Near-field BP (Back Propagation) imaging method for performing gain compensation based on antenna pattern

Abstract

The invention belongs to the technical field of radar imaging, and particularly relates to a near-field BP imaging method for gain compensation based on an antenna pattern. The method specifically comprises the following steps: step 1, measuring an actual directional diagram of an antenna under a darkroom condition; step 2, calculating a pixel value of any point in an imaging area based on a BP imaging method; step 3, calculating an angle between any pixel point in the imaging area and the transmitting-receiving antenna; step 4, according to the actually measured antenna pattern and the angle between the antenna and the pixel point, calculating the actual gain obtained by the radar echoes from different directions under each channel, namely the actual gain obtained by the transceiving antenna; and step 5, constructing a gain compensation matrix by using the actual gain obtained by each transmitting-receiving antenna, and compensating each pixel point of the imaging area by using the gain compensation matrix.

Description

Technical Field

[0001] The invention belongs to the technical field of radar imaging, and in particular relates to a near-field BP imaging method for gain compensation based on an antenna pattern. Background Art

[0002] The combination of multiple-input multiple-output (MIMO) technology and radar systems forms a new type of MIMO radar system, which has a high degree of design freedom and potential excellent performance. Compared with the traditional single-station radar system, it has obvious system advantages and has become a research hotspot in the radar field. First, the MIMO radar system has a flexible and diverse array structure design, which can enhance the system's data acquisition capability for targets in complex environments and improve multi-target detection capabilities and work efficiency; secondly, the MIMO radar system reduces the system's design requirements for antenna gain and directivity, thereby saving costs.

[0003] For MIMO radar systems, the transmitting antenna array synthesizes the transmitting antenna pattern, and the receiving antenna array synthesizes the receiving antenna pattern. When the radar system is working, at the transmitting end, the electromagnetic wave is concentratedly radiated by the transmitting antenna, and the specific transmitting gain can be obtained from the transmitting antenna pattern function. After being reflected by the target, it is received by the receiving antenna. Similarly, the receiving gain can be obtained from the receiving antenna pattern function. However, it is worth noting that when the detection scene is a multi-target scene, the orientation of each target is not consistent with the transmitting antenna array and the receiving antenna array, so the transmission gain and receiving gain obtained are also inconsistent. This leads to that for targets at the same distance and in different orientations, their echo signal energy is strong or weak. Against the background of the strong energy target echo, the weak energy target echo is masked and cannot be detected. This problem is caused by the directivity of the antenna pattern.

[0004] Traditional phased array radar technology controls the direction of the synthesized beam by controlling the phase of each array element. Under the prior condition of known target azimuth, the main lobe of the synthesized beam is directed to the target. When there are multiple targets in the scene, the direction of the beam is changed by controlling the phase shifter, and beam scanning is used to achieve multi-target detection. MIMO radar is combined with phased array technology. With the help of the principle of digital beamforming, each array element is given a different phase multiple times through complex signal processing algorithms to achieve directional control of the synthesized signal, that is, the formed "beam". Multiple beams with different directions are formed in real time, and multi-target scenes can be detected without beam scanning. Both of these multi-target detection methods start from the perspective of the array element signal phase and control the main lobe of one or more synthesized beams to point to each target. However, neither of these two methods can meet the real-time requirements. Summary of the invention

[0005] To solve the above problems, the present invention proposes a near-field BP imaging method based on antenna pattern function for gain compensation, which can significantly enhance the energy of large-angle targets and effectively realize real-time detection in multi-target scenarios.

[0006] The technical solution for implementing the present invention is as follows:

[0007] A near-field BP imaging method for gain compensation based on antenna pattern, the specific process is as follows:

[0008] Step 1: measure the actual radiation pattern of the antenna in a dark room;

[0009] Step 2: Calculate the pixel value of any point in the imaging area based on the BP imaging method;

[0010] Step 3, calculating the angle between any pixel point in the imaging area and the transceiver antenna;

[0011] Step 4: Calculate the actual gain of radar echoes from different directions in each channel based on the measured antenna radiation pattern and the angle between the antenna and the pixel point, that is, the actual gain obtained by the transceiver antenna;

[0012] Step 5: construct a gain compensation matrix using the actual gain obtained by each transceiver antenna, and use the gain compensation matrix to compensate each pixel in the imaging area.

[0013] Furthermore, in step 2 of the present invention, the pixel value of any point in the imaging area is calculated based on the BP imaging method as follows:

[0014]

[0015]

[0016] Where M and N represent the number of transmitting antennas and receiving antennas respectively, s(t) represents the transmitted signal, G t(q，m) , G r(q，n) Represent the gains of the transmitting antenna and the receiving antenna at pixel point q, α(x q ) represents the reflection coefficient, R tq , R rq Represents the distance between any pixel point q and the transmitting antenna and the receiving antenna, τ mnq Indicates the echo delay.

