External field traction type automatic ground clutter acquisition system and acquisition method thereof

Abstract

The application discloses an external field traction type automatic ground clutter collection system, which comprises a host computer, the host computer is connected with a motor control cabinet and a vector network analyzer, the vector network analyzer is connected with a power amplifier, the power amplifier is connected with an antenna, the antenna is arranged on a traction type automatic measurement platform, and the traction type automatic measurement platform is connected with the motor control cabinet. The system solves the problems of low measurement efficiency and poor measurement result accuracy of the existing radar, and the application further discloses an external field traction type automatic ground clutter collection method, which can accurately and efficiently collect ground clutter data and draw images.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic measurement technology, specifically relating to an automated ground clutter acquisition system for field traction, and also to an automated ground clutter acquisition method for field traction. Background Technology

[0002] Radar uses radio waves to detect targets and determine their spatial location. Radar emits electromagnetic waves to illuminate the target and receives its echo. In practical applications, the echo signal obtained by radar comes from the superposition of various complex ground environments, making it difficult to detect information about the target. Therefore, in radar detection, it is necessary to conduct in-depth research on the characteristics of ground clutter to improve the radar's anti-clutter capability.

[0003] Ground clutter measurement requires acquiring measurement data from antennas located in different orientations. Traditional antenna supports can only be moved manually, and existing antenna measurement platforms do not have automatic alignment functions during radar calibration, which can cause the antenna main axis to deviate from the target center. For these reasons, antenna measurement efficiency is low and measurement results are inaccurate. Summary of the Invention

[0004] The purpose of this invention is to provide an automated ground clutter acquisition system for field traction, which solves the problems of low measurement efficiency and poor measurement accuracy of existing radar systems.

[0005] Another objective of this invention is to provide an automated field clutter acquisition method.

[0006] The technical solution adopted in this invention is an outdoor traction-type automated ground clutter acquisition system, including a host computer, which is connected to a motor control cabinet and a vector network analyzer. The vector network analyzer is connected to a power amplifier, and the power amplifier is connected to an antenna. The antenna is set on a traction-type automated measurement platform, which is connected to the motor control cabinet.

[0007] The invention is further characterized in that,

[0008] The traction-type automated measurement platform includes a translation mechanism, a lifting mechanism, and a pitch and polarization mechanism. The pitch and polarization mechanism is connected to an antenna. The translation mechanism, lifting mechanism, and pitch and polarization mechanism are all connected to a motor control cabinet.

[0009] The lifting mechanism includes a support frame, the bottom of which is connected to a translation mechanism. A first servo motor is installed at the bottom of the support frame and above the translation mechanism. The output shaft of the first servo motor is connected to one end of a ball screw via a coupling. The other end of the ball screw is rotatably connected to the top of the support frame. A slider is fitted on the ball screw, and a slide block is installed on the side wall of the slider. The first servo motor is connected to a motor control cabinet, and a pitch and polarization mechanism is installed on the slide block.

[0010] The pitch and polarization mechanism includes a support plate with a support frame connected to it. A main shaft is installed inside the support frame, with both ends of the main shaft extending out of the support frame. A second bevel gear is fitted on the outer wall of the main shaft, meshing with a first bevel gear and a third bevel gear. A second servo motor is connected to the first bevel gear and is located on the inner wall of the support frame. The third bevel gear is connected to one end of a rod, and the other end of the rod is connected to a pitch angle adjustment handwheel via a coupling located inside the support frame. The adjustment end of the pitch angle adjustment handwheel is located below the support frame. Both ends of the main shaft are connected to one end of a connecting plate, and the other end of the connecting plate is connected to an end cap. The end cap is connected to a polarization angle dial via a rotating shaft, one end of which is connected to a third servo motor. A support is connected to the polarization angle dial and is connected to the antenna.

[0011] Another technical solution adopted in this invention is an outdoor traction-type automated ground clutter acquisition method, which employs an outdoor traction-type automated ground clutter acquisition system and is implemented according to the following steps:

[0012] Step 1: Calibrate the vector network analyzer and set the frequency required for measurement. Place the conducting sphere for calibration at the set position. Use the electromagnetic scattering characteristic error analysis algorithm to control the movement of the traction-type automated measurement platform to calibrate the antenna position and complete the radar calibration.

[0013] Step 2: Using polarization scattering matrix theory, establish the antenna S output by the vector network analyzer. 21 Relationship between parameters and radar cross section;

[0014] Step 3: Set the relevant parameters of the area to be collected for ground clutter. Take the calibration position obtained in Step 1 as the zero point, use a vector network analyzer to collect ground clutter signals within the set range, and transmit them to the host computer for image drawing to obtain the ground clutter image.

[0015] The invention is further characterized in that,

[0016] The specific process of step 1 is as follows:

[0017] Step 1.1: Calibrate the vector network analyzer and set the frequency required for measurement; place the conductor ball used for positioning at the set position.

