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This paper deals with signal wave ringing caused by the frequency characteristic of an antenna system in underground probing radar, which is one of important factors to affect the performance of a radar-based pipe locator. Evaluation constants of signal wave ringing caused by the frequency characteristic of an antenna system were defined. On the assumption that the radar antenna is a band pass filter which consists of a quadratic low pass filter and high pass filter, they were calculated and evaluated as a function of cut off frequency of low pass filter, high pass filter and dumping factor by means of computer simulation. As the result, it was found that the suitable frequency band of a radar antenna is 10MHz300MHz (at the dumping constant of 1.0) or 10MHz-600MHz (at the dumping constant of 0.2) to obtain less ringing. Next, radar antenna could get desirable frequency band by means of resistor loading, and a radarbased pipe locator was manufactured with these antennas for field trials. The system has tested at actual fields in Tokyo gas supplying area and it is found that the system is effective in about 80% of the area.

Signal Wave Ringing Caused by the Frequency Characteristic of the Antenna System for Underground Probing Radar