阅读说明：本技术 基于trm的穿墙雷达探测器 (TRM-based through-wall radar detector ) 是由 马月红 刘佳 剧畅洋 刘永泽 崔琳 张亭 于 2021-09-18 设计创作，主要内容包括：本发明公开了一种基于TRM的穿墙雷达探测器,涉及雷达探测装置技术领域。所述探测器包括控制模块,所述控制模块的控制信号输出端与雷达信号源的控制信号输入端连接,用于在所述控制模块的控制下输出雷达脉冲信号,所述雷达信号源的信号输出端与发射机模块的信号输入端连接,所述发射机模块的信号输出端与收发一体天线模块的信号输入端连接,所述收发一体天线模块的信号输出端与接收机模块的信号输入端连接,所述收发一体天线用于向墙体发射探测信号,并接收反射的探测信号；所述接收机模块的信号输出端与所述控制模块的信号输入端连接。所述探测器具有结构简单,成本低,且分辨率高,成像效果好等优点。(The invention discloses a through-wall radar detector based on TRM, and relates to the technical field of radar detection devices. The detector comprises a control module, a control signal output end of the control module is connected with a control signal input end of a radar signal source and used for outputting radar pulse signals under the control of the control module, a signal output end of the radar signal source is connected with a signal input end of a transmitter module, a signal output end of the transmitter module is connected with a signal input end of a receiving-transmitting integrated antenna module, a signal output end of the receiving-transmitting integrated antenna module is connected with a signal input end of a receiver module, and the receiving-transmitting integrated antenna is used for transmitting detection signals to a wall body and receiving reflected detection signals; and the signal output end of the receiver module is connected with the signal input end of the control module. The detector has the advantages of simple structure, low cost, high resolution, good imaging effect and the like.)

1. The utility model provides a through-wall radar detector based on TRM which characterized in that: the radar wall body detection device comprises a control module, wherein a control signal output end of the control module is connected with a control signal input end of a radar signal source and used for outputting radar pulse signals under the control of the control module, a signal output end of the radar signal source is connected with a signal input end of a transmitter module, a signal output end of the transmitter module is connected with a signal input end of a receiving-transmitting integrated antenna module, a signal output end of the receiving-transmitting integrated antenna module is connected with a signal input end of a receiver module, and the receiving-transmitting integrated antenna is used for transmitting detection signals to a wall body and receiving reflected detection signals; the signal output end of the receiver module is connected with the signal input end of the control module, and the human-computer interaction module is connected with the control module in a bidirectional mode and used for inputting control commands and displaying output data.

2. The TRM-based through-the-wall radar detector of claim 1, wherein: the receiving and transmitting integrated antenna comprises a dielectric plate (1), the whole body of the dielectric plate (1) is rectangular, floor planes (2) are formed on the front side and the rear side of the upper surface of the dielectric plate (1), two extending portions (3) extending inwards are arranged at two ends of the floor planes (2) on the front side and the rear side, a certain distance is kept between the two extending portions (3) on the left side and between the two extending portions (3) on the right side, a signal band (4) is located in the middle of the upper surface of the dielectric plate (1), one end of the signal band (4) is connected with the floor plane (2) on the front side, the other end of the signal band (4) is connected with the floor plane (2) on the rear side, a first main radiation patch (5) is located on the upper surface of a dielectric substrate (1) of a space formed by the signal band (4) and the floor plane (2) on the left side, and a second main radiation patch (6) is located on the signal band (4) and the floor plane (2) on the right side And the first main radiating patch (5) and the second main radiating patch (6) are not in contact with the floor plane (2) and the signal band (4) on the upper surface of the dielectric substrate (1) of the combined space.

3. The TRM-based through-the-wall radar detector of claim 2, wherein: the first main radiation patch (5) and the second main radiation patch (6) are symmetrically arranged on the upper surface of the dielectric plate (1) on two sides of the signal band, the first main radiation patch (5) and the second main radiation patch (6) are identical in structure, the first main radiation patch (5) comprises a rectangular tail portion (51) and a triangular radiation portion (52), one end of the tail portion (51) is located on the upper surface of the dielectric plate (1) between the extension portions (3) of the floor plane (2), the other end of the tail portion (51) is connected with the radiation portion (52), and the tip end of the radiation portion (52) faces towards the signal band (4).

