JP3214710B2 - Dipole antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dipole antenna used as a borehole radar for underground exploration.

[0002]

2. Description of the Related Art A borehole radar for underground exploration hangs a dipole antenna suspended in an elongated cylindrical sonde in a vertical hole dug in the ground, and radiates radio waves and receives reflected waves. The purpose of this study is to search for the distribution of cracks and faults in the ground and the buried objects that caused reflected waves by repeating the process while changing the insertion depth. In addition to such a reflective borehole radar, transmitting and receiving dipole antennas are inserted into each of a plurality of vertical holes dug at appropriate intervals in the ground, and radio waves transmitted through the ground between the vertical holes There is also a transmission type that receives a message. As the dipole antenna, a symmetric feed type is used.

[0003]

Generally, in a borehole radar, the attenuation of radio waves propagating in the ground is considerably large, and there is a limit in increasing the level of radiated radio waves in terms of withstand voltage of elements of a pulse generation circuit. is there. For this reason, the reflection type narrows the exploration range around the vertical hole, and the transmissive type narrows the interval between the vertical holes. There is.

[0004]

A dipole antenna according to the present invention includes a mechanism for adjusting an electric length, and receives a monopolar pulse waveform excited from a symmetrical feeding point to produce a bipolar monocycle pulse having substantially equal peak values. By radiating a radio wave having a waveform, a pulse having a waveform having a large peak-to-peak value is radiated.

[0005]

FIG. 1 is a sectional view showing the structure of a main part of a dipole antenna for a borehole radar according to an embodiment of the present invention. Reference numerals 11 and 12 denote inner conductors, 21 and 22 denote outer conductors, and 31 and 32 denote the same. It is a power supply line.

The inner conductors 11 and 12 are made of metal pipes of the same shape such as copper. The outer conductor 21 has a tip portion 21a made of a metal plate such as copper that draws an arc along the inner wall surface of the cylindrical sonde to be accommodated, and is joined to the tip portion by welding or the like and slides inside the inner conductor 11. And a base portion 21b of a metal pipe such as copper which can be freely fitted. Likewise other outer side conductor 22, and the distal end portion 2 2 a made of a metal plate to draw an arc along the inner wall surface of the sonde of the accommodating cylindrical, the inner conductor 12 is joined by welding to the distal portion slidably comprising a root portion 22 b of the metal pipe and fitting inside. Feeding lines 31 and 32 connected to the inner conductors 11 and 12 are connected to a feeding line such as a coaxial cable via a balun (not shown).

The mechanical connection between the inner conductors 11 and 12 is performed by using a suitable member having a low dielectric constant (not shown). Metal pipes 21b and 2 into metal pipes 11 and 12
By adjusting the insertion depth of 2b, the electric length 2L of the dipole antenna is adjusted.

According to the experimental results of the present inventor, dipole antennas having the same shape as shown in FIG. 1 are installed for transmission and reception, and the unipolar pulse as shown in FIG. , The receiving side received a bipolar pulse as illustrated in FIG. 2B. The conversion from a unipolar pulse to a bipolar pulse as shown in (A) and (B) is performed on the transmitting dipole antenna, which is considered to be radiated from the transmitting dipole antenna. Further, the present inventor adjusts the relationship between the excitation pulse width τ and the electric length 2L of the dipole antenna such that 2L / τ = kc / (ε ^1/2 ) (1) As shown by the dotted line in FIG. 2B, it was confirmed that the absolute value of the peak value on the negative polarity side could approach a value almost equal to the peak value on the positive polarity side. Here, c is the propagation speed of a radio wave in a vacuum, k is a constant, and ε is the average dielectric constant in soil.

[0009] From the above, the inventor of FIG.
(B) by selecting a bipolar pulse having the same peak value as a transmission pulse as shown in FIG. 1 as a transmission pulse and adjusting the relationship between the electric length 2L of the dipole antenna and the pulse width τ according to the equation (1). Peak-to-
He came to think that a pulse whose peak value was tripled might be received. According to the experimental results of the inventor, a bipolar pulse having the same peak value as shown in FIG. 3A is selected as a transmission pulse, and the relationship between the electrical length 2L of the dipole antenna and the excitation pulse width τ is expressed by ( By adjusting according to the expression (1), it was confirmed that a reception pulse in which the peak-to-peak value as shown in FIG.

[0010] As described above, the search range around the vertical hole of the borehole radar using the dipole antenna and the interval between the vertical holes can be increased by the increase in the receiving sensitivity accompanying the expansion of the peak-to-peak value, The work and effort of the geological search can be greatly reduced. However, in practice, despite the fact that the dielectric constant in the soil around the well varies greatly depending on the nature of the soil, for example, the content of soil, sand, water, etc., a high pressure for generating a large amplitude excitation pulse is required. Because the element constant of the charge / discharge circuit cannot be easily changed,
It is difficult to change the pulse width τ, and as a result, it is difficult to obtain the relationship of the expression (1).

Therefore, according to the present invention, the excitation pulse width τ
Instead of changing the electric length 2L of the dipole antenna so as to correspond to the dielectric constant that changes depending on the soil properties of the search area, the relationship of the expression (1) is realized.

The present invention has been described above by taking as an example a case where the present invention is applied to a borehole radar. However, the dipole antenna of the present invention is not limited to the borehole radar and can be applied as an antenna of other appropriate radar devices.

[0013]

As described in detail above, the dipole antenna of the present invention is provided with a mechanism for adjusting the electric length, and receives the excitation of the unipolar pulse waveform from the symmetric feed point to obtain the bipolar antenna having substantially the same peak value. Since the configuration is such that a radio wave having a monocycle pulse waveform is radiated, the peak-to-peak value of the reception waveform can be tripled. Therefore, for example, when the present invention is applied to a borehole radar, the number of vertical holes is reduced, and labor and time for searching are greatly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a dipole antenna for a borehole radar according to one embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating an excitation pulse waveform (A) and a reception pulse waveform (B) of the borehole radar of FIG.

FIG. 3 is a waveform diagram illustrating an excitation pulse waveform (A) and a reception pulse waveform (B) of the borehole radar of FIG. 1;

[Explanation of symbols]

 11,12 Inner conductor 21,22 Outer conductor 21a, 22a Tip of outer conductor 21b, 22b Root of outer conductor 31,32 Feed line

Claims (1)

(57) [Claims] [Claim 1 further comprising an electrical length of the adjustment mechanism, that radiate radio waves of double polarity monocycle pulse waveform of substantially equal peak values by receiving excitation unipolar pulse waveform from the symmetry feeding point
A dipole antenna, a dielectric constant an electrical length of the dipole antenna 2L, near
Is ε, the propagation speed of radio waves in vacuum is c,
Where τ is the width of the electrical waveform, 2L / τ = kc / ε ^1/2 , and k is the electrical length of the electrical length by the electrical length adjusting mechanism in accordance with a constant relationship.
A dipole antenna, wherein adjustment is performed .