An anti-jamming radar antenna and an anti-jamming low-frequency ground penetrating radar system

Abstract

This invention provides an anti-jamming radar antenna and an anti-jamming low-frequency ground-penetrating radar system. The radar antenna includes a metal back cavity with a V-shaped cavity structure, and the anti-jamming radar antenna is positioned directly below the metal back cavity. The anti-jamming radar antenna and anti-jamming low-frequency ground-penetrating radar system provided by this invention overcome the problems of low anti-jamming capability, shallow detection depth, and inconvenient exploration associated with existing low-frequency ground-penetrating radars used in urban applications.

Description

Technical Field

[0001] This invention relates to the field of ground penetrating radar technology, and in particular to an anti-jamming radar antenna and an anti-jamming low-frequency ground penetrating radar system. Background Technology

[0002] Since the 16th National Congress of the Communist Party of China, my country's urbanization has developed rapidly. With the rapid advancement of urbanization, the demand for urban underground space development is constantly increasing, and developing underground space will become an important national development strategy in the next stage. Advanced detection and monitoring technologies and equipment are key to leading the development of urban underground space. Currently, commonly used urban underground space detection technologies, in addition to drilling, include ground-penetrating radar (GPR), shallow seismic surveys, high-density electrical resistivity tomography (EDT), shallow transient electromagnetic methods (TEM), inter-well CT, and micro-motion geophysical methods. However, for high-resolution detection of shallow geological layers in urban underground space, especially for the detection of shallow geological stratification within 30-50 meters, underground bunkers, underground cavities, and karst caves, GPR technology has unique advantages, not only in its high resolution but also in its high detection efficiency and good detection results.

[0003] Existing conventional ground-penetrating radar products, especially low-frequency ground-penetrating radars, all use unshielded plate or rope structures without rearward shielding of the antennas. They generally adopt a separate transmit and receive working mode. In order to quickly and effectively acquire data, it is necessary to synchronize the transmitted and received signals between the receiving and transmitting antennas. Currently, cables or optical fibers are mostly used to synchronize the signals, and then the host is connected through a cable to send commands and transmit data.

[0004] Existing conventional ground-penetrating radar (GPR) products, especially low-frequency unshielded GPR, are not specifically designed for urban underground space detection and have several shortcomings when applied to this application. First, conventional low-frequency GPR uses unshielded plate or rope structures without rearward shielding of the antenna. While radiating electromagnetic waves underground, the radar antenna also radiates into the air. When these airborne electromagnetic waves encounter targets on the urban surface such as buildings, power lines, utility poles, and bridges, they are reflected / scattered. These reflected / scattered electromagnetic waves intertwine with the reflected / scattered waves from underground geological targets, creating interference and generating false information. Second, conventional GPR generally employs a separate transmit and receive mode. To achieve rapid and effective data acquisition, synchronization of the transmitted and received signals between the receiving and transmitting antennas is required. Currently, this is often achieved using cables or fiber optic connections. Commands are then sent and data is transmitted via cables to the main unit. The cable connections between the various components of the GPR increase the complexity and difficulty of system operation, significantly limiting the convenience and flexibility of the GPR. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an anti-interference radar antenna and an anti-interference low-frequency ground penetrating radar system, which overcomes the problems of low anti-interference capability, shallow detection depth and inconvenience of exploration of existing low-frequency ground penetrating radar when used in cities.

[0006] To solve the above-mentioned technical problems, the present invention provides an anti-jamming radar antenna, the anti-jamming radar antenna comprising: a metal back cavity, the metal back cavity having a V-shaped cavity structure, and the anti-jamming radar antenna being disposed directly below the metal back cavity.

[0007] In some embodiments, the anti-jamming radar antenna has an antenna arm with a butterfly antenna structure, and the end of the antenna arm is provided with a semi-elliptical slot structure.

[0008] In some implementations, four resistors are also provided in the sharpened portion of the semi-elliptical slotted structure.

[0009] In some embodiments, a rectangular metal surface is located in the middle of the top surface of the V-shaped cavity.

