Wideband fully-polarized radar full-link error simple calibration method based on single metal wire

Abstract

The invention discloses a broadband fully-polarized radar full-link error simple calibration method based on a single metal wire. The invention relates to a broadband fully-polarized radar full-link error simple calibration method based on a single metal wire, which can be used for carrying out polarization calibration on full-link errors of a fully-polarized radar system. According to the method, the full-link error calibration of the broadband full-polarization radar can be realized only by using a single metal wire, and the attitude loose constraint condition is considered. According to the invention, the calibration precision can be ensured while the attitude dependence is reduced and the experimental process is simplified, so that the broadband full-polarization radar can be effectively supported to obtain high-precision polarization information. Compared with the prior art, the technology considers the influence of all system errors, only a single metal wire needs to be measured, the experiment difficulty is reduced to a great extent, and engineering implementation is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of precision measurement and calibration, specifically relating to a simplified calibration method for the full-link error of broadband fully polarized radar based on a single metal wire. Background Technology

[0002] Accurate polarization information is crucial for radar target detection, enhancement, and identification. However, fully polarized radar systems are inevitably affected by polarization errors such as channel imbalance and antenna crosstalk during operation, leading to distorted measurement results. With the emergence of new-generation broadband fully polarized radar systems employing stepped-frequency waveforms, the independent channel gains introduced between different channels further exacerbate the complexity of the errors.

[0003] Traditional full-polarization radar polarization calibration methods are typically designed for narrowband applications and cannot effectively solve for the independent channel gain introduced by the system in broadband situations, thus failing. To address this issue, Welsh et al. proposed Full Polarization Calibration Technology (FPCT), which combines two dihedral reflectors at specific angles with a calibrator whose polarization scattering characteristics are known, achieving the solution for all error factors. The effectiveness of this method was verified in an anechoic chamber. However, FPCT has strict requirements on the calibrator's orientation and requires measuring three calibrators individually, resulting in a cumbersome experimental procedure and making it unsuitable for radars deployed in complex field environments. To relax the requirements on the calibrator's orientation, Li Muyang et al. proposed a dual-calibrator joint polarization calibration method (DTCT). This method uses a metal sphere and a metal wire at a specific angle for joint polarization calibration. However, this method requires using a UAV to separately suspend the two calibrators, making the experimental procedure still relatively complex; furthermore, the modeling process does not consider the influence of antenna crosstalk, limiting its applicability in low-isolation radar systems. Summary of the Invention

[0004] In view of this, the present invention provides a simplified calibration method for the end-to-end error of broadband fully polarimetric radar based on a single metal wire. This method achieves end-to-end error calibration of broadband fully polarimetric radar using only a single metal wire while also taking into account relaxed attitude constraints. The present invention reduces attitude dependence and simplifies the experimental procedure while still ensuring calibration accuracy, thus effectively supporting broadband fully polarimetric radar in acquiring high-precision polarization information.

[0005] This invention is operated according to the following steps: Step 1: Measure the azimuth of the metal wire by rotating the radar beam at a constant speed to obtain the sequence of measured polarization scattering matrices over one complete rotation cycle. ; Step 2: Based on the amplitude fluctuation characteristics of the main channel of the metal wire, the measurement polarization scattering matrix when the roll angle of the metal wire is 45° is obtained from the measurement data. And thus solve for the coupling error parameters. , and ; Step 3: Combining the four-channel ripple characteristics of the metal wire with the obtained coupling error parameters, further solve for the antenna crosstalk. Two candidate results containing ambiguity were obtained. and And based on antenna characteristics, the correct solution is obtained by deambiguation. ; Step 4: Utilize , , and The true value of the target scattering matrix is ​​obtained by compensating for the measured scattering matrices of other targets.

[0006] Beneficial effects: 1. Using a single calibration body (single metal wire): This overcomes the problem that traditional polarization calibration methods require multiple calibration bodies of different types or attitudes. Traditional methods often combine dihedral reflectors (for amplitude and phase calibration), dihedral reflectors, or tilted metal wires (for decoupling cross-polarization errors), which are cumbersome and require complex site layout. This invention uses only a single standard metal wire, which greatly simplifies the preparation, deployment, and maintenance costs of the calibration body, and minimizes the physical threshold for calibration. 2. No restrictions on the orientation of the calibration object: This reduces operational constraints during calibration. Traditional methods require the calibration object to be precisely placed in a specific orientation (e.g., the axis of the dihedral angle aligned with the radar, or the wire at a specific 45° polarization angle), which requires a precision turntable and complex alignment operations, making field implementation extremely difficult. This method allows the wire to be placed in any (non-zero) orientation, requiring only natural suspension or simple erection, making field calibration exceptionally convenient and robust, significantly improving the method's practicality and operability. Attached Figure Description