[0017] Furthermore, the calculation of the angle in step three of the present invention is:

[0018] Assume that the coordinates of any point q in the imaging area are (x q ,y q), then the angle θ1 between the point and the transmitting antenna and the angle θ2 between the point and the receiving antenna can be expressed as:

[0019]

[0020]

[0021] Among them, (x t，m ,y t，m ) represents the coordinates of the transmitting antenna, (x r，n ,y r，n ) represents the coordinates of the receiving antenna.

[0022] Furthermore, the compensation for each pixel point q in the imaging area of ​​the present invention is:

[0023]

[0024]

[0025]

[0026] Among them, m=1, 2,...M, n=1, 2,...N.

[0027] Beneficial effects:

[0028] The present invention is applied to real-time detection in multi-target scenarios. Since the antenna is directional, for large-angle targets, the angle between it and the transceiver antenna is outside the beam width, so the gain obtained is relatively small. In the multi-target scenario, its echo energy will be significantly weaker than that of small-angle targets, and it is very easy to be covered up during imaging. The present invention compensates for radar data in different directions, realizes effective enhancement of the energy of large-angle targets in multi-target scenarios, can significantly enhance the energy of large-angle targets, and effectively realizes real-time detection in multi-target scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 It is the through-the-wall radar system used in the experimental verification of the present invention;

[0031] Figure 2 is the antenna pattern function actually measured during experimental verification of the present invention;

[0032] Figure 3is a diagram of a BP imaging algorithm taking antenna radiation patterns into consideration according to the present invention;

[0033] Figure 4 It is a static target experimental scene during experimental verification of the present invention;

[0034] Figure 5 It is the static target experimental result of the present invention during experimental verification;

[0035] Figure 6 It is a moving target experimental scenario during experimental verification of the present invention;

[0036] Figure 7 It is the moving target experimental result during the experimental verification of the present invention. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] It should be noted that the following embodiments and features in the embodiments may be combined with each other in the absence of conflict; and, based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making any creative work are within the scope of protection of the present disclosure.

[0039] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein may be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an aspect described herein may be implemented independently of any other aspect, and two or more of these aspects may be combined in various ways. For example, any number of aspects described herein may be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein may be used to implement this device and / or practice this method.

[0040] The design concept of the present invention is as follows: in order to solve the problem of weak energy of large-angle targets in multi-target scenarios, firstly, after analyzing the composition of the antenna pattern in the near field, the antenna pattern function is measured under darkroom conditions; secondly, the gain obtained by radar echoes from different directions in each channel is determined, and then the gain to be compensated is determined according to the difference between the gain in the maximum direction and the gain in other directions; finally, a gain compensation matrix is ​​constructed with the help of digital beamforming technology to compensate for radar data in different directions, thereby achieving effective enhancement of the energy of large-angle targets in multi-target scenarios.

[0041] The embodiment of the present application provides a near-field BP imaging method for gain compensation based on an antenna pattern function, which is implemented by the following steps:

[0042] Step 1: Measure the actual radiation pattern of the antenna in a dark room;

[0043] Figure 1 The MIMO radar array used in the present invention is shown. Figure 2 The antenna radiation pattern at multiple frequencies measured in a dark room.

[0044] Step 2: Calculate the pixel value at any point q in the imaging area based on the BP imaging method;

[0045] like Figure 3 As shown in the figure, by the BP algorithm, the pixel value at any point q in the imaging area can be expressed as:

[0046]

[0047]

[0048] Where M and N represent the number of transmitting antennas and receiving antennas respectively, s(t) represents the transmitted signal, G t(q，m) , G r(q，n) Represent the gains of the transmitting antenna and the receiving antenna at pixel point q, α(x q ) represents the reflection coefficient, R tq , R rq Represents the distance between any pixel point q and the transmitting antenna and the receiving antenna, τ mnq Indicates echo delay.

[0049] In this step, G t(q，m) With G r(q，n) It is an unknown parameter and needs to be calculated based on the direction pattern and the angle between the pixel and the transmitting and receiving antennas.

[0050] Step 3: Calculate the angle between any point in the imaging area and the transmitting and receiving antennas;

[0051] Assume that the coordinates of any point q in the imaging area are (x q ,y q ), then the angle θ1 between the point and the transmitting antenna and the angle θ2 between the point and the receiving antenna can be expressed as:

[0052]

[0053]

[0054] Among them, (x t，m ,y t，m ) represents the coordinates of the transmitting antenna, (x r，n ,y r，n ) represents the coordinates of the receiving antenna.

