Autodyne Proximity Sensor with Temperature Compensated Biasing Network

In this paper, design and analysis of an Ultra High Frequency (UHF) Autodyne proximity sensor is presented. This sensor generates and transmits the tunable RF signal and receives the reflected signal. It generates the IF frequency corresponding to the Doppler shift of the received echo. It can be tuned for detection of different Doppler offsets by IF signal filtering. The sensor is based on a single transistor Clapp oscillator. It includes capacitor loaded short loop antenna in the feedback circuit to provide 180° phase shift which is required for oscillation along with the needed radiation for short range application. The sensor circuit is fabricated and tested on a 20 mil FR4 substrate with planar capacitors and inductors to minimize the production cost. The sensor can detect the movement of targets up to 13 m range.