A clutter suppression method for UAV ground penetrating radar and a transceiver array device

Abstract

The present invention discloses a clutter suppression method for an unmanned aerial vehicle ground-penetrating radar and a transceiver array device, which belongs to the technical field of ground-penetrating radar. The device of the present application includes a single receiving antenna, multiple groups of transmitting antennas and a signal source. All antennas are homogeneous and all antenna ports are located at the same horizontal height. The signal source can simultaneously provide two excitation signals of the same frequency, equal amplitude and opposite phase to the transmitting antenna; each group of transceiver antennas includes two transmitting antennas and a receiving antenna located at the midpoint of the line connecting the feeding points of the two transmitting antennas, and the feeding ports of the transceiver antennas are located on a straight line. The receiving antenna is installed on a telescopic turntable, and the axial rotation direction of the receiving antenna can be achieved by adjusting the telescopic turntable to ensure that when multiple groups of transmitting antennas share the same receiving antenna, the polarization directions of the transceiver antennas are consistent. Based on the device, the present application realizes a clutter suppression method for underground target echo signals. The present application solves the problem that underground target echo signals are easily submerged in strong clutter and difficult to be effectively extracted.

Description

Technical Field

[0001] The present application relates to the technical field of underground target detection by UAV ground-penetrating radar, and in particular to a clutter suppression method and a transceiver array device for UAV ground-penetrating radar. Background Art

[0002] UAV ground penetrating radar is the product of the combination of traditional ground penetrating radar and UAV. With the rapid development of UAV technology and the realization of miniaturization of ground penetrating radar, the foundation has been laid for the development of UAV ground penetrating radar non-destructive testing technology.

[0003] Ground-penetrating radar (GPR) is a geophysical tool that uses very high frequency (VHF) (30-300 MHz) and ultra-high frequency (UHF) (300-3000 MHz) electromagnetic waves to detect underground structures. GPR uses a transmitting antenna to radiate electromagnetic waves into the ground. When these waves propagate through the ground, they are reflected by interfaces with differing electrical parameters (dielectric constant, conductivity, and magnetic permeability). The partially reflected signals received by the receiving antenna provide information about the underground structure and target properties. GPR can be deployed in a variety of ways, depending on the application requirements and exploration scenarios. Traditional GPR is primarily carried on the ground, typically in handheld, push-type, or vehicle-mounted modes for non-destructive testing or detection. The transmitting and receiving antennas are typically placed close to the ground, or the antenna ports are positioned at a certain height (typically less than 1 meter) above the ground. Ground-mounted ground-penetrating radar is difficult or impossible to implement in environments with complex terrain or many obstacles (such as mountains, glaciers, swamps, deserts or large buildings, etc.) and in conditions where surveyors cannot reach. In addition, it also has certain limitations for the needs of rapid detection or inspection of large areas or long distances.

[0004] With the development of drone and ground-penetrating radar (GPR) technology, UAV GPR has emerged as an emerging technology, gradually meeting human needs for exploring complex terrain. While the hardware technology for UAV GPR is gradually maturing, significant challenges remain in signal processing. Clutter suppression and weak signal extraction are two key technical issues in UAV GPR data processing, directly impacting the detection capability, accuracy, and identification of underground targets. Clutter refers to interference components in the UAV GPR echo signal that are unrelated to the target signal. These include surface reflections, coupling signals between transmitting and receiving antennas, and electromagnetic interference. The presence of clutter can significantly reduce the system's detection performance, target resolution, and the reliability of data interpretation. During the operation of a UAV ground-penetrating radar (GPR), the transmitting and receiving antenna ports onboard the aircraft are typically at a certain height above the ground (usually greater than 1 meter), at which point the ground-reflected wave signal is strong. The transmitting antenna radiates electromagnetic wave signals from the feed end. During propagation, this signal is gradually coupled to the receiving antenna through the air medium, forming a significant spatial coupling effect and a high coupled signal strength. Furthermore, because the surface soil, gravel, and other materials are non-uniform loss media, some electromagnetic waves entering the ground are scattered. The effective echo signal of the underground detection target is weak and easily submerged by the direct-coupled wave and the ground-reflected wave. Therefore, exploring how to suppress clutter and extract the effective echo signal of the underground target is particularly important for the detection and identification of underground targets by UAV GPR.

[0005] Clutter suppression can improve the signal-to-noise ratio (SNR), reduce false alarms and missed alarms, enhance target resolution, adapt to complex environments, improve data processing efficiency, provide accurate target positioning, enhance system robustness, support the implementation of high-order algorithms, and reduce decision-making risks. Currently, clutter suppression is mainly achieved through signal enhancement technology, time-frequency analysis, noise suppression, machine learning, and deep learning. However, these clutter suppression methods primarily rely on signal processing to post-process the collected data.

