CN117538940B - Stepping frequency ground penetrating radar system based on VNA and working method - Google Patents
Stepping frequency ground penetrating radar system based on VNA and working method Download PDFInfo
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Abstract
The invention discloses a stepping frequency ground penetrating radar system based on a VNA (virtual network analysis), which comprises an acquisition trolley and a meter arranged on a wheel of the acquisition trolley, wherein the meter is connected with a computer through a USB (universal serial bus) to serial port line, the computer is also connected with a vector network analyzer, an output port of the vector network analyzer is connected with an input port of a power amplifier, an output port of the power amplifier is connected with a transmitting antenna, the input port of the vector network analyzer is also connected with an output port of a low-noise power amplifier, and an input end of the low-noise power amplifier is connected with a receiving antenna which is arranged on the acquisition trolley. The invention solves the problems that the manual control sampling in the prior art can cause serious spectrum deformation of an actual echo and the imaging quality is declined. The invention also discloses a working method of the stepping frequency ground penetrating radar system based on the VNA.
Description
Technical Field
The invention belongs to the technical field of ground penetrating radar systems, relates to a stepping frequency ground penetrating radar system based on VNA, and further relates to a working method of the stepping frequency ground penetrating radar system.
Background
Ground penetrating radar uses interactions between electromagnetic waves and underground objects to obtain information of underground objects. The radar emits a pulsed signal, and when the signal encounters an underground object, a portion will be reflected back to form an echo signal. By receiving and processing these echo signals, the location, shape and characteristics of the subsurface target can be inferred. The ground penetrating radar has the unique advantage of being capable of carrying out nondestructive detection on objects in a visual opaque medium, and has great application value in scenes such as underground pipeline detection, road hole detection, building structure detection, land mine detection and the like. The Synthetic Aperture (SAR) imaging method is applied to the ground penetrating radar, so that target information can be better restored; the ultra-wideband stepping frequency waveform is applied to the ground penetrating radar, so that the resolution of the one-dimensional range profile can be improved without losing the detection depth, and the method has great research significance.
Frequency stepping is an improved radar operation that obtains more information from the subsurface by transmitting pulsed signals at different frequencies. By changing the frequency of the transmitted signal, the underground target information with different depths or different physical properties can be obtained. The frequency stepping technology can improve the sensitivity and resolution of detection and accurately position and identify various underground targets. SAR is a method that uses radar technology to achieve high resolution imaging of ground targets. The method comprises the steps of installing a proper antenna on a radar platform, transmitting and receiving pulse signals at different frequencies, and then collecting echo signals of ground targets. Imaging of a ground target can be achieved by coherent processing and synthesis of multiple received signals. SAR imaging technology has the advantages of high resolution, large field angle, non-invasiveness and the like, and is widely applied to the fields of earth observation, military reconnaissance and the like.
In the prior art, although the frequency stepping and SAR imaging technology is applied to a ground penetrating radar measurement system, the Fourier transform in the frequency domain imaging algorithm needs to be uniformly sampled, the frequency stepping and SAR imaging technology is sensitive to the motion state change and the gesture change when the ground penetrating radar system operates, and the frequency spectrum of an actual echo is often seriously deformed due to the fact that the conventional ground penetrating radar system does not have automatic uniform sampling and manual control of the uniform sampling, so that the imaging quality is degraded.
Disclosure of Invention
The invention aims to provide a stepping frequency ground penetrating radar system based on VNA, which solves the problems that the manual control sampling in the prior art can cause serious spectral deformation of an actual echo and the imaging quality is declined.
Another object of the present invention is to provide a working method of a VNA-based step frequency ground penetrating radar system.
The technical scheme includes that the VNA-based stepping frequency ground penetrating radar system comprises a collection trolley, wherein a meter counter is arranged on wheels of the collection trolley, the meter counter is connected with a computer through a USB (universal serial bus) to serial port line, the computer is also connected with a vector network analyzer through a network line, an output port of the vector network analyzer is connected with an input port of a power amplifier, an output port of the power amplifier is connected with a transmitting antenna, the input port of the vector network analyzer is also connected with an output port of a low-noise power amplifier, an input end of the low-noise power amplifier is connected with a receiving antenna, and the receiving antenna, the low-noise power amplifier, the vector network analyzer, the power amplifier, the transmitting antenna and the computer are all arranged on the collection trolley.
