KR20030020722A - Ground penetration radar - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground exploration radar capable of nondestructively analyzing and measuring positions of metals and nonmetallic materials buried underground, and comprising: a transmitting antenna for injecting a predetermined signal into an object under investigation; An antenna configured to receive a reflection signal reflected back from the probe; Search signal transmission / reception means for providing the predetermined signal to the transmission antenna and receiving a reflected signal received through the reception antenna to obtain a difference between the transmission signal and the received signal; Generates a predetermined oscillation frequency control signal based on the signal from the probe signal transmission / reception means, transmits it to the probe signal transmission / reception means, performs real-time A / D conversion of the signal from the probe signal transmission / reception means, and then performs fast Fourier transform. Digital signal processing means for outputting the result value; And a built-in program including a predetermined function, and having information providing means for displaying an image of the object on the screen based on a result value outputted from the digital signal processing means, thereby embedding metal underground. The location of the embedding of nonmetallic bodies can be simply and nondestructively examined.

Description

Ground penetration radar

The present invention relates to a ground exploration radar, and more particularly, to a ground exploration radar to determine the location of metal and non-metal buried underground using the frequency modulated continuous wave (FMCW).

Conventionally, there are two methods of exploring underground objects on the ground using ground exploration radar. The first method involves drilling two boreholes and inserting a transmitter / receive antenna into each borehole. Second, injecting electromagnetic waves into the surface from the surface or structure surface in close proximity to the ground, and continuously There is a method of receiving a signal reflected from the plane.

However, in the case of using the former borehole method, the disadvantage of having to drill a borehole on the ground surface, structural safety problems, public facilities (eg, electricity, gas pipes, communication lines, etc.) buried underground in the process of drilling boreholes are destroyed. To cause problems.

In addition, when the latter method is used, detection of only metal bodies is possible, and detection is difficult at a close distance (for example, within 30 cm).

The present invention has been proposed to solve the above-described problems, and an object of the present invention is to provide a ground exploration radar capable of overcoming the limitation of the permittivity, surface state, and the like of the topsoil surface and broadening the range of detection.

Another object of the present invention is to provide a ground exploration radar for non-destructively analyzing and measuring the positions of metals and nonmetallic materials buried underground.

1 is a graph illustrating a relationship between frequency and time of a radar of an embodiment of the present invention in which a frequency modulated continuous wave (FMCW) scheme is employed;

2 is a block diagram of a ground exploration radar according to an embodiment of the present invention;

3 is a configuration diagram of the antenna unit shown in FIG.

4 is a detailed configuration diagram of the digital signal processor shown in FIG. 2;

FIG. 5 is a diagram showing an example of a filter constituting an input portion of a digital signal processor shown in FIG. 4;

6A is a view showing an operation screen of the AD converter shown in FIG. 4;

6B is a view showing an operation screen of the DA converter shown in FIG. 4;

7 is a view showing the overall specifications for the ground exploration radar according to an embodiment of the present invention,

8 is a flowchart for explaining an operation of a digital signal processing unit shown in FIG. 4;

FIG. 9 is a flowchart illustrating a fast Fourier transform process in FIG. 8;

FIG. 10 is a diagram illustrating an example of an exploration result screen displayed on a monitor by a ground exploration radar according to an exemplary embodiment of the present invention.

※ Explanation of code for main part of drawing

10: probe signal transmission and reception unit 11: microwave variable frequency oscillator

12 filter 13 directional coupler

14 delay line 15 amplifier

16 mixer 20 antenna portion

21 transmitting antenna 22 receiving antenna

30 digital signal processing unit 31 low pass filter

32: low frequency amplifier 33: control circuit

34: analog / digital converter 40: computer

51, 52: analog filter 53, 54: AD converter

55: digital signal processor 56, 57: DA converter

58: UART (Universal Asynchronous Receiver Transmitter) chip

59: MAX232 chip

In order to achieve the above objects, the ground exploration radar according to a preferred embodiment of the present invention receives a transmission antenna for inputting a predetermined signal to an object under investigation and a reflection signal reflected back from the object. An antenna configured to receive antennas; Search signal transmission / reception means for providing the predetermined signal to the transmission antenna and receiving a reflected signal received through the reception antenna to obtain a difference between the transmission signal and the received signal; Generates a predetermined oscillation frequency control signal based on the signal from the probe signal transmission / reception means, transmits it to the probe signal transmission / reception means, performs real-time A / D conversion of the signal from the probe signal transmission / reception means, and then performs fast Fourier transform. Digital signal processing means for outputting the result value; And information providing means for embedding a program including a predetermined function and displaying an image of the object on the screen based on a result value output from the digital signal processing means.