[0018] Step 1.2: Based on the far / near field discrimination conditions, the host computer issues commands to control the movement of the traction-type automated measurement platform, thereby moving the antenna to the far field range;

[0019] In step 1.2, the far / near field discrimination condition is:

[0020] R = 2D 2 / λ (1)

[0021] In equation (1), D is the antenna aperture, λ is the antenna operating wavelength, and R is the distance between the antenna and the conducting sphere;

[0022] Step 1.3: Using the conducting sphere as a calibration body, the backscattering radar cross section value of the ideal conducting sphere is obtained according to the Mie series scattering theory;

[0023] Step 1.4, based on the radar equations and S 21 The definition of the conducting sphere at a given frequency is obtained by using the S-value. 21 Theoretical value;

[0024] Step 1.5: By changing the distance between the antenna and the conducting sphere, and the operating frequency of the antenna, the S value at any azimuth of the antenna can be obtained. 21 Theoretical sweep frequency curve;

[0025] Step 1.6: During the measurement process, fix the antenna position and use a vector network analyzer to perform scattering measurements on the conducting sphere. This will directly yield the S-wave velocity of the conducting sphere within a given frequency range. 21 The measured value is then changed, and the antenna position is changed and measured again to finally obtain the S value at any azimuth of the antenna. 21 Measured values ​​sweep frequency curve;

[0026] Step 1.7, take the S at any azimuth of the antenna obtained in Step 1.5. 21 The theoretical frequency sweep curve and the S-curve at any azimuth of the antenna obtained in step 1.6 21 The measured frequency sweep curves are fused to obtain the azimuth correction S. 21 Frequency sweep matrix;

[0027] Step 1.8: Use curve similarity analysis to analyze a certain orientation S. 21 The frequency sweep curve of the measured value and the azimuth correction S obtained in step 1.7 21 Similarity comparison is performed on all curves in the frequency sweep matrix, and the orientation correction S is applied. 21 The frequency sweep matrix and a certain orientation S 21 The frequency sweep curve of the measured values ​​serves as the current fast correction curve for that azimuth.

[0028] Step 1.9, use root mean square error analysis S 21The degree of dispersion between the measured sweep curve and its corresponding current fast calibration curve, let S be the dispersion. 21 The measured value sweep curve is The current fast calibration curve is The root mean square error can then be expressed as:

[0029]

[0030] When the root mean square error is less than 0.03, the S can be considered acceptable. 21 The measurement curve is similar to the current fast calibration curve. The antenna position corresponding to the current fast calibration curve is extracted as the current antenna azimuth.

[0031] Step 1.10: Use the current antenna azimuth obtained in step 1.9 as the initial position for high-precision calibration. Set the root mean square error to be less than 0.01 to obtain the final calibration azimuth.

[0032] Step 1.11: Calculate the difference between the current antenna azimuth and the final calibration azimuth. Use this difference as the moving distance of the traction-type automated measurement platform. The host computer sends this moving distance information to the motor controller. The motor controller sends a signal to the motor driver. The motor driver drives the traction-type automated measurement platform to move, thus completing the radar calibration.

[0033] In step 1.3, the expression for calculating the backscattering radar cross section of the ideal conducting sphere is:

[0034]

[0035] In equation (2), n is the order of the Hankel function. For the first kind of Hankel function of a sphere, Let be the derivative of the first kind of Hankel function of the sphere, k = 2π / λ, and a be the radius of the conducting sphere.

[0036] In step 1.4, the radar equation is:

[0037]

[0038] In equation (3), P t For transmission power, P r R is the received power, R is the distance between the antenna and the conducting sphere, σ is the radar cross section, and G is the antenna gain.

[0039] S 21 The defining formula is:

[0040] S 21 =10lg(P) r / P t (4)

[0041] S of a conducting sphere at a given frequency 21 The expression for the theoretical value is:

[0042]

[0043] In equation (5), G is the antenna gain and R is the distance between the antenna and the conducting sphere.

[0044] In step 2, antenna S 21 The relationship between the parameters and the radar cross section is expressed as follows:

[0045]

[0046]

[0047] In equation (6), L is the distance between the measurement location and the antenna, and S 21 Let σ(f) be the forward transmission coefficient of the antenna, and σ(f) be the radar cross section in the frequency domain.

[0048] In step 3, the acquired ground clutter signal needs to be converted into a time-domain signal through inverse Fourier transform. The expression for the inverse Fourier transform is:

[0049]

[0050] In equation (7), N is the number of frequency sweep sampling points, f is the frequency, t is the time variable, σ(t) is the radar cross section in the time domain after inverse Fourier transform, j is the imaginary unit, j=√-1.

