Unmanned aerial vehicle ground penetrating radar clutter suppression method and transceiving array device

Abstract

The invention discloses an unmanned aerial vehicle ground penetrating radar clutter suppression method and a transceiving array device, and belongs to the technical field of ground penetrating radars. The device comprises a single receiving antenna, multiple groups of transmitting antennas and a signal source, all the antennas are homogeneous, all antenna ports are located at the same horizontal height, and the signal source can provide two paths of excitation signals with the same frequency, the same amplitude and the opposite phase for the transmitting antennas at the same time; each group of transmitting and receiving antennas comprises two transmitting antennas and a receiving antenna located at the midpoint of a connecting line of feeding points of the two transmitting antennas, and feeding ports of the transmitting and receiving antennas are located on the same straight line. The receiving antenna is installed on the telescopic rotary table, the axial rotation direction of the receiving antenna can be achieved by adjusting the telescopic rotary table, and it is ensured that when multiple sets of transmitting antennas share the same receiving antenna, the polarization directions of the transmitting antennas and the receiving antennas are consistent. The clutter suppression method of the underground target echo signal is realized based on the device. According to the invention, the problem that underground target echo signals are easily submerged in strong clutters and are difficult to effectively extract is solved.

Description

Technical Field

[0001] The present application relates to the technical field of underground target detection by unmanned aerial vehicle ground penetrating radar, and in particular to a clutter suppression method and a transceiver array device for unmanned aerial vehicle 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 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. Ground penetrating radar radiates electromagnetic waves toward the ground through the transmitting antenna. When the electromagnetic waves propagating in the stratum encounter an interface with different electrical parameters (dielectric constant, conductivity, and magnetic permeability), reflection will occur. According to the partial reflected wave signal received by the receiving antenna, the underground structure and target attribute information can be obtained. There are various ways to carry ground penetrating radar. Different carrying platforms can be selected according to different application requirements and exploration scenarios. Traditional ground penetrating radar is mainly carried on the ground, generally in handheld, hand-pushed and vehicle-mounted modes for non-destructive testing or detection. Its transceiver antenna is usually close to the ground or the transceiver antenna port is at a certain height from the ground (generally less than 1 meter). 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 need for rapid detection or inspection of large areas or long distances.

[0004] With the development of UAV and GPR technology, UAV GPR has emerged as an emerging technology and is gradually meeting human exploration needs for complex terrain. Although the hardware technology of UAV GPR has gradually matured, there are still great challenges in signal processing. For example, clutter suppression and weak signal extraction are two key technical issues in the data processing of UAV GPR. These issues directly affect the detection capability, detection accuracy and recognition effect of underground targets. Among them, clutter refers to the interference components in the echo signal of UAV GPR that are unrelated to the target signal, including surface reflection, transceiver antenna coupling signal, electromagnetic interference, etc. The presence of clutter will significantly reduce the system's detection performance, target resolution capability and the reliability of data interpretation. During the operation of the UAV ground penetrating radar, the transmitting and receiving antenna ports carried by the body are usually at a certain height from the ground (usually greater than 1 meter), and the ground reflected wave signal is relatively strong at this time; the transmitting antenna radiates electromagnetic wave signals from the feeding end, and during the propagation process, the signal is gradually coupled to the receiving antenna through the air medium, forming a significant spatial coupling effect, and the coupled signal intensity is relatively high; at the same time, since the surface soil, sand and gravel are non-uniform loss media, some electromagnetic waves entering the stratum are scattered. The effective echo signal of the underground detection target is a weak signal and is easily submerged in the direct coupling wave and the ground reflected wave. Therefore, it is particularly important to explore how to suppress clutter and extract the effective echo signal of the underground target for the detection and identification of underground targets by the UAV ground penetrating radar.

[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. At present, clutter suppression is mainly achieved by signal enhancement technology, time-frequency analysis, noise suppression, machine learning and deep learning, but these clutter suppression methods mainly use signal processing methods to post-process the collected data to achieve clutter suppression.

