CN114280606A - Ground microwave deformation monitoring system - Google Patents
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Abstract
Translated fromChinese
Description
Technical Field
The invention belongs to the field of microwave deformation monitoring, and particularly relates to a ground-based microwave deformation monitoring system.
Background
The existing ground-based microwave deformation monitoring radar generally has two working modes of a real aperture and a synthetic aperture. The application of the real aperture working mode comprises bridge amplitude and frequency monitoring, tower-shaped change monitoring, wind driven generator blade vibration monitoring and the like, and the synthetic aperture working mode comprises terrain measurement and slope safety monitoring, dam and tailing dam safety monitoring, glacier and volcano detection and the like. The effective application of the ground microwave deformation monitoring radar in the aspect of safety monitoring makes the ground microwave deformation monitoring radar become an important monitoring means for guaranteeing the safety of people's lives and properties.
The method is different from the characteristics of large scale and large revisiting period of satellite-borne and airborne microwave radars, and the ground microwave deformation monitoring radar can perform rapid and high-precision deformation monitoring on a specific area. However, due to the difference in the distance between the targets and the difference in the reflectivity, the strength of the echo signal is different. The existing ground microwave deformation monitoring radar can normally perform amplification processing of fixed gain on signals before analog-to-digital conversion is performed on echo signals, when a fixed gain conditioning mode is adopted, the echo signals are stronger for a short-distance target, the receiver is easily saturated, the echo signals of the long-distance target are very weak, quantization errors after analog-to-digital conversion are larger, and therefore the fixed gain conditioning mode cannot adapt to the received signals of a large dynamic range of a ground microwave deformation monitoring system, and the detection range of the radar is reduced. In addition, most of the existing ground microwave deformation monitoring radar systems adopt a step-frequency continuous wave system, measurement is realized by using a vector network analyzer, and the defects of large size, heavy equipment, low system integration level, poor real-time performance, high cost, low overall practicability and the like exist, so that the application of the ground microwave deformation monitoring radar in a real scene is greatly limited.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a ground-based microwave deformation monitoring system, so that the technical problems of large volume, heavy equipment, poor real-time performance and high cost of the conventional monitoring system are solved.
To achieve the above object, according to one aspect of the present invention, there is provided a ground-based microwave deformation monitoring system, including: the system comprises a transmitting front-end module, a receiving front-end module, a signal acquisition and processing module, a transmitting antenna and a receiving antenna;
the transmitting front-end module comprises a controller, a DDS (direct digital synthesizer), a phase-locked loop A, a phase-locked loop B, a quadrature modulator, a first frequency mixer, a band-pass filter, a power divider and a radio frequency amplifier; the controller respectively controls the DDS, the phase-locked loop A and the phase-locked loop B to generate a linear frequency modulation continuous wave baseband signal S1, a first local oscillation signal P1 and a second local oscillation signal P2; after being modulated by the quadrature modulator, S1 and P1 are sequentially input to the first mixer and the band-pass filter together with P2 for mixing and filtering to obtain a radio-frequency signal S2; s2 is divided into two signals S21 and S22 by the power divider, wherein S21 is amplified by the radio frequency amplifier and then transmitted to a monitoring area by the transmitting antenna so as to detect deformation information of a monitored target;
the receiving front-end module comprises a low noise amplifier and a second mixer; the echo signal received by the receiving antenna is amplified by the low noise amplifier and then is mixed with the echo signal input into the second mixer from S22 to obtain a difference frequency signal;
and the signal acquisition and processing module processes the difference frequency signal to obtain the deformation information of the monitored target.
Preferably, the system comprises a real aperture mode of operation and a synthetic aperture mode of operation;
in the real aperture operating mode, the transmitting antenna and the receiving antenna are fixed;
in the synthetic aperture mode of operation, the transmit and receive antennas move.
Preferably, in the real aperture operating mode, the transmitting antenna and the receiving antenna are fixedly mounted on a tripod;
and under the synthetic aperture working mode, the transmitting antenna and the receiving antenna are arranged on the linear guide rail and move horizontally on the linear guide rail.
Preferably, in the synthetic aperture operating mode, the positions of the transmitting antenna and the receiving antenna on the guide rail are detected by a photoelectric switch arranged on the linear guide rail and connected with the controller.
