A full polarization radar step-by-step polarization calibration method based on metal ball and metal wire

Abstract

The application provides a full polarization radar step-by-step polarization calibration method based on a metal ball and a metal wire. Firstly, the full polarization measurement model is optimized in combination with the frequency modulation step frequency waveform characteristics. Then, the metal ball is used to calibrate the amplitude and phase inconsistency of the main channel, and the attitude of the metal wire in the air is determined by using the calibrated result of the main channel. Finally, the metal wire is used to compensate for the residual inconsistency between channels of the system, and the polarization calibration is completed. Compared with the existing polarization calibration algorithm, the method considers the error caused by the broadband condition, and there is no error caused by the position placement when multiple target calibration is performed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of full polarization radar, and particularly relates to a polarization calibration method based on a metal ball and a metal wire. BACKGROUND

[0002] The full polarization radar system is adopted by many radars, such as a synthetic aperture radar, a weather radar, a ground penetrating radar and an insect radar. As one of important radar target characteristics, the polarization information acquired by the full polarization radar is widely used in clutter suppression, detection, target parameter inversion and tracking. In order to accurately acquire the target polarization information, the polarization calibration of the full polarization radar needs to be performed first.

[0003] The traditional polarization calibration of the full polarization radar is designed for a narrow band case, and the amplitude-phase inconsistency introduced by the system in a wide band case is not considered. In addition, the traditional polarization calibration method usually introduces errors due to different positions when measuring by using multiple calibration bodies. SUMMARY

[0004] Therefore, the application provides a step-by-step polarization calibration method based on a metal ball and a metal wire, which can calibrate the wideband full polarization radar, avoid errors caused by target placement in the traditional radar polarization calibration, and make the polarization calibration easy to implement. This is helpful for different types of full polarization radars to acquire polarization information with higher accuracy.

[0005] A step-by-step polarization calibration method based on a metal ball and a metal wire includes the following steps:

[0006] The system model of a high-resolution full polarization radar system with frequency-stepped frequency is expressed as:

[0007]

[0008] wherein S hh , S vv , S hv and S vh represent elements of each channel of the target polarization scattering matrix; r represents the target distance, k0 represents the wave number; R h , R v , T h , T v represent the amplitude-phase inconsistency of the H receiving channel, the V receiving channel, the H transmitting channel and the V transmitting channel in the radio frequency link respectively; S 13 represents the amplitude-phase inconsistency of the H channel of the antenna; S 24 represents the amplitude-phase inconsistency caused by the V channel of the antenna; and represent the amplitude-phase inconsistency coefficients introduced by the stepped frequency imaging of different channels respectively, represents the Hadamard product of the matrix, and let:

[0009]

[0010]

[0011]

[0012]

[0013] Then the system model is represented as:

[0014]

[0015] The real value of PSM of the metal ball is measured by radar:

[0016]

[0017] where σ ball is the RCS of the metal ball; the measured value of PSM of the metal ball by radar is:

[0018]

[0019] and respectively represent each channel element of the polarization scattering matrix when the metal ball is used as a target;

[0020] Then the estimated value of is obtained as

[0021]

[0022] In the measurement process of the metal wire, the radar is controlled to be vertically observed, then the metal wire is straightened, carried to the position approximately parallel to the H polarization direction in the beam center, and the PSM of the metal wire at different angles is continuously collected in the process of azimuth rotation;

[0023] When the metal wire is-45° relative to the H polarization direction of the radar, the real PSM of the metal wire is:

[0024]

[0025] Aline represents the echo intensity of the metal wire, which is related to the size of the metal wire;

[0026] Then the measured PSM of the metal wire is:

[0027]

[0028] Then the estimated value of is obtained by the element of ​

[0029]

[0030]

[0031] When the metal wire is 45° relative to the radar H polarization direction, the real PSM of the metal wire is:

[0032]

[0033] The measured PSM of the metal wire is:

[0034]

[0035] Then the estimated value of is calculated by the element of

[0036]

[0037] After calculating and, the other measured targets are compensated by matrix operation to obtain the real PSM of the calibrated target:

[0038] The present application has the following beneficial effects:

[0039] The present application provides a step-by-step polarization calibration method for full polarization radar based on metal ball and metal wire, which firstly optimizes the full polarization measurement model combined with the frequency modulation step frequency waveform characteristics, then calibrates the amplitude and phase inconsistency of the main channel by using the metal ball, and determines the attitude of the metal wire in the air by using the calibrated result of the main channel, finally compensates all system residual channel inconsistencies by using the metal wire to complete the polarization calibration; compared with the existing polarization calibration algorithm, the present application considers the error caused by the wideband condition, and does not exist the error caused by the position placement during multi-target calibration. BRIEF DESCRIPTION OF DRAWINGS

[0040]

[0041] Fig. 1 is the amplitude curve of the metal wire scattering matrix element varying with angle under ideal condition.

