CN117741656A - Unmanned aerial vehicle aviation ground penetrating radar based on low frequency ultra wideband air coupling antenna - Google Patents

Abstract

The invention discloses an unmanned aerial vehicle aviation ground penetrating radar based on a low-frequency ultra-wideband air coupling antenna, which comprises an unmanned aerial vehicle, a ground penetrating radar transceiver main body, a low-frequency ultra-wideband air coupling transceiver antenna, a laser radar altimeter, an attitude meter and a GPS module; the ground penetrating radar transceiver main body comprises a signal source module, a transmitter module, a radio frequency cancellation module, a receiver module and a data preprocessing and control module. The invention adopts the low-frequency ultra-wideband air coupling receiving and transmitting antenna, solves the air coupling problem of the aviation ground penetrating radar, utilizes the advantage of a stepping frequency continuous wave radar detection system, introduces a low-frequency wideband frequency hopping filter in a receiver module, effectively improves the sensitivity of the receiver, adopts the maximum radiation direction avoiding technology on the mounting mode of the receiving and transmitting antenna, and combines the radio frequency cancellation module of the ground penetrating radar transceiver to eliminate wideband strong interference signals generated by direct coupling of the receiving and transmitting antenna, thereby realizing the detection of a large-depth underground structure.

Description

A UAV aerial ground-penetrating radar based on low-frequency ultra-wideband air-coupled antenna

Technical field

The invention belongs to the technical field of ground penetrating radar, and specifically relates to a UAV aerial ground penetrating radar based on a low-frequency ultra-wideband air-coupled antenna.

Background technique

Ground penetrating radar is an efficient shallow geophysical detection technology. Compared with traditional geophysical methods, ground-penetrating radar has the advantages of high detection resolution, fast and convenient, simple operation, and strong anti-interference ability. The detection principle is that when the electromagnetic waves emitted by the transmitting antenna propagate in the formation, if they encounter objects (targets) with different electromagnetic properties, forward and backward scattering will occur. Scattered waves will also form new scattering between multiple targets and within the target. The scattered waves propagating towards the ground will be picked up by the receiving antenna. As the antenna moves, the ground-penetrating radar records the electromagnetic wave signals at each measurement point. After signal processing and analysis, the geological layering and the material of each layer can be determined, and underground targets can be identified. Ground-penetrating radar has an extremely wide range of applications. It plays an important role that cannot be replaced by other detection methods in scientific and technological fields such as engineering inspection, environmental protection, cultural relics and archaeology, disaster rescue, anti-terrorism security inspection, resource exploration, hydrology and water conservancy.

Currently, ground-penetrating radars are mostly mounted on trolleys or ground mobile platforms such as cars and trains to perform tasks such as shallow flaw detection on urban roads, underground pipeline detection, and hidden disease detection on highways and railways. Its working frequency band is generally high, and the detection depth is only a few meters. The coupling mode of the ground penetrating radar transceiver antenna is mostly the ground coupling mode where the antenna works close to the ground. Generally, the antenna is close to the ground 0.5cm ~ 1cm. For large-scale detection of areas heavily covered by vegetation, areas with large terrain undulations, or areas that are inaccessible to humans, ground-based ground penetrating radar is powerless, but aerial ground-penetrating radar can be a very effective detection method. The aerial ground-penetrating radar antenna must be suspended on a platform with a certain height and movement. The electromagnetic waves emitted by the transmitting antenna must propagate through geometric diffusion in the air (air coupling), and then enter the underground after being coupled by the ground. When encountering the stratigraphic interface, it will occur. After reflection, refraction, scattering, etc., part of the energy propagates upward to the receiving antenna of the aerial ground penetrating radar, and is coupled and received by the receiving antenna and recorded. Based on the received radar echo signal, the underground geology is further inferred through signal processing, data imaging, etc. structure.

Previous studies have shown that applying ground-penetrating radar to detect non-obvious landslides is an effective detection method. However, many non-obvious landslide fault disturbance zones are more than ten or even twenty meters deep underground. Generally, ground or aviation detection methods The detection depth of ground penetrating radar is far from meeting the detection requirements. Therefore, it is very necessary to carry out research on large-depth low-frequency aerial ground penetrating radar. It is of great significance for my country to improve the level of disaster prevention and reduction of landslides, collapses and other disasters and reduce the hazards of disasters. It is also of great significance for expanding the application of geophysical detection technology and enriching the electromagnetic field. The connotation of exploration law is of great value.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the present invention provides a UAV aerial ground-penetrating radar based on a low-frequency ultra-wideband air-coupled antenna. The ground-penetrating radar is mounted on the UAV, which solves the problem of the limited applicable scenarios of traditional ground-based ground-penetrating radar. The problem.