4. The TRM-based through-the-wall radar detector of claim 1, wherein: the radar signal source comprises a synchronous control module and two direct digital frequency synthesizers, the control signal input ends of the two direct digital frequency synthesizers at the control signal input end level of the synchronous control module are respectively connected with the signal output end of the control module, the two signal output ends of the synchronous control module are respectively connected with the signal input end of one direct digital frequency synthesizer, the signal output end of the direct digital frequency synthesizer is respectively connected with the two signal input ends of the radar pulse signal output end module, and the radar pulse signal output end module generates an electromagnetic pulse with the duration being nanosecond level under the triggering of the synchronous pulse.

5. The TRM-based through-the-wall radar detector of claim 4, wherein: the direct digital frequency synthesizer uses an AD9914 type chip.

6. The TRM-based through-the-wall radar detector of claim 1, wherein: the control module comprises a clock distribution control module and an ADC data acquisition module, wherein the clock distribution control module is used for generating clock distribution signals, and the ADC data acquisition module is used for processing signals sent by the receiver.

7. The TRM-based through-the-wall radar detector of claim 1, wherein: the man-machine interaction module comprises an imaging display module and a key module, the key module is connected with the signal input end of the control module and used for inputting a control signal, and the imaging display module is connected with the signal output end of the control module and used for displaying a detected object.

8. The TRM-based through-the-wall radar detector of claim 1, wherein: the radar detector generates an electromagnetic pulse with nanosecond duration under the triggering of the synchronous pulse through a radar signal source, and then transmits an electromagnetic wave signal through a receiving and transmitting integrated antenna module; the electromagnetic signal passes through the non-metal wall body and irradiates to a target to be detected, the target reflects the electromagnetic signal, namely, the target reflects the electromagnetic signal to play a role of a secondary source, the reflected signal passes through the wall body again and is received by a receiving and transmitting integrated antenna module at the front end of a receiver module, then the received signal is subjected to sampling, amplification and filtering processing, the signal is sent to an imaging link, and imaging display of the target is achieved through imaging processing software.

9. The TRM-based through-the-wall radar detector of claim 8, wherein: the electromagnetic pulse signal penetrates through the wall to the inner side of the wall to conceal the target to be detected, the signal is reflected by the target and is received by a receiving antenna arranged on one side of the excitation source, and the received signal is recorded firstly; after N position signals are obtained, corresponding wall surface reflection removing processing is carried out on the signals, then time reversal is carried out on the signals in a time domain or phase conjugation is carried out on the signals in a frequency domain, the reversed signals are transmitted from respective receiving positions through transmitting antennas, and the signals are converged at the target position through the same path.

10. The TRM-based through-the-wall radar detector of claim 8, wherein: the combined surface of the receiving antenna and the transmitting antenna is called as a time reversal mirror TRM, and the time reversal mirror TRM in the ultra-wideband through-wall radar imaging has the following principle:

a microwave pulse source is arranged at r₀The excitation source emits a time-domain narrow pulse p (t), and the signal passes through a time-invariant medium and irradiates r_nN is 1,2, …, the target of N is r_nThe incident field at (a) is:

fourier transform for time domain pulses:

forward green functionThe wave equation is satisfied:

where ε (r) is the dielectric constant, μ (r) is the permeability;

n target reflection signals serve as N secondary sources, and the secondary sources equivalent to an incident field are as follows:

E_R(r_n,w)≈c_n(w)E_F(r_n,w)；

c_n(w),n＝1,2,…,N,c_n(w) is the frequency dependent reflection coefficient of the target, N represents the reflection characteristics of N targets;

when a secondary source signal passes through the invariable medium, the secondary source signal is received by a receiving antenna, the signal records enough long time T on a time domain to ensure that a multi-scattering signal is also accurately received, and the signal received at a receiving antenna point k is as follows:

in a through-the-wall radar environment, the background information can be determined, and thus the background signal is denoted as E_G(r_kT); the target signal in the frequency domain is:

χ(r_k) Representing the impact from the receiving end;

the time-domain signal is time-reversed, and the time-reversed signal is re-transmitted back through the respective receiving positions, so that the time-space signal at the field point r is:

in the frequency domain:

"x" indicates the complex conjugate,representing the calculation of the green's function from the receiving antenna to the field point;

according to the radar imaging principle, the azimuth imaging resolution depends on the aperture of a receiving array, in a homogeneous medium, the azimuth resolution is λ L/a, a is the physical aperture, L is the propagation distance, λ is the carrier wavelength, and for finite or Gaussian TRM, the effective aperture is:

thereby making λ L/a_e＜λL/a。

Technical Field

The invention relates to the technical field of radar detection devices, in particular to a through-wall radar detector based on TRM.

Background

The electromagnetic wave transmitted by the through-wall radar has the characteristics of strong penetrability, high resolution, good anti-interference performance and the like, the electromagnetic wave of a specific pulse is transmitted to a target on the surface of a shielding main body, the target reflected echo signal is received and then subjected to signal processing, and finally the detection result of the echo signal is subjected to two-dimensional or three-dimensional imaging display through a through-wall imaging algorithm, so that information such as the shape and the motion state of the target is acquired. The ultra-wideband through-wall detection technology is a new technology developed in recent years, can penetrate through non-metallic media (brick walls, ruins and the like), does not need any electrode or sensor to contact with a living body, and detects a hidden moving object in a certain space. However, the through-wall radar detector in the prior art is complex in structure and high in cost.

Disclosure of Invention

The through-wall radar detector is simple in structure, low in cost, high in resolution and good in imaging effect.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the utility model provides a through-wall radar detector based on TRM which characterized in that: the radar wall body detection device comprises a control module, wherein a control signal output end of the control module is connected with a control signal input end of a radar signal source and used for outputting radar pulse signals under the control of the control module, a signal output end of the radar signal source is connected with a signal input end of a transmitter module, a signal output end of the transmitter module is connected with a signal input end of a receiving-transmitting integrated antenna module, a signal output end of the receiving-transmitting integrated antenna module is connected with a signal input end of a receiver module, and the receiving-transmitting integrated antenna is used for transmitting detection signals to a wall body and receiving reflected detection signals; the signal output end of the receiver module is connected with the signal input end of the control module, and the human-computer interaction module is connected with the control module in a bidirectional mode and used for inputting control commands and displaying output data.

The further technical scheme is as follows: the receiving and transmitting integrated antenna comprises a dielectric plate, the whole dielectric plate is rectangular, floor planes are formed on the front side and the rear side of the upper surface of the dielectric plate, two ends of the two floor planes on the front side and the rear side are provided with extension parts extending inwards, a certain distance is kept between the two ends of the extension part, the signal belt is positioned in the middle of the upper surface of the dielectric slab, one end of the signal band is connected with the floor plane at the front side, the other end of the signal band is connected with the floor plane at the rear side, the first main radiation patch is positioned on the upper surface of the dielectric substrate of the space enclosed by the signal band and the floor plane at the left side part, the second main radiation patch is positioned on the upper surface of the dielectric substrate of the space enclosed by the signal band and the floor plane at the right side part, the first main radiating patch and the second main radiating patch are not in contact with the floor plane and the signal band.

The further technical scheme is as follows: the first main radiation patch and the second main radiation patch are symmetrically arranged on the upper surface of the dielectric slab on two sides of the signal strip, the first main radiation patch and the second main radiation patch are identical in structure, the first main radiation patch comprises a rectangular tail and a triangular radiation part, one end of the tail is located on the upper surface of the dielectric slab between the extension parts of the floor planes, the other end of the tail is connected with the radiation part, and the tip of the radiation part faces towards the signal strip.

The further technical scheme is as follows: the radar signal source comprises a synchronous control module and two direct digital frequency synthesizers, the control signal input ends of the two direct digital frequency synthesizers at the control signal input end level of the synchronous control module are respectively connected with the signal output end of the control module, the two signal output ends of the synchronous control module are respectively connected with the signal input end of one direct digital frequency synthesizer, the signal output end of the direct digital frequency synthesizer is respectively connected with the two signal input ends of the radar pulse signal output end module, and the radar pulse signal output end module generates an electromagnetic pulse with the duration being nanosecond level under the triggering of the synchronous pulse.