Preferably, the signal acquisition and processing module comprises a self-adaptive gain processing module, a signal acquisition card and an imaging and deformation extraction module;
and after receiving the synchronous signal from the controller, the signal acquisition card performs analog-to-digital conversion on the difference frequency signal conditioned by the adaptive gain processing module and then sends the difference frequency signal to an imaging and deformation extraction module for imaging and deformation extraction processing to obtain deformation information of the monitored target.
Preferably, in the real-aperture working mode, the imaging and deformation extraction module performs M (M is greater than or equal to 2) time domain coherent accumulation on the difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card, and performs fast fourier transform to obtain a peak value corresponding to the monitoring target in a frequency domain, so as to calculate the distance between the monitoring target; and then, carrying out interference processing on the frequency domain data obtained after two adjacent measurements to obtain a phase difference caused by target deformation, and carrying out phase unwrapping to obtain a real phase difference so as to convert to obtain the target deformation.
Preferably, in the synthetic aperture working mode, the imaging and deformation extraction module performs fast fourier transform on a difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card in a distance direction to realize distance direction focusing, and realizes azimuth direction focusing by a frequency scaling algorithm to obtain a two-dimensional radar complex image of a monitored target scene; the difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card is a two-dimensional difference frequency data matrix; and obtaining a plurality of two-dimensional radar complex images through multiple scanning and imaging processing, obtaining interference patterns measured twice through interference processing, and obtaining a two-dimensional deformation pattern of the target scene through interference pattern filtering and two-dimensional phase unwrapping.
Preferably, the adaptive gain processing module includes a variable gain amplifier for amplifying the difference frequency signal, and a detector for controlling an amplification gain of the variable gain amplifier.
Preferably, the transmit front-end module further comprises a first low-pass filter disposed between the DDS and the quadrature frequency modulator;
the receiving front-end module further comprises a second low-pass filter arranged between the second frequency mixer and the signal acquisition and processing module.
Preferably, the controller is an FPGA.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. the ground microwave deformation monitoring system provided by the invention adopts linear frequency modulation continuous waves, and compared with a traditional ground deformation monitoring radar system adopting a step frequency continuous wave system, the system greatly reduces the scanning period and improves the real-time property of the system. The existing ground microwave interference radar mostly adopts a step frequency continuous wave system, a vector network analyzer is utilized to realize one-dimensional measurement, hundreds of frequency points in a designed bandwidth need to be transmitted, a complete scanning bandwidth needs more than about 1 second, the observation time of more than half an hour is needed for the next complete scanning in a synthetic aperture mode, and the measurement cannot be realized in time because the complete scanning period is too long. The one-dimensional measurement period can be realized by controlling the DDS by using the FPGA, is generally controlled within the range of 1-10ms, can realize 50Hz one-dimensional target vibration monitoring, can finish one-time two-dimensional data acquisition within 10 seconds, and effectively improves the working efficiency and the real-time property of the system.
2. The ground microwave deformation monitoring system provided by the invention adopts a linear frequency modulation continuous wave system, utilizes components such as DDS (direct digital synthesizer) and PLL (phase locked loop) to generate a transmitting signal, and can reduce the system cost while reducing the volume and weight of equipment compared with the defects that the existing system usually adopts a vector network analyzer, which has the defects of large volume, heavy equipment, high price, difficult transportation of an area with complex terrain, high use cost and incapability of realizing wide application and the like; the difference frequency signal after the self-adaptive gain processing is sampled by the linear frequency modulation continuous wave system foundation microwave deformation monitoring radar, and the bandwidth of the difference frequency signal is far smaller than the bandwidth of a base band of a transmitting signal, so that the requirement on the sampling rate of an ADC (analog to digital converter) is greatly reduced, the data rate in the whole data chain is reduced, and the adoption of high-performance transmission and storage elements is avoided, thereby further reducing the system cost. The system provided by the invention has the advantages of light weight, low cost, high real-time performance and high integration degree.
3. The ground microwave deformation monitoring system provided by the invention obtains the difference frequency signal with stable amplitude in a self-adaptive gain conditioning mode, overcomes the defects of a fixed gain method, reduces the amplitude variation range of the difference frequency signal, can fully utilize the sampling precision of a signal acquisition card, improves the signal-to-noise ratio of the system, enlarges the dynamic range of a receiver and enhances the monitoring capability of the system. The adaptive gain processing module adopts a negative feedback control mode to process the amplitude of the input signal and feed the processed input signal back to the variable gain amplifier, and the signal output with stable amplitude is obtained by inputting difference frequency signals with different amplitudes.