[0051] The beneficial effects of this invention are:

[0052] (1) The field-traction automated ground clutter acquisition system of the present invention is equipped with a traction automated measurement platform, which includes a translation mechanism, a lifting mechanism, and an elevation and polarization mechanism, which can realize the movement and adjustment of the antenna in any direction, thereby avoiding manual adjustment of the antenna and greatly improving the measurement efficiency and measurement accuracy of the radar antenna.

[0053] (2) The field-traction automated ground clutter acquisition method of the present invention adopts an electromagnetic scattering characteristic error analysis algorithm based on Mie series scattering theory and radar equations, which solves the azimuth error caused by calibration problems in traditional measurement, establishes the control relationship between the host computer and the translation mechanism, lifting mechanism, pitch and polarization mechanism, realizes automatic calibration, and can set ground clutter acquisition parameters, draw images of the acquired ground clutter data, and obtain visualized ground clutter images. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the structure of the field-traction automated ground clutter acquisition system of the present invention;

[0055] Figure 2 This is a schematic diagram of the lifting mechanism in the field-traction automated ground clutter acquisition system of the present invention.

[0056] Figure 3 This is a schematic diagram of the elevation and polarization mechanism in the field-traction automated ground clutter acquisition system of the present invention.

[0057] Figure 4 This is a front view of the elevation and polarization mechanism in the field-traction automated ground clutter acquisition system of the present invention.

[0058] Figure 5 This is a diagram showing the automatic calibration results in the field-traction automated ground clutter acquisition method of the present invention;

[0059] Figure 6 This is a diagram showing the ground clutter acquisition results obtained by the field-traction automated ground clutter acquisition method of the present invention.

[0060] In the diagram, 1. Host computer, 2. Vector network analyzer, 3. Power amplifier, 4. Motor control cabinet, 5. Traction-type automated measurement platform, 6. Antenna;

[0061] 51. Translation mechanism; 52. Lifting mechanism; 53. Pitching and polarization mechanism;

[0062] 521. First servo motor; 522. Ball screw; 523. Slide; 524. Bracket; 525. Slider;

[0063] 531. Support plate, 532. Main shaft, 533. Second servo motor, 534. First bevel gear, 535. Second bevel gear, 536. Pitch angle adjustment handwheel, 537. Coupling, 538. Rod, 539. Third bevel gear, 540. Pitch angle dial, 541. Support frame, 542. Connecting plate, 543. End cap, 544. Rotating shaft, 545. Polarization angle dial, 546. Support. Detailed Implementation

[0064] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0065] Example 1

[0066] This invention relates to an automated field clutter acquisition system, such as... Figure 1As shown, the system includes a host computer 1, which is connected to the motor control cabinet 4 via a network cable. The host computer 1 is also connected to a vector network analyzer 2 via a network cable. By installing the KeysightIO library suite, Keysight Command Expert, and the corresponding MATLAB library, and then connecting the network cable and setting the IP address of the host computer 1 so that the vector network analyzer 2 and the host computer 1 are on the same subnet, the communication can be completed. The vector network analyzer 2 is a Keysight series instrument. The vector network analyzer 2 is connected to a power amplifier 3, which is connected to an antenna 6 via an RF cable. The antenna 6 is mounted on a traction-type automated measurement platform 5, which is connected to the motor control cabinet 4 via a data transmission line.

[0067] The traction-type automated measurement platform 5 includes a translation mechanism 51, which is existing technology, used to adjust the movement of the antenna 6 along the X-axis. A lifting mechanism 52 is provided on the translation mechanism 51, and a pitch and polarization mechanism 53 is provided on the lifting mechanism 52. The pitch and polarization mechanism 53 is connected to the antenna 6. The translation mechanism 51, the lifting mechanism 52, and the pitch and polarization mechanism 53 are respectively connected to the motor control cabinet 4 through data transmission lines.

[0068] like Figure 2 As shown, the lifting mechanism includes a bracket 524. The bottom end of the bracket 524 is connected to a translation mechanism 51. A first servo motor 521 is installed at the bottom of the bracket 524 and above the translation mechanism 51. The output shaft of the first servo motor 521 is connected to one end of a ball screw 522 via a coupling. The other end of the ball screw 522 is rotatably connected to the top end of the bracket 524. A slider 525 is fitted on the ball screw 522. A slide block 523 is installed on the side wall of the slider 525. The first servo motor 521 is connected to a motor control cabinet 4. A pitch and polarization mechanism 53 is installed on the slide block 523. The first servo motor 521 drives the ball screw 522 to rotate, the ball screw 522 drives the slider 525 to move up and down, and the slider 525 drives the slide block 523 to move up and down, thereby realizing the adjustment of the vertical position of the antenna 6.