The further technical scheme is as follows: the control module comprises a clock distribution control module and an ADC data acquisition module, wherein the clock distribution control module is used for generating clock distribution signals, and the ADC data acquisition module is used for processing signals sent by the receiver.

The further technical scheme is as follows: the man-machine interaction module comprises an imaging display module and a key module, the key module is connected with the signal input end of the control module and used for inputting a control signal, and the imaging display module is connected with the signal output end of the control module and used for displaying a detected object.

The further technical scheme is as follows: the radar detector generates an electromagnetic pulse with nanosecond duration under the triggering of the synchronous pulse through a radar signal source, and then transmits an electromagnetic wave signal through a receiving and transmitting integrated antenna module; the electromagnetic signal passes through the non-metal wall body and irradiates to a target to be detected, the target reflects the electromagnetic signal, namely, the target reflects the electromagnetic signal to play a role of a secondary source, the reflected signal passes through the wall body again and is received by a receiving and transmitting integrated antenna module at the front end of a receiver module, then the received signal is subjected to sampling, amplification and filtering processing, the signal is sent to an imaging link, and imaging display of the target is achieved through imaging processing software.

The further technical scheme is as follows: the electromagnetic pulse signal penetrates through the wall to the inner side of the wall to conceal the target to be detected, the signal is reflected by the target and is received by a receiving antenna arranged on one side of the excitation source, and the received signal is recorded firstly; after N position signals are obtained, corresponding wall surface reflection removing processing is carried out on the signals, then time reversal is carried out on the signals in a time domain or phase conjugation is carried out on the signals in a frequency domain, the reversed signals are transmitted from respective receiving positions through transmitting antennas, and the signals are converged at the target position through the same path.

Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: this application the detector can make echo signal energy bigger through adopting the time reversal mirror technique, is favorable to the high resolution formation of image, and simultaneously, the use of the integrative integrated antenna of receiving and dispatching all saves on area, consumption and size to a certain extent, and the signal source that adopts AD9914 chip and FPGA chip to make control chip has solved the problem that spread spectrum module structure is complicated, with high costs to the good performance is applicable to in the through-the-wall radar system. The detector has wider application prospect in the fields of roadway fighting, counter terrorism, riot prevention, disaster relief and the like, and can generate greater economic benefit and positive social benefit.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a schematic block diagram of a detector according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of the integrated radar antenna according to the embodiment of the present invention;

FIG. 3 is a schematic block diagram of a radar signal source according to an embodiment of the present invention;

FIG. 4 is a flow chart illustrating the detection principle of the detector according to the embodiment of the present invention;

wherein: 1. a dielectric plate; 2. a floor plane; 3. an extension portion; 4. a signal band; 5. a first primary radiating patch; 51. a tail portion; 52. a radiation section; 6. a second main radiating patch; 7. a wall body; 8. and (5) a target to be detected.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

As shown in fig. 1, an embodiment of the present invention discloses a through-wall radar detector based on a TRM, including a control module, where a control signal output end of the control module is connected with a control signal input end of a radar signal source for outputting a radar pulse signal under the control of the control module, a signal output end of the radar signal source is connected with a signal input end of a transmitter module, a signal output end of the transmitter module is connected with a signal input end of a transceiver antenna module, a signal output end of the transceiver antenna module is connected with a signal input end of a receiver module, and the transceiver antenna is used for transmitting a detection signal to a wall and receiving a reflected detection signal; the signal output end of the receiver module is connected with the signal input end of the control module, and the human-computer interaction module is connected with the control module in a bidirectional mode and used for inputting control commands and displaying output data.

The radar signal source is used for generating various linear frequency modulation signals, stepping frequency signals and other radar signals. The transmitter module is used for transmitting the signal generated by the signal source. The receiver module is used for receiving the echo signal and processing the echo signal such as filtering and amplifying. The control module is used for synchronous control of the multi-transmitting and multi-receiving radar system and signal processing such as echo signal sampling, and the multi-transmitting and multi-receiving radar system can detect distance direction and direction information of a target in real time.