[0010] In some implementations, the rectangular metal surface is at a certain distance from the antenna surface.

[0011] In some embodiments, the two sides of the V-shaped cavity are two symmetrically arranged inclined planes, which connect the rectangular metal surface and the side arm of the back cavity.

[0012] Furthermore, the present invention also provides an anti-jamming low-frequency ground-penetrating radar system, the system comprising: an anti-jamming radar antenna, including a transmitting antenna for transmitting ultra-wideband radar pulse signals and a receiving antenna for receiving ultra-wideband radar echo signals, wherein both the transmitting and receiving antennas are anti-jamming radar antennas as described above; a large-amplitude pulse transmitter connected to the transmitting antenna for generating periodic ultra-wideband radar pulse signals, wherein the ultra-wideband radar pulse signals have large amplitude characteristics; and a wireless synchronization receiver connected to the receiving antenna for sampling the ultra-wideband radar echo signals received by the receiving antenna to obtain high-fidelity echo signals.

[0013] In some implementations, the amplitude of the ultra-wideband radar pulse signal is greater than 3000V.

[0014] In some embodiments, the wireless synchronization receiver includes: a limiting protection circuit for limiting the echo signal; a time gain circuit connected to the limiting protection circuit for variable gain amplification of the limited signal; a first analog-to-digital conversion circuit connected to the time gain circuit for analog-to-digital conversion of the amplified signal; a signal buffer module connected to the first analog-to-digital conversion circuit for buffering the signal processed by the first analog-to-digital conversion circuit; a fixed gain circuit connected to the limiting protection circuit for fixed gain amplification of the limited signal; a second analog-to-digital conversion circuit connected to the fixed gain circuit for analog-to-digital conversion of the fixed gain signal; and a synchronization module connected to the second analog-to-digital conversion circuit for transmitting internal data according to internally set trigger conditions.

[0015] In some implementations, the system further includes: a PC host computer connected to the wireless synchronization receiver via a network interface, used to communicate with the wireless synchronization receiver, obtain the echo signal uploaded by the wireless synchronization receiver, process and analyze the echo signal, and display the processing and analysis results. The PC host computer communicates with the wireless synchronization receiver via LAN or WiFi.

[0016] With this design, the present invention has at least the following advantages:

[0017] 1. Both the transmitting and receiving antennas have V-shaped rearward shielding housings, which can effectively shield various interference signals from the ground when working in urban environments;

[0018] 2. The transmitter's pulse output amplitude is greater than 3000V, increasing the detection depth;

[0019] 3. Wireless synchronization between the transmitting and receiving units is achieved through high-speed real-time sampling, which improves the flexibility of equipment operation and eliminates the need for synchronization cables between transmission and reception;

[0020] 4. The receiver and the host PC can communicate via either a wired LAN connection or a Wi-Fi connection to issue commands and upload data, which improves the convenience of equipment operation. Attached Figure Description

[0021] The above is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1 This is a schematic diagram of the anti-interference low-frequency ground-penetrating radar system provided in an embodiment of the present invention;

[0023] Figure 2 It is a 3D view of the anti-jamming radar antenna and its shielding housing;

[0024] Figure 3 This is a flowchart of the antenna synchronization process of a ground-penetrating radar system. Detailed Implementation

[0025] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] In an exemplary embodiment of the present invention, an anti-jamming radar antenna and an anti-jamming low-frequency ground-penetrating radar system are provided. Figure 1 This is a schematic diagram of the anti-interference low-frequency ground-penetrating radar system applicable to urban underground space exploration according to an embodiment of the present invention. Figure 2 It is an anti-jamming radar antenna and shielding housing. Figure 3 This is a diagram illustrating the wireless synchronization process of a ground-penetrating radar system.

