Radar type underground searching apparatus

• US 4,905,008 A
• Filed: 07/05/1988
• Issued: 02/27/1990
• Est. Priority Date: 11/08/1986
• Status: Expired due to Fees

• Current Assignee: Osaka Gas Company Limited
• Original Assignee: Osaka Gas Company Limited
• Inventors: Kawano, Akio, Tsunasaki, Masaru
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US07/238,096
• Time in Patent Office: 602 Days
• Field of Search: 342/72, 342/118
• US Class Current: 342/22
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 7/34 Gain of receiver varied automatically during pulse-recurrence period, e.g. anti-clutter gain control

Abstract

This radar type underground searching apparatus is a system for detecting the presence and location of buried objects such as gas pipes buried in the ground. This apparatus includes a pulse generating unit which periodically generates pulse, and a transmitting antenna through which the pulse is sent into the ground. Pulses reflected from an object in the ground and reaching the ground surface are detected by a receiving antenna, and a reflected wave corresponding to each pulse wave received by the receiving antenna is amplified in a radio-frequency amplifier where in the amplification is increasing each time a group of pulses are transmitted. By sampling the output of the radio-frequency amplifier with a sampler at a series of reflex time, each being succeedingly delayed by a fixed period from the transmitting timing of each pulse wave, as the reference, a low-frequency signal which is formed by extending one reflected wave in time base is obtained, and the waveform thereof is displayed on a waveform display unit. On the screen of the display unit, the presence of objects will be detected by the presence of peaks in the low-frequency signal caused by the reflection from the objects and the depths of the objects will be detected by the time at which the peaks appear on the screen. By this construction, the attenuation of radio waves in the ground can be compensated without arising waveform distortion.

Claims

1. A radar type underground searching apparatus comprising:

a pulse generating unit for periodically generating pulses having a fixed peak value;

a transmitting antenna for transmitting the pulses generated by said pulse generating unit from the ground surface into the ground;

a receiving antenna for catching reflected pulses caused by objects buried in said ground;

a housing for screening electromagnetic radiation and having one side open, said transmitting antenna and said receiving antenna being disposed in said housing;

a radio-frequency amplifier for amplifying a reflected wave corresponding to each of said pulses with an amplification which increases each time pulses are transmitted;

a sampler for obtaining a low-frequency signal formed by the extension of said reflected wave in time base by sampling the output of said radio-frequency amplifier at a series of sampling times, each being succeedingly delayed by a fixed period from the transmitting timing of each pulse wave; and

a waveform display unit for displaying the wave-form of a low-frequency signal appearing at the output of said sampler;

said transmitting antenna and said receiving antenna including;

a pair of antenna elements each made of a plate shaped like an isosceles triangle bent to form an obtuse angle between a vertex portion and a trapezium portion and having a fold line between said vertex portion and said trapezium portion generally running parallel with the trapezium base of said isosceles triangle and nearly symmetrically abutted to each other at each said vertex portion, each said vertex portion having a height arranged approximately equal to the height of said housing, and each said trapezium portion lying in the same plane in general as the open side of said housing;

a first load resistor and a second load resistor each connected at one of their ends to respective ends of the trapezium base of one antenna element of said pair of antenna elements;

a third load resistor and a fourth load resistor each connected at one of their ends connected to respective ends of the trapezium base of the other antenna element of said pair of antenna elements;

a first conductor and a second conductor each connected at one of their ends to respective other ends of said first resistor and said second resistor;

a third conductor and a fourth conductor each connected at one of their ends to respective other ends of said third resistor and said fourth resistor;

a fifth load resistor connected between said first conductor and said third conductor; and

a sixth load resistor connected between said second conductor and said fourth conductor;

whereby the presence of said objects is detected by the presence of peaks in said low-frequency signal caused by the reflection from said objects and the depth of said objects is detected by the time of the appearance of said peaks.