JPH0427511B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an apparatus for exploring underground pipes using radio waves. More specifically, the present invention relates to a buried pipe exploration device that uses a circularly polarized antenna driven by a broadband electrical pulse signal to collect reflection information from underground.

"Prior Art" A conventional device of this type is shown in FIG. This is based on the principle of pulse radar, which is used in the air for various purposes, but because the distance to the buried object is short, it requires higher distance measurement resolution than airborne radar. Therefore, a baseband impulse signal is used, which has a much narrower pulse width than airborne radar, with a pulse width of several nanoseconds at most. As is well known, impulse signals have an extremely wide frequency band. It is well known that having such an extremely wide frequency band contributes to improving distance resolution. Here, the relationship between frequency band and distance resolution will be explained.

For example, assuming that there is one object in the exploration space, the transmitted radio signal is reflected by the object and returns. The basic principle of radar is to determine the distance to an object by detecting this reflected wave and measuring the elapsed time between transmission and reception. Next, the definition of distance resolution is usually considered as follows. First, assume that two objects are located in the exploration space at distances r ₁ and r ₂ from the measurement device. At this time, if the reflected signals from each object can be detected separately, it is possible to identify the two objects and measure the distance to each object. However, since the radio signal used for exploration has a finite duration T,
There is a limit to the distance at which two objects can be separated and identified (minimum distance Δr=r ₂ −r ₁ ). That is, the shorter the duration T of the signal, the smaller the difference in distance can be identified. Considering the round trip time of the radio signal, Δr is proportional to T.

That is, if the propagation speed of the radio signal is v, Δr>
Two objects can be separated and identified if there is a distance difference of v·T/2.

By the way, suppose that a certain radio signal u(t) is transmitted from an antenna for object exploration. At this time, the frequency component (spectrum) of the signal is u
It can be calculated by Fourier transforming (t). According to this, a certain frequency
If f1 is an infinitely continuous sine wave, then
It has a frequency component only at f=f1, and the other components are zero. On the other hand, the shortest pulse (numerically represented by the δ function) contains all frequency components equally. In this way, the spectrum of any waveform u(f) can be similarly determined by Fourier transformation. Further, the frequency bandwidth of the signal is defined by the frequency width when the spectral amplitude becomes 3 dB smaller than the maximum value.

To summarize the above relationship, radio signal (pulse)
There is an inversely proportional relationship between the duration T and the frequency bandwidth Δf included in the spectrum.

Further, contrary to the above explanation, when there is a radio wave signal having a frequency bandwidth Δf, the duration time T of the radio wave signal can be found by performing inverse Fourier transform on this signal.
Once the duration T is determined, the minimum distance Δr between two objects that can be identified by the radio signal is determined. In other words, since Δf and T are in an inversely proportional relationship as mentioned above, the larger Δf (broadband), the shorter the duration T becomes, making it possible to distinguish between small distance differences Δr (higher distance resolution can be achieved). ) becomes like this.

In FIG. 1, an impulse-like electrical signal with an extremely wide frequency band generated by a pulse transmitter 1 passes through a T/R switch 2 which has the function of switching between a transmission state and a reception state, and is transmitted to a single wideband antenna 3. Powered, the broadband antenna 3 radiates an impulse-like radio signal 4 toward the ground. The radio wave signal 4 is reflected by the underground pipe 5, detected by the broadband antenna 3, converted into a radio wave signal again, and guided to the receiver 7 through the T/R switch 2 switched to the receiving state, where it is amplified. It is recorded in the data recorder 8 as waveform data without applying width or the like. Furthermore, it is displayed on the graphics recorder 9 as necessary. Exploration is performed by moving the antenna and collecting waveform data to each measurement location.
There is also a method of separating the antenna section 10 into an antenna 11 dedicated to transmission and an antenna 12 dedicated to reception, as shown in FIG. 2, without using the T/R switch 2, but they are essentially the same. .

In the above-mentioned conventional device, the transmitting and receiving antennas 3 are limited to those that generate so-called linearly polarized waves, such as dipole antennas as shown in FIG. was. This is because, in order to obtain distance resolution suitable for detecting objects at relatively short distances, the radio wave signal emitted from the antenna when an impulse-like broadband electric signal is applied must also have an impulse-like pulse width. This is because it needs to be small, and in order to meet this condition,
This is because it is necessary to use an antenna with less deformation of pulses due to the antenna, that is, less influence of dispersion, and dipole antennas have been considered suitable.