[0006] However, there are few studies on pre-data acquisition clutter suppression schemes achieved through physical layer optimization and hardware preprocessing. For example, in a triangular array ground-penetrating radar antenna device, a barrel-shaped shielding shell is used to shield the coupling between the four antenna groups, and the signal-to-noise ratio is improved by delay superposition and summation to enhance the signal strength in the target area. However, this method is sensitive to delay accuracy, has poor adaptability to non-stationary signals, and the computational complexity is inconsistent with real-time performance, and there are problems such as residual signal aliasing. Although this solution discloses a means of suppressing clutter before data acquisition, it is more suitable for scenarios with low requirements for signal integrity and real-time performance; the mainstream post-acquisition clutter suppression scheme relies on algorithm flexibility and is suitable for complex environments that require dynamic adjustment, but it requires a balance between computational cost and performance loss, and it is difficult to meet the actual needs of effective extraction of UAV ground-penetrating radar echo signals.‌ Summary of the Invention

[0007] The present application provides a clutter suppression method for UAV ground-penetrating radar and a transceiver array device, aiming to solve the problem that ground reflected waves and air-coupled waves in the echo signals of existing UAV ground-penetrating radar are difficult to effectively suppress, and to provide a new solution for the effective extraction of weak echo signals of underground targets.

[0008] On one hand, the present application provides a UAV ground penetrating radar transceiver array device, which includes a transceiver antenna array, a pulse signal source, and an antenna rack;

[0009] The antenna mount has a cross-shaped structure, with a frustoconical box at its center. The sides of the frustoconical box are provided with multiple movably connected hollow arms of equal length. The angle between adjacent arms is adjustable, and a transmitting antenna is fixed to the end of each arm. The center of the frustoconical box is a telescopic turntable with adjustable length. A coaxial cable connector is provided at the center of the telescopic turntable for connecting to the receiving antenna. That is, the present application can achieve a hard connection with the receiving antenna through the coaxial cable connector at the center of the telescopic turntable. The height of the receiving antenna can be adjusted by adjusting the telescopic scale of the telescopic turntable, and the port orientation of the receiving antenna can be adjusted by adjusting the axial rotation direction of the telescopic turntable.

[0010] The transceiver antenna array includes multiple groups of reciprocal transceiver antennas, each group of which includes two transmitting antennas and one receiving antenna, and each group of transceiver antennas shares the same receiving antenna. The two transmitting antennas of each group of transceiver antennas are deployed at the ends of the two supporting arms of the antenna bracket, and together with the receiving antenna deployed at the center of the telescopic turntable, form a transceiver antenna group.

[0011] The pulse signal source is used to simultaneously feed excitation signals with the same waveform characteristics but opposite phases to two transmitting antennas in the same group;

[0012] When in working state, the position of the support arm is adjusted so that the receiving antenna of the same group is located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group, and the three antennas in the same group are arranged in a straight line; by adjusting the axial rotation direction of the telescopic turntable, the receiving port and the excitation port of each group of transceiver antennas are in a straight line, and by adjusting the telescopic scale of the telescopic turntable, the antenna ports of the two transmitting antennas and the receiving antenna in the same group are at the same horizontal height.

[0013] Furthermore, the support arm can also be set as a through arm passing through the truncated cone-shaped box body, and the through arm is movably connected at the center position of the truncated cone-shaped box body through the center point (the angle between adjacent support arms is adjustable), and then the two transmitting antennas of the same group of transmitting and receiving antennas are deployed at both ends of the same support arm, so that the three antennas of the same group are arranged in a line; thereby directly making the receiving antenna located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas of the same group, and eliminating the need to adjust the support arm position in the working state, so as to achieve a structure in which the three antennas are arranged in a line. At this time, the corresponding UAV ground-penetrating radar clutter suppression method and transceiver array device are specifically as follows: the antenna bracket has a cross-type structure, the center position of which is the truncated cone-shaped box body, and the side of the truncated cone-shaped box body is provided with a plurality of support arms with a hollow structure passing through the truncated cone-shaped box body, and the support arms are movably connected at the center position of the truncated cone-shaped box body through their center points; The transceiver antenna array includes multiple groups of reciprocal transceiver antennas, each group of transceiver antennas includes two transmitting antennas and one receiving antenna, and each group of transceiver antennas shares the same receiving antenna; wherein, the two transmitting antennas of each group of transmitting antennas are deployed at the two ends of the same arm of the antenna bracket, and constitute a group of transceiver antennas with the receiving antenna deployed at the center of the telescopic turntable; and the distance between the two transmitting antennas and the receiving antenna in the same group is equal; the pulse signal source is used to simultaneously feed the two transmitting antennas in the same group with excitation signals with the same waveform characteristics (such as signal style, amplitude, frequency, period and other parameters) but opposite phases; in the working state, by adjusting the axial rotation direction of the telescopic turntable, the receiving port and the excitation port of each group of transceiver antennas are in a straight line, and the polarization direction of the antenna is ensured to be the same; by adjusting the telescopic scale of the telescopic turntable, the antenna ports of the two transmitting antennas and the receiving antenna in the same group are at the same horizontal height.