[0006] However, there are few studies on pre-data collection 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 scheme discloses a means of suppressing clutter before data collection, this scheme 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 method for suppressing clutter of a 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 effectively extracting 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 rack 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 movably connected hollow structures and arms of equal length. 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 is a telescopic turntable with adjustable length. A coaxial cable connector is provided at the center of the telescopic turntable for connecting the receiving antenna. That is, the present application can realize 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 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 transceiver antennas are deployed at the ends of the two arms of the antenna bracket, and together with the receiving antenna deployed at the center of the telescopic turntable, form a group of transceiver antennas;

[0011] The pulse signal source is used to simultaneously feed excitation signals with the same waveform characteristics but inverse 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 feeding points of the two transmitting antennas of the same group, and the three antennas of the same group are arranged in a straight line; the receiving port and the excitation port of each group of transceiver antennas are in a straight line by adjusting the axial rotation direction of the telescopic turntable, and the antenna ports of the two transmitting antennas and the receiving antenna of the same group are at the same horizontal height by adjusting the telescopic scale of the telescopic turntable.

[0013] Furthermore, the support arm can also be set as a through arm that passes through the truncated cone box body, and the through arm is movably connected at the center position of the truncated cone 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 transceiver antennas are deployed at the two ends of the same support arm, so that the three antennas in the same group are arranged in a line; thereby, the receiving antenna is directly located at the midpoint of the line connecting the antenna feed points of the two transmitting antennas in the same group, and the adjustment of the support arm position in the working state is omitted to achieve a structure in which the three antennas are arranged in a line. At this time, the corresponding unmanned aerial vehicle ground penetrating radar clutter suppression method and transceiver array device are specifically as follows: the antenna bracket is a cross-type structure, the center position of which is a truncated cone box body, and the side of the truncated cone box body is provided with a plurality of support arms with a hollow structure that pass through the truncated cone box body, and the support arms are movably connected at the center position of the truncated cone 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 inverse phase; 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 unmanned aerial vehicle 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 distances from the receiving antenna to the two transmitting antennas are 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 position of the transmitting antenna is fixed, and the receiving antenna shared by each group can be rotated in the axial direction to ensure that the polarization directions of the transceiver antennas in the group are the same during each measurement.

[0015] That is, in the present invention, since the two transmitting antennas in the same group are located at the ends of adjacent arms, and the arms are of equal length, the receiving antennas in the same group are located at the center of the antenna hanger, and the receiving antenna is located at the midpoint of the line connecting the antenna feeding points of the two transmitting antennas in the same group; at the same time, the position and port orientation of each group of transmitting antennas in the transceiver antenna array are adjustable; by adjusting the rotation angle of the turntable (i.e., adjusting its axial rotation direction), the direction of the receiving antenna port can be adjusted to make it the same as the polarization direction of the transmitting antenna in the same group. The material, structure and working performance (polarization mode, gain, S parameter, input impedance and other performance parameters) of all transceiver antennas are the same. The unmanned aerial vehicle ground penetrating radar is equipped with a pulse signal source, which can be an excitation signal with the same waveform characteristics (such as signal style, amplitude, frequency, period and other parameters) but inverse phase for the two transmitting antennas in the same group. The two pulse signals radiated by the pulse signal source have the same waveform style, the same peak-to-peak value of the pulse signal, and the same pulse width, but the initial phases of the two pulse signals are 0° and 180° respectively. The pulse signal source is respectively 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 simultaneously fed into the two transmitting antennas in the same group.

[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 the adjustment of the height and rotation direction of the receiving antenna.

