN111948616A and application publication date November 17, 2020 obtains an identification instruction for the radar RCS measurement accuracy, determines a calibration satellite according to the identification instruction; determines the RCS reference value of the calibration satellite; determines the visible time period of the calibration satellite to the radar according to the RCS reference value of the calibration satellite; tracks and measures the calibration satellite by the radar during the visible time period to obtain measurement data; determines error statistics based on the measurement data; when the error statistics meet the preset accuracy standards, it is determined that the radar target RCS measurement accuracy meets the identification requirements, but the document does not mention how to correct the circular polarization mismatch loss of the antenna transceiver beam. Summary of the invention

[0005] The technical problem to be solved by the present invention is how to correct the circular polarization mismatch loss of the antenna transceiver beam to improve the RCS measurement accuracy of the space target.

[0006] The present invention solves the above technical problems through the following technical solutions:

[0007] The antenna circular polarization mismatch loss correction method applied to space target RCS measurement includes the following steps:

[0008] S1. Based on the relationship between the Faraday rotation angle, the frequency of the electromagnetic wave, and the total electron concentration in the ionosphere, the theoretical value of the Faraday rotation angle within the frequency band is obtained;

[0009] S2, obtain the circular polarization axis ratio of the transmit and receive beams based on the pattern test;

[0010] S3. Use the polarization mismatch formula to process the theoretical value of the Faraday rotation angle and the circular polarization axis ratio test value to obtain the circular polarization loss correction value.

[0011] The method of the invention first obtains the theoretical value of the Faraday rotation angle within the frequency band based on the relationship between the Faraday rotation angle, the frequency and the total content of the ionospheric electron concentration, then obtains the circular polarization axis ratio of the transmitting and receiving beams based on the directional pattern test, and then uses the polarization mismatch formula to process the theoretical value of the Faraday rotation angle and the circular polarization axis ratio test value to obtain the circular polarization loss correction value. The correction method is easy to implement in engineering and can improve the RCS measurement accuracy of the radar for the space target. The invention fills the blank of the circular polarization mismatch loss correction of the antenna transmitting and receiving beams.

[0012] As a further improvement of the technical solution of the present invention, the theoretical value of the Faraday rotation angle within the frequency band is obtained based on the relationship between the Faraday rotation angle and the frequency of the electromagnetic wave and the electromagnetic concentration of the ionosphere in step S1, specifically:

[0013] When electromagnetic waves pass through the ionosphere, their polarization axis has a Faraday rotation effect. The Faraday rotation angle Ω also changes with the total electron concentration in the ionosphere. The Faraday rotation angle in the band above VHF is:

[0014]

[0015] Where Ω represents the Faraday rotation angle, f represents the frequency of the electromagnetic wave, and B LF represents the average geomagnetic field strength, dl represents the differential along the propagation path, and Ne represents the electron density.

[0016] As a further improvement of the technical solution of the present invention, the circular polarization loss correction value is obtained by processing the Faraday rotation angle theoretical value and the circular polarization axis ratio test value using the polarization mismatch formula described in step S3, specifically:

[0017] The circular polarization mismatch loss of the transmit and receive beams is calculated by the following formula:

[0018]

[0019] Where L represents the circular polarization mismatch loss of the transmit and receive beams, AR1 and AR2 are the axial ratios of the transmit and receive antennas, and Ω is the Faraday rotation angle. The correction table of the circular polarization mismatch loss of the transmit and receive beams with frequency and scanning angle is calculated based on the test values ​​of the axial ratios of the transmit and receive antennas AR1 and AR2 and the theoretical value of the Faraday rotation angle Ω.

[0020] Antenna circular polarization mismatch loss correction system applied to space target RCS measurement, including: Faraday rotation angle theoretical value calculation module, circular polarization axis ratio test module, circular polarization loss correction module;

[0021] The Faraday rotation angle theoretical value calculation module is used to obtain the Faraday rotation angle theoretical value within the frequency band based on the relationship between the Faraday rotation angle and the frequency of the electromagnetic wave and the total electron concentration of the ionosphere;

[0022] The circular polarization axial ratio test module is used to obtain the circular polarization axial ratio of the transmitting and receiving beams based on the directional pattern test;

[0023] The circular polarization loss correction module is used to process the Faraday rotation angle theoretical value and the circular polarization axis ratio test value using the polarization mismatch formula to obtain the circular polarization loss correction value.

[0024] As a further improvement of the technical solution of the present invention, the Faraday rotation angle theoretical value calculation model is described in which the relationship between the Faraday rotation angle and the frequency of the electromagnetic wave and the electromagnetic concentration of the ionosphere is used to obtain the Faraday rotation angle theoretical value within the frequency band, specifically:

[0025] When electromagnetic waves pass through the ionosphere, their polarization axis has a Faraday rotation effect. The Faraday rotation angle Ω also changes with the total electron concentration in the ionosphere. The Faraday rotation angle in the band above VHF is:

[0026]

[0027] Where Ω represents the Faraday rotation angle, f represents the frequency of the electromagnetic wave, and B LF represents the average geomagnetic field strength, dl represents the differential along the propagation path, and Ne represents the electron density.