The present invention is also characterized in that,
The acquisition trolley is provided with two layers, and the computer is placed on the upper strata of acquisition trolley, and receiving antenna, low noise power amplifier, vector network analysis appearance, power amplifier and transmitting antenna all are placed on the lower floor, and portable power source has still been placed on the upper strata of acquisition trolley, and low noise power amplifier, vector network analysis appearance, power amplifier, computer all pass through the cable and connect portable power source.
The vector network analyzer and the computer are connected through a LAN port.
The power amplifier is connected with the vector network analyzer and the transmitting antenna through radio frequency wires, and the low-noise power amplifier is connected with the receiving antenna and the vector network analyzer through radio frequency wires.
The working method of the stepping frequency ground penetrating radar system based on the VNA adopts the stepping frequency ground penetrating radar system based on the VNA, and is implemented according to the following steps:
Step 1, selecting a test field, selecting a straight line in the test field area as a measurement route of an acquisition trolley, uniformly dividing the route, and taking each dividing point as a detection point;
step 2, setting a computer (7) to control the vector network analyzer (4) and the meter counter (1);
Step 3, when detecting, after the acquisition trolley (9) reaches each detection point of the planned route in step 1, transmitting electromagnetic wave signals and receiving echo signals;
And 4, processing echo signal data collected by each detection point by a computer (7), and then carrying out SAR imaging by using a back projection BP algorithm according to the processed echo signal data to finally obtain a two-dimensional or three-dimensional image of the target.
The step 2 is specifically as follows: connecting each component of the VNA-based stepping frequency ground penetrating radar system, setting IP addresses of a computer (7) and a vector network analyzer (4), then ping the computer (7) and the vector network analyzer (4) through ping commands of cmd of the computer to pass the IP addresses, installing Keysight IO library suite and Keysight Command Expert two driving programs on the computer (7) to control the vector network analyzer (4) in a visa programming mode, reading data on a display screen of the meter (1) in a serial port communication mode through Visual Studio software programming on the computer (7) and realizing internal triggering, enabling the VNA-based stepping frequency ground penetrating radar system to perform radar detection at equal intervals, and sending SCPI commands through Visual Studio software programming on the computer (7) to set radio frequency parameters of the vector network analyzer (4), wherein the radio frequency parameters specifically comprise: starting frequency, cut-off frequency and frequency point number;
Judging whether the vector network analyzer (4) and the meter counter (1) are successfully set, if so, pushing the acquisition trolley (9) to start detection, and if not, returning to the setting step to solve the fault.
Judging whether the vector network analyzer (4) is successfully set in the step 2 specifically comprises the following steps:
If the setting is successful, the numerical values of the set starting frequency, cut-off frequency and frequency point number are displayed in the vector network analyzer, after the setting is successful, the vector network analyzer (4) keeps continuously transmitting electromagnetic wave signals and receiving echo signals, if the setting is failed, the set numerical values are not displayed, and the step 3 is returned to solve the fault;
In the step 2, whether the meter counter (1) is successfully set is specifically:
The computer (7) reads the data of the meter counter (1) in real time, if the data is read correctly, the internal triggering is carried out every time the acquisition trolley (9) moves at an equal interval, namely, every time the acquisition trolley (9) moves at an equal interval, the computer (7) sends a data reading instruction, and echo signals received by the vector network analyzer (4) are read; if the reading is incorrect or no internal trigger is made, the setup step is returned to resolve the fault.
The step 3 is specifically as follows:
When in detection, after the acquisition trolley (9) reaches each detection point of the planned route in the step 1, the vector network analyzer (4) transmits electromagnetic wave signals, then the amplitude and the power of signals generated by the vector network analyzer (4) are amplified by the power amplifier (5), the electromagnetic wave signals are transmitted by the transmitting antenna (6), the electromagnetic wave detects targets through underground media, then the receiving antenna (2) receives echo signals, then the echo signals received by the receiving antenna (2) amplify the voltage or the current of the received signals to a higher level by the low-noise power amplifier (3) and then are input into the vector network analyzer (4), and the computer (7) reads the echo signals received by the vector network analyzer (4).