However, with the device explained in Figure 1, in addition to reflections from the buried pipes, reflections from the ground surface, strata, and stones other than the buried object to be explored are also received as noise, so it is difficult to detect noise from the buried pipes. There was a problem in that it was often difficult to extract the signal.

In order to solve this problem, as shown in Fig. 3, the antenna unit 13 is a cross dipole antenna in which the transmitting antenna 14 and the receiving antenna 15 are arranged orthogonally, and only the orthogonal polarized wave components generated by the reflector are received. A device configured to do this has been proposed. This is because reflected signals from planar reflectors such as the earth's surface or strata produce almost no orthogonal linearly polarized components, while objects with strong anisotropy, such as buried pipes, are particularly susceptible to transmission in the longitudinal direction of the pipe. Based on the principle that the maximum orthogonal polarization component is generated when the polarization plane of linearly polarized waves makes an angle of 45 degrees, unnecessary noise can be reduced and only buried pipes can be used for effective detection. It was hot. However, when attempting to explore a buried pipe with this type of device, the location and orientation of the buried object are unknown, so the plane of polarization of the antenna must be determined in advance.
It is impossible to adjust to a 45° angle and is not necessarily an effective exploration method. In particular, if the transmitting or receiving antenna is parallel to the buried pipe, the receiving or transmitting antenna, respectively, will be perpendicular to the pipe and no reflected signal will occur in the received waveform. The drawback was that the tubes were often overlooked. To solve the problem of having to align the polarization direction in advance with respect to the buried pipe, we can mechanically rotate the cross dipole antenna while searching for the direction in which the maximum signal is generated. Alternatively, a person skilled in the art could easily think of a way to overcome this by arranging multiple dipole antennas radially and sequentially electrically switching them to rotate the plane of polarization, but the former requires a complicated structure. However, the latter has the disadvantage of not being able to conduct efficient exploration, and the latter has the problem that the structure of the antenna becomes complex and the antenna characteristics deteriorate due to the arrangement of many elements in the vicinity, making it difficult to configure an effective device. Can not.

“Object of the invention” The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a buried pipe exploration device capable of searching a buried object having strong anisotropy such as a buried pipe with good resolution regardless of the direction of the buried object. Another object of the present invention is to provide a buried pipe exploration device that can reduce noise and efficiently explore buried pipes.

"Structure of the Invention" Mechanically rotating the antenna or radially arranging dipole antennas in many different directions may unnecessarily complicate the structure of the antenna or reduce the efficiency of exploration. In order to construct an exploration device that can explore the buried pipe regardless of its direction without having to do so and without the contradiction that the antenna must be installed in a specific direction with respect to the buried pipe in an unknown direction, it is necessary to set the polarization plane. It is sufficient to use a signal that causes the to rotate on its own. For example, elliptically polarized waves generally have such properties. Here, we will explain using circularly polarized waves whose amplitude is constant regardless of direction and which is considered suitable for exploration among elliptical polarized waves.Circularly polarized waves are polarized waves whose plane of polarization rotates over time. It is well known that there are right-handed and left-handed polarized waves that are perpendicular to each other depending on the direction of rotation of the plane of polarization, and that the reflection characteristics of circularly polarized waves strongly depend on the shape of the reflecting object. In other words, there are some unavoidable reflections from underground other than buried pipes, and circularly polarized waves can reduce and suppress these unnecessary reflected components better than linearly polarized waves. . For example, typical unwanted signals include reflections from planar structures such as geological formations or paved surfaces, or reflections from approximately spherical objects such as stones. In detecting reflected signals from objects with little or no directionality, normal linearly polarized waves transmitted and received using the same antenna or a pair of parallel antennas always have the same magnitude. Returns the amplitude of the reflection. In other words, with linearly polarized waves, reflected signals due to differences in the shape of buried objects and reflected signals due to the orientation of the pipe mentioned above are all expressed only by amplitude changes (large and small), so the signal from the pipe and the signal from other sources are different. There is no ability to separate signals (noise). Therefore, with linear polarization, this unwanted noise makes clear exploration of the tube difficult.

Furthermore, as mentioned above, the use of the cross-dipole antenna has the effect of reducing unnecessary reflections as mentioned above, but at the same time, there are limitations of this technology (i.e. It is difficult to conduct an effective exploration because it is not possible to orient the object at a 45-degree angle, and it takes time to conduct an exploration.)