4. According to the ground microwave deformation monitoring system, the FPGA is used as a controller to control the whole signal receiving and transmitting and data collecting process, the control time sequence of the DDS and the PLL can be accurately realized, and therefore the parallel processing capability and the accurate control capability of the system are integrally improved; and the operation speed is high, and the device can be quickly synchronized with the acquisition card.
Drawings
FIG. 1 is a schematic structural diagram of a foundation microwave deformation monitoring system provided by the present invention;
FIG. 2 is a schematic view of the working process of the ground-based microwave deformation monitoring system provided by the present invention;
FIG. 3 is a schematic diagram illustrating connection between an FPGA and peripheral devices in the ground-based microwave deformation monitoring system according to the present invention;
FIG. 4 is a schematic diagram of generation of a sawtooth wave modulated chirp continuous wave radar difference frequency signal in the ground-based microwave deformation monitoring system provided by the present invention;
FIG. 5 is a schematic view of the working principle of the ground-based microwave deformation monitoring system in the real aperture mode according to the present invention;
fig. 6(a) and fig. 6(b) are a graph of a one-dimensional target distance image and a deformation effect and a graph of a one-dimensional target distance image and a time relation effect in a real aperture working mode of the ground-based microwave deformation monitoring system provided by the invention, respectively;
fig. 7(a), 7(b), and 7(c) are respectively a two-dimensional complex image, a cross-sectional view, and a deformation effect view of the ground-based microwave deformation monitoring system in the synthetic aperture working mode according to the present invention.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
1-a controller; 2-DDS; 3-a first low-pass filter; a 4-quadrature modulator; 5-a first mixer; 6-phase locked loop A; 7-phase locked loop B; 8-band pass filter; 9-power divider; 10-a radio frequency amplifier; 11-an imaging and deformation extraction module; 12-a signal acquisition card; 13-an adaptive gain processing module; 14-a second low-pass filter; 15-a second mixer; 16-a low noise amplifier; 17-a transmitting antenna; 18-a receiving antenna; 19-a tripod; 20-proximity switch a; 21-a linear guide rail; 22-proximity switch B.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The embodiment of the invention provides a ground-based microwave deformation monitoring system, which comprises: the system comprises a transmitting front-end module, a receiving front-end module, a signal acquisition and processing module, a transmitting antenna and a receiving antenna;
the transmitting front-end module comprises a controller, a DDS (direct digital synthesizer), a phase-locked loop A, a phase-locked loop B, a quadrature modulator, a first frequency mixer, a band-pass filter, a power divider and a radio frequency amplifier; the controller respectively controls the DDS, the phase-locked loop A and the phase-locked loop B to generate a linear frequency modulation continuous wave baseband signal S1A first local oscillator signal P1A second local oscillator signal P2；S1And P1Modulated by the quadrature modulator, and P2Sequentially inputting the signals to the first frequency mixer and the band-pass filter for frequency mixing and filtering to obtain a radio-frequency signal S2；S2Is divided into two paths of signals S by the power divider21、S22Wherein S is21The signal is amplified by the radio frequency amplifier and then transmitted to a monitoring area by the transmitting antenna so as to detect deformation information of a monitored target;
the receiving front-end module comprises a low noise amplifier and a second mixer; the echo signal received by the receiving antenna is amplified by the low noise amplifier and then is compared with S22Inputting the signal to the second mixer for mixing to obtain a difference frequency signal;
and the signal acquisition and processing module processes the difference frequency signal to obtain deformation information of the monitoring area.
Preferably, the transmit front-end module further comprises a first low-pass filter disposed between the DDS and the quadrature frequency modulator;
the receiving front-end module further comprises a second low-pass filter arranged between the second frequency mixer and the signal acquisition and processing module.
Preferably, the controller is an FPGA.
Preferably, the signal acquisition and processing module comprises a self-adaptive gain processing module, a signal acquisition card and an imaging and deformation extraction module;
and after receiving the synchronous signal from the controller, the signal acquisition card performs analog-to-digital conversion on the difference frequency signal conditioned by the adaptive gain processing module and then sends the difference frequency signal to an imaging and deformation extraction module for imaging and deformation extraction processing to obtain deformation information of the monitored target.