In the step 4, the computer (7) processes the echo signal data collected by each detection point specifically:
The echo signal data received by the computer (7) is that the real part and the imaginary part of the echo signal electric field are added to obtain the electric field, and then the electric field is used in the follow-up SAR imaging algorithm.
In the step 4, SAR imaging is specifically performed by using a back projection BP algorithm according to the processed echo signal data, wherein the SAR imaging specifically comprises the following steps:
performing inverse Fourier transform on the electric field to obtain a one-dimensional range profile, performing pulse compression on the one-dimensional range profile, performing grid division on an imaging scene by utilizing up-sampling of the range profile, calculating the distance between the pulse at each detection point transmitted by a transmitting antenna (6) and a grid point, calculating double-pass time delay according to the distance, finding out data with the same time delay in an echo signal according to the time delay, namely, the grid point receives the echo signal at the detection point time, then multiplying the echo signal by phase compensation, performing back projection on the echo signal multiplied by the phase compensation to the grid, performing coherent superposition on the data from the last detection point to the grid point, traversing all detection points, and finally obtaining the SAR image.
The beneficial effects of the invention are as follows:
the invention adopts the meter to collect the movement distance data of the ground penetrating radar system in real time and uploads the movement distance data to the computer. The meter and the vector network analyzer are integrated by a computer, so that the ground penetrating radar system can be controlled to finish equidistant motion measurement sampling according to different measurement frequencies and sampling requirements, the measurement accuracy is greatly improved, and the SAR imaging quality is ensured.
Drawings
FIG. 1 is a schematic diagram of a step frequency ground penetrating radar system based on a VNA of the present invention;
FIG. 2 is a flow chart of a method of operation of the VNA-based step frequency ground penetrating radar system of the present invention;
FIG. 3 is a diagram of a step frequency signal scanning process in a method of operating a VNA-based step frequency ground penetrating radar system of the present invention;
FIG. 4 is a diagram of an electromagnetic propagation model of a ground penetrating radar system in a method of operating a VNA-based step frequency ground penetrating radar system of the present invention;
FIG. 5 is a flow chart of an SAR imaging algorithm employed in the method of operation of the VNA based step frequency ground penetrating radar system of the present invention;
fig. 6 is a diagram of SAR imaging results of the ground penetrating radar experiment of embodiment 3 of the present invention.
In the figure, 1, a collection trolley, 2, a receiving antenna, 3, a low-noise power amplifier, 4, a vector network analyzer, 5, a power amplifier, 6, a transmitting antenna, 7, a computer, 8, a mobile power supply and 9, the collection trolley.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
Example 1
The stepping frequency ground penetrating radar system based on the VNA is structurally shown in fig. 1, and comprises a collecting trolley 9, wherein a meter counter 1 is arranged on wheels of the collecting trolley 9, the meter counter 1 is connected with a computer 7 through a USB (universal serial bus) to serial port line, the computer 7 is further connected with a vector network analyzer 4 through a network cable, an output port of the vector network analyzer 4 is connected with an input port of a power amplifier 5, an output port of the power amplifier 5 is connected with a transmitting antenna 6, an input port of the vector network analyzer 4 is further connected with an output port of a low-noise power amplifier 3, an input end of the low-noise power amplifier 3 is connected with a receiving antenna 2, and the receiving antenna 2, the low-noise power amplifier 3, the vector network analyzer 4, the power amplifier 5, the transmitting antenna 6 and the computer 7 are all arranged on the collecting trolley 9.
The acquisition trolley 9 is provided with two layers, the computer 7 is placed on the upper layer of the acquisition trolley 9, the receiving antenna 2, the low-noise power amplifier 3, the vector network analyzer 4, the power amplifier 5 and the transmitting antenna 6 are all placed on the lower layer, the mobile power supply 8 is also placed on the upper layer of the acquisition trolley 9, and the low-noise power amplifier 3, the vector network analyzer 4, the power amplifier 5 and the computer 7 are all connected with the mobile power supply 8 through cables.
The vector network analyzer 4 and the computer 7 are connected via a LAN port.