[0017] Furthermore, the support arm of the antenna bracket is made of high-strength lightweight pipe, and the material can be metal (such as aluminum alloy, titanium alloy), composite fiber (such as carbon fiber, glass fiber, composite fiber, etc.) or engineering plastic, etc. The coaxial line, power supply line, etc. can be inserted into the hollow tube, that is, the hollow structure is used to arrange the connecting line for connecting the transmitting antenna at its end with 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: min ≧2L 2 / λ, where L is the maximum aperture size 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 of a UAV ground penetrating radar, which performs the following steps based on the UAV ground penetrating radar transceiver array device of the present application:

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

[0022] Adjust the position of the support arm so that the receiving antenna of the same group is located at the midpoint of the line connecting the antenna feeding points of the two transmitting antennas of the same group; (If the support arm is a through arm passing through the truncated cone box, the two transmitting antennas of the same group are already located at the two ends of the support arm, and this step can be omitted);

[0023] 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 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 level;

[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 coupled wave between the transmitting and receiving antennas of the current working antenna group are offset (because the two transmitting antennas in the same group are symmetrically positioned relative to the receiving antenna and the radiation signal waveforms are inversely phased, the strong ground reflected wave and the air direct coupled wave between the transmitting and receiving antennas are offset), thereby achieving clutter suppression of the UAV ground penetrating radar echo signal.

[0025] The present invention realizes the clutter suppression of the UAV ground penetrating radar transceiver array from the perspective of hardware design. Based on the optimization of the transceiver antenna system configuration of the UAV ground penetrating radar, the two transmitting antennas in each group share one receiving antenna in a single measurement, and the excitation signal source simultaneously feeds the two transmitting antennas with excitation signals with the same waveform characteristics but inverted phases. The principle of mutual superposition and cancellation of the same-frequency, equal-amplitude and inverted phase signals is used to directly suppress the ground reflection and the air direct-coupled wave, so that the receiving antenna directly receives the echo signal after strong clutter suppression. The present invention greatly eliminates the shortcomings of traditional clutter suppression technology, such as poor adaptability to complex environments, easy loss of target signals, poor robustness to noise, low data processing efficiency, reliance on artificial 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 signals and the ground strong reflection wave signals that are superimposed and canceled due to their symmetrical positions. The effective echo signals of underground targets can be directly extracted. The position of the strong reflection point of the target body can be determined based on the zero field value received by the receiving antenna.

[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 combining multiple transceiver antenna arrays can be used to locate underground targets and determine the burial direction of the targets based on the flight trajectory of the UAV and data processing of the transceiver antenna array signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and easily 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 Indicates 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 from 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 received by the receiving antenna after being reflected by the target object.

[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 A simulation modeling schematic 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 and 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 the technical scheme in this specification better understood by the personnel in the technical field, the technical scheme of the embodiment of the present application will be described in detail and completely in conjunction with the drawings in the embodiment 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 the field without making creative work belong to the scope of protection of the present application. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals 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 comprising 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 similar items in the following drawings, and thus, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0042] In the description of the present 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 inventive product is usually placed when in use. They are only for the convenience of describing the present 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, and therefore should not be understood as a limitation on the present 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 bracket; wherein the antenna bracket 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 hollow structures and equal-length arms that are movably connected, 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 a receiving antenna; that is, the present application can realize a hard connection with the receiving antenna through a 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 a plurality of 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; wherein, the two transmitting antennas of each group of transmitting antennas are deployed at the ends of the two arms of the antenna bracket, and form a group of transmitting and receiving antennas with the receiving antenna deployed at the center of the telescopic turntable; 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 but inverse phases, and the signals radiated by the two transmitting antennas are received by the receiving antenna after being reflected by the ground; in the working state, the position of the arm is adjusted so that the receiving antenna in the same group is located at the midpoint of the line connecting the antenna feeding 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 transmitting and receiving antennas are in a straight line (that is, by adjusting the axial rotation direction of the telescopic turntable, the port direction of the receiving antenna is adjusted to make it the same as the polarization direction of the transmitting antenna in the same group), 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.

[0044] In one embodiment, the support arm can also be set as a through arm that passes through the truncated cone-shaped box body, and then the two transmitting antennas of the same group of transceiver antennas are deployed at the two ends of the same support arm, so that the three antennas of 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 of the same group, thereby eliminating the process of adjusting the support arm position in the working state.