[0069] The maximum speed of the servo motor in the lifting mechanism 52 is:

[0070]

[0071] In the formula, N R This is the maximum speed of the servo motor, in r / min; V max P represents the maximum operating speed of the lifting mechanism, in m / s; B is the lead screw pitch in mm; i is the transmission ratio from the motor to the lead screw.

[0072] like Figure 3As shown, the pitch and polarization mechanism 53 includes a support plate 531, on which a support frame 541 is connected. A main shaft 532 is disposed inside the support frame 541, with both ends of the main shaft 532 extending out of the support frame 541. A second bevel gear 535 is sleeved on the outer wall of the main shaft 532, and the second bevel gear 535 respectively meshes with a first bevel gear 534 and a third bevel gear 539. The first bevel gear 534 is connected to a second servo motor 533, which is disposed on the inner wall of the support frame 541. The third bevel gear 539 is connected to one end of a rod 538, and the other end of the rod 538 is connected to a pitch angle adjustment handwheel 536 via a coupling 537. Next, the coupling 537 is located inside the support frame 541, the adjustment end of the pitch angle adjustment handwheel 536 is located below the support frame 541, both ends of the main shaft 532 are connected to one end of the connecting plate 542, one end of the main shaft 532 is also provided with a pitch angle scale 540, the other end of the connecting plate 542 is connected to the end cover 543, the end cover 543 and the polarization angle scale 545 are connected through the rotating shaft 544, the polarization angle scale 545 can rotate relative to the end cover 543, one end of the rotating shaft 544 is connected to a third servo motor, the polarization angle scale 545 is connected to a support 546, and the support 546 is connected to the antenna. In use, the second servo motor 533 drives the first bevel gear 534 to rotate, the first bevel gear 534 drives the second bevel gear 535 to rotate, and the second bevel gear 535 drives the main shaft 532 to rotate, thereby adjusting the pitch angle. The pitch angle can also be adjusted manually by rotating the pitch angle adjustment handwheel 536, which drives the rod 538 to rotate, the rod 538 drives the third bevel gear 539 to rotate, and the third bevel gear 539 drives the main shaft 532 to rotate, thereby adjusting the pitch angle. The third servo motor drives the rotating shaft 544 to rotate, the rotating shaft 544 drives the polarization angle dial 545 to rotate, and the polarization angle dial 545 drives the support 546 to rotate, thereby adjusting the polarization angle. The polarization angle can also be adjusted manually by rotating the polarization angle dial 545 to drive the support 546 to rotate. The motor control cabinet 4 contains a motor controller and a motor driver. The motor controller is connected to the motor driver, which is connected to the translation mechanism 51, the first servo motor 521, and the pitch and polarization mechanism 53. The host computer 1 establishes communication with the motor controller through an RS-485 serial port to receive and send data. The host computer 1 sends a handshake signal to the motor controller. After receiving the request, the motor controller performs a CRC check. If there is no error, communication is successfully established, and pulses are sent to the motor driver. The motor driver receives the pulses and direction signals and drives the servo motor according to the command.

[0073] The host computer uses MATLAB to design the MATLAB App Designer interface to achieve human-computer interaction. The first-level menu of the interface consists of three buttons, which respectively realize the functions of exporting the current measurement data, exporting the calibration data, and closing the interface; the second-level menu consists of the orientation calibration module and the RCS measurement module.

[0074] The azimuth correction module consists of far-field azimuth measurement adjustment, vertical azimuth correction, and current azimuth S. 21 Image, corrected S 21 The system consists of four panels. The far-field azimuth measurement adjustment panel calculates the required far-field distance based on the radar antenna aperture, controlling the forward and backward movement of the traction-type automated measurement platform 5. This panel has five options: stop, high-speed forward mode, low-speed forward mode, high-speed backward mode, and low-speed backward mode, and displays the movement distance. The vertical azimuth correction has two options: rapid azimuth correction and high-precision azimuth correction. Different correction accuracy modes can be selected according to requirements. The rapid azimuth correction mode is used to obtain the backscattering radar cross-section value of an ideal conducting sphere based on the Mie series scattering theory, according to the radar equation and S... 21 The definition of the conducting sphere at a given frequency is obtained by using the S-value. 21 Theoretical value, obtain S at any azimuth of antenna 6 21 Theoretical sweep frequency curve and S 21 The measured values ​​are swept along a frequency curve, and the two curves are fused to obtain the azimuth correction S. 21 The frequency sweep matrix, through curve similarity analysis, identifies a specific orientation S. 21 Measured value sweep curve and azimuth correction S 21 By comparing the curves in the frequency sweep matrix, the current fast correction curve for that azimuth is obtained, and root mean square error analysis (RMSE) is used. 21 The dispersion of the measured frequency sweep curve and its corresponding current fast correction curve yields the current azimuth of antenna 6. The high-precision azimuth correction mode uses the current azimuth of antenna 6 as the initial position for high-precision calibration, further limiting the root mean square error to obtain the final calibrated azimuth. Current azimuth S 21 The image module is used to display the S currently measured by the Vector Network Analyzer 2 (VNA). 21 Image; Corrected S 21 The image module is used to quickly correct the S-axis of the curve. 21 Image and final calibration orientation S 21 Images and curve comparisons were performed.