The power amplifier 5 is connected with the vector network analyzer 4 and the transmitting antenna 6 through radio frequency wires, and the low-noise power amplifier is connected with the receiving antenna 2 and the vector network analyzer 4 through radio frequency wires.
The invention adopts the meter 1 to collect the movement distance data of the ground penetrating radar system in real time, the meter is connected with the computer through a USB to serial port line, and the data of the meter is read into the computer in the Visual Studio software in a serial port communication mode so as to realize the movement detection of the ground penetrating radar system;
The invention adopts the vector network analyzer 4 to collect data, and connects the vector network analyzer 4 with the computer 7 through the LAN port connection mode; an SCPI instruction is written in Visual Studio software to issue a measurement instruction to the vector network analyzer 4, so that the programmed control of a ground penetrating radar system measurement task is realized, and the measurement efficiency is remarkably improved; and the meter 1 and the vector network analyzer 4 are integrated through the computer 7, and the ground penetrating radar system is controlled to finish equidistant motion measurement sampling according to different measurement frequencies and sampling requirements, so that the measurement accuracy of the ground penetrating radar system is greatly improved.
And finally, carrying out data processing and SAR imaging according to the characteristics of data information acquired by the stepping frequency ground penetrating radar after the motion measurement of the ground penetrating radar system is finished, and completing the detection of an underground target.
The meter counter, the vector network analyzer and the SAR imaging algorithm are all integrated, so that the high-efficiency and flexible calculation and data processing of the device motion electromagnetic measurement system can be achieved, the convenience is provided for the ground penetrating radar to quickly acquire and process information, and finally the detection result is intuitively given.
The invention adopts a Synthetic Aperture Radar (SAR) imaging algorithm, and can generate high-resolution underground target images. By synthesizing the multi-echo signals, the definition and detail display of the image can be improved, and the accurate imaging and analysis of the underground target can be realized.
The invention can set different radio frequency parameters for the vector network analyzer through the computer 7, adopts pulse signals with different frequencies, analyzes the frequency change of the underground echo signals by utilizing the Doppler effect, and can detect underground targets in different depth ranges. The device has wide application prospect in the fields of geological exploration, resource detection and the like, and can detect deeper underground layers and more concealed targets.
According to the invention, through processing and analyzing the echo signals, the information of the targets can be extracted from the complex underground background, so that the accurate identification and analysis of different types of targets can be realized. This is very beneficial for resource exploration, military investigation, etc.
The method can process and analyze the acquired radar data in real time to perform SAR imaging, and provides quick and accurate target information. The real-time online analysis function can help a user to timely acquire information such as the target position, the shape characteristics and the like, and the working efficiency and the working accuracy are improved.
Example 2
The working method of the VNA-based step frequency ground penetrating radar system adopts the VNA-based step frequency ground penetrating radar system of the embodiment 1, and the flow is shown in figure 2, and is implemented specifically according to the following steps:
step 1, selecting a test field, selecting a straight line in the test field as a trolley measurement route, uniformly dividing the route, wherein each dividing point is a detection point;
Step2, connecting all components according to a VNA-based step frequency ground penetrating radar system;
Step 3, setting IP addresses of a computer 7 and a vector network analyzer 4, then ping the IP addresses of the computer 7 and the vector network analyzer 4 through ping commands of cmd of the computer, installing Keysight IO library suite and Keysight Command Expert two driving programs on the computer 7, realizing control of the vector network analyzer 4 through visa programming, reading data on a display screen of the meter 1 through Visual Studio software programming on the computer 7, realizing internal triggering, and enabling a stepping frequency ground penetrating radar system based on VNA to perform radar detection at equal intervals;
Step 4, sending an SCPI command through Visual Studio software programming on the computer 7 to set radio frequency parameters of the vector network analyzer 4, wherein the radio frequency parameters specifically include: the starting frequency, the cut-off frequency and the frequency point number, and the step frequency signal scanning process is shown in fig. 3; in the working process of the ground penetrating radar system, the computer can change the radio frequency parameters at any time according to actual conditions, so that the detection resolution and the maximum detectable depth are improved;
in a low loss homogeneous medium detection environment, the detection resolution is mainly related to the electromagnetic wave velocity of the subsurface medium and the frequency bandwidth of the radar signal.