On the other hand, when circularly polarized waves are used, a clear difference in reflection can be utilized between a signal from a directional object such as a tube and a signal from a non-directional reflector as described above. For example, in a flat layer, a change occurs in which the direction of rotation of polarized waves is reversed before and after reflection (right-handed polarized waves are converted to left-handed polarized waves). In addition, since the plane of polarization is automatically rotated and scanned, it is not only possible to investigate objects with strong anisotropy such as buried pipes without having to adjust the direction in advance.
It becomes possible to distinguish between tubes and other unnecessary reflections at the signal detection stage, which reduces the signal SN.
This increases the ratio and makes it possible to clearly explore only the pipeline, making it suitable as a buried pipe exploration device.

Although the use of circularly polarized waves has the above-mentioned advantages, driving a circularly polarized antenna with a broadband pulse signal has no advantage in terms of resolution, so it has traditionally been considered unsuitable for object exploration. was. In order to clarify this point, we will compare a linearly polarized antenna and a circularly polarized antenna, and explain the case where each antenna is driven in a wide band.

First, consider a dipole antenna as a basic and typical example of a linearly polarized antenna. When a voltage pulse is applied to the antenna element from the feeding point,
A signal current flows along the element toward the end of the antenna. This signal current radiates radio waves into the space around the antenna while flowing. At this time, when the supplied electrical energy is sent into space as a radiation wave, the electrical length of the element required until the efficiency of coupling between the antenna and the space becomes constant varies depending on the frequency. That is, if we look at the signals that appear as radio waves in space for each frequency, even if the electrical signals are applied at the same time, the signals that are radiated as radio waves will generally have a phase shift. by the way,
In a normal dieball antenna (the element length is 1/2 wavelength of the frequency component and is called a half-wavelength dieball), this element is relatively short and acts as a narrowband resonator, so it depends on this frequency. Waveform distortion due to phase delay is not observed to be very large. Rather, when a wideband applied signal is used, distortion called ringing appears due to narrowband antenna characteristics, deteriorating the resolution of exploration. Overcoming this problem has become a major challenge.

On the other hand, a typical example of a circularly polarized antenna is a spiral antenna in which the conductor has a spiral shape, so this will be explained as an example. A spiral antenna is an antenna that uses a relatively long spiral antenna element as a circularly polarized wave radiating element.As is well known, a spiral antenna can have broadband characteristics as a traveling wave antenna. The influence of the phase delay of the antenna becomes noticeable (this characteristic is called the dispersion characteristic of the antenna). For this reason, when the spiral antenna is driven by a wideband pulse, the radiated and received signal waveforms are modified to have significantly longer durations than the applied waveforms.

Due to this negative effect, antennas such as spiral antennas have traditionally been considered unsuitable for high-resolution exploration devices and short-range radars.

For example, examples of received signals by a dipole antenna and a spiral antenna corresponding to the above explanation are shown in FIGS. 4a and 4b, respectively. In this figure, FIG. 4b illustrates a received waveform 30 when a radio wave is transmitted by applying an impulse of about 1 nsec to a spiral antenna and received by a circularly polarized antenna. On the other hand, linearly polarized antennas such as dipole antennas used in conventional devices do not widen the pulse width, as shown in waveform 29 in Figure 4a, and are superior in terms of resolution. has been considered.

However, if the received wave obtained using a circularly polarized antenna is configured to compress the pulse after receiving it to obtain a narrow pulse, an exploration device with good resolution can be constructed while taking advantage of the characteristics of circularly polarized waves. It will be possible.

The present invention was made based on this idea, and includes a transmitter that generates a wideband pulse-like signal, and a circularly polarized wave having a wideband frequency component that receives the pulse-like signal from the transmitter. a transmitting antenna that generates an exploration signal; a receiving circularly polarized antenna that detects reflected signals from buried objects caused by the aforementioned exploration signals; and a receiver that receives and amplifies the reflected signals collected by the circularly polarized antenna. and a waveform shaping section that pulse-compresses the reflected signal and shapes it into a waveform with a short duration.

