Doppler radar microphone with logarithmic square‐law detector

Abstract

A Doppler radar based microphone is similar to an acoustic microphone except that it detects vibrations rather than sound. A microphone with a logarithmic square-law detector for monitoring honeybees is described. The performance of a logarithmic square-law detector is compared with a more conventional zero-intermediate frequency (IF), direct down conversion receiver. It is shown that unavoidable coupling between the transmitter and receiver as well as stationary clutter have the same effect in the square-law receiver as the local oscillator signal and mixer have in the direct down conversion receiver. The theoretical output of either configuration is formally the same. Both receiver designs were implemented in a low-cost, low-power radar microphone operating in the unlicensed 5.8 GHz industrial, scientific and medical band. The use of a logarithmic square-law detector resulted in a significant simplification of the radar microphone design as well as a 10 dB improvement in signal-to-noise ratio.