Hereinafter, a ground exploration radar according to an embodiment of the present invention will be described with reference to the accompanying drawings.

First, the principle of an embodiment of the present invention will be described with reference to the graph of FIG.

In FMCW the transmit frequency changes as a function of time. Assuming that the transmission frequency increases linearly with time as in FIG. 1, the signal returns after T = 2R / c time if there is a reflector at a distance R apart.

However, if this signal is heterodyne with the transmission signal through a nonlinear element such as a diode, a beat note f _b is generated. If the Doppler frequency shift does not exist, the bit frequency (differential frequency) measures the distance of the target, and thus f _b = f _r . Here, f _r is a bit frequency according to the target distance. Assuming that the rate of change of the carrier frequency is f ₀ , the bit frequency is expressed by Equation 1 below.

[Equation 1]

In practice, in FMCW radar, the frequency does not constantly change in one direction, but requires periodic modulation such as a triangular wave frequency modulation waveform. However, the modulation does not necessarily need to be a triangular waveform, but may be a sawtooth waveform, a sine waveform or any other waveform. In the case of triangular wave modulation, the bit frequency as a function of time is expressed by Equation 1 above. If the frequency is modulated at a rate of f _{m in} the Δf range, the distance R can be determined by measuring the bit frequency. In the case of distance measurement, a difference frequency due to a time delay between a frequency-modulated transmission signal and a signal propagated to a target and then returned is obtained, and distance information may be obtained using the fast Fourier transform (FFT). The relationship between the distance and the difference frequency of the linear FMCW radar is shown in Equation 2 below.

[Equation 2]

Where c is the luminous flux [m / s], R is the distance from the object [m], Is the bandwidth [GHz], epsilon is the dielectric constant of the medium and T is the sweep time. Here, in order for the difference frequency f _b to be maintained at a constant value, the frequency modulation characteristics of the voltage controlled oscillator (VCO) must be excellent. Linearity L, a measure for evaluating the frequency-controlled oscillator frequency characteristics, is defined as in Equation 3 below.

[Equation 3]

here, Wow Denotes the maximum and minimum values of tuning sensitivity within the modulation frequency range, respectively. Tuning sensitivity S is the ratio of output frequency change to unit control voltage change. That is, it is a value indicating the slope of the voltage-frequency modulation characteristic curve. The tuning sensitivity S is expressed by the following expression (4).

[Equation 4]

In Equation 4, the linearity of 0% means that the voltage-frequency modulation characteristic curve is a straight line, and the linearity of 0.1% or less should be maintained for a good FMCW radar system design.

The transmitted signal frequency F _t and the received signal frequency F _r can be expressed as follows.

F _t = f ₀ + (B _r / T) t ~~~~~~~~~~~~~~~~~~~ 0 <t <TF _t = f ₀ + B _r- (B _r / T ) (2T-t) ~~~~~ T <t <2T

And

F _r = f ₀ + (B _r / T) (t + t) + f _d ~~~~~~~~~~~ 0 <t <T

F _r = f ₀ + B _r- (B _r / T) (2T-t-τ) + f _d ~~~ T <t <2T ~

Where F _t = transmitted signal frequency, F _r = received signal frequency, B _r = frequency modulation bandwidth, f ₀ = frequency at time t = ₀ t, f _d = Doppler frequency transition, t = from sweep start Where T = sweep repetition interval of the transceiver, τ = elapsed time of the signal from the transmitter to the object and back. The IF output frequency is the difference in period T and 2T for the moving object with respect to velocity V _d . In this range, the frequency shift f _r and the Doppler frequency f _d due to time delay are defined by Equation 5 below.