The distance resolution Δd of a non-dispersive propagation medium can be expressed as:
Wherein N represents the number of frequency points, v is the speed of electromagnetic wave propagation in the medium, epsilon r is the relative dielectric constant, c represents the speed of light, B represents the bandwidth, Δf is the frequency interval between every two frequency points, namely (cut-off frequency-starting frequency)/(number of frequency points N-1), N coherent pulses form a step sweep frame, and the transmission process of the radar system after completing the transmission of a step sweep frame is a frequency scanning process. It can be seen that to increase the resolution of the detection (decrease Δd) there is a need to increase the frequency bandwidth B of the scanning signal.
The maximum detectable depth H of the step frequency radar is the product of the medium velocity v and the time window length W t:
H＝Wtv (2)
Since the ground penetrating radar system is measured in the frequency domain, the time response of which is obtained by IDFT (inverse discrete fourier transform), the maximum detectable distance of the ground penetrating radar is converted into a maximum time window length, i.e., a maximum ambiguity-free time length. I.e. if it is to be ensured that the maximum time length required after the IDFT is non-overlapping, it is necessary to ensure that its frequency sampling interval is sufficiently small. The maximum blur-free time length is controlled by the sweep frequency interval in the frequency domain, and the relationship is that:
the maximum detectable depth of the ground penetrating radar is therefore:
This distance is exactly determined by the blur free time of the IDFT and is therefore also called blur free distance. The maximum detectable depth is also derived from equation (2):
H＝(N-1)Δd (5)
the bandwidth (the difference between the cut-off frequency and the starting frequency) can be changed by changing the starting frequency and the cut-off frequency, and the larger the bandwidth is, the smaller the distance resolution is, and the resolution of detection is improved. Returning to formula 5, assuming that our bandwidth is unchanged, that is, the distance resolution is unchanged, we increase the frequency point number (that is, the point number divided over the entire frequency band), then the maximum detectable depth becomes larger; if N is unchanged, the change of the bandwidth can change the distance resolution and further change the maximum detection depth.
Step 5, judging whether the vector network analyzer 4 and the meter counter 1 are successfully set, if so, pushing the acquisition trolley 9 to start detection, and if not, returning to the step 3 to solve the fault;
The judgment whether the vector network analyzer 4 successfully sets is specifically as follows:
If the setting is successful, the numerical values of the set starting frequency, cut-off frequency and frequency point number are displayed in the vector network analyzer, after the setting is successful, the vector network analyzer 4 keeps continuously transmitting electromagnetic wave signals and receiving echo signals, if the setting is failed, the set numerical values are not displayed, and the step 3 is returned to solve the fault;
in step 5, whether the meter 1 is successfully set is specifically:
The computer 7 reads the data of the meter counter 1 in real time, if the reading is correct, the internal triggering is carried out every time the acquisition trolley 9 moves at an equal interval, namely, every time the acquisition trolley 9 moves at an equal interval, the computer 7 sends a data reading instruction to read echo signals received by the vector network analyzer 4; if the reading is incorrect or internal triggering is not carried out, returning to the step 3 to solve the fault;
Step 6, when the detection is performed, after the acquisition trolley 9 reaches each detection point of the planned route in step 1, the vector network analyzer 4 transmits electromagnetic wave signals, then the amplitude and the power of the signals generated by the vector network analyzer 4 are amplified by the power amplifier 5, so that the signals reach higher power level, then the electromagnetic wave signals are transmitted by the transmitting antenna 6, the electromagnetic wave penetrates through an underground medium to detect a target, then the receiving antenna 2 receives echo signals, then the echo signals received by the receiving antenna 2 amplify the voltage or the current of the received signals to a higher level by the low-noise power amplifier 3, and simultaneously the influence of noise is reduced as much as possible, so that the quality of the signals is improved, the signals are input into the vector network analyzer 4, and the computer 7 reads the echo signals received by the vector network analyzer 4;
Since energy attenuation in a lossy subsurface medium is huge and severe subsurface losses can reduce echo gain and limit maximum detection distance, a radar equation derived from wave equation can be used to describe the electromagnetic wave penetration capability in a lossy medium:
Wherein, Q rx/tx is the power ratio of the received signal to the transmitted signal of the probe vector network analyzer 4; η rηt is the antenna transceiving efficiency; g rGt is the antenna gain in the transmit-receive direction; g is the scattering gain of the target; sigma is the scattering cross-sectional area (m 2) of the target; lambda is the wavelength (m) of the electromagnetic wave in the medium; beta is the absorption coefficient of the medium; r is the distance (m) of the antenna to the target.