[0045] That is, a transceiver array device for a UAV ground-penetrating radar provided in an embodiment of the present application is mainly composed of a single receiving antenna, multiple groups of transmitting antennas and a pulse signal source. All antennas have the same structural dimensions and performance parameters 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 exact 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 through 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 the UAV ground-penetrating radar is working, each time a group of antennas is selected for detection, after the pulse signal source simultaneously feeds the excitation signal with the same waveform characteristics but inverse phase to the selected group of transmitting antennas each time, the strong ground reflection wave and the air direct coupling wave between the transmitting and receiving antennas can cancel each other out due to the opposite waveform phases, and the receiving waveform of the receiving antenna only contains the effective echo signal of the underground target. Therefore, the present application effectively solves the problem that the echo signal of the underground target is easily submerged in the strong clutter and difficult to be effectively extracted during the detection operation of the UAV ground-penetrating radar.

[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 represented by D i1 and D i2 The ground reflected wave signal is represented by R e-g1 and R e-g2 Indicated by R, the target reflected wave signal e-t1 and R e-t2 Indicates that Figure 1 Assume that the input signal is represented by M, the output signal is represented by N, and 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 receiving 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, 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 time, the echo signal received by the receiving antenna mainly contains the effective echo signal of the underground target. Therefore, this application does not need to perform additional measurements on the target-free ground in advance 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 of 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, target electromagnetic scattering, input characteristics and output characteristics.

[0063] In an exemplary embodiment of the present application, a clutter suppression transceiver array for a ground penetrating radar of an unmanned aerial vehicle is provided. Figure 2 As shown, the antenna bracket is a cross-shaped structure, and the corresponding transceiver antenna combination is also in a cross-shaped layout. The angle between the arms where two adjacent transceiver antennas are located can be adjusted according to the test needs, and the angles between the arms where multiple transceiver antennas are located can be equally spaced or unequally spaced. In order to simply describe the antenna layout of the present application, this embodiment is described with a "cross" antenna array composed of two transceiver antenna combinations.

[0064] In the UAV ground penetrating radar transceiver array device based on the "cross" antenna array shown in this embodiment, it includes: 4 transmitting antennas, which are mainly used to radiate detection signals; 1 receiving antenna is installed at the bottom of the bracket turntable, which is mainly used to receive echo signals. During the detection process, it is required that all transmitting antennas and receiving antenna ports are located at the same horizontal height; the pulse signal source simultaneously feeds the two transmitting antennas in the same group with excitation signals with the same waveform characteristics but inverted phases, that is, the two excitation signals entering each group of transmitting antennas are 180° apart in phase. Assuming that the direction perpendicular to the line connecting T1, R, and T2 is the survey line direction, a set of data is collected; by adjusting the rotation angle of the turntable, the receiving antenna R is rotated in the axial direction so that it is consistent with the radiation port direction of the transmitting antennas T3 and T4, and the polarization direction is the same, and the second set of data is collected; if multiple sets of transceiver antennas are selected, the rotation direction of the receiving antenna R can be adjusted in turn to ensure that the polarization direction of each set of antennas is the same, and multiple sets of detection data are collected and recorded in turn. 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 antenna bracket under the UAV. 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 R form a transceiver antenna array 1, and transmitting antenna T2, transmitting antenna T3, and R form a transceiver antenna array 2. The two transmitting antennas in each group have the same polarization mode, but the initial phases of the waveforms radiated by them differ by 180°.

[0066] The echo signal of each transmitting antenna array is received by the receiving antenna R, and the received signal can be appropriately amplified by the signal processing unit. Through the control instructions, the signal source can feed the same frequency, equal amplitude and opposite phase excitation signals to the transmitting and receiving antenna array 1 and the transmitting and receiving antenna array 2 in sequence; during the acquisition process, the relative position of each group of antennas remains unchanged, and the height from the ground remains unchanged. In the process of detecting the area to be measured, the echo signals along the measurement line direction and perpendicular to the measurement line direction can be obtained.