[0014] Compared with the structural design of the existing triangular array ground-penetrating radar antenna device, the UAV ground-penetrating radar transceiver array device of the present invention is composed of multiple groups of transceiver antennas, and each group of transceiver antennas shares a rotatable receiving antenna; each group of transceiver antennas includes two transmitting antennas and one receiving antenna, and the distance between the receiving antenna and the two transmitting antennas is equal. The three antennas are arranged in a "one" shape, and the three antenna ports are at the same horizontal height; in each group of transceiver antennas, the transmitting antenna is fixed in position, and the receiving antenna shared by each group can be rotated along the axial direction to ensure that the polarization direction of the transceiver antennas in the group is the same during each measurement.

[0015] Specifically, in the present invention, the two transmitting antennas in the same group are located at the ends of adjacent arms of equal length, and the receiving antennas in the same group are located at the center of the antenna mount, at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group. Furthermore, the position and port orientation of each transmitting antenna group in the transceiver antenna array are adjustable. By adjusting the rotation angle of the turntable (i.e., its axial rotation direction), the receiving antenna port orientation can be adjusted to align with the polarization orientation of the transmitting antennas in the same group. All transmitting and receiving antennas have identical materials, structures, and operating performance (polarization mode, gain, S-parameters, input impedance, and other performance parameters). The UAV ground-penetrating radar is equipped with a pulse signal source that simultaneously feeds excitation signals with identical waveform characteristics (e.g., signal pattern, amplitude, frequency, period, and other parameters) but opposite phases to the two transmitting antennas in the same group. The two pulse signals radiated by the pulse signal source have identical waveform patterns, equal peak-to-peak values, and the same pulse width, but their initial phases are 0° and 180°, respectively. The pulse signal source is connected to any two transmitting antennas in the same group in the antenna array, and two excitation signals with an initial phase difference of 180° are fed to the two transmitting antennas in the same group at the same time.

[0016] Furthermore, the telescopic turntable of the antenna bracket can be adjusted by program-controlled automatic adjustment or manual adjustment, both of which can achieve adjustment of the height and rotation direction of the receiving antenna.

[0017] Furthermore, the antenna mount's arms are made of high-strength, lightweight tubing, which can be made of metal (such as aluminum alloy or titanium alloy), composite fibers (such as carbon fiber, glass fiber, or composite fibers), or engineering plastics. The hollow tubes can be used to insert coaxial cables and power lines. This hollow structure allows for the wiring connecting the transmitting antenna at its end to the pulse signal source.

[0018] Furthermore, the transmitting antenna in the transceiver antenna array is an ultra-wideband directional transmitting antenna.

[0019] Furthermore, the minimum spacing d between each receiving antenna and the transmitting antenna of the transceiver antenna array is min Should meet: d min ≧2L 2 / λ, where L is the maximum aperture of the antenna and λ is the effective wavelength of the electromagnetic wave in the medium.

[0020] Another aspect of the present invention provides a method for suppressing clutter in a UAV ground-penetrating radar. The method is based on the UAV ground-penetrating radar transceiver array device of the present application and performs the following steps:

[0021] Selecting a group of transceiver antennas from the transceiver antenna array as a current working antenna group;

[0022] Adjust the support arm so that the receiving antenna in the same group is located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group. (If the support arm passes through the frustum-shaped box, the two transmitting antennas in the same group are already located at the two ends of the support arm, so this step can be omitted.)

[0023] Adjust the telescopic turntable of the antenna mount to adjust the axial rotation direction of the receiving antenna so that the receiving port and the excitation port of the transmitting and receiving antennas of the working antenna group are in a straight line and the polarization directions of the antennas are the same; and adjust the telescopic scale of the receiving antenna so that the antenna ports of the two transmitting antennas and the receiving antenna are at the same horizontal height;

[0024] The pulse signal source is controlled to simultaneously feed excitation signals with the same waveform characteristics but inverse phases to the two transmitting antennas of the current working antenna group, so that the ground reflected wave and the air direct coupling wave between the transmitting and receiving antennas of the current working antenna group are canceled out (because the two transmitting antennas in the same group are symmetrically positioned relative to the receiving antenna and the radiated signal waveforms are inversely phased, the strong ground reflected wave and the air direct coupling wave between the transmitting and receiving antennas are canceled out), thereby achieving clutter suppression of the UAV ground penetrating radar echo signal.

[0025] The present invention achieves clutter suppression for the UAV ground-penetrating radar transceiver array from a hardware design perspective. Based on the optimization of the UAV ground-penetrating radar's transceiver antenna system configuration, the two transmitting antennas in each group share a single receiving antenna during a single measurement. The excitation signal source simultaneously feeds excitation signals with identical waveform characteristics but opposite phases to the two transmitting antennas. By utilizing the principle of mutual superposition and cancellation of equal-amplitude, opposite-phase signals of the same frequency, the invention directly suppresses ground reflections and air-directed coupled waves, allowing the receiving antenna to directly receive the echo signal after strong clutter suppression. The present invention significantly eliminates the shortcomings of traditional clutter suppression technologies, such as poor adaptability to complex environments, susceptibility to target signal loss, poor robustness to noise, low data processing efficiency, reliance on manual parameter adjustment, limited ability to separate complex clutter, excessive reliance on preprocessing assumptions, difficulty in processing nonlinear clutter, lack of adaptability, and inability to effectively fuse multi-source information.