In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: a UAV aerial ground-penetrating radar based on a low-frequency ultra-wideband air-coupled antenna, including a UAV, a ground-penetrating radar transceiver body, and a low-frequency ultra-wideband air-coupled transceiver. Antenna, lidar altimeter, attitude meter and GPS module;

The main body of the ground-penetrating radar transceiver is mounted on a fixed plate in the middle of the landing gear of the UAV. The low-frequency ultra-wideband air-coupled transceiver antenna is suspended on the landing gear of the UAV and is connected to the UAV through a radio frequency line. The ground-penetrating radar transceiver is connected to the main body, the laser radar altimeter and the attitude meter are respectively fixed below and above the low-frequency ultra-wideband air-coupled transceiver antenna, and the GPS module is fixed on the machine of the UAV. on arm;

The main body of the ground penetrating radar transceiver includes a signal source module, a transmitter module, a radio frequency cancellation module, a receiver module, and a data preprocessing and control module;

The transmitter module is connected to the signal source module and the built-in upconverter of the receiver module through a built-in power divider, and the radio frequency cancellation module is connected to the transmitter through a built-in coupler and combiner. The machine module, the receiver module and the low-frequency ultra-wideband air-coupled transceiver antenna are connected, and the data preprocessing and control module is respectively connected to the signal source module, the transmitter module and the receiver through internal control signal lines. machine module connection.

Further, the signal source module includes a reference clock, a frequency synthesizer, a frequency multiplier and a band-pass filter connected in sequence;

The transmitter module includes a power splitter, a preamplifier, an adjustable attenuator, a drive amplifier, a power amplifier and a low-pass filter connected in sequence;

The radio frequency cancellation module includes a coupler, a vector modulator and a combiner connected in sequence; wherein the coupler and combiner are respectively connected to the transmitting antenna and the receiving antenna of the low-frequency ultra-wideband air-coupled transceiver antenna, and the vector The modulator is also controlled by a low frequency control circuit;

The receiver module includes a low noise amplifier, a frequency hopping filter, a variable gain amplifier, a first down converter, a band pass filter, a second down converter and a low pass filter connected in sequence; the second down converter The frequency converter is also connected to the low-frequency control circuit in the radio frequency cancellation module;

The receiver module also includes a temperature-compensated crystal oscillator and an up-converter. The temperature-compensated crystal oscillator is connected to the second down-converter and the up-converter respectively. The up-converter is also connected to the first down-converter respectively. Connect to the power splitter in the transmitter module;

The data preprocessing and control module includes an analog-to-digital converter and a baseband signal processing and main controller connected in sequence, wherein the baseband signal processing and main controller are also respectively connected to the frequency synthesizer and transmitter in the signal source module. The adjustable attenuator in the transmitter module and the frequency hopping filter connection in the receiver module.

Further, the working process of the radio frequency cancellation module is:

The low-frequency control circuit controls the amplitude and phase of the transmit signal input from the coupler to the vector modulator based on the size of the baseband signal generated by the demodulation of the receiver module, and generates a cancellation signal with the same amplitude and anti-phase as the direct wave signal received by the receiving antenna. and cancel in the combiner.

Further, under the action of the control signal of the data preprocessing and control module, the passband of the frequency hopping filter in the receiver module changes following the frequency change of the transmitted signal.

Furthermore, the transmitting antenna and receiving antenna of the low-frequency ultra-wideband air-coupled transceiver antenna have the same structure, and are both very high-frequency ultra-wideband folded monopole patch antennas, which include a dielectric substrate, a radiation patch antenna, an inductive cancellation patch and a grounding patch;

The radiating patch antenna is a monopole antenna with a symmetrical folded structure, which is arranged on the top layer of the dielectric substrate;

The induction cancellation patch and the ground patch are arranged on the bottom layer of the dielectric substrate.

Further, the radiation patch antenna includes an unfolded radiation patch and a folded radiation patch;

The folded radiation patch includes a longitudinally folded first patch branch, a transversely folded second patch branch, and a longitudinally folded and third patch branch;

The unfolded radiation patch is disposed below the midpoint of the second patch branch and perpendicular to the second patch branch;

The first patch branch and the third patch branch are symmetrically arranged with respect to the unfolded radiation patch.

Further, the feed point of the radiation patch antenna is provided at the beginning of the unfolded radiation patch.

