JPH04351983A - Horn antenna - Google Patents

Abstract

PURPOSE:To suppress the reflection at the ground surface at incidence and reflection time to efficiently use the electric wave of a radar for inquiry by having a hollow with a reverse horn shape in the center part of an inner space of a main body and filling the other part with a dielectric having dielectric constant close to that of the ground surface. CONSTITUTION:A hollow part 7 with a reverse horn shape is formed in the center part of the inner space of a horn-shape antenna main body 1 and the other part is filled with a dielectric 3 having low dielectric loss and dielectric constant close to that of the ground surface. Consequently, the transmission medium of an electric wave transmission route from the inner space of the main body 1 to underground 6 via the ground surface 5 changes continuously from air to the characteristic impedance of the ground surface 5, so that impedance comformity is obtained. As a result, the electric wave of a radar for inquiry which is led to a wave guide tube connecting part 2 can be transmitted efficiently to underground 6 while the reflection at the ground surface is suppressed as much as possible and reversely, the reflection wave from underground 6 can be led to the connecting part 2 while the reflection at the ground surface 5 is suppressed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention can be used as a transmitting/receiving antenna for an exploration radar that searches for gas pipes, water pipes, electric power, telephone cables, etc. buried in asphalt-paved ground or concrete without excavation. This relates to the horn antenna used.

0002

2. Description of the Related Art Conventionally, there has been known a technique for detecting the position of underground objects using frequency modulated continuous wave radar. FIG. 4 shows a schematic block diagram of an underground exploration radar system which is the basis of the present invention (see Japanese Patent Application No. 2-280353). In FIG. 4, 33 is on the ground, 34 is underground, 35 is the ground surface, and 36 is an object to be investigated buried in the ground 34 at a depth of about 1 m from the ground surface 35, for example, an underground pipe. 36a is a joint position.

Reference numeral 21 is a signal generator that generates a continuous wave obtained by frequency modulating a triangular wave, for example, where the center frequency is about several GHz (for example, 2 GHz) and the frequency of the triangular wave is, for example, 50 Hz.
That's about it. 22 is a directional coupler that branches the continuous wave output from the signal generator 1 into two paths. 23 is a circulator. 24 is a horn antenna with narrow directivity, such as a quadrangular pyramid, used for both transmission and reception (for example, one side of the aperture is 200 mm).
mm, length 300 to 600 mm), directional coupler 2
The continuous wave outputted from one output end of 2 is inputted through the circulator 23, and the continuous wave radio waves are radiated from the ground surface 35 toward the underground 34, and are emitted from the underground 34, for example, by the underground pipe 36. The reflected wave reflected from the ground surface 35 is received and returned to the circulator 23.

25 is a mixer, which mixes the continuous wave output from the other output end of the directional coupler 22 and the circulator 2.
3 and the reflected wave output from 3. 26 is mixer 2
A low-pass filter extracts the beat frequency components of continuous waves and reflected waves from the output of 5, and removes carrier waves of several GHz (for example, the above-mentioned 2 GHz). A low frequency amplifier 27 amplifies the beat frequency component output from the low pass filter 26. A frequency counter 28 detects the frequency value of the beat frequency component extracted by the low-pass filter 26 and amplified by the low-frequency amplifier 27.

A frequency-voltage conversion circuit 29 converts the output signal of the frequency counter 28 into a voltage signal. 30 is a comparator which compares the output signal of the frequency-voltage conversion circuit 29 with a reference signal to determine the beat according to the difference in distance from the ground surface 35 between the joint 36a of the underground pipe 36 and the parts other than the joint 36a. Detect frequency differences. The reference signals include the beat frequency when receiving the reflected wave at the joint 36a of the underground pipe 36 and the beat frequency when receiving the reflected wave at a part other than the joint 36a of the underground pipe 36. A voltage corresponding to an intermediate frequency is applied.

Reference numeral 31 is a buzzer that responds to the output signal of the comparator 30, and 32 is a display lamp. Next, the operation of this underground exploration radar device will be explained. In this underground exploration radar device, a signal generator 21 generates a frequency-modulated continuous wave, and the continuous wave output from the signal generator 21 is branched into two paths by a directional coupler 22. One of the continuous waves branched into two by the directional coupler 22 is sent to the horn antenna 24 through the circulator 23, and is radiated as a radio wave from the ground surface 35 above the underground pipe 36 toward the underground pipe 36. The other continuous wave is sent to the mixer 25. Continuous waves radiated from the ground surface 35 toward the underground pipe 36 propagate underground 34 and are reflected by the underground pipe 36, and the reflected waves propagate underground 34 again and exit from the ground surface 35. The signal is received by the horn antenna 24 and sent to the mixer 25 through the circulator 23.

The mixer 25 mixes the radio waves sent from the directional coupler 22 and the horn antenna 24 to the circulator 23.
mixed with the reflected waves sent through the This mixed wave includes beat frequency components of the continuous wave and the reflected wave. The beat frequency of these two waves differs depending on the time from emitting the continuous wave until receiving the reflected wave, and
If the distance from the underground pipe 36 to the underground pipe 36 differs, the beat frequency will also differ. Note that the horn antenna 24
are placed sufficiently close to each other, so the distance from the ground surface 35 to the horn antenna 24 can be ignored.