Further, as shown in fig. 1, the control module may include a clock distribution control module for generating a clock distribution signal and an ADC data acquisition module for processing a signal transmitted by the receiver. In addition, the human-computer interaction module may include an imaging display module and a key module, the key module is connected to a signal input end of the control module and is used for inputting a control signal, the imaging display module is connected to a signal output end of the control module and is used for displaying a detected object, it should be noted that the control module may further include other modules, and the specific form of the human-computer interaction module may also be other types, for example, a touch screen is used.

An ideal ultra-wideband antenna is frequency independent, however, the performance of a limited size antenna cannot be independent of frequency, and therefore the bandwidth of the ultra-wideband antenna must be limited. An antenna may be considered an ultra-wideband antenna as long as one or more of the parameters input impedance, far-field radiation pattern, polarization, and group delay remain constant or vary within an allowable range within the operating frequency band. According to the index requirements of the through-wall radar system, the standing-wave ratio and the half-power beam width are mainly considered, and the overall size requirement of the through-wall radar antenna is combined, so that the impedance bandwidth and the far-field radiation performance are improved, and the high beam width is realized. The antenna mainly comprises a medium substrate, a feeder line, a main radiator and a metal ground.

The monopole antenna and the radiation slot are combined together to form a novel planar antenna, and the combination mode not only can realize the broadband and the miniaturization of the antenna, but also can improve the consistency of far-field directional patterns of the antenna. The coplanar waveguide is a feeder structure which integrates a feeder line and a ground plane on the same plane of the dielectric plate, and a central feed wire is connected with the antenna patch and has a certain distance with the ground plane. The coplanar waveguide feed can increase the bandwidth of the planar antenna, is convenient for realizing series-parallel connection of components, is integrated with external components and circuits, is easy to change the characteristic impedance, has low dispersion and radiation loss, and reduces the cross loss between transmission lines in the circuit due to the existence of the ground plate.

The bandwidth of an ultra-wideband planar antenna is generally expressed by a standing wave ratio (VSWR), and the specific formula is as follows:

q is a quality factor of the planar antenna, and the basic method for expanding the frequency band of the planar antenna is to reduce the Q value of the equivalent resonant circuit of the antenna, that is, to reduce the relative dielectric constant and the thickness h of the dielectric plate and to increase the aspect ratio. It is known that the thicker the dielectric substrate, the smaller the relative permittivity and the larger the loss tangent, the smaller the quality factor Q, and the larger the bandwidth of the antenna. However, when the dielectric constant of the dielectric plate is reduced, the size of the antenna is also increased, so that the material of the dielectric substrate should be appropriately selected. The ultra-wideband through-wall radar antenna can work in a 1-3GHz frequency band and can be integrated in transceiving.

As shown in fig. 2, for the integrated transceiver antenna in the probe of the present application, the integrated transceiver antenna includes a dielectric plate 1, the whole of the dielectric plate 1 is rectangular, floor planes 2 are formed on the front and rear sides of the upper surface of the dielectric plate 1, two ends of the two floor planes 2 on the front and rear sides have extending portions 3 extending inward, a certain distance is maintained between the two extending portions 3 on the left side and between the two extending portions 3 on the right side, a signal strip 4 is located in the middle of the upper surface of the dielectric plate 1, one end of the signal strip 4 is connected to the floor plane 2 on the front side, the other end of the signal strip 4 is connected to the floor plane 2 on the rear side, a first main radiation patch 5 is located on the upper surface of the dielectric substrate 1 in a space enclosed by the signal strip 4 and the floor plane 2 on the left side, a second main radiation patch 6 is located on the upper surface of the dielectric substrate 1 in a space enclosed by the signal strip 4 and the floor plane 2 on the right side, the first and second main radiating patches 5 and 6 are not in contact with the floor plane 2 and the signal strip 4.