[0007] Figure 1 1. Schematic diagram of a metal wire measurement experiment; Figure 2 The curves showing the amplitude of the metal wire scattering matrix elements as a function of angle under ideal conditions are shown. Figure 3 The amplitude-inconsistent calibration performance of the proposed method under different signal-to-noise ratio conditions; Figure 4 The phase inconsistency calibration performance of the proposed method under different signal-to-noise ratio conditions; Figure 5 The polarization isolation calibration performance of the proposed method under different signal-to-noise ratio conditions is evaluated. Detailed Implementation

[0008] This invention presents a simplified calibration method for the end-to-end error of a broadband fully polarimetric radar based on a single metal wire. The method involves first establishing a system error model for the entire link in conjunction with the broadband fully polarimetric radar system. Then, by uniformly rotating the beam, 360-degree echo data of the metal wire within one complete cycle is acquired. Next, the echo data of the 45° metal wire is analyzed using the fluctuation characteristics of its main channel, and the coupling errors of the system channel independent gain and channel amplitude-phase imbalance are solved. Subsequently, the antenna crosstalk is further solved by combining the fluctuation characteristics of the four channels of the metal wire with the solved errors. Finally, the target measurement scattering matrix is ​​corrected based on the polarization error model to achieve high-precision polarization calibration.

[0009] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0010] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0011] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0012] Step 1: Measure the azimuth of the metal wire by rotating the radar beam at a constant speed to obtain the sequence of measured polarization scattering matrices over one complete rotation cycle. .

[0013] Sarabandi and colleagues described the fully polarized antenna as a four-port network and established a complete system polarization error model for a fully polarized radar system with a single antenna and dual polarization channels: (1) in, Representing the transpose of the matrix, the horizontal (h) and vertical (v) polarization components are chosen as the orthogonal basis for polarization measurements. The polarization scattering matrix of the noisy target is then measured under the backscattering convention. for (2) In this structure, the first subscript of each element in the polarization scattering matrix represents the receiving polarization state, and the second subscript represents the transmitting polarization state.

[0014] and The error matrices representing the receiving and transmitting channels, respectively, can be written as: (3) (4) in, , , and These respectively indicate an imbalance between the transmit and receive channels. and This indicates an imbalance in the channels of the transmitting and receiving antennas.

[0015] The crosstalk matrix of the antenna can be written as (5) in, and This indicates antenna leakage between the transmit and receive channels. , It can be assumed to be a symmetric matrix.

[0016] The true value of the target polarization scattering matrix can be written as (6) For broadband fully polarimetric radars using stepped-frequency waveforms, the four channels introduce additional independent channel gains. The system polarization error model of a broadband fully polarimetric radar can be more accurately described as follows: (7) in, The system channel gain matrix can be written as: (8) (7) can be expanded as (9) To simplify the solution process, common terms are extracted. (9) can be written as (10) Since the absolute amplitude of the target is obtained through RCS calibration, polarization calibration only requires relative calibration between different channels of the target. That is, it only needs to obtain the amplitude and phase information of each channel relative to the HH channel. Therefore... It can be discarded, and (9) can be further simplified to (11) (11) can be further written in vector form: (12) As can be seen from (12), the independent gain of the channel and the amplitude-phase imbalance of the transmit and receive channels are coupled together. To simplify the solution process, let (13) (14) (15) (12) can be further written as: (16) (16) contains , , and Four error factors are used to determine the true polarization scattering matrix of the target. It can be obtained through (17): (17) in, express The estimated value.

[0017] During the measurement of the metal wire, the radar can be controlled to observe the sky vertically. Then, two drones are used to carry the metal wire to the beam center, approximately parallel to the H-polarization direction, by pulling it with a thin line. The SM (Short-Ray Spectrum) of the metal wire is continuously collected at different angles during azimuth rotation. The calibration scenario is shown below. Figure 1 .

[0018] In actual measurement, the roll angle of the metal wire relative to H-polarization in the air is usually inconsistent with the azimuth angle of the radar beam. Therefore, before using the metal wire to solve for polarization error, it is necessary to select the PSM of the metal wire with the required angle from a PSM of one rotation period. This invention proposes a self-calculation method for the metal wire angle. The proposed method utilizes the variation characteristics of the main channel amplitude of the metal wire with the roll angle to achieve accurate calculation of the 45° metal wire angle. The specific principle is as follows: When the metal wire is parallel to the H-polarization direction in a plane perpendicular to the incident wave (roll angle is 0°), the scattering matrix of the metal wire is: (18) in, It is a constant related to the physical properties of the metal wire. Ideally... Extremely small (-30dB), negligible The scattering matrix of the metal wire with a roll angle of 0° can be written as follows: (19) The direction of H polarization rotates with the rotation of the radar beam, and the roll angle of the metal wire also changes accordingly.