Preferably, the adaptive gain processing module includes: the adaptive gain processing module comprises a variable gain amplifier and a detector, wherein the variable gain amplifier is used for amplifying the difference frequency signal, and the detector is used for controlling the amplification gain of the variable gain amplifier.
Specifically, the hardware part of the ground-based microwave deformation monitoring radar system provided by the invention takes FPGA as a main control partA device for generating a linear frequency modulation continuous wave base frequency signal S by the DDS through quadrature modulation and frequency mixing filtering processing in a transmitting chain1(first signal) modulated to a radio frequency signal S2(second signal) for transmitting and receiving electromagnetic waves through a pair of strongly directional antennas (e.g., horn antenna, directional planar antenna, etc.). In the receiving link, the second signal and the echo signal (third signal) after low-noise amplification are directly mixed and filtered to obtain a difference frequency signal (fourth signal). The difference frequency signal is fed to the acquisition card after being subjected to the adaptive gain processing (the fifth signal), and the signal processing is carried out locally or remotely after being transmitted. The adaptive gain processing module converts the amplitude of the input signal into voltage, and the higher signal amplitude corresponds to the higher voltage to control the variable gain amplifier to provide smaller amplification gain; the corresponding lower signal amplitude corresponds to a lower voltage, controlling the variable gain amplifier to provide a greater amplification gain. After passing through the adaptive gain amplifier, the difference frequency signals with different amplitudes are input to obtain signal output with stable amplitude.
As shown in fig. 1, taking thecontroller 1 as an FPGA as an example, the FPGA generates an accurate control timing sequence, controls theDDS 2 to generate a chirped continuous wave baseband signal, and the chirped continuous wave baseband signal is subjected to low pass filtering by a first low pass filter 3 (the first low pass filter is preferably an elliptic low pass filter), so as to filter high frequency noise and an out-of-band spurious frequency signal, thereby obtaining a first signal. The FPGA controls the phase-locked loop A6 (i.e. PLLA) to generate a first local oscillation signal, and then the chirp continuous wave baseband signal and the first local oscillation signal generated by the PLLA are fed into thequadrature modulator 4 together for quadrature modulation. The FPGA controls a phase-locked loop B7 (namely PLLB) to generate a second local oscillation signal, the output signal of thequadrature modulator 4 and the second local oscillation signal generated by the PLLB are fed into afirst mixer 5 together for mixing, and an upper sideband after mixing is obtained through a band-pass filter 8. At this time, a radio frequency signal of a chirped continuous wave, i.e., a second signal, is generated. The rf signal is divided into two parts by the power divider 9, and the two parts have the same phase, and one part is fed to the highpower rf amplifier 10 and then fed to the transmittingantenna 17.
The transmittingantenna 17 converts the high-frequency current signal into an electromagnetic wave to be transmitted to the detection area, the electromagnetic wave is backscattered after encountering a target, a part of the energy of the electromagnetic wave returns to the front end of the radar along the original path, the receivingantenna 18 converts the electromagnetic wave in the space into a high-frequency electric signal, the high-frequency electric signal is called an echo signal, and the high-frequency electric signal is amplified by the low-noise amplifier 16 to obtain a third signal. The third signal and the other output signal from the power divider 9 are fed into thesecond mixer 15 for mixing, so as to obtain a difference frequency signal containing multiple high frequency spurs.
Since the signal output by thesecond mixer 15 includes clutter signals such as high-frequency coupling from the front end of transmission, the output signal of thesecond mixer 15 is filtered by the second low-pass filter 14, and a difference frequency signal, i.e., a fourth signal, which can reflect the reflectivity of the target scene and the target phase information is obtained. The fourth signal is processed by the adaptivegain processing module 13 to obtain a fifth signal, and then the difference frequency signal is subjected to data acquisition by thesignal acquisition card 12. After obtaining the synchronous signal from the FPGA, thesignal acquisition card 12 performs analog-to-digital conversion on the difference frequency signal conditioned by the adaptivegain processing module 13, and performs imaging and deformation extraction and other processing on the local digital processor or the remote digital processor.