[Equation 5]

f _r = (2R / C) (B _r / T)

f _d = 2V _d f / C

Where V _d = radiation speed of the object, C = propagation speed, f = operating frequency, and R = range of the object. Radar Transceiver Range Is dependent on the sweeping bandwidth B_r,

If one frequency in one period is ( The theoretical detection range resolution

Same as Therefore, to obtain a 1m detection range, the theoretical FM bandwidth is required at least 150 MHz. Depends on the FM sweep bandwidth and the FFT beat signal sample interval, and the accuracy of the range measurement depends on the FM sweep linearity. Therefore, in order to obtain accurate distance information and fine resolution, the sweeping frequency bandwidth must be widened. However, in the case of a general voltage controlled oscillator (VCO), when the frequency bandwidth is widened, the output frequency is linearly proportional to the control voltage. Distance information is not concentrated to a precise point.

For this reason, the wideband frequency variable generator (ie, microwave variable frequency oscillator) used in the present invention is mostly made using YIG (Yttrium Iron Garnet).

According to the ground exploration radar according to the embodiment of the present invention having the above principle, the electromagnetic wave is incident from the surface of the earth or the surface of the structure to the inside of the surface, and subsequently receives the wave reflected back from the medium boundary surface. . Some of the electromagnetic waves reflect at the interface where the properties of the media change, and some of them continue to penetrate into the other media layers, whose propagation speed and wavelength depend on the dielectric constant of each medium through which they pass. The high reflection characteristic depends on the dielectric constant difference between different media. Therefore, if the characteristics of the medium (dielectric constant) and the time passed through the medium can be known, the thickness and position of the medium layer can be identified, and the presence, depth, location, and scale of the interface, internal cracks or cavities between the media can be determined. I can make it.

FIG. 2 is a block diagram of a ground exploration radar according to an embodiment of the present invention, which includes a transmission antenna 21 for injecting a predetermined signal into an object under investigation on the ground surface or a structure, and a reflection signal reflected and reflected from the object under investigation. An antenna unit 20 configured to receive the reception antennas 22; An probe signal transmitting / receiving unit (10) for providing the predetermined signal to the transmitting antenna (21) and receiving a reflected signal received through the receiving antenna (22) to obtain a difference between the transmitting signal and the received signal; Generates a predetermined oscillation frequency control signal based on the signal from the probe signal transceiver 10 and transmits it to the probe signal transceiver 10, and transmits the signal from the probe signal transceiver 10 in real time. A digital signal processor 30 for performing fast Fourier transform after the / D conversion and outputting the result value; And a computer 40 having a program including a predetermined function embedded therein and displaying an image of the object on the screen based on a result value output from the digital signal processing unit 30.

The probe signal transmitting / receiving unit 10 generates a sine wave having a constant amplitude and frequency (for example, a frequency of 3 to 6 GHz) that changes linearly with time, and generates a material called YIG (Yttrium Iron Garnet). A microwave variable frequency oscillator 11 used; A filter 12 having a characteristic of a low pass filter for removing harmonic components generated by the microwave variable frequency oscillator 11; A directional coupler (13) which separates the frequencies of 3 to 6 GHz through the filter (12) and transmits them to the transmitting antenna (21) and transmits the reflected signal received by the receiving antenna (22) to a circuit for processing; A delay line (14) for delaying the oscillation signal by an approximate delay time until the signal transmitted from the transmitting antenna (21) is received at the receiving antenna (22) so as to synchronize transmission / reception at the receiving end; An amplifier (15) for amplifying the reflected signal received by the receiving antenna (22) to a predetermined level; And a mixer 16 for generating a difference between a transmission signal input through the delay line 14 and a reception signal input through the amplifier 15.

The digital signal processor 30 converts an input signal into a digital signal, transmits the signal to the computer 40 using the signal, and uses the microwave variable frequency oscillator of the probe signal transmitter / receiver 10. In order to vary the frequency of (11) from 3 to 6 GHz, the power supply is varied. Therefore, in the embodiment of the present invention, the digital signal processor 30 is responsible for the overall control of the entire configuration.