Beat frequency components of continuous waves and reflected waves are extracted from the output of the mixer 25 by a low-pass filter 26 and further amplified by a low-frequency amplifier 27; A frequency counter 28 detects the frequency value of the beat frequency component, and a frequency-voltage conversion circuit 29 converts the output signal of the frequency counter 28 into a voltage signal.

By comparing the output signal of the frequency-voltage conversion circuit 29 with a reference signal by the comparator 30, the distance from the ground surface 35 between the joint 36a of the underground pipe 36 and the parts other than the joint 36a is determined. detect the difference in beat frequency according to the difference in the beat frequency. The output signal of this comparator 30 is applied to a buzzer 31 which is an alarm and a display lamp 3.
2 responds, and when the distance from the ground surface 35 to the underground pipe 36 becomes short, it makes a light emitting display or a sound, for example.

[0010] Therefore, while moving along the underground pipe 36 on the ground surface 35 above (directly above) the underground pipe 36, a continuous wave is emitted, the reflected wave is received, and the beats of both are transmitted. By detecting the frequency, converting the beat frequency into a voltage signal, and comparing it with a reference signal, the joint 36a of the underground pipe 36 can be detected.
It is possible to determine the difference in beat frequency due to the difference in distance from the ground surface 35 between the underground pipe 36 and the position other than the joint 36a, and therefore the distance from the ground surface 35 is shorter than other parts of the underground pipe 36. The position of the joint 36a can be detected.

Note that the horn antenna 24 is located directly above the underground pipe 36 by checking the buried position of the underground pipe 36 in advance, and is moved along the underground pipe 36 in this state. It is necessary to keep the distance between the horn antenna 24 and the ground surface 35 constant.

0012

[Problems to be Solved by the Invention] When the above-described underground exploration radar device is used to explore the underground pipe 36, most of the radio waves radiated from the horn antenna 24 are transmitted to the ground surface 35.
The level of radio waves reflected by the underground pipe 34 and propagated underground 34 becomes low, making it difficult to detect the underground pipe 36 buried approximately 1 m underground.

As described above, most of the radio waves radiated from the horn antenna 24 are reflected by the ground surface 35 and hardly propagate toward the ground 34 because the horn antenna 24
The permittivity of the opening (the permittivity of air) and the permittivity of the ground surface 35 (for example, the permittivity of asphalt; ε≒2.7) are significantly different, and an impedance mismatch occurs at the interface, causing radio waves to be reflected. This is thought to be because. The characteristic impedance of air is 370Ω, and the characteristic impedance of asphalt is 370×ε-1/2=225Ω.
It is.

Therefore, it is an object of the present invention to effectively propagate radio waves underground by suppressing reflection on the ground surface, or to effectively propagate radio waves reflected by objects from underground by suppressing reflection on the ground surface. An object of the present invention is to provide a horn antenna capable of receiving signals.

[0015]

[Means for Solving the Problems] The horn antenna of the present invention radiates radio waves from the ground surface to the ground, or receives radio waves emitted from the ground to the ground surface, and has an inverted horn shape in the center. The internal space of the antenna body is filled with a dielectric material having a cavity and having a low loss and a dielectric constant close to the dielectric constant of the ground surface layer.

[0016]

[Operation] According to the configuration of the present invention, the characteristic impedance of the propagation path of the radio wave from the internal space of the antenna body through the ground surface and reaching the ground is changed from the characteristic impedance when the propagation medium of the radio wave is air. The characteristic impedance of the surface changes continuously, making it possible to match the impedance to the ground surface, suppressing reflections on the ground surface and effectively propagating radio waves underground, or transmitting radio waves from underground. It is possible to effectively receive radio waves reflected by objects by suppressing their reflection on the ground surface. Furthermore, since a low-loss material is selected as the dielectric, the increase in loss in the dielectric itself can be reduced.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic cross-sectional view of a horn antenna according to an embodiment of the present invention. In FIG. 1, reference numeral 1 indicates a horn-shaped (square pyramid-shaped) antenna main body, and reference numeral 2 indicates a waveguide connection portion provided at a feeding end 1a of the antenna main body 1. Reference numeral 3 denotes a dielectric material such as paraffin which has a low loss and has a dielectric constant close to that of, for example, asphalt that exists on the ground surface 5, and is filled in the internal space of the antenna body 1, and has an inverted horn-shaped cavity 7 in the center. The feeding end 1a of the antenna body 1
The proportion of the cavity 7 in the cross-sectional area of the antenna main body 1 is gradually reduced from the opening end 1b to zero in this embodiment at the opening end 1b. In order to form the dielectric body 3 into the above shape, for example, a pyramid-shaped frame 4 made of paper or plastic is inserted into the antenna body 1 from the open end side, and the inner surface of the antenna body 1 and the frame 4 are aligned. It is created by melting and pouring a dielectric material 3 such as paraffin between the outer surface and solidifying it. As a result, dielectric 3
An inverted horn-shaped cavity 7 is formed at the center of the hole.