Further, the first main radiating patch 5 and the second main radiating patch 6 are symmetrically arranged on the upper surface of the dielectric plate 1 on both sides of the signal strip, the first main radiating patch 5 and the second main radiating patch 6 have the same structure, the first main radiating patch 5 includes a rectangular tail portion 51 and a triangular radiating portion 52, one end of the tail portion 51 is located on the upper surface of the dielectric plate 1 between the extending portions 3 of the floor plane 2, the other end of the tail portion 51 is connected with the radiating portion 52, and the tip of the radiating portion 52 faces the signal strip 4. In the integrated transmitting and receiving antenna according to the present invention, the dielectric plate 1 is made of a material in the related art, and the other materials are made of a metal material.

At present, a spread spectrum module is used for realizing a signal source of a GHz pulse signal, the structure is complex, the cost is high, so that according to the practical application background of an ultra-wideband radar, a multi-receiving ultra-wideband radar signal source needs to generate radar signals such as multi-channel synchronous stepping frequency signals, linear frequency modulation signals and the like, and the requirements on frequency hopping time precision, synchronous time precision and frequency resolution are high, so that the AD9914 chip of ADI company is selected. The AD9914 is a direct digital frequency synthesizer with a 12-bit DAC. The device adopts an advanced DDS technology and a high-speed and high-performance digital-to-analog converter to form a digital programmable complete high-frequency synthesizer, and can generate frequency-agile analog output sine waves up to 1.4 GHz. The main performance parameters are that the internal clock speed is 3.5 GSPS; integrating a 12-bit DAC; a frequency tuning resolution 190 pHz; automatic linear and non-linear frequency scanning capabilities; a 32-bit parallel data path interface; phase noise-128 dBc/Hz (shift frequency of 1kHz at 1396 MHz); the bandwidth SFDR < -50 dBc.

According to the parameters, the DAC of the AD9914 chip is 12 bits, the number of bits is large, the bit truncation of the phase accumulator is small, accordingly, the spurious signals are correspondingly reduced, the reference clock frequency of the AD9914 chip reaches 3.5GHz, the output frequency reaches 1.4GHz, the improvement is not small compared with that of a traditional DDS chip, the high clock frequency is related to the bandwidth of a spurious-free dynamic range (SFDR), the spurious signals are filtered by a filter more easily, the frequency conversion time of the AD9914 chip is ns magnitude, and the frequency resolution reaches 190 pHz. The AD9914 chip also has an automatic linear frequency scanning function, and the phase noise and the SFDR are well controlled. The control chip selects an FPGA chip, and the FPGA chip can simplify the system design, shorten the development period and realize flexible operation.

Further, as shown in fig. 3, the radar signal source includes a synchronization control module and two direct digital frequency synthesizers, and preferably, the direct digital frequency synthesizers use an AD9914 chip. The control signal input ends of two primary direct digital frequency synthesizers of the control signal input end of the synchronous control module are respectively connected with the signal output end of the control module, two signal output ends of the synchronous control module are respectively connected with the signal input end of one direct digital frequency synthesizer, the signal output end of the direct digital frequency synthesizer is respectively connected with two signal input ends of the radar pulse signal output end module, and the radar pulse signal output end module generates an electromagnetic pulse with the duration being nanosecond level under the triggering of the synchronous pulse.

As shown in fig. 4, a detection flow chart of the detector is that an electromagnetic pulse with a duration of nanosecond is generated by the radar signal source under the trigger of the synchronization pulse, and then the electromagnetic wave signal is transmitted via the transmitting antenna. The electromagnetic signal passes through the non-metal wall body and irradiates to a target to be detected, the target reflects the electromagnetic signal, namely, the target plays a role of a secondary source, the reflected signal passes through the wall body again and is received by an antenna at the front end of a receiver, after the signals are processed by sampling, amplifying, filtering and the like, the signals are sent to an imaging link, and imaging display of the target is realized through imaging processing software.