Electromagnetic waves radiated by the ground penetrating radar antenna penetrate through an underground medium to detect a target, and the radar antenna needs to be close to the ground surface as much as possible in order to ensure the detection effect. However, in order to adapt to the situations of actual uneven ground surface and the existence of obstacles and ensure that the distance between the radar and the target is as fixed as possible in the horizontal movement process of the radar, a method of fixing the distance between the antenna and the ground is generally adopted, and an electromagnetic propagation model of a ground penetrating radar system is shown in fig. 4.
Step 7, the computer 7 processes the echo signal data collected by each detection point, then carries out SAR imaging by using a back projection BP algorithm according to the processed echo signal data, and finally obtains a two-dimensional or three-dimensional image of the target;
The processing of the echo signal data collected by each detection point by the computer 7 specifically includes:
The echo signal data received by the computer 7, namely the real part and the imaginary part of the echo signal electric field, are added to obtain an electric field, and then the electric field is used in a subsequent SAR imaging algorithm;
SAR imaging by using a back projection BP algorithm according to the processed echo signal data specifically comprises the following steps:
Performing inverse Fourier transform on the electric field to obtain a one-dimensional range profile, performing pulse compression on the one-dimensional range profile, performing grid division on an imaging scene by utilizing up-sampling of the range profile, calculating the distance between the pulse at each detection point transmitted by the transmitting antenna 6 and a grid point, calculating double-pass time delay according to the distance, finding out data with the same time delay in the echo signal according to the time delay, namely, the grid point receives the echo signal at the detection point time, then multiplying the echo signal by phase compensation, performing back projection on the echo signal multiplied by the phase compensation to the grid, performing coherent superposition on the data from the last detection point to the grid point, traversing all detection points, and finally obtaining the SAR image, wherein the flow is shown in figure 5.
Example 3
Based on the embodiment 1 and the embodiment 2, specifically:
Step (1): the open field is selected as an experimental test field, and a metal ball with the diameter of 20cm is placed on the field to simulate a detection target buried in the field. The detection path of the collection trolley 9 is selected as a straight line, the linear motion distance of the collection trolley 9 is planned to be 2m, and the metal ball is placed at a position 1m away from the center of the path.
Step (2): preparing a testing instrument: the system comprises a mobile power supply, a computer, a power amplifier, a low-noise power amplifier, a vector network analyzer, a radio frequency line, a broadband horn antenna and a loading acquisition trolley 9 with a meter;
Step (3): connecting a vector network analyzer with a computer through a LAN port network cable, firstly, carrying out ping communication on the IP address of the computer and the IP address of the vector network analyzer, and then adopting two driving programs of Keysight IO library suite and Keysight Command Expert to realize control on the vector network analyzer in a visa programming mode;
Step (4): the meter counter is connected with the computer through a USB-to-serial port line, and data on a display screen of the meter counter is read and internal triggering is realized in a mode of realizing serial port communication through Visual Studio programming, so that the ground penetrating radar device can perform radar detection at equal intervals.
Step (4): connecting a receiving and transmitting antenna with a vector network analyzer; and selecting a radio frequency line with proper length, and simultaneously reducing the loss generated by overlong radio frequency line as far as possible according to the connection length requirement of the vector network analyzer to the antenna, so that the length of the radio frequency line used in the experiment is 1.6m. Two broadband horn antennas are selected to obtain quasi-single-station radar scattering data, the horn antennas are arranged on the chassis of the acquisition trolley 9, the antennas are a fixed distance away from the ground, and the antenna bracket is made of a material with good bearing performance.