[0075] The RCS measurement module is used to establish the antenna S output by the vector network analyzer 2. 21The relationship between parameters and radar cross section is established. Relevant parameters for the area to be acquired for ground clutter are set, ground clutter signals are acquired, and images are plotted to obtain a ground clutter image. The RCS measurement module consists of two panels: parameter setting and measurement result image plotting. The parameter setting panel is used to set the S... 21 The measurement starts at the frequency, cutoff at the frequency, step length, and acquisition range. Clicking the parameter setting button inputs parameters into the VNA, and clicking the clear image button clears the currently plotted image. The measurement result image plotting panel displays the current measurement data and images of different parameters calculated from the measurement data, including the real and imaginary parts of the field strength amplitude, S... 21 A graph showing how the phase angle changes with frequency.

[0076] Example 2

[0077] The present invention provides an automated ground clutter acquisition method for field traction, which employs the aforementioned automated ground clutter acquisition system and is implemented according to the following steps:

[0078] Step 1: Calibrate the vector network analyzer 2 and set the parameters required for measurement, including the start frequency, cutoff frequency, step length, acquisition range, and the frequency required for measurement. Place the conductor ball used for positioning at the center of the turntable. Use the electromagnetic scattering characteristic error analysis algorithm to control the movement of the traction-type automated measurement platform 5 to calibrate the antenna position and complete the radar calibration.

[0079] The specific process of step 1 is as follows:

[0080] Step 1.1: Calibrate the vector network analyzer 2 and set the frequency required for measurement; place the conductor ball used for positioning at the set position.

[0081] Step 1.2: Based on the far / near field discrimination conditions, the host computer 1 issues a command to control the movement of the traction-type automated measurement platform 5, thereby moving the antenna 6 to the far field range;

[0082] The criteria for distinguishing between far and near fields are:

[0083] R = 2D 2 / λ (1)

[0084] In equation (1), D is the antenna aperture, λ is the antenna operating wavelength, and R is the distance between the antenna and the conducting sphere;

[0085] Step 1.3: Using the conducting sphere as a calibration body, the backscattering radar cross section value of the ideal conducting sphere is obtained according to the Mie series scattering theory;

[0086] The expression for calculating the backscattering radar cross section of an ideal conducting sphere is:

[0087]

[0088] In equation (2), n is the order of the Hankel function. For the first kind of Hankel function of a sphere, Let be the derivative of the first kind of Hankel function of the sphere, k = 2π / λ, and a be the radius of the conducting sphere;

[0089] Step 1.4, based on the radar equations and S 21 The definition of the conducting sphere at a given frequency is obtained by using the S-value. 21 Theoretical value;

[0090] The radar equation is:

[0091]

[0092] In equation (3), P t For transmission power, P r R is the received power, R is the distance between the antenna and the conducting sphere, σ is the radar cross section, and G is the antenna gain.

[0093] S 21 The defining formula is:

[0094] S 21 =10lg(P) r / P t (4)

[0095] S of a conducting sphere at a given frequency 21 The expression for the theoretical value is:

[0096]

[0097] In equation (5), G is the antenna gain, and R is the distance between the antenna and the conducting sphere;

[0098] Step 1.5: By changing the distance between antenna 6 and the conducting sphere, and the operating frequency of the antenna, the S value at any position of antenna 6 can be obtained. 21 Theoretical sweep frequency curve;

[0099] Step 1.6: During the measurement process, fix the position of antenna 6 and use vector network analyzer 2 to perform scattering measurements on the conducting sphere. This will allow you to directly obtain the S-wave velocity of the conducting sphere within a given frequency range. 21 The measured value is then changed, and the position of antenna 6 is changed and measured again. Finally, the S value at any position of antenna 6 is obtained. 21 Measured values ​​sweep frequency curve;

[0100] Step 1.7, take the S at any azimuth of antenna 6 obtained in step 1.5. 21 The theoretical sweep curve and the S-curve at any azimuth of antenna 6 obtained in step 1.6 21The measured frequency sweep curves are fused to obtain the azimuth correction S. 21 Frequency sweep matrix;

[0101] Step 1.8: Use curve similarity analysis to analyze a certain orientation S. 21 The frequency sweep curve of the measured value and the azimuth correction S obtained in step 1.7 21 Similarity comparison is performed on all curves in the frequency sweep matrix, and the orientation correction S is applied. 21 The frequency sweep matrix and a certain orientation S 21 A curve similar to the frequency sweep curve of the measured value is used as the current fast correction curve for that azimuth;

[0102] Step 1.9, use root mean square error analysis S 21 The degree of dispersion between the measured sweep curve and its corresponding current fast calibration curve, let S be the dispersion. 21 The measured value sweep curve is The current fast calibration curve is The root mean square error can then be expressed as:

[0103]

[0104] When the root mean square error is less than 0.03, the S can be considered acceptable. 21 The measurement curve is similar to the current fast calibration curve. The antenna position corresponding to the current fast calibration curve is extracted as the current antenna 6-axis position. This process is the fast calibration mode.