In one aspect of the invention, the configuration includes a mechanism for moving the transmitting circularly polarized antenna and the receiving circularly polarized antenna, and a position signal generator that generates a signal indicating the position of the antenna. . The waveform shaping section digitizes and pulse-compresses the received reflected signal, shaping it into a pulse waveform with a short duration, or converts the received reflected signal into a pulse compressor using an analog element such as a surface acoustic wave element. A function that compresses pulses and shapes them into a pulse waveform with a short duration, or converts and inversely transforms the received reflected signal into the frequency domain, and equalizes the phase and amplitude of the frequency component to reduce dispersion and generate the reflected signal. It has a function of forming a frequency distribution wider than the signal waveform, and thereby pulse-compresses the reflected signal and shapes it into a pulse waveform with a short duration. The combination of transmitting and receiving antennas may be a combination of transmitting antennas and receiving antennas with orthogonal polarization characteristics, or a combination of transmitting antennas and receiving antennas with equal polarization characteristics.

"Embodiment" FIG. 5 shows an embodiment of the present invention.
In this figure, a transmitter 16 generates a broadband electrical signal, typically an impulse signal 17, to excite a circularly polarized antenna 18 for transmission. A circularly polarized signal 19 is transmitted underground from the circularly polarized antenna 18 . If, for example, the above-mentioned spiral antenna is specifically used as the circularly polarized antenna, the radiated signal 19 will be affected by the characteristics of the antenna and will travel underground with a waveform different from that of the electrical signal 17. signal 19
A portion of the light is reflected by the layered structure 21 on the earth's surface or underground, and also passes through and reaches the object 20, where it is reflected or scattered and detected through the receiving circularly polarized antenna 23. At this time, preferably,
The signal is sampled and detected and converted into a time-stretched low frequency signal to facilitate subsequent processing. If you make it sufficiently short, the receiver 24
It may be provided in the section. In the receiver 24, the waveform signal is subjected to amplification and filtering to reduce noise components whose band is significantly different from that of the signal from underground, and then AD converted and stored in the memory 25. The signals stored in the memory 25 are sequentially read out and pulse-compressed by the waveform shaping section 26. The waveform shaping unit 26 includes circularly polarized antennas 18 and 23 for transmission and reception that have been used in advance.
It has a transfer function stored in memory, and calculates between this and the waveform signal sent from 24 to compensate for the effect of waveform distortion caused by the antenna.
Synthesizes impulses with short pulse width and good resolution. Regarding specific pulse compression, for example, the inventors' earlier patent application No. 136060/1983
It is also possible to perform this by known methods such as the pulse compression method as described in No. 58-38878). An example of its configuration and its operating principle are described below.

Pulse compression, in other words, compresses the received signal by
(t), where the spectrum is V(f), is a filtering process that converts an arbitrary distorted waveform into a waveform with a short duration (close to the δ function).

An example of the pulse compression filter H(f) used in this filtering process is given in the above cited document.
Based on theoretical considerations regarding signals, H(f)=V ^* (f)/(1−λ)+λ·|V(f)| ² * indicates a complex conjugate.

It is given by the formula.

This equation becomes a well-known inverse filter when λ=1, and a matched filter when λ=0. It is well known in signal processing theory that an inverse filter has the characteristic of converting an input waveform into a δ function, but it is generally difficult to realize a perfect form. on the other hand,
It is also well known that the matched filter has the characteristic of optimal detection (signal detection with maximum S/N ratio) in the presence of random noise.

The above filter is a first example of a general filter that includes these filters and can be applied to a wider class of signals. As λ is set to a value closer to 1, the waveform V(t) becomes a sharper pulse W(t) with a shorter duration. In practice, λ is determined in consideration of the noise characteristics of the signal to be detected, and the device is operated under conditions that optimize the degree of noise removal and pulse compression.

Moreover, in reality, the output waveform V(t) from the receiver
A certain waveform V1(t) containing the response of the object
Focusing on this, we perform FFT (fast Fourier transform) on this to obtain V1(f), and based on this, we first create a filter H(f).
Create. Then, each waveform V(t) is passed through this filter H(f). That is, W(f)=H(f)V(f) is created. Here, V(f) is modulated in amplitude and phase by H(f). Further, by performing inverse FFT to restore the waveform W(t) in the time domain, a pulse-compressed waveform with high resolution can be obtained.

Examining the spectrum of the compressed waveform, the function of this filter is to equalize the phase shift for each frequency, correct the frequency characteristics of the amplitude to approach equal amplitude levels, and create a waveband with a wider band than the original wave number. It can be clearly confirmed that it is a spectral signal and that the above two points are true.

