A sensor circuit included in a computer system may include multiple antennas, a control circuit, a mixer circuit, a transmitter circuit and a filter circuit. The control circuit may generate a baseband signal, which the mixer circuit may modulate using a modulation signal to generate a transmit signal. The transmitter circuit may transmit the transmit signal using a first antenna. The filter circuit may be configured to track a carrier frequency of the transmit signal and filter a reflected version of the transmit signal to generate an output signal.