This horn antenna has a dielectric material 3 having an inverted horn-shaped cavity 7 in the center filled in the internal space of the antenna body 1 and having a low loss and a dielectric constant close to the dielectric constant of the layer on the ground surface. Therefore, the proportion of the cavity 7 in the cross-sectional area of the antenna body 1 gradually decreases from the feeding end 1a of the antenna body 1 to the open end 1b in the internal space of the antenna body 1. Therefore, the characteristic impedance of the propagation path of the radio wave from the internal space of the antenna body 1 through the ground surface 5 to the underground 6 is determined from the characteristic impedance when the radio wave propagation medium is air. Since the characteristic impedance changes continuously, impedance matching can be achieved. As a result, it is possible to suppress reflections as much as possible when the radio waves guided to the waveguide connection part 2 pass through the internal space of the antenna body 1 and propagate to the underground 6 through the ground surface 5, thereby transmitting the radio waves to the underground 6. It can be propagated effectively. Conversely, radio waves from underground 6 can also be effectively transmitted to waveguide connection portion 2 by suppressing reflection at ground surface 5. Note that arrow A in FIG. 1 indicates the propagation of radio waves.

FIG. 2 shows a schematic diagram of a measuring device for measuring the attenuation characteristics of radio waves when the internal space of a horn antenna is filled with paraffin, when it is filled with soil, and when it is hollow. In FIG. 2, 11 is a transmitting antenna consisting of a horn antenna, 12 is also a receiving antenna, and 13 is a spectrum analyzer. 14 is a wooden box with a width of 500mm,
It is filled with sand 15, and a transmitting antenna 11 and a receiving antenna 12 are opposed to each other with a wooden box 14 in between. The dielectric constant of wood is approximately 2.5 to 3.5, which is approximate to the dielectric constant of asphalt, approximately 2.7, and the dielectric constant of paraffin is approximately 2.3.

In the measuring device of FIG. 2, the transmitting antenna 1
The receiving antenna 12 receives radio waves propagated through the wooden box 14 and the Masago soil 15 therein, and the transmitting antenna 11 and the receiving antenna 12 are made of paraffin having the cavity 7 as in the above embodiment. The attenuation characteristics of radio waves were measured using a spectrum analyzer 13 while changing the frequency of the radio waves, in the case of filling with dielectric material 3 consisting of 3, filling with soil instead of paraffin, and in the case of a cavity (conventional example). . The measurement results are shown in FIG. Curve X1 shows the case filled with paraffin, and curve X2
Curve X3 shows the case of a cavity, and curve X3 shows the case of filling with soil.

From this figure, it is clear that the attenuation of radio waves is smaller when the horn antenna is filled with paraffin as a dielectric material than when it is hollow. Furthermore, the reason why the attenuation is larger when the dielectric is filled with soil than when it is a cavity is thought to be because the soil contains water and the loss in the soil itself is large. Therefore, it is desirable to fill the horn antenna with a material with low loss. In addition to paraffin, examples of low-loss dielectrics include glass (dielectric constant: approximately 7.0), phenol resin (dielectric constant: approximately 5.0), and ceramic (dielectric constant: approximately 6.0). I can give it to you.

When searching for objects such as underground pipes with the radar exploration device shown in FIG. 4 using a horn antenna whose internal space is filled with a dielectric material as described above, it is necessary to reduce the reflection of radio waves on the ground surface. Since it can be suppressed, it is possible to effectively explore objects buried in deeper places. Conversely, even if the antenna power supplied to the horn antenna is kept low, the object can be sufficiently searched, and measures against leakage of radio waves can be easily taken.

[0023]

Effects of the Invention According to the horn antenna of the present invention, a dielectric material having an inverted horn-shaped cavity at the center in the internal space of the antenna body has a low loss and has a dielectric constant close to the dielectric constant of the layer on the ground surface. Since the characteristic impedance of the radio wave propagation path from the internal space of the antenna body through the ground surface to the ground is continuous from the characteristic impedance when the radio wave propagation medium is air to the characteristic impedance when the propagation medium is the ground surface. This makes it possible to achieve impedance matching with the earth's surface, suppressing reflections on the earth's surface and effectively propagating radio waves underground, or transmitting radio waves reflected by objects underground. It can be effectively received by suppressing reflections on the ground surface.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a horn antenna according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a measuring device that measures the attenuation characteristics of radio waves when the internal space of a horn antenna is filled with paraffin and soil and when the horn antenna is hollow.

FIG. 3 is a characteristic diagram showing the attenuation characteristics of radio waves obtained by the measuring device of FIG. 2;

FIG. 4 is a block diagram of a radar exploration device that is the basis of this invention.

[Explanation of symbols]

1 Antenna body 3 Dielectric 5 Ground surface 6 Underground

Claims (1)

[Claims] Claim 1: A horn antenna that emits radio waves from the ground surface to the ground or receives radio waves emitted from the ground to the ground surface, the antenna having a low loss having an inverted horn-shaped cavity in the center, and A horn antenna characterized in that an internal space of an antenna body is filled with a dielectric material having a dielectric constant close to that of a layer on the earth's surface.