[0027] Please refer to Figure 1 , Figure 2 , Figure 3 This embodiment of an anti-interference low-frequency ground-penetrating radar system suitable for urban underground space detection includes: an anti-interference radar antenna and shielding housing, mainly used for transmitting and receiving electromagnetic pulse signals and shielding back interference signals; a large-amplitude pulse transmitter, mainly used for generating periodic pulse signals; a wireless synchronization receiver, mainly used for high-fidelity sampling of radar echo signals, buffering and sending them to a PC host computer; and a PC host computer, mainly used for radar control and radar data acquisition, storage and display functions.

[0028] The following sections provide a detailed description of each component of the anti-interference low-frequency ground-penetrating radar system applicable to urban underground space exploration in this embodiment.

[0029] (1) Anti-interference radar antenna and shielding housing

[0030] In this embodiment, the antenna arm used is a deformable dish antenna structure 101, such as... Figure 2 As shown, both the transmitting and receiving antennas employ this type of antenna structure, with the end slotted structure as follows: Figure 2 As shown, a semi-elliptical slotted structure is used, with four resistors applied to the sharpened portions formed by the slotted structure to absorb reflected current and suppress tailing oscillations. Specifically, the sharpened portions are the pointed tips formed between different slotted structures.

[0031] Because planar butterfly antennas exhibit omnidirectional radiation characteristics similar to dipoles, a metallic cavity is needed to suppress back radiation and shield back interference signals. In this embodiment, a V-shaped cavity structure 102 is used as the metallic cavity. Figure 2As shown, the ultra-wideband butterfly transmitting and receiving antennas are mounted directly below the back cavity. In the top surface of the V-shaped cavity 102, there is a rectangular metal surface in the middle, positioned at a certain distance from the antenna surface. Two symmetrical inclined surfaces connect the rectangular metal surface to the side arms of the back cavity. The V-shaped cavity 102 significantly reduces the voltage standing wave ratio in the low-frequency band, improving the time-domain waveform fidelity. The V-shaped cavity 102 design reduces the overall antenna size while improving its radiation performance, and it is also less prone to deformation and has greater rigidity.

[0032] By optimizing the antenna arm type, end slot structure, metal back cavity shape and size, loading resistance and feeding interval, the low-frequency ground penetrating radar antenna achieves rearward shielding, efficient pulse signal transmission and high-sensitivity reception, thereby enabling effective detection of deep geological targets in urban environments.

[0033] (2) Large amplitude pulse transmitter

[0034] This embodiment is applicable to an anti-interference low-frequency ground-penetrating radar system for urban underground space exploration. The large-amplitude pulse generation circuit is an external trigger excitation circuit, which is triggered by the transmission trigger control module to generate a pair of symmetrical positive and negative pulse signals with an amplitude of ±1500V, a pulse base width of 15-200ns, and a repetition frequency of 10kHz.

[0035] Please refer to Figure 1 The transmission channel 200 and the large-amplitude pulse transmitter include: a transmission trigger control module 201, a trigger drive circuit 202, a pulse generation circuit 203, and a high-voltage circuit 204. The transmission trigger control module 201 connects to the receiver via Bluetooth, receives a start command from the receiver, and initiates pulse signal generation. The transmission trigger control module 201 is connected to the trigger drive circuit 202, the trigger drive circuit 202 is connected to the pulse generation circuit 203, the high-voltage circuit 204 is connected to the pulse generation circuit 203, and the pulse generation circuit 203 is finally connected to the transmitting antenna to radiate the generated pulse signal.

[0036] Alternatively, the large-amplitude pulse transmitter circuit can be omitted, and a pulse transmitter that meets the above conditions can be provided directly from an external source, which can also achieve the present invention.

[0037] (3) Wireless synchronization receiver

[0038] This embodiment describes an anti-interference low-frequency ground-penetrating radar system suitable for urban underground space detection. The wireless synchronization receiver processes the radar echo signal received by the receiving antenna at the front end and then sends it to an RF analog-to-digital converter for real-time sampling. The system determines when to start uploading the collected data based on a trigger voltage. This wireless synchronization receiver features 16-bit resolution, a maximum sampling rate of 1 GSPS, an input bandwidth of 1.2 GHz, a high signal-to-noise ratio, and a local noise level as low as -159 dBFS / Hz. The time-varying gain circuit at the front end improves the system's detection sensitivity, thereby increasing the system's dynamic range.

