CN103955008B - A kind of amplitude calibration method for Multi probe near-field scattering imaging - Google Patents

Abstract

The invention provides an amplitude calibration method for multi-probe near-field scattering imaging, step 1: use a multi-probe detection system to measure background scattering data; step 2: measure the scattering data of the target to be measured; step 3: measure the metal plate scattering data ; Step 4: Perform background cancellation on the target to be measured to obtain scattering data, and perform imaging processing on the obtained data to obtain imaging results; Step 5: Perform background cancellation on the calibration metal plate to obtain scattering data, and use RMA algorithm to perform imaging processing on it to obtain imaging Result; step 6: use the formula to calibrate the imaging results, and obtain the imaging results of the target to be measured after calibration. Using the above scheme, the azimuth and amplitude calibration of microwave/millimeter wave imaging can be performed. It is mainly used for multi-probe imaging systems with poor amplitude accuracy. Simple calibration parts are used to directly calibrate the imaging results to improve imaging accuracy.

Description

An Amplitude Calibration Method for Multi-Probe Near-field Scatter Imaging

technical field

The invention belongs to the technical field of amplitude calibration of multi-probe near-field scattering imaging, and in particular relates to an amplitude calibration method for multi-probe near-field scattering imaging.

Background technique

Multi-probe near-field scattering imaging technology avoids the long-term data acquisition process caused by mechanical movement in scanning imaging, improves the real-time performance of microwave and millimeter wave imaging, and has broad application prospects in the fields of security inspection, non-destructive flaw detection, and target scattering characteristic distribution testing. . Range Migration Algorithm (RMA) is a commonly used imaging algorithm in synthetic aperture radar technology. However, when the RMA algorithm is used for multi-probe system imaging, for the target imaging with the same scattering intensity, in the azimuth direction, the center position of the imaging area and the edge position image The magnitude of the difference is relatively large, that is, the imaging result cannot correctly reflect the distribution of the scattering characteristics of the target.

The scattering ability of target objects to electromagnetic waves is generally described quantitatively by radar cross section (RCS). Microwave and millimeter wave imaging technology can visually display the distribution of RCS scattering centers in the target area with images, and is an effective means for electromagnetic stealth testing of targets. , especially for near-field imaging, the system can be set up in a small area to achieve imaging analysis of the target area, and has been widely used in geographic detection, security inspection, wall penetration detection, and non-destructive testing.

Due to the high real-time requirements for imaging in applications such as security inspection and through-wall detection, the demand for multi-probe testing is also increasing. Multi-probe near-field imaging uses multiple transmitting antennas and multiple receiving antennas, through switch switching or waveform modulation. The electromagnetic scattering data measurement of the target area is completed in a very short time, and then the scattering image of the target area is obtained by using the corresponding algorithm to invert, which is also called multiple-input multiple-output (MIMO) imaging. Multi-probe near-field imaging does not require mechanical scanning of the target area, which avoids the long-term data acquisition process and provides a solution for real-time applications of microwave and millimeter wave imaging.

Range Migration Algorithm (RMA) is a commonly used algorithm in synthetic aperture radar (SAR) imaging technology. Since the traditional RMA algorithm is based on the collected data of spontaneous and self-receiving combined with mechanical scanning, when it is applied to a multi-transmit and multi-receive system, it needs to perform single-site, etc. efficiency, or separate the spectrum domains of the transceiver antennas, the former needs to consider the difference between the phase difference of the actual transceiver antenna and the equivalent single-site transceiver phase, and the latter does not need to be considered.

At present, the RMA algorithm mostly adopts the equivalent phase center method in the application process of multi-probe imaging technology. For example, Gregory L.Charvat et al. adopted the equivalent uniform sampling method in "An Ultrawideband (UWB) Switched-Antenna-Array Radar Imaging System". The point array form, which considers the phase calibration method, uses a slender metal rod to place in the array imaging area, which is equivalent to the scattering point of the two-dimensional surface, and compares the phase difference between the measured phase of each channel and the theoretical single site phase difference different for phase calibration. Xiaodong Zhuge et al. used the algorithm of spectral domain separation of transceiver antennas in "Three-DimensionalNear-Field MIMO Array Imaging Using Range Migration Techniques", but the test targets were placed in the center of the imaging area, and the amplitude accuracy was not considered.

Through the analysis of domestic and foreign references and similar technologies, the calibration of multi-probe near-field imaging systems mostly only uses a rod-shaped or spherical scatterer for calibration, or the amplitude accuracy is not considered, and no calibration is performed. The use of rod or spherical scatterers can only be used for phase calibration, which can eliminate the phase difference between the actual transceiver antenna phase difference and the equivalent single site, but because the calibration piece is equivalent to a scattering point, amplitude calibration cannot be performed.

Therefore, there are defects in the prior art and need to be improved.

Contents of the invention

The technical problem to be solved by the present invention is to provide an amplitude calibration method for multi-probe near-field scattering imaging aiming at the deficiencies of the prior art.