[0105] S extracted from a vector network analyzer 21 The measurement data are single-frequency point data at the set frequency intervals, which are discrete sample data. The root mean square error can measure the deviation between the sample value and the standard value. It is the average of the sum of squares of the prediction error. It not only avoids the problem that positive and negative errors cannot be added, but also better reflects the impact of large numerical errors on curve similarity analysis.

[0106] Step 1.10: Take the current antenna azimuth 6 position obtained in step 1.9 as the initial position for high-precision calibration. Set the root mean square error to be less than 0.01, and the final calibration azimuth can be obtained. This process is high-precision calibration.

[0107] Step 1.11: Calculate the difference between the current antenna 6 azimuth and the final calibration azimuth. Use this difference as the moving distance of the traction-type automated measurement platform 5. The host computer 1 sends the moving distance information to the motor controller. The motor controller sends the signal to the motor driver. The motor driver drives the traction-type automated measurement platform 5 to move, thus completing the radar calibration.

[0108] Step 2, use a vector network analyzer to output antenna S 21The parameter, namely the forward transmission coefficient, is similar to the radar cross section (RCS) and reflects the characteristic information of the radar target. Using polarization scattering matrix theory, the antenna S output by the vector network analyzer 2 is established. 21 Relationship between parameters and radar cross section;

[0109] The radar cross section (RCS) is usually represented by the symbol σ. It is not an actual area, but a measure that reflects the ability of an object to scatter electromagnetic waves in the receiving direction.

[0110] Based on the premise of plane wave illumination, the incident energy density of the wave is:

[0111]

[0112] In the formula, E in H in These are the electric field strength and magnetic field strength of the incident electric field, respectively, and Y0 is the admittance of free space;

[0113] The total power intercepted by the target is:

[0114]

[0115] If this power is radiated isotropically, the scattered power density at a distance R from the target is:

[0116]

[0117] If the scattered field E is used s Indicates power density:

[0118]

[0119] Combining the above equations, we get:

[0120]

[0121] Antenna S 21 The relationship between the parameters and the radar cross section is expressed as follows:

[0122]

[0123] In equation (6), L is the distance between the measurement location and the antenna, and S 21 Let σ(f) be the forward transmission coefficient of the antenna, and σ(f) be the radar cross section in the frequency domain.

[0124] Step 3, set the relevant parameters for the area to be collected for ground clutter, including: S 21The starting frequency, cutoff frequency, step length, and acquisition range are measured. The calibration position obtained in step 1 is used as the zero point. The ground clutter signal within the set range is acquired by the vector network analyzer 2 and transmitted to the host computer 1 for image drawing. The resulting ground clutter image can then be displayed and exported by the host computer 1.

[0125] This invention measures ground clutter using a vector network analyzer 2, enabling the acquisition of ground clutter characteristics in the frequency domain. The acquired ground clutter signal is then converted into a time-domain signal via an inverse Fourier transform. The expression for the inverse Fourier transform is:

[0126]

[0127] In equation (7), N is the number of frequency sweep sampling points, f is the frequency, t is the time variable, σ(t) is the radar cross section in the time domain after inverse Fourier transform, j is the imaginary unit, j=√-1.

[0128] Example 3

[0129] The measurement of ground clutter requires that the target be within the far field range of the antenna under test. The frequency range of the calibration vector network analyzer 2 is set to 12-15 GHz, and the antenna aperture is 15 cm. Based on the frequency range and antenna aperture of the radar antenna, combined with formula (1), the far field distance of the antenna under test is 2.25 m. The antenna is then moved to the far field range.

[0130] Before data acquisition, calibration is required to ensure the accuracy of the acquired signals. Figure 5 As shown, a scale is installed next to the lifting mechanism to record the current azimuth of the antenna. The initial azimuth of the antenna under test is 42.39 cm. The five images on the right side of the scale show the S-axis of the conducting sphere corresponding to the five azimuth positions moved during rapid calibration. 21 Measurement results, calculation of five S in rapid calibration 21 The root mean square error between the measurement results and the standard values ​​is shown in Table 1.

[0131] Table 1. Root mean square error at each location in fast calibration mode.