[0039] Please refer to Figure 1 The receiving channel 300 includes a wireless synchronization receiver comprising: a limiting protection circuit 301, a time-varying gain circuit 302, a first analog-to-digital converter (ADC) 303, a signal buffer module 304, a fixed gain circuit 305, a second ADC 306, and a synchronization module 307. The receiving antenna is connected to the limiting protection circuit 301, which is connected to both the time-varying gain circuit 302 and the fixed gain circuit 305. The time-varying gain circuit 302 is connected to the first ADC 303, and the fixed gain circuit 305 is connected to the second ADC 306. The first ADC 303 is connected to the signal buffer module 304 within the FPGA, and the second ADC 306 is connected to the synchronization module 307 within the FPGA. By setting appropriate trigger conditions within the synchronization module 307, the data in the signal buffer module 304 is transmitted to a PC via the communication module 401 for storage, display, and processing.

[0040] (4) PC host computer

[0041] In this embodiment, an anti-interference low-frequency ground-penetrating radar system suitable for urban underground space detection is described. The PC host computer stores and displays the radar echo signal received by the wireless receiver from the receiving channel 300 and the data sent up through the transmitting channel 400, and issues various control commands to control the operation of the ground-penetrating radar.

[0042] Please refer to Figure 1 The data transmission channel 400 includes a communication module 401 and a PC host computer 402. The communication module 401 and the PC host computer 402 communicate via LAN / WIFI in a wired / wireless manner using the TCP / IP protocol. The PC host computer 402 acts as the TCP / IP host, and the ground-penetrating radar acts as the TCP / IP client. Communication between the ground-penetrating radar and the PC host computer can be selected via either wired (LAN) or wireless (WIFI) methods, allowing for easy switching between the two. This ensures high-speed and reliable communication while increasing the flexibility of equipment operation, enabling the equipment to adapt to harsher working environments.

[0043] The working process of an anti-interference low-frequency ground-penetrating radar system suitable for urban underground space detection in this embodiment is as follows:

[0044] Step 1: After setting the parameters in the data acquisition software within the PC host computer 402, the parameters and start command are sent to the receiver via communication channel 400. The receiver communicates with the transmitter via Bluetooth, sends a start command to the transmission trigger control module 201, and sets the corresponding transmission repetition frequency. Different transmission frequencies are configured according to different antennas. The trigger drive circuit 202 receives the TTL trigger signal from the transmission trigger control module. This TTL trigger signal is a square wave signal with an amplitude of 3.3V, a pulse width of 200ns, and a repetition frequency of 10kHz to 100kHz. The trigger drive circuit 202 drives this trigger signal to obtain a pulse with a smaller leading edge. The trigger signal is sent to the pulse generation circuit 203. The core of the pulse generation circuit 203 is a trigger-type spark switch, which generates positive and negative high voltage (±2500V) through the high voltage circuit 204. When the trigger drive circuit 202 sends the shaped trigger signal, the trigger spark switch is broken down instantly, generating a pair of balanced Gaussian positive and negative pulse signals. This signal is directly sent to the dipole transmitting antenna 101 as a feed signal, and the electromagnetic pulse signal is radiated out through the antenna. While radiating the electromagnetic pulse signal outward, the V-shaped shielding cavity 102 shields the electromagnetic pulse signal radiated backward by the dipole transmitting antenna 101, thereby avoiding the introduction of some ground interference information.

