Balanced topology to cancel Tx leakage in CW radar

Balanced topology in radar front-end is presented, which can reduce Tx leakage to receiver drastically. The balanced radar front-end which is composed of a differential cross-coupled oscillator, two Lange couplers, and a Wilkinson combiner is implemented using commercially available InGaP/GaAs heterojunction bipolar transistor technology. The tuning range of voltage control oscillator is 320 MHz from 25.307 to 25.627 GHz. The peak output power is 0.8 dBm. Average Tx-to-Rx isolation is about 40.5 dB. Since the isolation of the Lange coupler is 19 dB, the additional cancellation due to balanced topology is expected to be 21.5 dB. The chip size is 1.05 /spl times/ 1.70 mm/sup 2/.