Generally, in a standard homodyne radar a radio-frequency(RF) signal generated by an oscillator is used for both, thetransmitted signal and the local oscillator (LO). Well controlleddistribution of the input power between antenna andmixer is crucial. A transceiving mixer at 76.5GHz is presented,where this distribution is done by use of a rat-racecoupler. In a conventional transceiver the oscillator signalis split into the transmitted and in the LO signal by a directionalcoupler. A second directional coupler is needed inorder to merge the received and the LO signal at the mixer.In our design the purpose of splitting and merging the signalsis realized with only one coupler. Elimination of the secondcoupler reduces losses significantly.
The received signal is down-converted to the intermediatefrequency (IF) by use of a balanced mixer. For small relativespeed in a CW-Doppler-radar or short distance in a FMCWradarthe IF is very small. Therefore 1/f noise is a significantvalue. In order to achieve good 1/f noise characteristics,Schottky diodes were used. The diodes were flip-chipbonded onto a microstrip circuit on a Al2O3 substrate.\
The assembled transceiver was measured on-waver. Aninput power of 7 dBm was applied. The measured outputpower was 3 dBm and the conversion loss 9 dB. A noise figureof 15.3 dB was measured at 100 kHz.