Further, the induction cancellation patch covers the radiation patch antenna;

The area of the radiation patch antenna covered by the induction cancellation patch is proportional to the attenuation of the high-frequency end signal.

Further, the distance between the ground patch and the feeding point of the radiating patch antenna is a first spacing;

The size and first spacing of the ground patch are determined according to the target impedance of the monopole patch antenna.

The beneficial effects of the present invention are:

(1) The present invention adopts a line antenna scheme that is different from the area antenna used in general ground-coupled ground-penetrating radar. By folding the monopole antenna, the structural size of the antenna is greatly reduced, and by introducing an inductive offset patch Setting the distance between the ground patch and the feed point expands the gain bandwidth and impedance bandwidth of the antenna, not only extending the relative operating bandwidth of the antenna to 178.95%, but also reducing the lowest operating frequency of the antenna to 10MHz. As a result, a lightweight and miniaturized low-frequency ultra-wideband air-coupled transceiver antenna is produced, which solves the air coupling problem of UAV aerial ground-penetrating radar.

(2) The stepped frequency continuous wave radar system used in the present invention has the advantage of instantaneous narrow bandwidth. A low-frequency broadband frequency hopping filter is used in the receiver module, which effectively improves the sensitivity of the receiver. At the same time, the mounting method of the transmitting and receiving antennas is improved. The use of maximum radiation direction avoidance technology, combined with the radio frequency cancellation module of the ground-penetrating radar transceiver, greatly eliminates the strong broadband interference signal generated by the direct coupling of the transceiver antenna, effectively improving the dynamic range of the receiver, and thus achieving deep underground detection.

(3) The present invention uses a low-frequency step frequency continuous wave signal in the signal source module, and increases the output power of the transmitter module, thereby increasing the electromagnetic wave energy entering the ground, thereby further increasing the detection depth.

Description of drawings

Figure 1 is a schematic structural diagram of the UAV aerial ground penetrating radar provided by the present invention.

Figure 2 is a functional block diagram of the main body of the ground penetrating radar transceiver provided by the present invention.

Figure 3 is a functional block diagram of the data preprocessing and control module provided by the present invention.

Figure 4 is a schematic structural diagram of the very high frequency ultra-wideband folded monopole patch antenna provided by the present invention.

Figure 5 is a schematic diagram of the normalized current distribution of the monopole antenna provided by the present invention.

Figure 6 is a schematic diagram of the three-dimensional radiation pattern simulation results provided by the present invention.

Figure 7 is a schematic diagram of the impedance and return loss simulation results provided by the present invention.

Figure 8 is a schematic diagram of the matched impedance and return loss simulation results provided by the present invention.

Figure 9 is a schematic diagram of the impedance and return loss test results provided by the present invention.

Figure 10 is a comparison of transmission parameters measured when two antennas provided by the present invention are close to each other.

Among them: 1. Dielectric substrate; 2. Unfolded radiation patch; 3. First patch branch; 4. Third patch branch; 5. Induction cancellation patch; 6. Ground patch; 7. Second patch Branch; 8. UAV; 9. Ground-penetrating radar transceiver body; 10. Low-frequency ultra-wideband air-coupled transceiver antenna; 11. Lidar altimeter; 12. Attitude meter; 13. GPS module.

Detailed ways

The specific embodiments of the present invention are described below to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the technical field, as long as various changes These changes are obvious within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions and creations utilizing the concept of the invention are protected.

The embodiment of the present invention provides a UAV aerial ground penetrating radar based on a low-frequency ultra-wideband air-coupled antenna. As shown in Figure 1, it includes a UAV 8, a ground-penetrating radar transceiver body 9, and a low-frequency ultra-wideband air-coupled transceiver. Antenna 10, lidar altimeter 11, attitude meter 12 and GPS module 13;

The ground penetrating radar transceiver body 9 is mounted on a fixed plate in the middle of the landing gear of the UAV 8, and the low-frequency ultra-wideband air-coupled transceiver antenna 10 is suspended on the landing gear of the UAV 8, and Connected to the ground penetrating radar transceiver body 9 through radio frequency lines, the lidar altimeter 11 and the attitude meter 12 are respectively fixed below and above the low-frequency ultra-wideband air-coupled transceiver antenna 10, and the GPS module 13 Fixed on the arm of the drone 8;

The ground penetrating radar transceiver body 9 includes a signal source module, a transmitter module, a radio frequency cancellation module, a receiver module, and a data preprocessing and control module;

The transmitter module is connected to the signal source module and the built-in upconverter of the receiver module through a built-in power divider, and the radio frequency cancellation module is connected to the transmitter through a built-in coupler and combiner. The machine module, the receiver module and the low-frequency ultra-wideband air-coupled transceiver antenna 10 are connected, and the data preprocessing and control module is respectively connected to the signal source module, the transmitter module and the Receiver module connections.