The digital signal processor 30 is a low-pass filter 31 that passes only the low-frequency signal that is a necessary signal because the signal input through the mixer 16 is a low frequency component of 1MHz or less and a high frequency signal of a predetermined GHz band is mixed. ; A low frequency amplifier (32) for amplifying the low frequency signal passing through the low pass filter (31) to a predetermined level to enable signal processing at a later stage; A control circuit unit 33 for synchronizing synchronization between the transmission and reception circuits and for varying and outputting a control signal (for example, a voltage component) for determining an oscillation frequency of the microwave variable frequency oscillator 11; And an analog / digital converter 34 for converting an analog signal of 1 MHz or less output from the low frequency amplifier 32 into a digital signal and transmitting the same to the computer 40.

The computer 40 is an information providing means for receiving a digitally converted signal through AD conversion from the analog / digital converter 34 and displaying the screen based on a program programmed therein. In the present invention, the computer 40 configures the user interface using a program called Boland's Delphi (which is very similar to MS's Visual Basic), and an optimum result for the currently received radar signal is displayed on the monitor screen. Is displayed on. That is, the computer 40 has a graphical user interface (GUI) internally, and receives a digital signal output after being processed by the digital signal processor 30 to display an image processed screen on a monitor. The program built into the computer 40 includes a correction function, a resolution adjustment function, a waveform analysis function, and the like.

The correction function is a function of initializing the strength of the signal input from the digital signal processor 30, and plays an important role in the initial setting of the hardware. Of course, the program is run without the correction function, but the resolution of the object to be checked is reduced, and the shape cannot be easily distinguished. Therefore, the correction work is very important when the hardware is first driven to obtain data.

In addition, the resolution adjustment function is a function to make it easier to check the object by adjusting the result output on the monitor step by step.

The waveform analysis function is a function for storing the obtained results and taking an average or performing various numerical operations to obtain an optimized result. Simply observe the waveform in real time and store it in memory when data analysis is difficult, then process the data to get more accurate results.

Although the computer 40 is illustrated as an information providing means in the embodiment of the present invention, a program having the correction function, the resolution adjustment function, and the waveform analysis function can be embedded in the portable device such as a laptop or a PDA, and image processing is possible. If applicable, it can be applied to the portable device.

3 is a configuration diagram of the antenna unit shown in FIG. 2, wherein the transmitting antenna 21 and the receiving antenna 22 constitute an antenna unit, and the characteristics of the transmitting antenna 21 and the receiving antenna 22 are the same. .

In Fig. 3, the SMA connector is a kind of connector. Since the attenuation of the BNC connector used at a frequency of 1 GHZ or less is large in the 3 to 6 GHz band, an SMA connector that can be used up to 18 GHz is used.

In the antenna part of FIG. 3, since the cavity is covered on the back of the monopole antenna, directivity is formed on only one side, and thus the gain is higher than that of a general monopole.

Accordingly, the antenna portion of FIG. 3 uses a cavity-backed monopole antenna to satisfy the C band (3 to 6 GHz) frequency band. The reason why the cavity-backed monopole antenna is used is that the antenna for the subsurface radar should be placed close to the ground and radiate more energy to the ground, so the air must have minimal directivity and power loss. Solves this. The standing wave ratio (SWR) of the antenna part of FIG. 3 is 1: 1.5 or less in the 3 to 6GHz band as a result of the experiment.

And, the antenna portion of FIG. 3 operates with a spacing between at least 2 cm on the earth's surface (or the surface of any structure). The reason for this is that the antenna must be in close contact with the surface and have good mobility, but because the surface is not always flat, the antenna must be able to operate at a certain distance from the surface. In this case, a reflection is created which depends on the relative dielectric constant between the air and the surface. This unwanted reflection (i.e. surface reflection) not only reduces antenna efficiency, but also detects the object indefinitely, thus allowing for a mobility of 2 cm between the antenna and the ground (or surface of any structure). In addition, the meaning of the surface spacing changes the performance of the antenna and creates a strong reflection from the ground, reducing the ability of the ground probe radar to detect objects, but by minimizing the delay line 14.