Step (6): the SCPI commands are programmed by Visual Studio software on the computer to set the various parameters of the vector network analyzer, which in this embodiment are as follows: initial frequency: 1GHz, cut-off frequency: frequency point number 2 GHz: 201, measurement mode: s21, performing S21;
step (7): judging whether the setting of the parameters of the vector network analyzer is successful, and if the setting is successful, displaying the set numerical value in the vector network analyzer; if the setting fails, the setting value is not displayed, and the step (3) is returned to solve the failure;
Step (8): judging whether the reading of the meter counter of the acquisition trolley 9 is correct or not and whether the meter counter can trigger internally in the Visual Studio, and setting the acquisition trolley 9 to trigger once every 0.2 m; if the reading is correct, the internal triggering is performed every 0.2m of movement of the acquisition trolley 9, and a radar detection instruction is sent out and data is received; if the reading is incorrect or internal triggering is not carried out, returning to the step (4) to solve the fault;
Step (9): after the parameters of the vector network analyzer and the meter counter of the acquisition trolley 9 are successfully set, the acquisition trolley 9 is pushed to start detection;
Step (10): pushing the acquisition trolley 9 to move according to a preset path, combining the movement distance data read back by the meter counter of the acquisition trolley 9 to control the acquisition trolley 9 to trigger internally every time the acquisition trolley 9 moves at a fixed distance, sending a radar detection instruction and uploading the generated echo data to a computer;
Step (11): the computer receives the data uploaded by the stepping frequency ground penetrating radar and stores the data;
step (12): the movement of the collection trolley 9 is stopped after the preset path is completed, and the detection is finished.
Step (13): all data were imported into a radar algorithm and SAR imaging was performed using a Back Projection (BP) algorithm, the results of which are shown in fig. 6.
According to the experimental result diagram of fig. 6, the ground penetrating radar device can detect the information such as the position and the size of the metal ball. According to the preferred embodiment of the invention, the method can be used for accurately measuring the underground target, completing online data processing, and utilizing a Back Projection (BP) algorithm to perform SAR imaging, thereby providing a feasible scheme for real-time analysis.
Claims (7)
1. The working method of the stepping frequency ground penetrating radar system based on the VNA is characterized by comprising a collecting trolley (9), wherein a meter counter (1) is arranged on a wheel of the collecting trolley (9), the meter counter (1) is connected with a computer (7) through a USB (universal serial bus) to serial port line, the computer (7) is also connected with a vector network analyzer (4) through a network cable, an output port of the vector network analyzer (4) is connected with an input port of a power amplifier (5), an output port of the power amplifier (5) is connected with a transmitting antenna (6), an input port of the vector network analyzer (4) is also connected with an output port of a low-noise power amplifier (3), an input end of the low-noise power amplifier (3) is connected with a receiving antenna (2), and the receiving antenna (2), the low-noise power amplifier (3), the vector network analyzer (4), the transmitting antenna (6) and the computer (7) are placed on the collecting trolley (9) specifically:
Step 1, selecting a test field, selecting a straight line in the test field area as a measurement route of an acquisition trolley, uniformly dividing the route, and taking each dividing point as a detection point;
Step 2, setting control of a computer (7) on a vector network analyzer (4) and a meter counter (1), wherein the control is specifically as follows: connecting each component of the VNA-based stepping frequency ground penetrating radar system, setting IP addresses of a computer (7) and a vector network analyzer (4), then ping the computer (7) and the vector network analyzer (4) through ping commands of cmd of the computer to pass the IP addresses, installing Keysight IO library suite and Keysight Command Expert two driving programs on the computer (7) to control the vector network analyzer (4) in a visa programming mode, reading data on a display screen of the meter (1) in a serial port communication mode through Visual Studio software programming on the computer (7) and realizing internal triggering, enabling the VNA-based stepping frequency ground penetrating radar system to perform radar detection at equal intervals, and sending SCPI commands through Visual Studio software programming on the computer (7) to set radio frequency parameters of the vector network analyzer (4), wherein the radio frequency parameters specifically comprise: starting frequency, cut-off frequency and frequency point number;
judging whether the vector network analyzer (4) and the meter counter (1) are successfully set, if so, pushing the acquisition trolley (9) to start detection, and if not, returning to the setting step to solve the fault;
wherein, judge whether vector network analyzer (4) set up successfully specifically is:
If the setting is successful, the numerical values of the set starting frequency, cut-off frequency and frequency point number are displayed in the vector network analyzer, after the setting is successful, the vector network analyzer (4) keeps continuously transmitting electromagnetic wave signals and receiving echo signals, if the setting is failed, the set numerical values are not displayed, and then the fault is solved;
Judging whether the meter counter (1) is successfully set or not specifically comprises the following steps:
The computer (7) reads the data of the meter counter (1) in real time, if the data is read correctly, the internal triggering is carried out every time the acquisition trolley (9) moves at an equal interval, namely, every time the acquisition trolley (9) moves at an equal interval, the computer (7) sends a data reading instruction, and echo signals received by the vector network analyzer (4) are read; if the reading is incorrect or internal triggering is not carried out, returning to the setting step to solve the fault;
Step 3, when detecting, after the acquisition trolley (9) reaches each detection point of the planned route in step 1, transmitting electromagnetic wave signals and receiving echo signals;
And 4, processing echo signal data collected by each detection point by a computer (7), and then carrying out SAR imaging by using a back projection BP algorithm according to the processed echo signal data to finally obtain a two-dimensional or three-dimensional image of the target.