Further, even if a convolution operation is performed between the received signal V(t) and the response function h(t) of the pulse compression filter obtained by inverse FFT, a mathematically equivalent result is obtained. The above characteristics can be easily realized by software, and it is also possible to configure a digital filter having these characteristics.

Alternatively, as a second example, the following configuration is also possible.

Since large distortions in the waveform are due to the characteristics of the spiral antenna, the relationship between the voltage waveform applied to the antenna and the radiated waveform, that is, the signal conversion characteristic A(f), must be determined by calculation or experiment in advance. The amplitude and phase frequency characteristics of A(f) are stored in memory. Let the FFT of the signal from the receiver be V(f), and calculate the phase and amplitude of A(f) included in V(f) (Actually, it is known that in a spiral antenna, waveform distortion due to phase shift is large. )
By shifting the phase and increasing/decreasing the amplitude by canceling out, it is possible to obtain an impulse-like waveform with a short duration that is close to the applied signal.

Although this method is simple, it has a limited effect of correcting only the distortion caused by the antenna itself. On the other hand, the first method compresses pulses including distortion caused by underground propagation, and has broader results.

In the above two examples, configuration examples of the pulse compression means have been explained, and it has been explained that the configuration can be realized as a digital filter. To summarize these basic functions, (1) a function that equalizes the phase shift for each frequency in the received waveform, and (2) a function that corrects the frequency characteristics of the amplitude to bring it closer to the same amplitude level and restore the original (3) A function to convert and inversely transform the received waveform into the frequency domain due to the need to handle the waveform in both the frequency domain and the time domain (FFT is usually used)
is essential.

In this case, a function for performing noise reduction processing such as averaging using a plurality of waveforms may be added to the memory 25 before performing pulse compression.

On the other hand, a position signal generator provided in the mechanism 22 for moving the antenna generates a position coordinate signal, which is received by the receiver 24 and stored in the memory 25 in correspondence with the reflected signal from underground. I plan to save it. The pulse-compressed waveform is arranged in the order of position coordinates and recorded on a graphics recorder or CRT.
27, or stored in a data recorder 28 for more advanced signal processing or resolution display.

In the above explanation, we have taken up an example in which the reflected signal is AD converted, stored as a digital signal in memory, and digital signal processing is performed to perform pulse compression. It is clear that if it is configured with analog elements, it is possible to configure a waveform shaping section that performs real-time processing without going through the process of converting it into a digital signal and processing it in advance. It is clear that the invention can be practiced without departing from the spirit of the invention.

Next, a more specific embodiment of the antenna portion used in the present invention will be described. FIG. 6 is a diagram showing the details of the antenna portion of the embodiment shown in FIG. 5. The antenna 31 consists of a transmitting antenna 32 and a receiving antenna 33, both of which transmit and receive circularly polarized waves. For example, it has the shape of a spiral antenna suitable for
form a spiral whose polarization characteristics are orthogonal to each other. The circularly polarized wave radiated from the transmitting antenna 32 is reflected underground, but on a reflector with low anisotropy such as the earth's surface or a geological layer shown at 21 in FIG. Compared to the wave component, the component that is orthogonal to the incident wave and the polarized wave is large, and in the case of a linear reflector with strong anisotropy such as a buried pipe as shown in 20, the incident wave This results in the reflection of orthogonal polarization components with a magnitude approximately equal to that of the incident wave, and a reflection of the same polarization component as the incident wave. The receiving antenna 33 can detect these reflected signals, and a comprehensive search including anisotropic objects is performed.

FIG. 7 shows another embodiment for carrying out exploration focusing on signals from objects with strong anisotropy, such as buried pipes. For example, it consists of 32' and 33' in the shape of a spiral antenna, which is suitable for
32' and 33' differ from the embodiment shown in FIG. 6 in that they have shapes with equal polarization characteristics. When this configuration is adopted, the object 20 with strong anisotropy in FIG.
The reflection from the ground is detected in the same way as in Fig. 6, but since the polarization state of the reflected wave is perpendicular to that of the antenna 33', it is detected from the ground surface or a reflector with small anisotropy such as 21 in Fig. 5. signal is reduced, and exploration with emphasis on buried pipes can be carried out.