Technical scheme of the present invention is as follows:

A method of amplitude calibration for multi-probe near-field scattering imaging, comprising the following steps:

Step 1: Use the multi-probe detection system to measure the background scattering data S ₀ or set S ₀ =0;

Step 2: Measure the scattering data S of the target to be measured;

Step 3: Place a metal plate larger than the area to be imaged at the same position from the target to be measured, and measure the metal plate scattering data S _std ;

Step 4: Perform background cancellation on the target to be measured to obtain the scattering data SS ₀ , and use the RMA algorithm to perform imaging processing on it to obtain the imaging result f(x,y);

Step 5: Perform background cancellation on the calibration metal plate to obtain the scattering data S _std -S ₀ , and use the RMA algorithm to perform imaging processing on it to obtain the imaging result f _std (x,y);

Step 6: Use the formula to calibrate the imaging results to obtain the calibrated imaging results f _cali (x, y) of the target to be measured. Formula 1:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; .</span>$

In the amplitude calibration method, the target to be measured is a flat metal plate.

This calibration method can be used for all kinds of imaging test systems in microwave/millimeter wave frequency bands, not only for multi-probe imaging systems using RMA algorithm for imaging calibration, but also for imaging results of various microwave/millimeter wave imaging systems using other algorithms Calibration, the present invention can perform azimuth and amplitude calibration of microwave/millimeter wave imaging, and is mainly used for multi-probe imaging systems with poor amplitude accuracy. Simple calibration parts are used to directly calibrate the imaging results to improve imaging accuracy.

Description of drawings

Fig. 1 is a schematic diagram of multi-probe near-field imaging in the present invention;

Fig. 2 is a flow chart of the method of the present invention.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

In the multi-probe near-field imaging model shown in Figure 1, 101 is the transmitting antenna, 102 is the receiving antenna, the x and y directions are the azimuth direction, the z direction is the distance direction, the probe is located in the xy plane where z=0, the target Located in the first half of space where z>0.

As shown in FIG. 2 , the present invention is based on the principle of uniform reflection of a plane reflector, and uses a metal plate as a calibration object to perform amplitude calibration. Different from the phase calibration method, the theoretical distribution of near-field scattering cannot be obtained simply based on the phase delay when using a plate-shaped calibrator, and the present invention will use its imaging results for calibration. The obtained metal plate imaging result is f _bo (x, y), and the image of the target to be measured is processed by the following formula 1 to complete the calibration. Formula one:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}$

The specific implementation steps of using this method for multi-probe near-field scattering imaging are as follows:

Step 1: Using a multi-probe detection system to measure the background scattering data S ₀ ;

Step 2: Measure the scattering data S of the target to be measured;

Step 3: Place a metal plate larger than the area to be imaged at the same position from the target to be measured, and measure the metal plate scattering data S _std ;

Step 4: Perform background cancellation on the target to be measured to obtain the scattering data SS ₀ , and use the RMA algorithm to perform imaging processing on it to obtain the imaging result f(x,y);

Step 5: Perform background cancellation on the calibration metal plate to obtain the scattering data S _std -S ₀ , and use the RMA algorithm to perform imaging processing on it to obtain the imaging result f _std (x,y);

Step 6: Use the formula to calibrate the imaging results to obtain the calibrated imaging results f _cali (x, y) of the target to be measured.

Note: Step (1) can be omitted, if omitted, S ₀ =0.

This calibration method can be used for all kinds of imaging test systems in microwave/millimeter wave frequency bands, not only for multi-probe imaging systems using RMA algorithm for imaging calibration, but also for imaging results of various microwave/millimeter wave imaging systems using other algorithms Calibration, the present invention can perform azimuth and amplitude calibration of microwave/millimeter wave imaging, and is mainly used for multi-probe imaging systems with poor amplitude accuracy. Simple calibration parts are used to directly calibrate the imaging results to improve imaging accuracy.

It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the protection scope of the appended claims of the present invention.

Claims (2)

1. an amplitude calibration method for multi-probe near-field scattering imaging, characterized in that, comprising the following steps: Step 1: Use the multi-probe detection system to measure the background scattering data S ₀ or set S ₀ =0; Step 2: Measure the scattering data S of the target to be measured; Step 3: Place a metal plate larger than the area to be imaged at the same position from the target to be measured, and measure the metal plate scattering data S _std ; Step 4: Perform background cancellation on the target to be measured to obtain the scattering data SS ₀ , and use the RMA algorithm to perform imaging processing on it to obtain the imaging result f(x,y); Step 5: Perform background cancellation on the calibration metal plate to obtain the scattering data S _std -S ₀ , and use the RMA algorithm to perform imaging processing on it to obtain the imaging result f _std (x,y); Step 6: Use the formula to calibrate the imaging results to obtain the calibrated imaging results f _cali (x, y) of the target to be measured. Formula 1: ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; cali</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; std</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; .</span>$ 2. The amplitude calibration method according to claim 1, wherein the target to be measured is a flat metal plate.