4 is a detailed configuration diagram of the digital signal processor shown in FIG. 2, wherein the digital signal processor 30 includes two channels of analog input terminals to increase data processing speed. The analog signals input from the analog input terminals 1 and 2 are respectively input to analog filters 51 and 52 connected correspondingly. The analog filters 51 and 52 perform the function of the low pass filter 31 shown in FIG.

The low frequency signals filtered by the analog filters 51 and 52 are input to the AD converters 53 and 54, respectively, between the analog filters 51 and 52 and the AD converters 53 and 54. The low frequency amplifier 32 is omitted in FIG.

That is, the input part of the digital signal processor 30 is composed of a butter-worth type analog filter 51 and 52 and AD converters 53 and 54 having large anti-aliasing characteristics. The analog filters 51 and 52 prevent aliasing of the digital system and are configured in consideration of the input signal and the sampling frequency of the digital system. Accordingly, in the present invention, the cut-off frequency of the analog filters 51 and 52 is set to 2 KHz in consideration of the maximum frequency of the output signal of the probe signal transceiver 10. In addition, the butter-worth type analog filters 51 and 52 having the anti-aliasing characteristics may include resistors R1 and R2, capacitors C1 and C2, and an OP amplifier, as shown in FIG. The resistors R1 and R2 are connected in series to the non-inverting terminal (+) of the OP amplifier located between the input terminal Vi and the output terminal Vo, and the capacitor (+) is connected to the non-inverting terminal (+) of the OP amplifier. C1) may be grounded, and the capacitor C2 may be connected to the output side of the OP amplifier and the middle of the resistors R1 and R2.

The digital signal AD converted from the AD converters 53 and 54 is output to the digital signal processor 55. Here, the operation waveforms of the AD converters 53 and 54 are as illustrated in FIG. 6A. The digital signal processor 55 is constructed using TI's TMS320C32-50 board, which is high-performance and capable of real-time FFT (Fast Fourier Transform) and floating operations. The serial signal of the computer which is the user interface means 40 through the UART (Universal Asynchronous Receiver Transmitter) chip 58 and the MAX232 chip 59 through the digital signal processor 55 and the conversion process such as digital filtering. Connected to the port.

The signal output from the digital signal processor 55 is also input to the DA converters 56 and 57, and the DA converters 56 and 57 become the control circuit section 33 of FIG. The DA converters 56 and 57 are devices for generating an input of the microwave variable frequency oscillator 11 of the probe signal transceiver 10, and have a 16-bit resolution, so that the precision of the microwave variable frequency oscillator 11 is accurate. Frequency control is possible. Operation waveforms of the DA converters 56 and 57 are as illustrated in FIG. 6B.

7 is a general specification (for example, method, frequency of use, measurement method, measurement distance, antenna specification, specification of DSP chip, specification of ADC, power supply, error rate, etc.) for ground detection radar according to an embodiment of the present invention. Software, scanning points, etc.).

Next, the operation of the ground exploration radar according to the embodiment of the present invention will be described.

First, looking at the operation of the probe signal transmission and reception unit 10, if the speed of the microwave in the medium is known, it is possible to measure the distance of the object by measuring the bidirectional traveling speed and the delay time τ.

That is, the difference between the frequency of the microwave variable frequency oscillator 11 and the received frequency (another frequency) varies linearly with respect to time and therefore is always constant and proportional to the bidirectional propagation time tau. As a result of this, a method for differential frequency measurement can be found.

