Patent ID: 7102487

Claim:
A detector for detecting a target object approaching and retreating, said detector comprising: an oscillator device for generating a transmission wave: a branching device for branching said transmission wave generated by said oscillator device; a transmission device for transmitting said transmission wave into space as electromagnetic waves; a reception device for receiving the transmission wave transmitted by said transmission device and reflected by said target object; a mixer for mixing a reception signal received by said reception device and a branched signal branched by said branching device to output a mixed signal; and a judging device for switching on a detection output indicating said object approaching and retreating based on an increase and a decrease of said mixed signal outputted from said mixer; wherein a detection distance is set within ¼ wavelength of frequency effective for the detection and wherein said oscillator device generates a non-sinusoidal wave with frequency less than ⅕ of frequency effective for the detection.