[0045] Step Two: Please refer to Figure 3The emitted electromagnetic pulse signal propagates and reflects underground before being received by the receiving antenna 101. The receiving antenna 101 first sends the received echo signal to the amplitude limiting protection circuit 301 for amplitude limitation to prevent the subsequent circuits from being burned out due to excessively strong direct waves, thus providing input protection. The signal after passing through the amplitude limiting protection circuit 301 is sampled in two paths: one as a synchronization signal and the other as a data signal. The data signal is first sent to the time-varying gain circuit 302 for amplification. The time-varying gain circuit 302 consists of a 6-bit digitally controlled attenuator, a low-pass filter, and an amplifier. The cascaded digitally controlled attenuator and amplifier effectively realize the function of a variable gain amplifier. This circuit not only improves the signal-to-noise ratio of the receiver but also increases the dynamic range of the receiver. The total gain of the entire receiver's front-end signal link is between -8 and 42 dB, and the operating frequency range is DC to 1.5 GHz. The signal after the time-varying gain is sent to the first analog-to-digital converter 30. 3. Analog-to-digital conversion is performed. The core of this analog-to-digital conversion circuit is a high-speed radio frequency signal analog-to-digital converter chip with 16-bit resolution, an input bandwidth of 1.2GHz, and a sampling rate of up to 1GSPS, which fully meets the data sampling requirements of low-frequency ground-penetrating radar (5MHz~50MHz). The converted digital data is sent to the signal buffer module inside the FPGA. This module contains buffered data, and 16-bit × 8192 dual-port RAM space is allocated for it using the abundant on-chip resources of the FPGA. The data is stored cyclically from top to bottom to ensure data continuity. The signal sampled as a synchronization signal is first sent to the fixed gain circuit 305 for fixed gain to ensure the consistency of the triggering conditions, and then sent to the second analog-to-digital conversion circuit 306 for signal sampling. The core of this analog-to-digital conversion circuit is the same as that of the first analog-to-digital conversion circuit 303, which is a high-speed radio frequency signal analog-to-digital converter chip with 16-bit resolution and an input bandwidth of 1.2GHz.With a sampling rate of up to 1 GSPS at 2 GHz, the sampling consistency is fully guaranteed. The converted digitized data is sent to the synchronization module 307 inside the FPGA. The data buffered by the synchronization module 307 is not stored in RAM, but is stored as a temporary variable. The acquired data is continuously compared with the set threshold Sref. Once the acquired data Sn > Sref, the recording enable signal RecEn flag of the signal buffer module in the sampling path is immediately enabled, and the data at this time is recorded at position n in RAM. This ensures that the signal is within one repetition frequency period. Stable triggering is required, meaning only direct radar waves can trigger it. Sref should be set as small as possible. Starting from the enable position n recorded in RAM, address t bits backwards. The value of t can be set by the data acquisition software via parameter sending. The purpose of this operation is to send the complete direct wave information as the initial position reference signal for the radar echo. Afterwards, continue storing data in RAM until the stored data reaches the set number of sampling points N (N≤8192). Then, stop writing data to RAM, latch the data recorded in RAM, and simultaneously start the data transmission enable signal SendEn to initiate data transmission.

[0046] Step 3: After data transmission is initiated, the data transmission pointer of the communication module 401 is set to bit nt. N data points starting from bit nt in the RAM are transmitted to the PC host computer 402 via the network chip for storage and display, according to the number of sampling points sent by the PC host computer 402. Once the N data transmissions are complete, data storage is restarted, and the radar echo signal continues to be sequentially stored in the RAM from the bit following the last recorded position. When communicating via network, either wired network cable or wireless WIFI can be selected, thus improving the ease of use of the device. Wired and wireless methods... The switching of modes is operated by turning the power on and off of the wireless communication module. When the power of the wireless communication module is turned on through an external switch, the FPGA determines and selects the wireless communication module as the communication link. Conversely, if the wireless communication module is not powered on, the FPGA determines and selects the wired communication module as the communication link through a flag. After the receiver successfully communicates with the PC host computer 402, the data acquisition software in the PC host computer 402 issues radar control commands through the network and sets parameters such as dielectric constant, number of sampling points, sampling frequency, gain mode, gain value, trigger level, time delay, accumulation count, measurement accuracy, and triggering method.