In the embodiment of the present invention, specifically, based on the structure shown in Figure 1, the main body of the ground penetrating radar transceiver is mounted on a carbon fiber plate in the middle of the UAV landing gear, and the low-frequency ultra-wideband air-coupled transceiver antenna avoids technology in the direction of maximum radiation. , the transversely folded second patch branches 7 of the transceiver antenna are spliced together in parallel and opposite directions, and then tied to the landing gear with high-strength Kevlar fiber, and connected to the ground-penetrating radar transceiver body and lidar altimeter through radio frequency lines. The GPS module and the attitude meter are respectively glued below and above the antenna to record the flight height and attitude of the antenna relative to the ground during the flight to facilitate error correction of subsequent data collection. The GPS module is glued to the arm of the UAV. During the flight Record the latitude and longitude information.

In the embodiment of the present invention, Figure 2 is a functional block diagram of the main body of a ground penetrating radar transceiver, which specifically includes a signal source module, a transmitter module, a radio frequency cancellation module, a receiver module, and a data preprocessing and control module.

In this embodiment, the signal source module in Figure 2 includes a reference clock, a frequency synthesizer, a frequency multiplier and a band-pass filter connected in sequence;

Specifically, the signal source module uses a frequency synthesizer to generate 5MHz to 90MHz radar wave signals. Under the action of the control signal of the data preprocessing and control module, the amplitude, frequency, and phase of the radar wave signal are controlled based on the reference clock. The signal is then frequency multiplied. After the frequency multiplication of the device, a stepped frequency continuous wave signal with a frequency band of 10MHz to 180MHz, a frequency step of 1MHz, and a pulse repetition period of 100μs is generated. The frequency step amount of this signal is adjustable, ranging from 0.5MHz to 2MHz, and the adjustment interval is 0.5MHz; the pulse repetition period is adjustable, from 50μs to 200μs, and the adjustment interval is 10μs. The generated step frequency continuous wave signal passes through a bandpass After the filter, it is sent to the transmitter module.

In this embodiment, the transmitter module in Figure 2 includes a power splitter, a preamplifier, an adjustable attenuator, a driving amplifier, a power amplifier and a low-pass filter connected in sequence;

Specifically, the transmitter module is based on a three-stage amplifier and an adjustable attenuator to amplify the power of the step frequency continuous wave signal generated by the signal source module. Under the action of the control signal, the attenuation range of the adjustable attenuator is controlled to adjust the transmission Signal power consistency. The step frequency continuous wave signal enters the transmitter module, and the power divider divides the signal into two channels. One channel is sent to the transmit channel as a transmit signal for power amplification and gain adjustment, and the other channel is sent to the upconverter of the receiver for upconversion. The up-converted signal serves as the first local oscillator signal of the receiver. The frequency of the first local oscillator signal is the sum of the frequency of the temperature-compensated crystal oscillator and the frequency of the transmit signal. After the transmit signal power is amplified to 5W through the power amplifier, it enters the radio frequency Cancellation module.

In this embodiment, the radio frequency cancellation module in Figure 2 includes a coupler, a vector modulator and a combiner connected in sequence; wherein the coupler and combiner are respectively connected to the transmitting antenna of the low-frequency ultra-wideband air-coupled transceiver antenna. Connected to the receiving antenna, the vector modulator is also connected to the low-frequency control circuit;

Specifically, the working process of the radio frequency cancellation module is:

The low-frequency control circuit controls the amplitude and phase of the transmit signal input from the coupler to the vector modulator based on the size of the baseband signal generated by the demodulation of the receiver module, and generates a cancellation signal with the same amplitude and anti-phase as the direct wave signal received by the receiving antenna. and cancel in the combiner.

Furthermore, the RF cancellation module uses a low-frequency ultra-wideband matching circuit and a broadband vector modulator to make the output cancellation signal and the direct wave signal approximately equal in amplitude and reverse, thereby achieving the effect of broadband direct wave cancellation.