[0132]

[0133] Note: The first rise and the first fall are based on the initial position, the second rise is based on the position of the first rise, and the second fall is based on the position of the first fall.

[0134] As shown in Table 1, the minimum root mean square error value is located at the first descent (i.e., 39.55 cm). Therefore, the suboptimal position solution obtained after rapid orientation calibration is 39.55 cm.

[0135] Figure 5The five images on the left side of the central scale show the S-axis of the conducting sphere corresponding to the five positions moved during high-precision calibration. 21 Measurement results. Calculation of five S values ​​in high-precision calibration. 21 The root mean square error between the measurement results and the standard values ​​is shown in Table 2.

[0136] Table 2. Root mean square error at each position in high-precision calibration mode.

[0137]

[0138] Note: The first rise and the first fall are based on the initial position, the second rise is based on the position of the first rise, and the second fall is based on the position of the first fall.

[0139] As shown in Table 2, the minimum root mean square error is located at the first rise (i.e., 40.17 cm). The final calibration result obtained after rapid calibration and high-precision orientation calibration is 40.17 cm, which is the final calibration position.

[0140] Set the relevant parameters for the area to be acquired for ground clutter. Based on previous data and calibration locations, using the calibration point as the zero point, acquire ground clutter signals at locations 5cm and 10cm above and below the calibration point. After acquisition, select image plotting to obtain the ground clutter image, as shown below. Figure 6 As shown.

Claims

1. An automated ground clutter acquisition method for field traction, characterized in that, An outdoor traction-type automated ground clutter acquisition system is adopted, including a host computer (1), which is connected to a motor control cabinet (4) and a vector network analyzer (2). The vector network analyzer (2) is connected to a power amplifier (3), and the power amplifier (3) is connected to an antenna (6). The antenna (6) is set on a traction-type automated measurement platform (5), and the traction-type automated measurement platform (5) is connected to the motor control cabinet (4). The specific steps are as follows: Step 1, calibrate the vector network analyzer (2), place the conductor ball in the set position, use the electromagnetic scattering characteristic error analysis algorithm to control the traction-type automated measurement platform (5) to move, calibrate the antenna position, and complete the radar calibration; The specific process of step 1 is as follows: Step 1.1, calibrate the vector network analyzer (2) and set the frequency required for measurement, and place the conductor ball used for positioning at the set position; Step 1.2: Based on the far / near field discrimination conditions, the host computer (1) issues a command to control the movement of the traction-type automated measurement platform (5), thereby moving the antenna (6) to the far field range; The criteria for distinguishing between far and near fields are: （1） In equation (1), Antenna aperture, The operating wavelength of the antenna. R The distance between the antenna and the conducting sphere; Step 1.3: Using the conducting sphere as a calibration body, the backscattering radar cross section value of the ideal conducting sphere is obtained according to the Mie series scattering theory; Step 1.4, based on the radar equations and S 21 The definition of the conducting sphere at a given frequency is obtained by using the S-value. 21 Theoretical value; Step 1.5: By changing the distance between the antenna (6) and the conducting sphere, as well as the operating frequency of the antenna, the S at any orientation of the antenna (6) can be obtained. 21 Theoretical sweep frequency curve; Step 1.6: During the measurement process, fix the position of the antenna (6) and use the vector network analyzer (2) to perform scattering measurement on the conducting sphere. Then, the S-frequency of the conducting sphere within the given frequency range can be directly obtained. 21 The measured value is then changed, the antenna (6) position is changed and measured again, and finally the S value at any orientation of the antenna (6) is obtained. 21 Measured values ​​sweep frequency curve; Step 1.7, take the S at any azimuth of the antenna (6) obtained in step 1.

5. 21 The theoretical sweep curve and the S at any azimuth of the antenna (6) obtained in step 1.6 21 The measured frequency sweep curves are fused to obtain the azimuth correction S. 21 Frequency sweep matrix; Step 1.8: Use curve similarity analysis to analyze a certain orientation S. 21 The frequency sweep curve of the measured value and the azimuth correction S obtained in step 1.7 21 Similarity comparison is performed on all curves in the frequency sweep matrix, and the orientation correction S is applied. 21 The frequency sweep matrix and a certain orientation S 21 A curve similar to the frequency sweep curve of the measured value is used as the current fast correction curve for that azimuth. Step 1.9, use root mean square error analysis S 21 The degree of dispersion between the measured sweep curve and its corresponding current fast calibration curve, let S be the dispersion. 21 The measured value sweep curve is The current fast correction curve is Then the root mean square error can be expressed as: When the root mean square error is less than 0.03, the S can be considered acceptable. 21 The measurement curve is similar to the current fast calibration curve. The antenna position corresponding to the current fast calibration curve is extracted as the current antenna (6) azimuth. Step 1.10: Take the current antenna (6) azimuth obtained in step 1.9 as the initial position for high-precision calibration, and set the root mean square error to be less than 0.01, then the final calibration azimuth can be obtained; Step 1.11: Calculate the difference between the current antenna (6) azimuth and the final calibration azimuth. Use this difference as the moving distance of the traction-type automated measurement platform (5). The host computer (1) sends the moving distance information to the motor controller. The motor controller sends the signal to the motor driver. The motor driver drives the traction-type automated measurement platform (5) to move, thus completing the radar calibration. Step 2: Using polarization scattering matrix theory, establish the antenna S output by the vector network analyzer (2). 21 Relationship between parameters and radar cross section; Step 3: Set the relevant parameters of the area to be collected for ground clutter, take the calibration position obtained in step 1 as the zero point, use a vector network analyzer (2) to collect ground clutter signals within the set range, and transmit them to the host computer (1) for image drawing to obtain the ground clutter image.