The work flow of the foundation microwave deformation monitoring system provided by the invention is shown in figure 2:
1. the method comprises the following steps of taking an FPGA as a main controller, and controlling a DDS to generate a first signal;
2. performing quadrature modulation and frequency mixing up-conversion on the first signal and a local oscillation signal generated by a phase-locked loop A to obtain a second signal;
3. the second signal passes through a second power divider, one path of the second signal is amplified by a radio frequency amplifier and then fed to a transmitting antenna, after electromagnetic waves touch a monitoring target, part of energy returns to a receiving antenna along the original path, and the second signal is amplified by a low-noise amplifier to obtain a third signal;
4. mixing the third signal with the other path of output of the two power dividers, and filtering to obtain a fourth signal;
5. the fourth signal passes through a self-adaptive gain module to obtain a fifth signal;
6. and acquiring the fifth signal, and performing imaging and interference processing locally or remotely after transmitting the fifth signal to obtain a scene target image and deformation information. In the local processing, a digital processor (such as a DSP but not limited to the DSP) is used for carrying out various post-processing such as Fourier transform, and the post-processing result is sent to a remote place in a wired or wireless mode; the other mode is that the sampled data are directly transmitted to a remote place, post-processing such as imaging and deformation extraction is carried out on the remote place, and the characteristic of low data rate after analog-to-digital conversion of the fifth signal is a necessary condition for realizing the remote post-processing.
The ground microwave deformation monitoring system provided by the invention solves the problem of larger fourth signal amplitude difference caused by target reflectivity change, meets the adaptability to target distance change, enlarges the dynamic range of a receiver, obtains a larger detection range under the condition of unchanged transmitting power, and improves the signal-to-noise ratio; by processing the fifth signal containing the reflectivity and the phase information of the target scene, the requirements on the sampling rate, the data transmission speed and the hardware storage space are reduced, the system complexity is reduced, the miniaturization is realized, the system cost is saved, the real-time performance of the system is improved, and the monitoring requirement on the rapid deformation target scene is met.
Preferably, the system comprises a real aperture mode of operation and a synthetic aperture mode of operation.
In particular, the system can operate in both real aperture and synthetic aperture modes.
In the real aperture mode of operation, the transmit antenna and the receive antenna are fixed.
Further, in the real aperture operating mode, the transmitting antenna and the receiving antenna are fixedly mounted on a tripod.
In particular, in the real aperture mode of operation, the radar sensor is mounted in a fixed position, for example: adopts a mode of mounting on the tripod.
In the real aperture mode, as shown in fig. 1, the transmittingantenna 17 and the receivingantenna 18 are mounted on atripod 19, and the system can perform one-dimensional distance and deformation monitoring. Based on the monitored one-dimensional distance and deformation information, the actual vibration frequency of the target can be monitored, and the eigenfrequency of the monitored target is analyzed based on the result, so that the health state of the monitored target is analyzed.
As the cycle of the frequency modulation pulse transmitted by the linear frequency modulation continuous wave radar sensor can utilize the FPGA to configure theDDS 2, the pulse cycle can be adjusted between 1ms and 10ms, and the target vibration condition with the frequency as high as 50Hz can be measured.
Further, in the real aperture operating mode, the imaging and deformation extraction module 11 performs M (M is greater than or equal to 2) time domain coherent accumulation on the difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card (to improve the signal-to-noise ratio), and performs fast fourier transform to obtain a peak value corresponding to the monitoring target in the frequency domain (after performing fast fourier transform processing on the difference frequency signal, the difference frequency signal is transformed from a time domain representation to a frequency domain representation, which refers to the frequency domain of the difference frequency signal); and then, carrying out interference processing on the frequency domain data obtained after two adjacent measurements to obtain a phase difference caused by target deformation, and carrying out phase unwrapping to obtain a real phase difference so as to convert to obtain the target deformation.
Specifically, the imaging and deformation extraction module improves the signal-to-noise ratio through M times (M is more than or equal to 2) of coherent accumulation in the time domain, and obtains a one-dimensional range profile through fast Fourier transform processing to obtain target distance information (namely, M times of time domain coherent accumulation is carried out, and fast Fourier transform is carried out to obtain a peak value corresponding to a target in the frequency domain to obtain a target distance); then, carrying out interference processing on the data after multiple measurements to obtain a phase difference caused by target deformation, and obtaining a real phase difference through phase unwrapping so as to convert to obtain the target real deformation; and finally, carrying out Fourier transform on the continuous target deformation data to obtain target vibration frequency, obtaining different vibration modes of the target through empirical mode decomposition, and obtaining the eigenfrequency of the target according to forced residual vibration.