Well, in the case of Fig. 7, since the shapes of 32' and 33' are the same, it is also possible to switch the transmitting state and receiving state with a T/R switch and adopt a configuration in which one antenna is shared. . Furthermore, in the case of a configuration in which the transmitting and receiving antennas are separated, both antennas may be installed with a certain distance apart. The above explanation uses a spiral antenna as an example, but
Of course, it is not limited to this only.

In addition, in the above explanation, an impulse was used as an example of a wideband pulse signal to be applied, but it is also possible to use a different form of a wideband pulse waveform, such as a truncated sine wave or a chirp pulse, without departing from the spirit of the present invention. It is clear that the present invention can be applied without doing so.

"Effects of the Invention" As explained above, in the present invention, a circularly polarized antenna is used to collect reflected signals as a broadband impulse signal, and signal processing is performed to eliminate significant waveform distortion inherent in the characteristics of the circularly polarized antenna. Since it is configured so that it can be compensated for by It is possible to achieve both the advantages of detectability.
Furthermore, by the action of circularly polarized waves, it is also possible to provide a device that can detect only objects with strong anisotropy, such as buried pipes, while suppressing signals from reflectors with low anisotropy, such as the ground surface or strata. It becomes possible.

Furthermore, if the size of the antenna is fixed, an antenna with a much longer conductor length than a normal linearly polarized dipole antenna can be used, so a relatively small antenna can provide a wider band than a normal dipole antenna. This is advantageous in constructing a high-resolution exploration device using broadband signals. Furthermore, the advantage is that exploration can be carried out efficiently while moving the antenna because it successfully incorporates the physical polarization rotation phenomenon without using complicated antenna configurations or mechanisms such as mechanical antenna rotation. There is.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a conventional buried pipe exploration device using a linearly polarized antenna, Figure 2 is a conceptual diagram of a linear polarized antenna used in a conventional buried pipe exploration equipment, and Figure 3 is a conventional A conceptual diagram of a cross dipole antenna used in the device, FIG. 4a is a diagram showing an example of a received waveform of a linearly polarized antenna, FIG. 4b is a diagram showing an example of a received waveform of a circularly polarized antenna, FIG. 5 is a schematic configuration diagram of an embodiment of the present invention,
FIG. 6 and FIG. 7 are both schematic configuration diagrams showing configuration examples of the antenna section used in the device of the present invention. 16... Transmitter, 18... Circularly polarized wave antenna for transmission, 20... Buried pipe, 22... Mechanism for moving the antenna (position signal generator), 23... Circularly polarized wave antenna for reception, 24... Receiver, 26...waveform shaping section.

Claims (1)

[Claims] 1. A device that uses radio waves to collect information from underground objects and explore underground pipes, comprising: a transmitter that generates a broadband pulse-like signal; a transmitting antenna that receives a pulse-like signal and generates a circularly polarized exploration signal having a broadband frequency component; and a receiving circularly polarized antenna that detects a reflected signal from a buried object caused by the exploration signal. and,
A buried pipe exploration device comprising: a receiver that receives and amplifies a reflected signal collected by the circularly polarized antenna; and a waveform shaping section that pulse-compresses the reflected signal and shapes it into a waveform with a short duration. 2. A mechanism for moving the transmitting circularly polarized antenna and the receiving circularly polarized antenna, and a position signal generator that generates a signal indicating the position of each of the transmitting and receiving circularly polarized antennas. A buried pipe exploration device according to claim 1. 3. A waveform shaping section that digitizes and pulse-compresses the reflected signal and shapes it into a waveform with a short duration.
The underground pipe exploration device described above. 4. A waveform shaping section for shaping the reflected signal into a waveform with a short duration by pulse-compressing the reflected signal using a pulse compressor using an analog element such as a surface acoustic wave element. The underground pipe exploration device described above. 5. It has a function of converting and inversely converting the reflected signal into the frequency domain, and a function of equalizing the phase and amplitude of the frequency components to form a frequency distribution with small dispersion and a wider band than the reflected signal waveform, and 3. The buried pipe exploration device according to claim 1, further comprising a waveform shaping section that pulse-compresses the reflected signal and shapes it into a pulse waveform with a short duration. 6. The buried pipe exploration device according to claim 1 or 2, comprising a combination of a transmitting antenna and a receiving antenna whose polarization characteristics are orthogonal. 7. The buried pipe exploration device according to claim 1 or 2, comprising a combination of a transmitting antenna and a receiving antenna with equal polarization characteristics.