2. The field-traction automated ground clutter acquisition method according to claim 1, characterized in that, In step 1.3, the expression for calculating the backscattering radar cross section of the ideal conducting sphere is: （2） In equation (2), n Let Hankel's function be the order of the function. For the first kind of Hankel function of a sphere, The derivative of the first kind of Hankel function of the sphere, , a Let be the radius of the conducting sphere.

3. The field-traction automated ground clutter acquisition method according to claim 1, characterized in that, In step 1.4, the radar equation is: （3） In equation (3), For transmission power, For received power, R The distance between the antenna and the conducting sphere. Radar cross section, Antenna gain; S 21 The defining formula is: （4） S of a conducting sphere at a given frequency 21 The expression for the theoretical value is: （5） In equation (5), G For antenna gain, R The distance between the antenna and the conducting sphere is denoted as .

4. The field-traction automated ground clutter acquisition method according to claim 1, characterized in that, In step 2, antenna S 21 The relationship between the parameters and the radar cross section is expressed as follows: （6） In equation (6), L To measure the distance between the location and the antenna, This represents the forward transmission coefficient of the antenna. This represents the radar cross section in the frequency domain.

5. The field-traction automated ground clutter acquisition method according to claim 1, characterized in that, In step 3, the acquired ground clutter signal needs to be converted into a time-domain signal through inverse Fourier transform. The expression for the inverse Fourier transform is: （7） In equation (7), N This represents the number of frequency sweep sampling points. f For frequency, t For time variables, It is the radar cross section in the time domain after inverse Fourier transform. The imaginary unit is j = √-1.

6. The field-traction automated ground clutter acquisition method according to claim 1, characterized in that, The traction-type automated measurement platform (5) includes a translation mechanism (51), a lifting mechanism (52) is provided on the translation mechanism (51), a pitch and polarization mechanism (53) is provided on the lifting mechanism (52), the pitch and polarization mechanism (53) is connected to the antenna (6), and the translation mechanism (51), the lifting mechanism (52), and the pitch and polarization mechanism (53) are respectively connected to the motor control cabinet (4).

7. The field-traction automated ground clutter acquisition method according to claim 6, characterized in that, The lifting mechanism includes a bracket (524), the bottom end of which is connected to a translation mechanism (51). A first servo motor (521) is provided at the bottom of the bracket (524) and above the translation mechanism (51). The output shaft of the first servo motor (521) is connected to one end of a ball screw (522) via a coupling. The other end of the ball screw (522) is rotatably connected to the top of the bracket (524). A slider (525) is sleeved on the ball screw (522). A slide block (523) is provided on the side wall of the slider (525). The first servo motor (521) is connected to a motor control cabinet (4). A pitch and polarization mechanism (53) is provided on the slide block (523).

8. The field-guided automated ground clutter acquisition method according to claim 6, characterized in that, The pitch and polarization mechanism (53) includes a support plate (531), on which a support frame (541) is connected. A main shaft (532) is provided inside the support frame (541), with both ends of the main shaft (532) extending out of the support frame (541). A second bevel tooth (535) is sleeved on the outer wall of the main shaft (532). The second bevel tooth (535) meshes with a first bevel tooth (534) and a third bevel tooth (539). The first bevel tooth (534) is connected to a second servo motor (533), which is located on the inner wall of the support frame (541). The third bevel tooth (539) is connected to one end of a rod (538). 8) The other end is connected to the pitch angle adjustment handwheel (536) via a coupling (537). The coupling (537) is located inside the support frame (541). The adjustment end of the pitch angle adjustment handwheel (536) is located below the support frame (541). Both ends of the main shaft (532) are connected to one end of the connecting plate (542). The other end of the connecting plate (542) is connected to the end cover (543). The end cover (543) is connected to the polarization angle scale (545) via a rotating shaft (544). One end of the rotating shaft (544) is connected to a third servo motor. A support (546) is connected to the polarization angle scale (545). The support (546) is connected to the antenna.

Images