In the synthetic aperture mode of operation, the transmit and receive antennas move.
Further, in the synthetic aperture operating mode, the transmitting antenna and the receiving antenna are mounted on a linear guide rail and horizontally move on the linear guide rail.
Further, under the synthetic aperture working mode, the positions of the transmitting antenna and the receiving antenna on the guide rail are detected through a photoelectric switch which is arranged on the linear guide rail and connected with the controller.
Specifically, in the synthetic aperture operating mode, the radar sensor (i.e., the transmitting antenna and the receiving antenna) is mounted on the linear guide rail, and the radar sensor horizontally moves on the linear guide rail at a constant speed by the driving of the stepping motor to form the synthetic aperture.
Furthermore, in the synthetic aperture working mode, the imaging and deformation extraction module carries out fast Fourier transform in the distance direction to realize distance direction focusing on the difference frequency signals conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card (the antenna in the synthetic aperture mode obtains a one-dimensional array with the length of M at N different positions of the guide rail, and the difference frequency signals in a frequency modulation period are stored in the one-dimensional array; and obtaining a plurality of two-dimensional radar complex images through multiple scanning and imaging processing, obtaining interference patterns measured twice through interference processing, and obtaining a two-dimensional deformation pattern of the target scene through interference pattern filtering and two-dimensional phase unwrapping.
As shown in fig. 1, the transmittingantenna 17 and the receivingantenna 18 are mounted on alinear guide rail 21, a proximity switch a 20 and a proximity switch B22 (wherein, the proximity switch may be a photoelectric proximity switch) are mounted on thelinear guide rail 21, the transmittingantenna 17 and the receivingantenna 18 horizontally move on thelinear guide rail 21 to realize a synthetic aperture, and a target scene image and a deformation result are obtained through post-processing such as local or remote imaging and deformation, so that the whole set of system is completed.
It will be appreciated that the relative positions of the transmit and receive antennas remain constant at all times (e.g., about 30cm apart), and that they move together (the relative positions remain constant) as they move.
The imaging and deformation extraction module obtains distance and phase information of the target from the distance direction through fast Fourier transform to a frequency domain; in the azimuth direction, the radar sensor moves along the linear guide rail to form a synthetic aperture, azimuth signals have a linear frequency modulation characteristic due to Doppler effect, azimuth focusing is achieved through a frequency scaling algorithm, azimuth information of a target is obtained, two-dimensional focusing imaging is achieved, and a two-dimensional radar complex image of a target scene is obtained. And carrying out differential interference processing on the two complex images at different moments in the same monitoring area to obtain the phase difference of the two complex images, and obtaining micro-deformation information of a monitored target through phase unwrapping and deformation inversion so as to realize the imaging and deformation monitoring task of the system.
The system provided by the invention takes the FPGA as a main control unit, controls the DDS circuit, the two PLL circuits and the receiving and transmitting antenna module, acquires two proximity switch signals and realizes synchronization with a data acquisition card, and obtains a difference frequency echo with stable amplitude by the self-adaptive gain processing module. The FPGA is synchronous with the acquisition card, so that the data acquisition of the difference frequency signal after the self-adaptive gain processing is realized, and the imaging processing and the deformation extraction processing are carried out locally or remotely.
The schematic diagram of the connection between the FPGA and the peripheral device is shown in fig. 3. Preferably, the FPGA selects EP4CE15E22C8N from Altera corporation, and uses Verilog HDL hardware description language to perform programming in QuartusII 13.1 environment, and the functional simulation and the timing simulation are completed in model sim environment. The FPGA has an unlimited erasable function, program debugging can be carried out by fully utilizing a JTAG interface, and then the generated pof file is solidified into an SRAM (static random access memory), wherein the SRAM is EPCS4SI8 of Intel corporation. The chip MC100LVEL16D is adopted to convert a crystal oscillator of 50MHz into a differential signal, provide a reference clock in a differential form for the DDS, and then send the reference clock to the differential input end of theDDS 2 chip. The proximity switch A20 and the proximity switch B22 are both connected with the FPGA to detect the position of the radar sensor on thelinear guide rail 21, and the position is alternately used as a start mark and an end mark of the transmission and the reception of the radar sensor which reciprocates on thelinear guide rail 21, so that the idle stroke condition is avoided during movement, and the monitoring efficiency is improved. During the continuous transmitting period, theFPGA 1 continuously acquires the difference frequency signal through the IO triggersignal acquisition card 12. Due to the high-performance parallel processing capability and accurate time sequence control capability of the FPGA, the system can realize the communication with external signals and the synchronization with thesignal acquisition card 12 while accurately controlling components such as theDDS 2, and the like, so that the system can realize the high-efficiency work.
