An Active Self-Interference Cancellation Coupler with 60 dB Isolation Applied in a 24 GHz SFCW Radar

This work introduces a planar implementation of a self-interference cancellation coupler designed for 24 GHz continuous wave radar frontends. An active IQ modulator path is utilized to suppresses the most severe TX-RX-leakage components. Instead of using a closed control loop to minimize leakage, an precise offline calibration is used. We showed the reproducibility of this approach with repeated isolation measurements applying the calibrated control values for the cancellation modulator. An isolation of about 60 dB in a range of 23.0 GHz to 24.25 GHz is achieved. A novelty of this work is the implementation of the RF domain canceller in a monostatic radar setup to investigate the influence of TX leakage in the presence of close weak reflecting targets. The results of the stepped-frequency continuous wave radar measurements show a significant reduction of the leakage power and an increased target peak magnitude, reducing the effect of RX frontend saturation.