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

[0068] The FDTD method (finite difference time domain) is used to construct a physical model of the UAV ground penetrating radar detecting underground pipelines. A group of transceiver antennas in the transceiver array device are 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 of air ε 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; the transmitting and receiving antennas are both ideal dipole antennas, and the height h1 of the transmitting and receiving antennas from the ground is 1.3 m, and the distance d1 between the receiving antenna and the transmitting antenna is 0.4 m, among which 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 cannot be understood as limiting the present application.

[0070] Assume that the excitation signal is a Ricker wavelet, and the center frequency of the excitation signal is 250 MHz. 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 (whose waveform is shown in FIG. 1 ) into T1. Figure 4 As shown by the solid line in the figure, the echo signal characteristics under the condition that the receiving antenna R receives 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 of 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 in the figure 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 in the figure 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, and it is very easy to be submerged in the air coupling wave and ground reflection wave signals under actual test conditions. In the dual-transmit and single-receive mode, the excitation waveform signal fed by the signal source to the transmitting antennas T1 and T2 at the same time has the same waveform characteristics but is inverted. 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 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 it is the pipeline echo signal; Figure 7 Figure 5 shows that part of the pipeline reflected wave signal is first reflected by the ground, and part of the ground reflected wave is reflected again by the upper interface of the pipeline and received by the receiving antenna R. Because the ground reflected wave and the air coupled wave are effectively suppressed, the reflected wave signal of the pipeline is very obvious, and the signal-to-noise ratio is significantly improved, which is convenient for effectively amplifying the target echo signal; in addition, more abundant reflected wave signals appear in the waveform after clutter suppression, which is convenient for further confirming the buried depth of the pipeline. The simulation results show that: by simultaneously feeding the excitation signal with the same waveform characteristics but inverse phase into the transmitting antenna, the superposition and cancellation of the air coupled wave and the ground reflected wave of the UAV ground penetrating radar can be realized, so as to achieve the purpose of 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 rack 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 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. The center of the truncated cone-shaped box is a telescopic turntable with adjustable length. A coaxial cable connector is provided at the center of the telescopic turntable for connecting the receiving antenna. 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 in each group of transceiver antennas are deployed at the ends of the two arms 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 pulse signal source is used to simultaneously feed excitation signals with the same waveform characteristics but inverse phases to two transmitting antennas in the same group; 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 feeding points of the two transmitting antennas of the same group, and the three antennas of the same group are arranged in a straight line; the receiving port and the excitation port of each group of transceiver antennas are in a straight line by adjusting the axial rotation direction of the telescopic turntable, and the polarization directions of the antennas are ensured to be the same; the antenna ports of the two transmitting antennas and the receiving antenna of the same group are at the same horizontal height by adjusting the telescopic scale of the telescopic turntable.

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 bracket is in a cross-shaped structure, with a truncated cone-shaped box at its center. A plurality of arms passing through the hollow structure of the truncated cone-shaped box are arranged on the side of the truncated cone-shaped box, and 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 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 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; and 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 inverse phases to two transmitting antennas in the same group; When in working state, the receiving port and excitation port of each group of transceiver antennas are in a straight line by adjusting the axial rotation direction of the telescopic turntable, and the polarization directions of the antennas are ensured to be the same; the antenna ports of the two transmitting antennas and receiving antennas in the same group are at the same horizontal height by adjusting the telescopic scale of the telescopic turntable.

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

7. A method for suppressing clutter of an unmanned aerial vehicle ground penetrating radar, characterized in that: Based on the UAV ground penetrating radar transceiver array device of 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 position of the support arm 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 of 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 dimensions 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 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 offset.

8. A method for suppressing clutter of an unmanned aerial vehicle ground penetrating radar, characterized in that: Based on the UAV ground penetrating radar transceiver array device of claim 2, the following steps are performed: 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 dimensions 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 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 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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