In this embodiment, the receiver module in Figure 2 includes a low-noise amplifier, a frequency hopping filter, a variable gain amplifier, a first downconverter, a bandpass filter, a second downconverter and a low-pass filter connected in sequence. filter; the second downconverter is also connected to the low-frequency control circuit in the radio frequency cancellation module;

The receiver module also includes a temperature-compensated crystal oscillator and an up-converter. The temperature-compensated crystal oscillator is connected to the second down-converter and the up-converter respectively. The up-converter is also connected to the first down-converter respectively. Connect to the power splitter in the transmitter module. Among them, the signal output by the frequency synthesizer in the signal source module is divided into two channels at the power divider of the transmitter module. One channel is sent to the preamplifier as a transmit signal, and the other signal is sent to the upconverter built in the receiver module for up-conversion. frequency conversion. The two signals generated by the temperature-compensated crystal oscillator in the receiver module are up-converted together with the signal output by the power divider built into the transmitter module to obtain the first local oscillator signal of the receiver. The first local oscillator signal is received by the receiving antenna. The target echo signal is down-converted in the first down-converter to obtain an intermediate frequency signal carrying target information. Another signal generated by the temperature-compensated crystal oscillator serves as the second local oscillator of the receiver, and is down-converted with the intermediate frequency signal in the second down-converter to obtain an analog baseband signal.

Specifically, the receiver module adopts a superheterodyne reception method and obtains an analog baseband signal with high spectral purity, low background noise and carrying underground target information through a secondary frequency conversion structure, providing a high signal-to-noise ratio for the data preprocessing module. baseband signal.

In this embodiment, a frequency hopping filter is introduced in the receiver module. Under the action of the control signal of the data preprocessing and control module, its passband changes with the frequency of the transmitted signal. For example, when the signal source generates 10MHz~ When the signal is 20MHz/step 1MHz, the passband of the filter is 10MHz~20MHz, and so on until 170MHz~180MHz.

Specifically, the frequency hopping filter is introduced to take advantage of the instantaneous narrow bandwidth of the frequency-stepped continuous wave radar system. The frequency hopping filter contains 17 filter channels. The filter channels are switched by switching the high-speed electronic switch on and off under the action of the synchronous control signal of the data preprocessing and control module. In order to keep the rectangular coefficient unchanged during the movement of the passband, a method of changing the capacitance and inductance at the same time is adopted. Compared with the traditional method of only changing the capacitance, a more consistent rectangular coefficient can be obtained.

In this embodiment, the data preprocessing and control module in Figure 2 includes an analog-to-digital converter and a baseband signal processing and main controller connected in sequence, wherein the baseband signal processing and main controller are also connected to the signal source respectively. Frequency synthesizer in the module, adjustable attenuator in the transmitter module and frequency hopping filter connections in the receiver module.

Specifically, the functional block diagram of the data preprocessing and control module is shown in Figure 3, in which the baseband signal processing and main controller include a digital signal processor, an embedded microprocessor, an FPGA (Field Programmable Gate Array) and a data memory, and Connect a variety of sensors and peripherals. The baseband signal processing is mainly to perform inverse Fourier transform on the baseband digital signal converted by the analog-to-digital converter in the digital signal processor, and synthesize the frequency domain data into a one-dimensional range image. Embedded microcontrollers and FPGAs mainly generate various control signals of the system, receive and store data from various sensors and peripherals to facilitate later error correction.

In the embodiment of the present invention, the transmitting antenna and the receiving antenna of the low-frequency ultra-wideband air-coupled transceiver antenna have the same structure. They are both very high-frequency ultra-wideband folded monopole patch antennas. As shown in Figure 4, they include a dielectric substrate 1 and a radiation patch antenna. , induction cancellation patch 5 and grounding patch 6; the radiation patch antenna is a monopole antenna with a symmetrical folding structure, which is arranged on the top layer of the dielectric substrate 1; the induction cancellation patch 5 and the grounding patch 6 are arranged on the The bottom layer of dielectric substrate 1.

In this embodiment, the radiation patch antenna includes an unfolded radiation patch 2 and a folded radiation patch; the folded radiation patch includes a longitudinally folded first patch branch 3, a transversely folded second patch branch 7, and a longitudinally folded second patch branch 7. The folded and third patch branches 4; the unfolded radiation patch 2 is arranged below the midpoint of the second patch branch 7 and perpendicular to the second patch branch 7; the first patch branch 3 and the third patch The patch branches 4 are arranged symmetrically with respect to the unfolded radiation patch 2 .

In this embodiment, the radiating patch antenna structure in Figure 4 is formed by folding the monopole antenna. Compared with the traditional unfolded monopole antenna, the length of the antenna is reduced and the goal of miniaturization of the antenna is achieved. , and when the lowest operating frequency of the antenna is reduced to 10MHz, the length of the antenna is only 1/15 of the standard half-wave dipole antenna. Its specific folding length is determined according to the required operating frequency band and the size of the target antenna.