[0026] Furthermore, when detecting underground targets, when it is detected that the field value received by the receiving antenna is zero (at this time the underground target is located directly below the receiving antenna), the position of the reflection point of the underground target closest to the receiving antenna or the ground is obtained based on the position directly below the receiving antenna. This position can be called the strongest reflection point of the underground target closest to the receiving antenna or the ground.

[0027] The technical solution provided by the present invention brings at least the following beneficial effects:

[0028] (1) Each group of transmitting antennas is fed with excitation signals with the same waveform characteristics but in opposite phases. The receiving antenna located at the midpoint of the two transmitting antennas can receive the air direct-coupled wave signal and the ground strong reflection wave signal that are superimposed and offset due to their symmetrical positions. It can directly extract the effective echo signal of the underground target. According to the zero field value received by the receiving antenna, the position of the strong reflection point of the target body can be determined.

[0029] (2) The echo signals received by the receiving antenna mainly contain the effective echo signals of underground targets, which can greatly simplify the signal processing process and make it easy to amplify the weak echo signals of underground targets;

[0030] (3) It is easy to amplify weak echo signals of underground targets without causing saturation of the receiving front end, making it easy to use automatic gain control to amplify target signals, which is beneficial to the analysis and processing of target echoes;

[0031] (4) The echo signals obtained by the combination of multiple transceiver antenna arrays can be processed according to the flight trajectory of the UAV and the data of the transceiver antenna array signals to locate the underground target and determine the burial direction of the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0033] Figure 1 Schematic diagram of the operation of any group of transmitting and receiving antennas in the embodiment of the present application, wherein T1 and T2 represent two transmitting antennas, and R represents a receiving antenna; T r1 、T r2 They represent the electromagnetic wave signals radiated to the target by the transmitting antenna T1 and the transmitting antenna T2, respectively. s Represents the electromagnetic wave signal scattered by the target; D i1 and D i2 Respectively represent the air-coupled wave signals between the receiving antenna and the two transmitting and receiving antennas T1 and T2; R e-g1 and R e-g2 They represent the reflected wave signals formed by the radiation signals of the two transmitting antennas T1 and T2 passing through the ground; R e-t1 and R e-t2 They respectively represent the reflected wave signals reflected by the target and received by the receiving antenna.

[0034] Figure 2 A schematic diagram of a UAV ground-penetrating radar clutter suppression method and a transceiver array device provided in an embodiment of the present application.

[0035] Figure 3 This is a simulation modeling diagram and parameter settings for an embodiment of the present application.

[0036] Figure 4 Schematic diagram of the waveform of the excitation signal.

[0037] Figure 5 Schematic diagram of the waveform of the direct-coupled wave signal received by the receiving antenna R in the single-transmit single-receive mode.

[0038] Figure 6 Schematic diagram of the waveform of the signal received by the receiving antenna R in the single-transmit and single-receive mode.

[0039] Figure 7 Schematic diagram of the waveform of the target signal received by the receiving antenna R in the dual-transmit and single-receive mode. DETAILED DESCRIPTION

[0040] In order to make those skilled in the art better understand the technical solutions in this specification, the technical solutions of the embodiments of the present application will be described in detail and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the embodiments described with reference to the drawings are exemplary and are intended to be used to explain the present application, and cannot be understood as limiting the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0041] Like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0042] In the description of this application, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on this application.

[0043] The embodiment of the present application discloses a UAV ground-penetrating radar transceiver array device, which includes a transceiver antenna array, a pulse signal source and an antenna mount; wherein the antenna mount is a cross-type structure, the center position of which is a truncated cone-shaped box body (which can be set to a flat truncated cone-shaped box body), and the side of the truncated cone-shaped box body is provided with a plurality of movably connected hollow structures and equal-length arms, the angle between adjacent arms is adjustable, and a transmitting antenna is fixed at the end of each arm; the center of the truncated cone-shaped box body is a telescopic turntable with adjustable length, and the center position of the telescopic turntable is provided with a coaxial cable connector‌ for connecting to a receiving antenna; that is, the present application can realize a hard connection with the receiving antenna through the coaxial cable connector‌ (such as an SMA (Sub-Miniature-A) coaxial connector) at the center position of the telescopic turntable (the center position is optimal); the height of the receiving antenna can be adjusted by adjusting the telescopic scale of the telescopic turntable, and the port orientation of the receiving antenna can be adjusted by adjusting the axial rotation direction of the telescopic turntable; the transceiver antenna array includes multiple groups of reciprocal transceiver antennas, each group of receiving Each transmitting antenna includes two transmitting antennas and one receiving antenna, and each group of transmitting and receiving antennas shares the same receiving antenna. The two transmitting antennas in each group are deployed at the ends of the two supporting arms of the antenna mount, forming a group of transmitting and receiving antennas with the receiving antenna deployed at the center of the telescopic turntable. A pulse signal source is used to simultaneously feed excitation signals with identical waveform characteristics but opposite phases to the two transmitting antennas in the same group. The signals radiated by the two transmitting antennas are reflected by the ground and received by the receiving antenna. When in operation, the position of the supporting arms is adjusted so that the receiving antenna in the same group is located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group, and the three antennas in the same group are arranged in a straight line. The axial rotation direction of the telescopic turntable is adjusted so that the receiving port and the excitation port of each group of transmitting and receiving antennas are aligned (i.e., the port direction of the receiving antenna is adjusted by adjusting the axial rotation direction of the telescopic turntable so that it aligns with the polarization direction of the transmitting antenna in the same group). The telescopic range of the telescopic turntable is adjusted so that the antenna ports of the two transmitting antennas and the receiving antenna in the same group are at the same horizontal height.