[0028] As a further improvement of the technical solution of the present invention, the circular polarization loss correction module uses the polarization mismatch formula to process the Faraday rotation angle theoretical value and the circular polarization axis ratio test value to obtain the circular polarization loss correction value, specifically:

[0029] The circular polarization mismatch loss of the transmit and receive beams is calculated by the following formula:

[0030]

[0031] Where L represents the circular polarization mismatch loss of the transmit and receive beams, AR1 and AR2 are the axial ratios of the transmit and receive antennas, and Ω is the Faraday rotation angle. The correction table of the circular polarization mismatch loss of the transmit and receive beams with frequency and scanning angle is calculated based on the test values ​​of the axial ratios of the transmit and receive antennas AR1 and AR2 and the theoretical value of the Faraday rotation angle Ω.

[0032] The advantages of the present invention are:

[0033] The method of the invention first obtains the theoretical value of the Faraday rotation angle within the frequency band based on the relationship between the Faraday rotation angle, the frequency and the total content of the ionospheric electron concentration, then obtains the circular polarization axis ratio of the transceiver beam based on the directional pattern test, and then uses the polarization mismatch formula to process the theoretical value of the Faraday rotation angle and the circular polarization axis ratio test value to obtain the circular polarization loss correction value. The correction method is easy to implement in engineering and can improve the RCS measurement accuracy of the radar for space targets. The invention fills the blank of the circular polarization mismatch loss correction of the antenna transceiver beam and has been applied in the target RCS measurement of a phased array radar. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flow chart of a method for correcting antenna circular polarization mismatch loss for measuring RCS of a space target according to an embodiment of the present invention;

[0035] Figure 2 FIG. 4 is a relationship diagram of the Faraday rotation angle, the frequency of the electromagnetic wave, and the total electron concentration (TEC) of the ionosphere according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0038] Embodiment 1

[0039] like Figure 1 As shown in FIG. 1 , the antenna circular polarization mismatch loss correction method for space target RCS measurement includes the following contents:

[0040] 1. Faraday rotation angle

[0041] When electromagnetic waves pass through the ionosphere, their polarization axis has a Faraday rotation effect. The Faraday rotation angle Ω also changes with the total electron concentration (TEC) of the ionosphere. The Faraday rotation angle in the band above VHF is:

[0042]

[0043] Where Ω represents the Faraday rotation angle, f represents the frequency of the electromagnetic wave, and B LF represents the average geomagnetic field strength, dl represents the differential along the propagation path, and Ne represents the electron density.

[0044] The Faraday rotation angle Ω depends on the frequency f of the electromagnetic wave and the average geomagnetic field strength B along the integration path. LF and the total ionospheric electron concentration TEC (unit: e / m 2 ), for 0.1G~10GHz band radio wave signal, when TEC is 10 16 e / m 2 to 10 19 e / m 2 When the Faraday rotation angle Ω caused by the ionosphere changes between Figure 1 shown.

[0045] 2. Circular polarization axis ratio

[0046] The change of antenna axial ratio with scanning angle is related to the specific form of antenna unit, and it is impossible to derive theoretical formula. Taking the antenna of a P-band long-range phased array radar as an example, the present invention uses the planar near-field scanning method to test the circular polarization axial ratio of the receiving and transmitting beams at multiple scanning angles in the frequency band in a microwave darkroom. The test values ​​are shown in Table 1.

[0047] Table 1 Test values ​​of antenna transmit / receive beam axis ratios as a function of frequency and scanning angle

[0048]

[0049]

[0050]

[0051] Table 1 (Continued) Test values ​​of antenna transmit / receive beam axis ratio as a function of frequency and scanning angle

[0052]

[0053]

[0054]

[0055] 3. Circular polarization mismatch loss of transmit and receive beams

[0056] The circular polarization mismatch loss of the transmit and receive beams can be calculated using the following formula:

[0057]

[0058] Where L represents the circular polarization mismatch loss of the transmit and receive beams, AR1 and AR2 are the axial ratios of the transmit and receive antennas, and Ω is the Faraday rotation angle.

[0059] According to the transmit and receive antenna axial ratio test values ​​AR1, AR2 and Figure 2 The theoretical value of the Faraday rotation angle Ω is calculated to obtain the correction table of the circular polarization mismatch loss of the transmitting and receiving beams with the frequency and scanning angle, as shown in Table 2.