In this embodiment, the feeding point of the radiation patch antenna is set at the beginning of the unfolded radiation patch 2 .

In this embodiment, the induction cancellation patch 5 covers the radiation patch antenna; further, the area of the radiation patch antenna covered by the induction cancellation patch 5 is proportional to the attenuation of the high-frequency end signal, that is, the larger the coverage area The larger the attenuation of the high-frequency end signal, the greater the attenuation. Based on this, the gain bandwidth of the antenna is expanded by setting the induction cancellation patch 5. Among them, the induction cancellation patch 5 is made of metal material, such as copper foil.

In this embodiment, the distance between the ground patch 6 and the feed point of the radiation patch antenna is the first spacing; further, the size and the first spacing of the ground patch 6 are based on the monopole patch. The target impedance of the antenna is determined.

In this embodiment, the antenna bandwidth is expanded by arranging the ground patch 6. This method can better meet the radiation efficiency of the antenna than simply using resistive loading to expand the antenna.

The monopole patch antenna provided in this embodiment has a simple structure and is easy to process. Compared with the existing ultra-wideband dipole patch antenna, it has a smaller size, lower operating frequency, wider gain bandwidth and better Consistent broadband radiation pattern for large depth aerial ground penetrating radar.

In this embodiment, when determining the operating frequency band and target size of the monopole patch antenna, a length of 1 meter, a width of 0.18 meters, and an operating frequency band of 10MHz-180MHz (relative bandwidth of 178.95%) are designed. Ultra-wideband folded monopole patch antenna takes the form of a transceiver antenna for aerial ground penetrating radar as an example to conduct subsequent simulations and determine antenna parameters.

When the operating frequency of the dipole antenna is reduced to 10MHz (wavelength is 30 meters), its length will exceed 10 meters. In order to meet the application requirements of large-depth aerial ground penetrating radar, the length of the antenna needs to be controlled within 1 meter. On this basis, the monopole antenna is an asymmetric form of the dipole antenna, and the folding method and folding size of the radiation patch antenna are determined according to the current distribution on the monopole antenna;

Among them, the current distribution I(z) on the dipole antenna is:

I(z)＝Isin[k(l-|z|],|z|≤l

In the formula, k=2π/λ is the phase constant, l is the length of the monopole, and z is the position of any point on the antenna.

Based on this, when l = 1.5m, the normalized current distribution of 10MHz, 50MHz, 100MHz and 180MHz signals will be as shown in Figure 5. Since the dipole antenna can be regarded as an expanded form of an open-circuit transmission line, Figure 5 0m in corresponds to the end of the antenna, and 1.5m corresponds to the feed point of the antenna.

As can be seen from Figure 5, the current distribution of signals at frequencies of 50MHz and below shows a monotonically increasing trend. In order to reduce the antenna length to 1m while ensuring the gain at the low-frequency end, the present invention sets the length of the unfolded radiation patch 2 to 0.99 m, the width is 1mm (based on impedance and power tolerance considerations), the total length of the two folded branches is 0.51m, the vertical width of the folded branches is 1mm, the horizontal width is 5mm (based on aesthetic appearance considerations), two The folding branch is designed as a symmetrical structure to ensure the symmetry of the radiation pattern.

According to the reverse current appearing in the antenna in the current distribution, the size and position of the induction cancellation patch 5 are determined. Specifically, it can be seen from Figure 5 that when the signal frequency is higher than 100MHz, a reverse current will appear on the antenna, which means that side lobes will appear in the radiation pattern of the antenna. In order to suppress the side lobes while expanding the gain of the antenna To reduce the bandwidth (ie, reduce the gain at the high-frequency end), the present invention introduces the induction cancellation patch 5. It can be known from the relevant theories of time harmonic fields and the law of electromagnetic induction that the induced current on the induction cancellation patch 5 tends to prevent the growth of the source current on the radiation patch, that is, it has a cancellation effect. In this embodiment, the induction cancellation patch 5 has a tendency to prevent the source current on the radiation patch from growing. The length of sheet 5 is set to 0.5m and the width is set to 0.18m.

For a monopole antenna, the impedance is adjusted by changing the distance between the feed point and the ground point. Since resistive loading will reduce the radiation efficiency of the antenna, and the shape of the monopole antenna is relatively fixed, this embodiment adopts a method of adjusting the distance between the feed point and the ground point to expand the impedance bandwidth of the antenna, connecting the feed point and the ground point. The spacing between locations is set to 35mm.