[0055] Step 4: Based on the measured antenna radiation pattern and the angle between the antenna and the pixel point, calculate the actual gain of the radar echo from different directions in each channel, that is, the actual gain obtained by the transceiver antenna.

[0056] In this step, the antenna pattern function can be obtained according to the antenna pattern, and then the angle value calculated in step 4 can be substituted into the antenna pattern function, so that the actual gain obtained by the transmitting and receiving antennas can be calculated for each pixel in the image.

[0057] Step 5: construct a gain compensation matrix using the actual gain obtained by each transceiver antenna, and use the gain compensation matrix to compensate each pixel point in the imaging area, thereby achieving compensation of radar echo data.

[0058] Calculate the gain of the pixel to be compensated under each channel and compensate it to the actual pixel value I q superior:

[0059]

[0060]

[0061]

[0062] Since then, a near-field BP imaging algorithm based on gain compensation of antenna pattern function has been completed, realizing energy enhancement of large-angle targets in multi-target scenarios.

[0063] Example:

[0064] In order to verify the effectiveness of the near-field BP imaging algorithm based on antenna pattern function for gain compensation proposed in this paper, static target experiment and moving target experiment were designed for analysis. Figure 4 As shown in the figure, the same anti-target was placed at 0°, -30°, -45°, -60° and -80° respectively. In order to compare the imaging effect in the multi-target scene before and after compensation, the data of the five experiments were integrated together for imaging. The results before and after compensation are shown in Figure 2. Figure 5 shown.

[0065] analyze Figure 5The experimental results shown in the figure show that the small-angle target is clearly visible before compensation, but the two large-angle targets at -60° and -80° are almost invisible, which indicates that the gain of the large-angle target is relatively small, and its energy is significantly lower than that of the other three small-angle targets, so it is covered in the imaging results. Analysis of the compensated imaging results shows that after compensation, the energy of the two large-angle targets at -60° and -80° is enhanced, which is comparable to the reflected echo energy of the other three targets, and the five targets are clearly visible. Therefore, it is shown that the proposed algorithm for gain compensation based on the antenna pattern function has a significant effect on enhancing the energy of large-angle targets in multi-target scenarios.

[0066] conduct Figure 6 In the moving target experiment shown in the figure, the two targets make uniform circular motion, and their trajectories relative to the antenna array are -90°→0°→-90° and 0°→90°→0° respectively. As shown in the figure, when one of the moving targets has a larger angle relative to the antenna main lobe beam and the other target has a smaller angle relative to the antenna main lobe beam, a frame in the experimental data is selected for imaging. The imaging results before and after compensation are shown in Figure 7 As shown in the analysis results, it can be seen that the energy of large-angle targets is weak and easily confused with clutter. After compensation, the energy of large-angle targets is enhanced, and the energy of two moving targets is similar. Therefore, the present invention has a significant effect on real-time detection of moving targets.

[0067] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A near-field BP imaging method for gain compensation based on antenna pattern, characterized in that: The specific process is: Step 1: measure the actual radiation pattern of the antenna in a dark room; Step 2: Calculate the pixel value of any point in the imaging area based on the BP imaging method; Step 3, calculating the angle between any pixel point in the imaging area and the transceiver antenna; Step 4: Calculate the actual gain of radar echoes from different directions in each channel based on the measured antenna radiation pattern and the angle between the antenna and the pixel point, that is, the actual gain obtained by the transceiver antenna; Step 5: construct a gain compensation matrix using the actual gain obtained by each transceiver antenna, and use the gain compensation matrix to compensate each pixel in the imaging area.

2. The near-field BP imaging method for gain compensation based on antenna pattern according to claim 1, characterized in that: In step 2, the pixel value of any point in the imaging area is calculated based on the BP imaging method as follows: Where M and N represent the number of transmitting antennas and receiving antennas respectively, s(t) represents the transmitted signal, G t(q,m) , G r(q,n) Represent the gains of the transmitting antenna and the receiving antenna at pixel point q, α(x q ) represents the reflection coefficient, R tq , R rq Represents the distance between any pixel point q and the transmitting antenna and the receiving antenna, τ mnq Indicates the echo delay.

3. The near-field BP imaging method for gain compensation based on antenna pattern according to claim 2, characterized in that: The angle calculation in step 3 is: Assume that the coordinates of any point q in the imaging area are (x q ,y q ), then the angle θ1 between the point and the transmitting antenna and the angle θ2 between the point and the receiving antenna can be expressed as: Among them, (x t,m ,y t,m ) represents the coordinates of the transmitting antenna, (x r,n ,y r,n ) represents the coordinates of the receiving antenna.

4. The near-field BP imaging method for gain compensation based on antenna pattern according to claim 2, characterized in that: The compensation for each pixel q in the imaging area is: Among them, m=1,2,...M, n=1,2,...N.

Images