[0042] Figure 1 Fig. 2(a) is the original metal wire four-channel echo, and Fig. 2(b) is the four-channel echo after metal ball calibration.

[0043]

[0044] Figure 3 ​​​​This is to account for the measurement error of insect orientation at different angles after calibration.

[0045] Figure 4 This is a flowchart of the method of the present invention. Detailed Implementation

[0046] This invention is a stepwise polarization calibration method for a fully polarized radar based on metal spheres and metal wires. Specific embodiments illustrate the implementation steps:

[0047] Step 1: Measure the metal sphere and obtain... The estimated value

[0048] Step two: Measure the metal wire at different angles using rotating radar, and then... Calibration wire data;

[0049] Step 3, using After calibration, the -45° wire echo is acquired, and other systematic errors are estimated. and

[0050] Step four, utilize and Compensation for other targets measured;

[0051] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0052] Let the target polarization scattering matrix (PSM) be:

[0053]

[0054] Where S hh S vv S hv and S vh These are the channel elements of the target polarization scattering matrix.

[0055] The scattering matrix of the target measured by radar is:

[0056]

[0057] Where M hh M vv M hv and M vh These are the channel elements of the scattering matrix.

[0058] The traditional narrowband fully polarized system model can be represented as:

[0059]

[0060] where r denotes the target distance, k0= 2π / λ denotes the wave number. R h v h v denote the amplitude and phase inconsistency caused by the H receive channel, V receive channel, H transmit channel and V transmit channel in the radio frequency link, respectively. 13 denotes the amplitude and phase inconsistency of the antenna H channel; S 24 denotes the amplitude and phase inconsistency caused by the antenna V channel; C1denotes the cross crosstalk between the antenna H transmit and V receive channels, and C2denotes the cross crosstalk between the antenna H receive and V transmit channels, the amplitudes of C1and C2are much smaller than 1. For a new system R h v h v 13 24 C1and C2are unknown, these parameters can be collectively referred to as system polarization errors.

[0061] For a high-resolution full-polarization system using frequency-modulated stepped frequency, in addition to the polarization errors shown in equation (3), there are also errors introduced due to the different imaging effects of the four polarization channels. Since the transmission characteristics of each channel are non-ideal, the return of each polarization channel needs to compensate for inter-pulse amplitude and phase errors, intra-pulse amplitude and phase errors, and inter-pulse time delay to ensure the imaging effect. To measure the inter-pulse amplitude and phase errors, intra-pulse amplitude and phase errors, and inter-pulse time delay of the radar transmitted stepped frequency signal, an additional standard target needs to be measured. However, it is usually difficult for the same target to meet the measurement needs of the four channels, so the standard target used to measure the inter-pulse amplitude and phase errors, intra-pulse amplitude and phase errors of each polarization channel will also be different, and the measurement scene will also be different, which will cause the final imaging effects of the distance images of the four polarization channels to be different. This is equivalent to introducing a multiplicative coefficient for each polarization channel, and the coefficients of different channels are usually different. Therefore, for a high-resolution full-polarization radar system using frequency-modulated stepped frequency, the polarization measurement model can be modeled as:

[0062]

[0063] where and denote the amplitude and phase inconsistency coefficients introduced by the stepped frequency imaging of different channels, denotes the Hadamard product of the matrix, and equation (4) can be further simplified as:

[0064]

[0065] ​​​​​​​​To reduce the complexity of the polarization calibration, C1 and C2 can be ignored for systems with high isolation. After ignoring the cross-talk, the new system model can be expressed as:

[0066]

[0067] Definition:

[0068]

[0069] Then (6) can be re-expressed as:

[0070]

[0071] Compared with the traditional narrowband measurement model, the system measurement model expressed by (8) has more complex inter-channel amplitude and phase inconsistency, and the traditional single-target polarization calibration algorithm is no longer applicable. For the system model expressed by (8), only and need to be estimated, and then the measurement results are compensated to ensure accurate relative relationships between each polarization channel, completing the polarization calibration.