[0044] In one embodiment, the support arm can also be set as a through arm that passes through the conical box body, and then the two transmitting antennas of the same group of transmitting and receiving antennas are deployed at both ends of the same support arm, so that the three antennas in the same group are arranged in a line, so that the receiving antenna is directly located at the midpoint of the line connecting the antenna feeding points of the two transmitting antennas in the same group, thereby eliminating the process of adjusting the support arm position in the working state.

[0045] That is, the transceiver array device of a UAV ground-penetrating radar provided in the embodiment of the present application is mainly composed of a single receiving antenna, multiple groups of transmitting antennas and a pulse signal source. The structural dimensions and performance parameters of all antennas are the same and all antenna ports are located at the same horizontal height. The pulse signal source can simultaneously provide the transmitting antenna with two excitation signals with the same waveform characteristics but inverse phases. Each group of transceiver antennas includes two transmitting antennas and a receiving antenna located at the midpoint of the line connecting the feeding points of the two transmitting antennas, and the feeding ports of the transceiver antennas are located on a straight line. The receiving antenna is installed at the center of the telescopic turntable. For example, if the telescopic turntable adopts a servo turntable, the receiving antenna can be installed directly below the servo turntable. The axial rotation direction of the receiving antenna can be adjusted by control instructions to ensure that when multiple groups of transmitting antennas share the same receiving antenna, the polarization directions of the transceiver antennas are consistent. When a UAV ground-penetrating radar is operating, each time a set of antennas is selected for detection, a pulse signal source simultaneously feeds excitation signals with identical waveform characteristics but opposite phases to each selected set of transmitting antennas. The strong ground reflection wave and the air-coupled wave between the transmitting and receiving antennas cancel each other out due to their opposite waveform phases, leaving the receiving antenna with only the valid echo signal of the underground target. Therefore, this application effectively solves the problem of underground target echo signals being easily submerged in strong clutter and difficult to effectively extract during UAV ground-penetrating radar detection operations.

[0046] In the embodiment of the present application, the working principle of the UAV ground penetrating radar transceiver array device when performing underground target detection is analyzed as follows:

[0047] For each set of transmitting and receiving antennas in operation, the responses of the two transmitting antennas and the single receiving antenna are expressed as T x1 、T x2 and R x Indicates that the air-coupled wave signal of the transmitting and receiving antenna is expressed by D i1 and D i2 Indicated by R, the ground reflected wave signal is e-g1 and R e-g2 Indicates that the target reflected wave signal is represented by R e-t1 and R e-t2 Indicates that Figure 1 Assume that the input signal is represented by M and the output signal is represented by N. The part of the electromagnetic pulse signal that only propagates in the air and does not enter the ground is represented by the early response:

[0048] N E1 =T x1 *(R e-g1 +D i1 )*R x *M;

[0049] N E2 =T x2 *(R e-g2 +D i2)*R x *M;

[0050] Among them, N E1 、N E2 They represent the early responses of the electromagnetic pulse signals of the transmitting antennas T1 and T2 respectively, and * represents the convolution in the time domain.

[0051] The part of the electromagnetic pulse signal that propagates into the ground and is reflected by the target is called the late response, which is expressed as:

[0052] N L1 =T x1 *R e-t1 *R x *M;

[0053] N L2 =T x2 *R e-t2 *R x *M;

[0054] Among them, N L1 、N L2 They represent the late responses of the electromagnetic pulse signals of the transmitting antennas T1 and T2 respectively.