The electromagnetic pulse signal penetrates through the wall to the inner side of the wall to conceal the target to be detected, the signal is reflected by the target and is received by a receiving antenna arranged on one side of the excitation source, and the received signal is recorded firstly. After N position signals are obtained, because the relative position information of the source point-wall surface-receiving unit is determined, the corresponding de-wall surface reflection processing can be carried out on the signals, then the signals are subjected to time reversal (or phase conjugation on a frequency domain) on a time domain, the reversed signals are transmitted from respective receiving positions by transmitting antennas, and the signals are converged at the position of a secondary source (namely a target position) through the same path. This is because the signals transmitted and received twice travel the same propagation path, and the reciprocity principle allows them to be accurately focused at the target location, whereas noise does not have this characteristic. The random environment serves as a matched filter in TRM imaging, when noise exists at a receiving end, the TRM technology can be well inhibited, and imaging with high contrast and resolution ratio can still be provided. Meanwhile, the phase drift caused by multiple scattering can be accurately counteracted at the target point, but is completely random at other positions, namely the coherent superposition of multipath is co-dominant at the target point and is completely random at other points. The combined surface of the receive-transmit antennas is known as the Time Reversal Mirror (TRM).

The technical principle of the time reversal mirror in the ultra-wideband through-wall radar imaging is as follows: a microwave pulse source is arranged at r₀The excitation source emits a time-domain narrow pulse p (t), and the signal passes through a time-invariant medium and irradiates r_nN is 1,2, …, the target of N is r_nThe incident field at (a) is:

here, theFourier transform for time domain pulses:

forward green functionThe wave equation is satisfied:

where ε (r) is a dielectric constant and μ (r) is a magnetic permeability.

N target reflection signals serving as N secondary sources equivalent to the incident field

E_R(r_n,w)≈c_n(w)E_F(r_n,w)

Where c is_n(w),n＝1,2,…,N,c_n(w) is the frequency dependent reflection coefficient of the targets, and N represents the reflection characteristics of the N targets.

When the secondary source signal passes through the invariable medium, the secondary source signal is received by a receiving antenna, wherein the signal records enough time T on the time domain to ensure that the multiple scattering signals are also accurately received, and the signal received on a receiving antenna point k is

In a through-the-wall radar environment, background information such as the distance from the wall to the antenna, the approximate thickness of the wall, etc. can be determined, and thus the background signal is denoted as E herein_G(r_kT). The target signal in the frequency domain is

χ(r_k) Indicating the effect from the receiving end.

The time-domain signal is time-inverted (equivalent to phase conjugation in the frequency domain), and the time-inverted signal is re-transmitted back through the respective receiving positions, so that the time-space signal at the field point r is:

in the frequency domain:

wherein "+" denotes a complex conjugate,representing the calculation of the green function from the receive antenna to the field point.

According to the radar imaging principle, the imaging resolution of the azimuth direction depends on the aperture of a receiving array, and in a uniform medium, the resolution of the azimuth direction is lambda L/a, a is a physical aperture, L is a propagation distance, and lambda is a carrier wavelength. However, in heterogeneous media, TRM technology has super-resolution properties and can achieve an effective aperture much larger than the actual physical aperture. For a finite or gaussian TRM, the effective pore size is:

thereby making λ L/a_eIs less than lambda L/a, and the resolution is improved.

Consider the use of Finite Difference Time Domain (FDTD), which is also the dominant algorithm for numerical simulation in the current through-wall radar field. The FDTD method takes Yee cells as space electromagnetic field discrete units, carries out grid division on a researched area, and carries out differential dispersion on a differential Maxwell rotation equation to convert the differential Maxwell rotation equation into a group of time domain propulsion formulas. The electromagnetic field and the magnetic field components of the electromagnetic field are alternately sampled in space and time, and the propagation of the electromagnetic wave and the interaction process of the electromagnetic wave and the dielectric body can be directly simulated along with the advance of time step, so that the time domain characteristic of the electromagnetic field is directly reflected, the characteristic enables the electromagnetic field to directly provide time domain information of very rich electromagnetic field problems, and a clear physical image is depicted for a complex physical process.

The detector can enable the energy of echo signals to be larger by adopting a time reversal mirror technology, high-resolution imaging is facilitated, meanwhile, the use of the receiving-transmitting integrated antenna is saved in area, power consumption and size, the problems of complex structure and high cost of a spread spectrum module are solved by using an AD9914 chip and an FPGA chip as signal sources of a control chip, and the detector is good in performance and suitable for a through-wall radar system.