First, using the trigonometric formula:

If a signal oscillated by the microwave variable frequency oscillator 11 and filtered by the filter 12 and then transmitted by the directional coupler 13 through the transmitting antenna 21 into the ground surface is called S ₁ , the detected object in the ground surface When the signal reflected from the screen and received by the reception antenna 22 is S ₂ , the transmitted signal S ₁ and the received signal S ₂ are defined as follows. (A ₁ is generally significantly larger than A ₂ )

When the signal S ₁ and S ₂ results are calculated using the trigonometric formula described above,

Where F is the difference frequency (Hz), s is the total length of the path from the object (m), c is the speed of light (m / s), [Hz]. The difference frequency F is linearly proportional to the bidirectional propagation time, and the amplitude of S_3 is linearly proportional to the reflectivity of the target (ie, the object). For complex objects, A ₁ >> A ₂ (assuming), we can get the sum of the cosine wave signals with the difference frequencies and amplitudes.

Therefore, some power is separated from the directional coupler 13 with respect to the shape of the reference signal S ₁ oscillated by the microwave variable frequency oscillator 11 and transmitted to the mixer 16 through the delay line 14. Thus, the mixer 16 multiplies the reference signal S ₁ by the reflected signal S ₂ in analog form and selects the low frequency component S ₃ (differential frequency) from the result.

Thereafter, the data (that is, the difference frequency) generated by the mixer 16 is input to the digital signal processor 30.

Accordingly, in the low pass filter 31 of the digital signal processor 30, since the signal input from the mixer 16 is mixed with low frequency components of 1 MHz or less and high frequency signals of GHz band, the low frequency which is a necessary signal among them. Only pass the signal. The passed low frequency signal is amplified by the low frequency amplifier 32 at a predetermined level and then transmitted to the control circuit unit 33 and the analog / digital converter 34. The control circuit unit 33 varies and outputs a voltage for determining the oscillation frequency of the microwave variable frequency oscillator 11 of the probe signal transmission / reception unit 10, and the analog / digital converter 34 is different from the difference frequency. The fast Fourier transform (FFT) of the difference frequency component S ₃ is detected to determine the object's position in order to determine the reflectivity values of the object (ie the object under the ground).

Referring to the flowchart of FIG. 8, the operation in the above-described digital signal processing unit 30 will be described in detail again as follows.

When data (analog signal) from the mixer 16 is input (step S10), the input data is filtered by the analog filters 51 and 52 of FIG. 4 and then subjected to sampling by the AD converters 53 and 54 in real time. After digital conversion, the digital signal processor 55 undergoes an FFT (Fast Fourier Transform) process (steps S12 and S14).

Thereafter, the analog-converted signal from the DA converters 56 and 57 is output as the oscillation frequency control signal for the microwave variable frequency oscillator 11, and on the other hand, the UART chip 58 and the MAX232 chip 59 are connected. It is transmitted via serial to the input of the computer 40.

Accordingly, the computer 40 performs image processing based on the input digital value to display the image of the object on the monitor (step S16).

Herein, a process of transmitting the value through the FET process to the input unit of the computer 40 will be described in detail with reference to the flowchart of FIG. 9. The value i sampled and input in step S12 is preset. If the size is larger than the value of one size (meaning a sampling size) (“No” in step S20 of FIG. 9), the sampled input value i is doubled and then the fast Fourier transform is performed again (step S22). S24).

If the sampled input value i is smaller than a preset size value (Yes in step S20), fast Fourier transform is performed based on the sampled input value i. .

If the result of the fast Fourier transform is smaller than "1" ("Yes" in step S26), the signal corresponding to the corresponding signal (i.e., should be displayed in blue) in the digital signal processor 55. ) Is transmitted to the computer 40 via the UART chip 58 and the MAX232 chip 59 (step S28), and the value of the fast Fourier transform is larger than "1" (in step S26). No "), the flow advances to step S30 to determine whether the result value of the fast Fourier transform is larger or smaller than " 2 ".

In step S30, if the result of the fast Fourier transform is smaller than " 2 ", the digital signal processor 55 sends a corresponding signal (i.e., a signal meaning that it should be displayed in yellow) to the UART chip. (58) and the MAX232 chip 59 to the computer 40 (step S32), and if the result of the fast Fourier transform is greater than " 2 ", the digital signal processor 55 A corresponding signal (that is, a signal that should be displayed in red) is transmitted to the computer 40 via the UART chip 58 and the MAX232 chip 59 (step S34).