The schematic diagram of the generation of the radar difference frequency signal of the sawtooth wave modulated chirp continuous wave system of the system provided by the invention is shown in fig. 4. When the system provided by the invention works, the transmittingantenna 17 transmits a sawtooth wave modulated linear frequency modulation continuous wave radio frequency signal, as shown by a solid line in figure 4, the bandwidth of the transmitted chirp signal is delta f, and the central frequency is f0With a frequency modulation period of Ta. Without regard to echo amplitude, the received chirp signal may be considered as a delayed version of the transmitted signal, as shown by the dashed line in fig. 4. After dechirp processing, the obtained difference frequency signal has a difference frequency f as shown by the dotted line in fig. 4b. The difference frequency is related to the target distance R and the parameters of the transmitted signal, and the relation is as follows:
a schematic diagram of the ground-based microwave deformation monitoring radar system in the real aperture operating mode is shown in fig. 5. And after dechirp processing is carried out on the echo signal, amplitude and phase information capable of reflecting target characteristics is obtained. Obtaining the frequency f of the target difference frequency signal after fast Fourier transformbThe distance information of the target can be obtained by formula (1). The phase information at the difference frequency point is the key to extract the deformation, and the phase is obtained by the first measurement in fig. 5
After the target moves a distance d along the sight line direction of the radar, the second measurement is carried out, and the phase position is obtained through the second measurement
When the target deformation exceeds half of the wavelength lambda of the emission signal, phase winding can occur, and the real phase difference
Can be calculated by the formulas (2) and (3). N represents the number of phase windings.
Target deformation d and phase difference
The relationship can be calculated by equation (4).
The one-dimensional target range profile and deformation effect graph of the ground-based microwave deformation monitoring radar system in the real-aperture working mode is shown in fig. 6 (a). The graph of the effect of the relationship between the working one-dimensional target range profile and the time in the ground deformation monitoring radar real aperture mode is shown in fig. 6 (b). In a simulation example of the present invention, the pulse width is selected to be 5ms, the bandwidth is 80MHz, the target point distance is set to be 5.6m, the vibration frequency is 0.5Hz, and the peak-to-peak value is 30cm of simple harmonic vibration. 40 sampling points are arranged in each frequency modulation period, 2400 frequency modulation period (12s) of data are collected in total, and a data matrix of 40 multiplied by 2400 is formed. In fig. 6(a), FFT is performed on the sample data to obtain a one-dimensional range profile of the target. The phase of the column of data is phase unwrapped along the time dimension at a distance of 5.6 m. In fig. 6(b), the solid line indicates the strain calculated from the phase change of the target before phase unwrapping, the dotted line indicates the strain calculated from the phase change of the target after phase unwrapping, and the set vibration information of the target after phase unwrapping is obtained.
The two-dimensional imaging effect diagram of the ground deformation monitoring radar synthetic aperture mode operation provided by the invention is shown in fig. 7 (a). In one example of the present invention, the target is set at a position of 0m in azimuth from 100m, and a point spread function is generated at the target position by two-dimensional focusing. Fig. 7(b) is a perspective sectional view and a distance sectional view of the target site shown in fig. 7 (a). The two-dimensional complex images focused twice are subjected to interference processing, and a target deformation result is obtained according to a formula (4), so that a two-dimensional deformation effect graph of the invention is obtained and is shown in fig. 7 (c). On the second measurement, the target is deformed by 2mm away from the radar with respect to the distance of fig. 7 (a).
