Self-Jamming and Interference Cancellation Techniques for Continuous Wave Bi-static Radar Systems

In a typical radar system, the signal which returns from the target is usually very weak compared to leakage from the transmitter and interference signal. This self-jamming signal, either due to reflected signal from close objects or due to transmit-receive antenna coupling, causes DC offset at the output of the mixer and saturates the IF amplifier, leading to reduced dynamic range, which is a well-known problem in radar engineering. This can be overcome using two different techniques; active and passive leakage cancellation. In the active method, the attenuator and the phase shifter are used to set the signal level that is the same amplitude as the interference signal and has a phase difference of 180 degrees. In the passive method, using a coupler sampled signal from the transmitter is brought to the desired amplitude and phase level by tuning the impedance connected to the coupling port. Namely, mismatch at coupling port determines both the amplitude and the phase of the reflected signal at the isolated port. When this signal is added to the received interference signal, the leakage and interference from environment are removed. Performance of these systems is simulated and compared using NI Microwave Office.