[0055] Therefore, the final receive response of the transmitting antennas T1 and T2 is expressed as:

[0056] N1=N E1 +N L1 =T x1 *(D i1 +R e-g1 +R e-t1 )*R x *M;

[0057] N2=N E2 +N L2 =T x2 *(D i2 +R e-g2 +R e-t2 )*R x *M;

[0058] If the transmitting antennas T1 and T2 are symmetrical relative to the receiving antenna R and the radiated signal waveforms are in phase with each other, then D i1 =-D i2 and R e-g1 =-R e-g2 This means that the early response N received by the receiving antenna E1 and N E2 is 0. Therefore, the two transmitting antennas radiate the same waveform characteristics but inverse phase signals, and the strong ground reflection wave and the air direct coupling wave between the transmitting and receiving antennas are offset, thereby achieving clutter suppression of the UAV ground penetrating radar echo signal.

[0059] At this point, the echo signal received by the receiving antenna mainly contains the valid echo signal of the underground target. Therefore, this application does not require additional measurements of the target-free ground to evaluate the ground reflection and antenna coupling effects. Then, the final output signal of any transmitting and receiving antenna combination is as follows:

[0060] N1=N L1 =T x1 *R e-t1 *R x *M;

[0061] N2=N L2 =T x2 *R e-t2 *R x *M;

[0062] If the underground target is located directly below the receiving antenna, then R e-t1 =-R e-t2 , which results in the field value received by the receiving antenna at this position being zero. However, if the horizontal distances from the target to the two transmitting antennas are not equal (e.g. Figure 1 As shown), then R e-t1 ≠-R e-t2 , then the effective echo signal from the underground target can be obtained. Therefore, N1 and N2 in the above formula are formed by the convolution of the radiation signal, the target electromagnetic scattering, the input characteristics and the output characteristics.

[0063] In an exemplary embodiment of the present application, a clutter suppression transceiver array for a UAV ground penetrating radar is provided. Figure 2 As shown, the antenna mount has a cross-shaped structure, and the corresponding transceiver antenna combination also has a cross-shaped layout. The angle between the arms of two adjacent transceiver antenna groups can be adjusted according to test needs. The angles of the arms of multiple transceiver antenna groups can be evenly spaced or unevenly spaced. To simplify the antenna layout of this application, this embodiment uses a "cross" antenna array composed of two transceiver antenna combinations to illustrate.

[0064] The UAV ground-penetrating radar transceiver array device based on a "cross" antenna array shown in this embodiment includes: four transmitting antennas, primarily for radiating detection signals; and a receiving antenna mounted at the bottom of a pylon turntable, primarily for receiving echo signals. During detection, all transmitting and receiving antenna ports must be located at the same level. A pulse signal source simultaneously feeds excitation signals with identical waveform characteristics but opposite phases to the two transmitting antennas in the same group. This means that the two excitation signals entering each transmitting antenna group differ by 180° in phase. Assuming the direction perpendicular to the line connecting T1, R, and T2 is the survey line direction, one set of data is collected. By adjusting the turntable's rotation angle, the receiving antenna R is rotated axially so that it aligns with the radiation ports of transmitting antennas T3 and T4, and has the same polarization direction, and a second set of data is collected. If multiple sets of transmitting and receiving antennas are used, the rotation direction of the receiving antenna R can be adjusted sequentially to ensure the same polarization direction for each antenna group. Multiple sets of detection data are then collected and recorded sequentially. According to the number of acquisition channels, the flight speed of the UAV is optimized and adjusted to achieve the detection of underground targets within a certain detection bandwidth along the survey line direction.

[0065] The "cross" shaped transceiver antenna array layout uses 4 transmitting antennas and 1 receiving antenna. The receiving antenna is located in the center of the "cross" and connected to the telescopic turntable, with equal spacing from each transmitting antenna. Figure 2 As shown. The transmitting antenna and receiving antenna are mounted on the bottom of the UAV by the antenna bracket. During the UAV ground penetrating radar flight detection, each antenna is guaranteed to be at the same level, and the transmitting antenna radiation port is vertically downward, perpendicular to the ground. Figure 2 As shown, transmitting antenna T1, transmitting antenna T2, and transmitting antenna R form transceiver antenna array 1, and transmitting antenna T2, transmitting antenna T3, and transmitting antenna R form transceiver antenna array 2. The two transmitting antennas in each group have the same polarization mode, but the initial phases of the waveforms they radiate are 180° apart.

[0066] The echo signals from each transmitting antenna array are received by receiving antenna R, and the received signals are appropriately amplified by the signal processing unit. Control instructions enable the signal source to sequentially feed excitation signals of the same frequency, amplitude, and opposite phases to transmitting and receiving antenna arrays 1 and 2. During the acquisition process, the relative position of each antenna group remains unchanged, and the height above the ground remains unchanged. During the detection of the area to be measured, echo signals along and perpendicular to the survey line can be obtained.

[0067] The following is a simulation result based on the above embodiment:

[0068] The FDTD method (finite-difference time-domain method) is used to construct a physical model of a UAV ground-penetrating radar detecting underground pipelines. A group of transceiver antennas in the transceiver array device is selected, and the clutter suppression effect of the UAV ground-penetrating radar transceiver array device proposed in the embodiment of the present application is verified through simulation.