Accordingly, the computer 40 receives the digital signal transmitted from the digital signal processor 30 and displays the optimal result screen in the form of image paper on the monitor through correction, resolution adjustment, waveform analysis, and the like (Fig. 10). In the case of Figure 10, by driving the computer 40 that is embedded with a program capable of outputting the image (that is, a program containing a correction function, resolution adjustment function, waveform analysis function), plastic mines (M14) made of plastic, metal ball, The measurements were taken with a metal pipe 10 cm deep in a box filled with wet sand. Ambient influences were not considered and the program was measured after the initial calibration. The measurements showed stronger signals in metals than plastics, and stronger signals in metal pipes, despite being buried deeper than other objects. And, it can be seen that the plastic object that could not be found in the metal detector can be detected.

As described in detail above, according to the present invention, the image resolution of the underground structure is improved by minimizing the surface reflection by setting the delay line, and the signal attenuation according to the depth of the soil is compensated to the maximum by using the fast Fourier transform, Non-destructive and simple inspection of the buried positions of metals and nonmetallic bodies buried underground is possible.

In addition, the present invention described above is applicable to non-destructive inspection equipment, plastic mine exploration, building structure diagnosis, short-range radar system, imaging system.

On the other hand, the present invention is not limited only to the above-described embodiment, but can be modified and modified within the scope not departing from the gist of the present invention, the technical idea to which such modifications and variations are also applied to the claims Must see

Claims (9)

An antenna comprising a transmitting antenna for inputting a predetermined signal to the object under the ground, and a receiving antenna for receiving the reflected signal reflected from the object to be returned; Search signal transmission / reception means for providing the predetermined signal to the transmission antenna and receiving a reflected signal received through the reception antenna to obtain a difference between the transmission signal and the received signal; Generates a predetermined oscillation frequency control signal based on the signal from the probe signal transmission / reception means, transmits it to the probe signal transmission / reception means, performs real-time A / D conversion of the signal from the probe signal transmission / reception means, and then performs fast Fourier transform. Digital signal processing means for outputting the result value; And A ground detection radar, comprising: a program including a predetermined function; and an information providing means for displaying an image of the object on the screen based on a result value output from the digital signal processing means. The method of claim 1, And the antenna is a cavity-backed monopole antenna that satisfies a constant operating frequency band and maintains a constant distance from the ground surface. The method of claim 2, And a predetermined operating frequency band satisfying the antenna is 3 to 6 GHz, and a distance from the ground surface is 2 cm. The method of claim 1, The probe signal transmitting and receiving means includes a microwave variable frequency oscillator for oscillating a signal of a predetermined frequency band; A filter for removing harmonic components generated by the microwave variable frequency oscillator; A directional coupler that separates a transmission signal through the filter and transmits the signal to the transmission antenna and transmits the reflection signal received by the reception antenna to a circuit for processing the signal; A delay line for delaying a transmission signal provided by the directional coupler by a predetermined time; And a mixer for generating a difference between the transmission signal from the delay line and the reception signal input from the reception antenna. The method of claim 4, wherein And the microwave variable frequency oscillator uses yttrium iron garnet (YIG). The method of claim 4, wherein The digital signal processing means may include: a low pass filter for passing only a low frequency signal among the signals input from the mixer; An AD converter for converting a low frequency signal through the plurality of low pass filters into a digital signal; A digital signal processor which receives the digital signal and performs fast Fourier transform and transmits the result value to the information providing means; And a control circuit unit generating an oscillation frequency control signal based on a signal from the digital signal processor and providing the oscillation frequency control signal to the microwave variable frequency oscillator. The method of claim 6, The cutoff frequency of the low pass filter is ground survey radar, characterized in that 2KHz. The method of claim 1, The program embedded in the information providing means includes a correction function for initializing the strength of the signal input from the digital signal processing means, and stepwise adjustment of the result output on the monitor, so that the identification of the object is easily performed. And a waveform analysis function for storing the result value from the digital signal processing means and performing an average calculation and various numerical operations to obtain an optimized result. The method of claim 1, And an image displayed on the monitor of the information providing means is an image of a metal body or a nonmetal body.