2. The working method of the VNA-based step frequency ground penetrating radar system according to claim 1, wherein the collection trolley (9) is provided with two layers, the computer (7) is placed on an upper layer of the collection trolley (9), the receiving antenna (2), the low noise power amplifier (3), the vector network analyzer (4), the power amplifier (5) and the transmitting antenna (6) are all placed on a lower layer, the upper layer of the collection trolley (9) is further provided with a mobile power supply (8), and the low noise power amplifier (3), the vector network analyzer (4), the power amplifier (5) and the computer (7) are all connected with the mobile power supply (8) through cables.
3. The method of operating a VNA-based step frequency ground penetrating radar system according to claim 2, characterized in that the vector network analyzer (4) and the computer (7) are connected via a LAN port.
4. A method of operating a VNA based step frequency ground penetrating radar system according to claim 3, characterized in that the power amplifier (5) is connected to the vector network analyzer (4) and the transmitting antenna (6) by radio frequency lines, and the low noise power amplifier is connected to the receiving antenna (2) and the vector network analyzer (4) by radio frequency lines.
5. The method for operating a VNA-based step frequency ground penetrating radar system according to claim 1, wherein the step 3 is specifically:
When in detection, after the acquisition trolley (9) reaches each detection point of the planned route in the step 1, the vector network analyzer (4) transmits electromagnetic wave signals, then the amplitude and the power of signals generated by the vector network analyzer (4) are amplified by the power amplifier (5), the electromagnetic wave signals are transmitted by the transmitting antenna (6), the electromagnetic wave detects targets through underground media, then the receiving antenna (2) receives echo signals, then the echo signals received by the receiving antenna (2) amplify the voltage or the current of the received signals to a higher level by the low-noise power amplifier (3) and then are input into the vector network analyzer (4), and the computer (7) reads the echo signals received by the vector network analyzer (4).
6. The method for operating the VNA-based step frequency ground penetrating radar system according to claim 5, wherein the processing of the echo signal data collected by each probe point by the computer (7) in step 4 is specifically:
The computer (7) receives the echo signal data, namely the real part and the imaginary part of an echo signal electric field, of the vector network analyzer (4), adds the real part and the imaginary part of the echo signal electric field to obtain an electric field, and then uses the electric field in a subsequent SAR imaging algorithm.
7. The method for operating the VNA-based step frequency ground penetrating radar system according to claim 6, wherein the step 4 of performing SAR imaging by using a back projection BP algorithm according to the processed echo signal data specifically includes:
Performing inverse Fourier transform on the electric field to obtain a one-dimensional range profile, performing pulse compression on the one-dimensional range profile, performing grid division on an imaging scene by utilizing up-sampling of the range profile, calculating the distance between each detection point time pulse transmitted by a transmitting antenna (6) and a grid point, calculating double-pass time delay according to the distance, finding out data with the same time delay in an echo signal according to the time delay, namely, the grid point receives the echo signal at the detection point time, then multiplying the echo signal by phase compensation, performing back projection on the echo signal multiplied by the phase compensation to the grid, performing coherent superposition on the data of the grid point of the last detection point, traversing all detection points, and finally obtaining the SAR image.
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