In this embodiment, based on the above parameter settings, the corresponding simulation results are shown in Figure 6 (the simulation software uses the three-dimensional electromagnetic simulation software HFSS). As can be seen from the figure, the 3dB gain bandwidth of the antenna is 170MHz (the relative bandwidth is 178.95 %, by definition, a relative bandwidth >20% is an ultra-wideband antenna), and within the operating frequency band of 10MHz-180MHz, the radiation directivity of the antenna is basically the same. It can also be seen from the changes in gain at each frequency point in Figure 6 that the current distribution of the monopole wire antenna also satisfies the above-mentioned current distribution formula. At the same time, we can also see the effect of the induction offset patch 5 in suppressing side lobes and expanding the gain bandwidth. .

The simulation results of antenna impedance and return loss are shown in Figure 7 ((a) is the impedance simulation, (b) is the return loss simulation). It can be seen from the figure that the impedance of the antenna is relatively convergent within the entire operating frequency band. , easy to match. The matched impedance and return loss simulation results are shown in Figure 8 (the simulation software uses the radio frequency circuit simulation software ADS). From Figure 8, it can be seen that the return loss of the antenna in the entire operating frequency band is less than -14.01dB.

The test results of impedance and return loss are shown in Figure 9 ((a) Impedance test, (b) Return loss test) (the test instrument uses a handheld RF analyzer N9914A). As can be seen from Figure 9, the measured antenna echo The loss is less than -14.06dB in the entire frequency band, which is basically consistent with the simulation results. In addition, since testing the antenna gain requires a microwave anechoic chamber, and this project team does not have such conditions, the transmission parameters (S21) measured when the two antennas are close to each other are used to characterize the radiation capability of the antenna. The test results of the transmission parameters are as shown in the figure As shown in 10, it can be seen from the figure that some frequency points within the working frequency band have strong radiation capabilities, but due to the influence of the test environment, the response within the entire working frequency band is not flat, so the test results can only be used as refer to.

In the description of the present invention, it should be understood that the terms "center", "thickness", "upper", "lower", "level", "top", "bottom", "inner", "outer", " The orientation or positional relationship indicated by "radial" and so on is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or component referred to must have a specific orientation. Constructed and operated in specific orientations and therefore not to be construed as limitations of the invention. Furthermore, the terms “first”, “second” and “third” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly specifying the number of technical features. Thus, a feature defined by "first", "second", "third" may explicitly or implicitly include one or more of these features.

The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, based on this The idea of the invention will be subject to change in the specific implementation and scope of application. In summary, the contents of this description should not be understood as limiting the invention.

Those of ordinary skill in the art will appreciate that the embodiments described here are provided to help readers understand the principles of the present invention, and it should be understood that the scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and these modifications and combinations are still within the protection scope of the present invention.

Claims (9)

1. The unmanned aerial vehicle aviation ground penetrating radar based on the low-frequency ultra-wideband air coupling antenna is characterized by comprising an unmanned aerial vehicle (8), a ground penetrating radar transceiver main body (9), a low-frequency ultra-wideband air coupling transceiver antenna (10), a laser radar altimeter (11), an attitude meter (12) and a GPS module (13);

the ground penetrating radar transceiver main body (9) is carried on a fixed plate in the middle of a landing gear of the unmanned aerial vehicle (8), the low-frequency ultra-wideband air coupling transceiver antenna (10) is hung on the landing gear of the unmanned aerial vehicle (8) and is connected with the ground penetrating radar transceiver main body (9) through a radio frequency line, the laser radar altimeter (11) and the attitude meter (12) are respectively fixed below and above the low-frequency ultra-wideband air coupling transceiver antenna (10), and the GPS module (13) is fixed on a horn of the unmanned aerial vehicle (8);

the ground penetrating radar transceiver main body (9) comprises a signal source module, a transmitter module, a radio frequency cancellation module, a receiver module and a data preprocessing and control module;

the transmitter module is respectively connected with the signal source module and the up-converter arranged in the receiver module through a built-in power divider, the radio frequency cancellation module is respectively connected with the transmitter module, the receiver module and the low-frequency ultra-wideband air coupling receiving and transmitting antenna (10) through a built-in coupler and a combiner, and the data preprocessing and control module is respectively connected with the signal source module, the transmitter module and the receiver module through internal control signal wires.