[0069] Assuming that the simulation medium is a non-magnetic isotropic medium, the relative dielectric constant ε' of the soil r =16, conductivity σ'=10 -3 Siemens / meter, relative dielectric constant ε of air r =1, conductivity σ = 0 Siemens / meter; the underground target is a cast iron pipe with an outer diameter D of 60 cm, a wall thickness d2 of 4 cm, and a buried depth h2 of 0.6 m; both the transmitting and receiving antennas are ideal dipole antennas, and the height h1 of both antennas from the ground is 1.3 m. The distance d1 between the receiving antenna and the transmitting antenna is 0.4 m. T1 and T2 are transmitting antennas, R is the receiving antenna, and T1 is located directly above the pipe. Figure 3 It should be noted that the above parameter settings are only specific parameter settings used in this simulation example, and do not indicate or imply that the present invention must have specific parameter settings, and therefore should not be understood as limiting the present application.

[0070] Assume that the excitation signal is Ricker wavelet, the center frequency of the excitation signal is 250 MHz, and its waveform is as follows: Figure 4 As shown. Without changing the simulation model background and target parameters, the distance between the transmitting and receiving antennas, the height above the ground and the operating frequency, by changing the number of transmitting antennas, the clutter suppression effect of the UAV ground penetrating radar transmitting and receiving array device proposed in the embodiment of the present application is verified during operation. First, a single-transmitting and single-receiving antenna mode is selected, that is, only the transmitting antenna T1 and the receiving antenna R are selected, and the signal source feeds an excitation signal (its waveform is shown as Figure 4 As shown by the solid line in the figure, the echo signal characteristics of the receiving antenna R receiving the radiation of a single transmitting antenna T1 are studied. In the single-transmit and single-receive mode, R receives the direct-coupled wave signal from the transmitting antenna T1, which is directly coupled to the receiving antenna R through the air (as shown in the figure). Figure 5 In the single-transmit and single-receive mode, the echo signal waveform received by the receiving antenna R (as shown in Figure 6 shown), Figure 6 Waveform 1 is the air-coupled wave signal received by R from T1 (i.e. Figure 5 Direct coupled wave signal in Figure 6 Waveforms 2 and 3 are the ground reflection wave signal and the pipeline reflection wave signal respectively. Figure 6 It can be seen that the echo signal of the metal pipe is still weak under ideal simulation conditions. Under actual test conditions, it is very easy to be submerged in the air-coupled wave and ground-reflected wave signals. In the dual-transmitter and single-receiver mode, the excitation waveform signals fed by the signal source to the transmitting antennas T1 and T2 at the same time have the same waveform characteristics but are inversely proportional. The excitation signal waveform is as follows: Figure 4As shown in (the solid line and the dotted line are the excitation signals fed into T1 and T2 simultaneously). The signal waveform received by the receiving antenna R located at the midpoint of the horizontal line connecting the two transmitting antennas T1 and T2 is as follows: Figure 7 As shown, Figure 7 The two echo signals (indicated by dotted lines) contained in the waveform have very small amplitudes, but there is no other strong clutter interference in the entire waveform; Figure 7 The solid line in the figure is the waveform of the weak received signal after amplification by 20 dB (i.e., gain = 20 dB). Compared with the echo signal received by the receiving antenna R in the single-transmit and single-receive mode, Figure 6 The air-coupled waves and ground reflections are cancelled out; Figure 7 4 in the figure is the pipeline echo signal; Figure 7 Figure 5 shows the echo signal received by receiving antenna R after a portion of the pipeline's reflected wave is first reflected by the ground, and a portion of the ground reflected wave is further reflected by the upper interface of the pipeline. Because the ground reflected wave and the air-coupled wave are effectively suppressed, the pipeline's reflected wave signal is very distinct, significantly improving the signal-to-clutter ratio and facilitating effective amplification of the target echo signal. Furthermore, a richer reflected wave signal appears in the clutter-suppressed waveform, further facilitating confirmation of the pipeline's burial depth. Simulation results show that by simultaneously feeding the transmitting antenna with excitation signals of identical but opposite phases, the UAV ground-penetrating radar achieves superposition and cancellation of the air-coupled wave and the ground reflected wave, achieving strong clutter suppression.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A UAV ground penetrating radar transceiver array device, comprising a transceiver antenna array, a pulse signal source and an antenna bracket, characterized in that: The antenna mount has a cross-shaped structure, with a frustoconical box at its center. The sides of the frustoconical box are equipped with multiple movably connected hollow arms of equal length. The angle between adjacent arms is adjustable, and a transmitting antenna is fixed at the end of each arm. At the center of the frustoconical box is an adjustable telescopic turntable with a coaxial cable connector at its center for connecting to the receiving antenna. The transceiver antenna array includes multiple groups of reciprocal transceiver antennas, each group of which includes two transmitting antennas and one receiving antenna, and each group of transceiver antennas shares the same receiving antenna. The two transmitting antennas in each group of transceiver antennas are deployed at the ends of the two supporting arms of the antenna bracket, and together with the receiving antenna deployed at the center of the telescopic turntable, form a transceiver antenna group. The pulse signal source is used to simultaneously feed excitation signals with the same waveform characteristics but opposite phases to two transmitting antennas in the same group; When in operation, the arm position is adjusted so that the receiving antenna of the same group is located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group, and the three antennas in the same group are arranged in a straight line; by adjusting the axial rotation direction of the telescopic turntable, the receiving port and excitation port of each group of transmitting and receiving antennas are in a straight line, and the polarization directions of the antennas are ensured to be the same; by adjusting the telescopic scale of the telescopic turntable, the antenna ports of the two transmitting antennas and the receiving antenna in the same group are at the same horizontal height.