[0060] Table 2 Variation of transmit / receive beam polarization mismatch loss with frequency scanning angle

[0061]

[0062]

[0063]

[0064] Table 2 (continued) Transmit and receive beam polarization mismatch loss changes with frequency scanning angle

[0065]

[0066]

[0067] The method of the present invention combines the axial ratio test value of the dual circularly polarized transceiver antenna and the ionospheric Faraday rotation effect, and provides the loss correction of the circular polarization mismatch of the antenna transceiver beam. The correction method is easy to implement in engineering, can improve the RCS measurement accuracy of the radar for space targets, and fills the gap in the circular polarization mismatch loss correction of the antenna transceiver beam.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for correcting antenna circular polarization mismatch loss for space target RCS measurement, characterized in that: The following steps are involved: S1. Based on the relationship between the Faraday rotation angle, the frequency of the electromagnetic wave, and the total electron concentration in the ionosphere, the theoretical value of the Faraday rotation angle within the frequency band is obtained; S2. derive the circular polarization axis ratio of the transmit and receive beams based on the pattern test; S3. Use the polarization mismatch formula to process the theoretical value of the Faraday rotation angle and the circular polarization axis ratio test value to obtain the circular polarization loss correction value.

2. The method for correcting antenna circular polarization mismatch loss for space target RCS measurement according to claim 1, characterized in that: The theoretical value of the Faraday rotation angle within the frequency band is obtained based on the relationship between the Faraday rotation angle, the frequency of the electromagnetic wave, and the electromagnetic concentration of the ionosphere in step S1, specifically: When electromagnetic waves pass through the ionosphere, their polarization axis has a Faraday rotation effect. The Faraday rotation angle Ω also changes with the total electron concentration in the ionosphere. The Faraday rotation angle in the band above VHF is: Where Ω represents the Faraday rotation angle, f represents the frequency of the electromagnetic wave, and B LF represents the average geomagnetic field strength, dl represents the differential along the propagation path, and Ne represents the electron density.

3. The method for correcting antenna circular polarization mismatch loss for space target RCS measurement according to claim 1, characterized in that: The circular polarization loss correction value is obtained by processing the Faraday rotation angle theoretical value and the circular polarization axis ratio test value using the polarization mismatch formula described in step S3, specifically: The circular polarization mismatch loss of the transmit and receive beams is calculated by the following formula: Where L represents the circular polarization mismatch loss of the transmit and receive beams, AR1 and AR2 are the axial ratios of the transmit and receive antennas, and Ω is the Faraday rotation angle. The correction table of the circular polarization mismatch loss of the transmit and receive beams with frequency and scanning angle is calculated based on the test values ​​of the axial ratios of the transmit and receive antennas AR1 and AR2 and the theoretical value of the Faraday rotation angle Ω. 4.An antenna circular polarization mismatch loss correction system applied to space target RCS measurement, characterized in that: include: Faraday rotation angle theoretical value calculation module, circular polarization axis ratio test module, circular polarization loss correction module; The Faraday rotation angle theoretical value calculation module is used to obtain the Faraday rotation angle theoretical value within the frequency band based on the relationship between the Faraday rotation angle and the frequency of the electromagnetic wave and the total electron concentration of the ionosphere; The circular polarization axial ratio test module is used to obtain the circular polarization axial ratio of the transmitting and receiving beams based on the directional pattern test; The circular polarization loss correction module is used to process the Faraday rotation angle theoretical value and the circular polarization axis ratio test value using the polarization mismatch formula to obtain the circular polarization loss correction value.

5. The antenna circular polarization mismatch loss correction system for space target RCS measurement according to claim 4, characterized in that: The Faraday rotation angle theoretical value calculation model described in the Faraday rotation angle theoretical value calculation model obtains the Faraday rotation angle theoretical value within the frequency band based on the relationship between the Faraday rotation angle and the frequency of the electromagnetic wave and the electromagnetic concentration of the ionosphere, specifically: When electromagnetic waves pass through the ionosphere, their polarization axis has a Faraday rotation effect. The Faraday rotation angle Ω also changes with the total electron concentration in the ionosphere. The Faraday rotation angle in the band above VHF is: Where Ω represents the Faraday rotation angle, f represents the frequency of the electromagnetic wave, and B LF represents the average geomagnetic field strength, dl represents the differential along the propagation path, and Ne represents the electron density.

6. The antenna circular polarization mismatch loss correction system for space target RCS measurement according to claim 4, characterized in that: The circular polarization loss correction module uses the polarization mismatch formula to process the Faraday rotation angle theoretical value and the circular polarization axis ratio test value to obtain the circular polarization loss correction value, which is specifically: The circular polarization mismatch loss of the transmit and receive beams is calculated by the following formula: Where L represents the circular polarization mismatch loss of the transmit and receive beams, AR1 and AR2 are the axial ratios of the transmit and receive antennas, and Ω is the Faraday rotation angle. The correction table of the circular polarization mismatch loss of the transmit and receive beams with frequency and scanning angle is calculated based on the test values ​​of the axial ratios of the transmit and receive antennas AR1 and AR2 and the theoretical value of the Faraday rotation angle Ω.

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