[0019] The PSM of the metal wire varies with the roll angle. The changes can be represented by a rotation matrix: (20) in, This is a rotation matrix. At this point, the amplitude of the four polarization channels of the metal wire varies with the roll angle as follows: Figure 2 As shown Substituting (20) into (16), we can obtain the measured values ​​of the four polarization channels of the wire at different roll angles: (twenty one) (twenty two) (twenty three) (twenty four) Step 2: Based on the amplitude fluctuation characteristics of the main channel of the metal wire, the measurement polarization scattering matrix when the roll angle of the metal wire is 45° is obtained from the measurement data. And thus solve for the coupling error parameters. , and .

[0020] (21)-(24) can be rearranged to obtain: (25) (26) (27) (28) It can be seen from (25) and (28) that, Can be regarded as After weighting factors The resulting offset version. This is to eliminate weighting factors. To normalize (25) and (28) by their respective maximum amplitude values, the following definition applies: (29) (30) Theoretical analysis shows that (29) and (30) are in The values ​​are always equal, that is (31) Therefore, the antenna azimuth angle corresponding to the 45° metal wire can be determined based on this characteristic, and the measurement scattering matrix of the 45° metal wire can be obtained. .

[0021] The theoretical scattering matrix of a 45° metal wire can be written as: (32) therefore According to (16), it can be expressed as (33) (34) (35) (36) Solving (33)-(36) simultaneously, we get: (37) (38) (39) This completes the process. , and The solution is still missing. Polarization calibration can then be completed.

[0022] Step 3: Combining the four-channel ripple characteristics of the metal wire with the obtained coupling error parameters, further solve for the antenna crosstalk. Two candidate results containing ambiguity were obtained. and And based on antenna characteristics, the correct solution is obtained by deambiguation. .

[0023] get Then, the measurement results of the HV polarization channel of the metal wire can be preliminarily corrected, as follows: (40) Combining (25) and (40), the superposition result of the measurements of the HH and HV channels for one cycle is as follows: (41) (42) Since the measurements from one period are superimposed, therefore in (41) and (42) and Eliminated during the superposition process, (41) and (42) can be transformed into: (43) (44) Combining (43) and (44), we get: (45) We can obtain: (46) or (47) It can be seen from (46) and (47) that There are two solutions that are reciprocals of each other, which are ambiguous. Because... This represents antenna crosstalk, typically with an amplitude less than 1. Therefore, solutions with amplitudes less than 1 are chosen as the correct solutions, as shown in the following expression: (48) Step 4: Utilize , , and The true value of the target scattering matrix is ​​obtained by compensating for the measured scattering matrices of other targets.

[0024] At this point, we have obtained , , and The estimated results can be used to perform polarization calibration via (17).

[0025] To verify the polarization calibration method described above, we tested its performance at different signal-to-noise ratios, and the results are as follows: Figure 3-5 .

[0026] This method is applicable to all polarimetric radars and can solve for and compensate for system error parameters.

[0027] In summary, the above are merely embodiments of the present invention based on single-data examples and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A simplified calibration method for end-to-end error of broadband fully polarimetric radar based on a single metal wire, characterized in that, Includes the following steps: Step 1: Measure the azimuth of the metal wire by rotating the radar beam at a constant speed to obtain the sequence of measured polarization scattering matrices over one complete rotation cycle. ; Step 2: Based on the amplitude fluctuation characteristics of the main channel of the metal wire, the measurement polarization scattering matrix when the roll angle of the metal wire is 45° is obtained from the measurement data. And thus solve for the coupling error parameters. , and ; Step 3: Combining the four-channel ripple characteristics of the metal wire with the obtained coupling error parameters, further solve for the antenna crosstalk. Two candidate results containing ambiguity were obtained. and And based on antenna characteristics, the correct solution is obtained by deambiguation. ; Step 4: Utilize , , and The true value of the target scattering matrix is ​​obtained by compensating for the measured scattering matrices of other targets.

2. The simplified calibration method for end-to-end error of broadband fully polarimetric radar based on a single metal wire as described in claim 1, characterized in that, The polarization calibration process can be completed by measuring only a single metal wire.

3. The simplified calibration method for end-to-end error of broadband fully polarimetric radar based on a single metal wire as described in claim 1, characterized in that, In step two, the measurement scattering matrix of the 45° metal wire is obtained analytically using the amplitude fluctuation characteristics of the main channel of the metal wire. The specific form of expression is: 。 4. The simplified calibration method for end-to-end error of broadband fully polarimetric radar based on a single metal wire as described in claim 1, characterized in that, In step three, the four-channel ripple characteristics of the metal wire, combined with the obtained coupling error parameters, are used to further solve for antenna crosstalk. The specific form of expression is: ； ； 。 5. The simplified calibration method for end-to-end error of broadband fully polarimetric radar based on a single metal wire as described in claim 1, characterized in that, In step three, the characteristics of antenna crosstalk amplitude are utilized by comparison. and The magnitude of the amplitude, and the correct judgment The specific expression is as follows: 。

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