2. A UAV ground penetrating radar transceiver array device, comprising a transceiver antenna array, a pulse signal source and an antenna bracket, characterized in that: The antenna hanger has a cross-shaped structure, with a truncated cone-shaped box at its center. The side of the truncated cone-shaped box is provided with a plurality of arms that pass through the hollow structure of the truncated cone-shaped box. The arms are movably connected at the center of the truncated cone-shaped box through their center points. The transceiver antenna array includes multiple groups of reciprocal transceiver antennas, each group of which includes two transmitting antennas and one receiving antenna, and each group of transceiver antennas shares the same receiving antenna. The two transmitting antennas in each group of transceiver antennas are deployed at the two ends of the same arm of the antenna bracket, and together with the receiving antenna deployed at the center of the telescopic turntable, form a group of transceiver antennas. The two transmitting antennas in the same group are equidistant from the receiving antenna. The pulse signal source is used to simultaneously feed excitation signals with the same waveform characteristics but opposite phases to two transmitting antennas in the same group; When in working state, the axial rotation direction of the telescopic turntable is adjusted so that the receiving port and the excitation port of each group of transmitting and receiving antennas are in a straight line, and the polarization directions of the antennas are ensured to be the same; the telescopic scale of the telescopic turntable is adjusted so that the antenna ports of the two transmitting antennas and the receiving antenna in the same group are at the same horizontal height.

3. The UAV ground penetrating radar transceiver array device according to claim 1 or 2, characterized in that: The adjustment mode of the telescopic turntable of the antenna bracket is program-controlled automatic adjustment or manual adjustment.

4. The UAV ground penetrating radar transceiver array device according to claim 1 or 2, characterized in that: The support arm of the antenna bracket is made of metal, composite fiber or engineering plastic.

5. The UAV ground penetrating radar transceiver array device according to claim 1 or 2, characterized in that: The transmitting antenna in the transceiver antenna array is an ultra-wideband directional transmitting antenna.

6. The UAV ground penetrating radar transceiver array device according to claim 1 or 2, characterized in that: The minimum distance d between each receiving antenna and the transmitting antenna of the transceiver antenna array min Should meet: d min ≧2L 2 / λ, where L is the maximum aperture of the antenna and λ is the effective wavelength of the electromagnetic wave in the medium.

7. A method for suppressing clutter of UAV ground penetrating radar, characterized in that: Based on the UAV ground penetrating radar transceiver array device according to claim 1, the following steps are performed: Selecting a group of transceiver antennas from the transceiver antenna array as a current working antenna group; Adjust the arm position so that the receiving antenna in the same group is located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group; Adjust the telescopic turntable of the antenna bracket to adjust the axial rotation direction of the receiving antenna so that the receiving port and the excitation port of the transceiver antenna of the working antenna group are in a straight line; and adjusting the telescopic scale of the receiving antenna so that the antenna ports of the two transmitting antennas and the receiving antenna are at the same level; The pulse signal source is controlled to simultaneously feed excitation signals with the same waveform characteristics but in opposite phases to the two transmitting antennas of the current working antenna group, so that the ground reflected wave and the air direct coupling wave between the transmitting and receiving antennas of the current working antenna group are offset.

8. A method for suppressing clutter of UAV ground penetrating radar, characterized in that: The UAV ground penetrating radar transceiver array device according to claim 2 performs the following steps: Selecting a group of transceiver antennas from the transceiver antenna array as a current working antenna group; Adjust the telescopic turntable of the antenna bracket to adjust the axial rotation direction of the receiving antenna so that the receiving port and the excitation port of the transceiver antenna of the working antenna group are in a straight line; and adjusting the telescopic scale of the receiving antenna so that the antenna ports of the two transmitting antennas and the receiving antenna are at the same level; The pulse signal source is controlled to simultaneously feed excitation signals with the same waveform characteristics but in opposite phases to the two transmitting antennas of the current working antenna group, so that the ground reflected wave and the air direct coupling wave between the transmitting and receiving antennas of the current working antenna group are offset.

9. The clutter suppression method according to claim 7 or 8, characterized in that: When detecting underground targets, when it is detected that the field value received by the receiving antenna is zero, the position of the reflection point of the underground target closest to the receiving antenna or the ground is obtained based on the position directly below the receiving antenna.

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