Wideband Self-Interference Cancellation Using Multi-Tap Filter in Radar Front End

Abstract

The largest hurdle in full duplex wireless systems is the self-interference introduced by the transmitted signal into the received signal. In multi antenna systems this interference is caused by the direct coupling between the transmitting and receiving antennas. In systems where the transmitter and receiver uses the same antenna the interference is caused by inadequate isolation between the transmitter and receiver front-ends. In most systems the transmitted power is orders of magnitude higher than the received signal power. This causes the interference to saturate the receiver and can damage the receiver. One way of reducing this interference is to include a filter in the microwave front-end. This filter uses the transmitted signal to generate an inverse of the interference and adds it to the receiver signal path.

In this thesis a multi-tap self-interference cancellation filter is designed, optimized and fabricated. The filter parameters are optimized using the basin-hopping algorithm combined with the Nelder-Mead downhill simplex algorithm. The filter is a multi-tap filter, where each tap contains phase shift, attenuation and delay elements. The filter is experimentally verified to reduce the self interference by 10.45 dB over a frequency band from 1GHz to 3GHz.