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A ground-based microwave deformation monitoring system is characterized by comprising: the system comprises a transmitting front-end module, a receiving front-end module, a signal acquisition and processing module, a transmitting antenna and a receiving antenna;
the transmitting front-end module comprises a controller, a DDS (direct digital synthesizer), a phase-locked loop A, a phase-locked loop B, a quadrature modulator, a first frequency mixer, a band-pass filter, a power divider and a radio frequency amplifier; the controller respectively controls the DDS, the phase-locked loop A and the phase-locked loop B to generate a linear frequency modulation continuous wave baseband signal S1A first local oscillator signal P1A second local oscillator signal P2；S1And P1Modulated by the quadrature modulator, and P2Sequentially inputting the signals to the first frequency mixer and the band-pass filter for frequency mixing and filtering to obtain a radio-frequency signal S2；S2Is divided into two paths of signals S by the power divider21、S22Wherein S is21The signal is amplified by the radio frequency amplifier and then transmitted to a monitoring area by the transmitting antenna so as to detect deformation information of a monitored target;
the receiving front-end module comprises a low noise amplifier and a second mixer; the echo signal received by the receiving antenna is amplified by the low noise amplifier and then is compared with S22Inputting the signal to the second mixer for mixing to obtain a difference frequency signal;
and the signal acquisition and processing module processes the difference frequency signal to obtain the deformation information of the monitored target.
2. The ground-based microwave deformation monitoring system of claim 1 wherein the system includes a real aperture mode of operation and a synthetic aperture mode of operation;
in the real aperture operating mode, the transmitting antenna and the receiving antenna are fixed;
in the synthetic aperture mode of operation, the transmit and receive antennas move.
3. The ground-based microwave deformation monitoring system of claim 2 wherein in the solid aperture mode of operation, the transmitting and receiving antennas are fixedly mounted on a tripod;
and under the synthetic aperture working mode, the transmitting antenna and the receiving antenna are arranged on the linear guide rail and move horizontally on the linear guide rail.
4. The system according to claim 3, wherein in the synthetic aperture mode of operation, the positions of the transmitting and receiving antennas on the guide rails are detected by optoelectronic switches disposed on the linear guide rails and connected to the controller.
5. The ground-based microwave deformation monitoring system according to any one of claims 1 to 4, wherein the signal acquisition and processing module comprises an adaptive gain processing module, a signal acquisition card and an imaging and deformation extraction module;
and after receiving the synchronous signal from the controller, the signal acquisition card performs analog-to-digital conversion on the difference frequency signal conditioned by the adaptive gain processing module and then sends the difference frequency signal to an imaging and deformation extraction module for imaging and deformation extraction processing to obtain deformation information of the monitored target.
6. The ground-based microwave deformation monitoring system of claim 5, wherein in the real-aperture operating mode, the imaging and deformation extraction module performs M (M is larger than or equal to 2) time-domain coherent accumulation on the difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card, and performs fast Fourier transform to obtain a peak value corresponding to a monitored target in a frequency domain, so as to calculate the distance between the monitored targets; and then, carrying out interference processing on the frequency domain data obtained after two adjacent measurements to obtain a phase difference caused by target deformation, and carrying out phase unwrapping to obtain a real phase difference so as to convert to obtain the target deformation.
7. The ground-based microwave deformation monitoring system of claim 5, wherein in the synthetic aperture operating mode, the imaging and deformation extraction module performs fast Fourier transform on the difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card in the distance direction to realize distance-direction focusing, and realizes azimuth-direction focusing by a frequency scaling algorithm to obtain a two-dimensional radar complex image of a monitored target scene; the difference frequency signal conditioned by the adaptive gain processing module and subjected to digital-to-analog conversion by the signal acquisition card is a two-dimensional difference frequency data matrix; and obtaining a plurality of two-dimensional radar complex images through multiple scanning and imaging processing, obtaining interference patterns measured twice through interference processing, and obtaining a two-dimensional deformation pattern of the target scene through interference pattern filtering and two-dimensional phase unwrapping.
8. The ground-based microwave deformation monitoring system of claim 5 wherein the adaptive gain processing module includes a variable gain amplifier for amplifying the difference frequency signal, and a detector for controlling the amplification gain of the variable gain amplifier.
9. The ground-based microwave deformation monitoring system of claim 1, wherein the transmitting front-end module further comprises a first low-pass filter disposed between the DDS and the quadrature frequency modulator;
the receiving front-end module further comprises a second low-pass filter arranged between the second frequency mixer and the signal acquisition and processing module.
10. The ground-based microwave deformation monitoring system of claim 1 wherein the controller is an FPGA.
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