PURPOSE: To identify a traveling body regardless of the polarization surface of an antenna by receiving the circular-polarized electromagnetic wave from a main body side with a linear polarization antenna and then receiving the linear-polarized electromagnetic wave from a traveling side with a circular polarization antenna at the main body side.
CONSTITUTION: A two-arm spiral antenna (circular polarization antenna) is sued for a transmission antenna SA1 and a reception antenna RA2 at a main body (MAIN) side and a linear polarization antenna is used for a reception antenna RA1 and a transmission antenna SA2. When the circular-polarized electromagnetic wave with a frequency of f is radiated from the antenna SA1 by the sicjnal and power from a feeder circuit S at the main body side, the antenna RAI at the travelin<j side receives it and the antenna SA2 transmits tcl a linear-polariz'' electromacjnetic wave with a double frequency of 2f. The electromacjnetic wave is transmitted by the antenna RA2 at the main body side and is sent to a comparison circuit COM via a demodulation circuit RG and then an alarm is generated when the strength, continuation time etc. of received electromacjnetic wave exceed a ref erence value.
AKAHA NORIYUKI
MASUKO YUKIO