[0072] In actual operation, the measurement results of the metal ball can be used to first obtain to complete the HH and VV channel calibration. The PSM of the metal ball is:

[0073]

[0074] where σ ball is the RCS of the metal ball. According to (8) and (9), the PSM of the metal ball measured by the radar is:

[0075]

[0076] Then the estimated value of can be obtained as

[0077]

[0078] The measurement results of the wire PSM can be expressed as:

[0079]

[0080] Using the calculated by (11), the measurement results of the wire expressed by (12) can be compensated as:

[0081]

[0082] As can be seen, after compensation using , M′line The relative relationship between the HH and VV channels is accurate. Using θ c This represents the angle between the wire angle and the H-polarization. Because at angle θ... c At point = π / 4 + πn / 2 (n∈Z), the echo amplitudes of the HH and VV channels of the metal wire are the same (e.g. Figure 1 If there exists a certain angle M′ line The HH and VV channel echoes are the same, at which point the wire angle is θ. c =π / 4 + πn / 2 (n∈Z).

[0083] During the measurement of the metal wire, the radar can be controlled to observe the sky vertically. Then, two drones are used to pull the metal wire to the center of the beam and to a position approximately parallel to the H-polarization direction by pulling with a thin line. The PSM of the metal wire at different angles is continuously collected during the azimuth rotation.

[0084] Assuming the initial metal wire is approximately parallel to the radar's H polarization direction, and the radar azimuth angle gradually increases, when M′ line When the HH and VV channel echoes are identical for the first time, the metal wire is at -45° relative to the radar H polarization direction, and the true PSM of the metal wire is:

[0085]

[0086] A line The echo intensity of the metal wire is related to the size of the metal wire.

[0087] The measured PSM is:

[0088]

[0089] Then it can be obtained through equation (15) The elements were calculated to obtain and The estimated value and

[0090]

[0091]

[0092] Assuming the radar azimuth angle gradually decreases, when M′ line When the HH and VV channel echoes are identical for the first time, the metal wire is at 45° relative to the radar H polarization direction, and the true PSM of the metal wire is:

[0093]

[0094] A line The echo intensity of the metal wire is related to the size of the metal wire.

[0095] The measured PSM is:

[0096]

[0097] Then it can be obtained through equation (19) The elements were calculated to obtain and The estimated value and

[0098]

[0099]

[0100] In the calculation and Then, matrix operations can be used to compensate for the target obtained from other measurements, resulting in the true PSM of the calibrated target:

[0101]

[0102] Figure 1 This is the curve showing the amplitude of the PSM element in a metal wire as a function of angle under ideal conditions.

[0103] Figures 2(a) and 2(b) show the echoes of the metal wire before and after the metal ball is calibrated.

[0104] To verify the polarization calibration method described above, the orientation of the insect target was tested, and the results are as follows: Figure 3 As shown. Insect orientation can be used to assess calibration accuracy; therefore, the calibration effect can be evaluated by calculating the calibrated insect orientation. The method of this invention is applicable to all-polarimetric radars and can solve for and compensate for system error parameters.

[0105] 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 step-by-step polarization calibration method based on metal balls and metal wires, characterized in that, The method comprises the following steps: The system model of the high-resolution full-polarimetric radar system with frequency-modulated stepped frequency is represented as: wherein, , , and denote the individual channel elements of the target polarization scattering matrix; denotes the target distance, denotes the wave number; , , , denote the amplitude and phase inconsistencies caused by the H receive channel, the V receive channel, the H transmit channel and the V transmit channel in the radio frequency chain, respectively; denotes the amplitude and phase inconsistency of the antenna H channel; denotes the amplitude and phase inconsistency caused by the antenna V channel; , , and denote the amplitude and phase inconsistency coefficients introduced by the stepped frequency imaging for different channels, denotes the Hadamard product of matrices, such that: The system model is re-represented as: The metal ball is measured by using the radar, and the true value of the PSM is: wherein, RCS for the metal sphere; the radar measured metal sphere PSM measurement is: , , and represent the individual channel elements of the polarization scattering matrix when the metal sphere is the target. then the estimate of :​ During the measurement of the metal wire, the radar is controlled to be vertically observed, then the metal wire is stretched, carried to the position approximately parallel to the H polarization direction in the beam center, and the PSM of the metal wire at different angles is continuously collected during the azimuth rotation; When the metal wire is-45° relative to the H polarization direction of the radar, the true PSM of the metal wire is: The wire echo strength is related to the wire size. The measured PSM of the metal wire is: Then the estimate of the element is calculated by , the estimate of the element , : When the metal wire is 45° relative to the H polarization direction of the radar, the true PSM of the metal wire is: The measured PSM of the metal wire is: Then the estimate of the element is calculated by , the estimate of the element , : After calculating , and , the other measured targets are compensated by matrix operation to obtain the real PSM of the calibrated target: 。

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