[0047] Step 4: After sending and setting the parameters, start the device to collect data, and record the received data in the PC host computer 402 via wired or wireless means. The whole process completes the working process of the anti-interference low-frequency ground penetrating radar system suitable for urban underground space detection in this embodiment.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, or alterations made by those skilled in the art using the disclosed technical content shall fall within the protection scope of the present invention.

Claims

1. An anti-interference low-frequency ground-penetrating radar system, characterized in that, include: An anti-jamming radar antenna includes a transmitting antenna for transmitting ultra-wideband radar pulse signals and a receiving antenna for receiving ultra-wideband radar echo signals, both of which are anti-jamming radar antennas. An anti-jamming radar antenna includes: a metal back cavity, the metal back cavity having a V-shaped cavity structure, and the anti-jamming radar antenna being disposed directly below the metal back cavity; The anti-jamming radar antenna has an antenna arm with a butterfly antenna structure, and the two sides of the anti-jamming radar antenna are formed by straight lines with corners; and the end of the antenna arm is provided with a semi-elliptical slot structure, which includes three semi-elliptical slots. In the sharpened section of the semi-elliptical slotted structure, four resistors are also provided; In the top surface of the V-shaped cavity, there is a rectangular metal surface in the middle part; The rectangular metal surface is at a certain distance from the antenna surface; The two sides of the V-shaped cavity are two symmetrically arranged inclined surfaces, which connect the rectangular metal surface and the side wall of the back cavity. A high-amplitude pulse transmitter, connected to a transmitting antenna, is used to generate periodic ultra-wideband radar pulse signals, which have high amplitude characteristics. The high-amplitude pulse transmitter includes: a transmission trigger control module, a trigger drive circuit, a pulse generation circuit, and a high-voltage circuit. The transmission trigger control module is connected to the receiver via Bluetooth, receives the start command from the receiver, and initiates the generation of the pulse signal. The transmission trigger control module is connected to the trigger drive circuit, the trigger drive circuit is connected to the pulse generation circuit, the high-voltage circuit is connected to the pulse generation circuit, and the pulse generation circuit is finally connected to the transmitting antenna to radiate the generated pulse signal. The amplitude of the ultra-wideband radar pulse signal is greater than 3000V; A wireless synchronization receiver, connected to a receiving antenna, is used to sample the ultra-wideband radar echo signal received by the receiving antenna to obtain a high-fidelity echo signal. The wireless synchronization receiver includes: Amplitude limiting protection circuit, used to limit the echo signal; The time gain circuit, connected to the limiting protection circuit, is used to amplify the limiting signal with variable gain. The first analog-to-digital converter circuit is connected to the time gain circuit and is used to perform analog-to-digital conversion on the amplified signal. A signal buffer module is connected to the first analog-to-digital converter circuit and is used to buffer the signal processed by the first analog-to-digital converter circuit. A fixed-gain circuit, connected to a limiting protection circuit, is used to fix the gain of the limiting signal; The second analog-to-digital converter circuit is connected to the fixed-gain circuit and is used to perform analog-to-digital conversion on the signal after fixed gain. The synchronization module, connected to the second analog-to-digital converter circuit, is used to send internal data according to the internally set trigger conditions; The data obtained by the synchronization module buffer is not stored in RAM, but is stored as a temporary variable. The acquired data is continuously compared with the set threshold Sref. Once the acquired data Sn>Sref, the recording enable signal RecEn flag of the signal buffer module in the sampling path is immediately enabled, and the data at this time is stored in the middle position n of RAM. In order to ensure that the signal can be stably triggered within one repetition frequency period, that is, only the direct radar wave can be triggered.

2. The anti-interference low-frequency ground-penetrating radar system according to claim 1, characterized in that, Also includes: The PC host computer connects to the wireless synchronization receiver via a network interface to communicate with the wireless synchronization receiver, obtain the echo signal uploaded by the wireless synchronization receiver, process and analyze the echo signal, and display the processing and analysis results. The PC host computer communicates with the wireless synchronization receiver via LAN or WiFi.

Images