2. The unmanned aerial vehicle aviation ground penetrating radar based on the low-frequency ultra-wideband air coupling antenna according to claim 1, wherein the signal source module comprises a reference clock, a frequency synthesizer, a frequency multiplier and a band-pass filter which are connected in sequence;

the transmitter module comprises a power divider, a preamplifier, an adjustable attenuator, a driving amplifier, a power amplifier and a low-pass filter which are connected in sequence;

the radio frequency cancellation module comprises a coupler, a vector modulator and a combiner which are connected in sequence; the coupler and the combiner are respectively connected with a transmitting antenna and a receiving antenna of the low-frequency ultra-wideband air coupling receiving and transmitting antenna (10), and the vector modulator is also controlled by a low-frequency control circuit;

the receiver module comprises a low noise amplifier, a frequency hopping filter, a variable gain amplifier, a first down-converter, a band-pass filter, a second down-converter and a low pass filter which are connected in sequence; the second down converter is also connected with a low-frequency control circuit in the radio frequency cancellation module;

the receiver module further comprises a temperature compensation crystal oscillator and an up-converter, wherein the temperature compensation crystal oscillator is respectively connected with the second down-converter and the up-converter, and the up-converter is also respectively connected with the first down-converter and a power divider in the transmitter module;

the data preprocessing and control module comprises an analog-to-digital converter and a baseband signal processing and main controller which are sequentially connected, wherein the baseband signal processing and main controller is also respectively connected with a frequency synthesizer in the signal source module, an adjustable attenuator in the transmitter module and a frequency hopping filter in the receiver module.

3. The unmanned aerial vehicle aviation ground penetrating radar based on the low-frequency ultra-wideband air coupling antenna according to claim 2, wherein the working process of the radio frequency cancellation module is as follows:

the low-frequency control circuit controls the amplitude and the phase of the transmitting signal input to the vector modulator by the coupler according to the size of the baseband signal generated by demodulation of the receiver module, generates a cancellation signal with equal amplitude and opposite phase to the direct wave signal received by the receiving antenna, and performs cancellation in the combiner.

4. The unmanned aerial vehicle ground penetrating radar based on the low-frequency ultra-wideband air coupling antenna according to claim 2, wherein the passband of the frequency hopping filter in the receiver module changes along with the frequency change of the transmitting signal under the control signal of the data preprocessing and control module.

5. The unmanned aerial vehicle aviation ground penetrating radar based on the low-frequency ultra-wideband air coupling antenna according to claim 1, wherein the transmitting antenna and the receiving antenna of the low-frequency ultra-wideband air coupling receiving and transmitting antenna (10) have the same structure, are all very high frequency ultra-wideband folded monopole patch antennas, and comprise a dielectric substrate (1), a radiation patch antenna, an induction cancellation patch (5) and a grounding patch (6);

the radiation patch antenna is a monopole antenna with a symmetrical folding structure and is arranged on the top layer of the dielectric substrate (1);

the induction cancellation patch (5) and the grounding patch (6) are arranged on the bottom layer of the dielectric substrate (1).

6. The unmanned aerial vehicle airborne ground penetrating radar based on the low frequency ultra wideband air coupling antenna according to claim 5, wherein the radiating patch antenna comprises an unfolded radiating patch (2) and a folded radiating patch;

the folded radiating patch comprises a first patch limb (3) folded longitudinally, a second patch limb (7) folded transversely, and longitudinally folded and third patch limbs (4);

the unfolded radiation patch (2) is arranged below the midpoint of the second patch branch (7) and is perpendicular to the second patch branch (7);

the first patch branch (3) and the third patch branch (4) are symmetrically arranged with respect to the unfolded radiation patch (2).

7. The unmanned aerial vehicle ground penetrating radar based on the low-frequency ultra-wideband air coupling antenna according to claim 6, wherein the feed point of the radiating patch antenna is arranged at the beginning end of the unfolded radiating patch (2).

8. The unmanned aerial vehicle airborne ground penetrating radar based on the low frequency ultra wideband air coupling antenna according to claim 6, wherein the inductive cancellation patch (5) covers the radiating patch antenna;

the area of the induction cancellation patch (5) covering the radiation patch antenna is in direct proportion to the attenuation of the high-frequency end signal.

9. The unmanned aerial vehicle ground penetrating radar based on the low-frequency ultra-wideband air-coupled antenna according to claim 6, wherein the distance between the ground patch (6) and the feeding point of the radiating patch antenna is a first pitch;

the size and the first spacing of the ground patch (6) are determined according to the target impedance of the monopole patch antenna.