Research Of FMCW Radar Leakage Signal Cancellation Techonology

The leakage of transmitter is the shortcoming of any CW (Continuous Wave) radarsystem especially in CW radar with single-antenna. So the CW radar is constrained forthis. In order to solve the problem of the transmit leakage in single-antenna radar systemto improve the isolation. An analog RF canceller is designed in this paper based on thesingle-antenna FMCW (Frequency Modulated Continuous Wave) radar system withcirculator. A simple adder circuit is masterly used in the canceller to compensate for theDC offset of voltage which is inevitable and difficult to eliminate in any analog mixer.The accuracy of cancellation is further improved for the solution the of the DC offset.The RF canceller operates in S-band from1.89GHz-2GHz; the cancellation ratio ismeasured at static single-point frequency and dynamic frequency sweep. The minimumcancellation ratio is36dB and the maximum is51dB at single-point frequency. And it isabove33dB with the bandwidth of110MHz in different sweeping rates. Thecancellation ratio with DC offset compensation is improved about15dB at single-pointfrequency and9dB at frequency sweep compared with the uncompensated one. It isabove30dB when the leakage power has been changed. So the cancellation circuit canbe adapted for the leakage power.Firstly, the advantages and applications of CW radar are introduced from thedevelopment process of it. The fatal flows–transmit signal leakage is elicited from thereason of CW limitation. The advantages and disadvantages of many kinds of methodsand solutions are compared, analyzed and summarized. The requirements and impact ofperformance of cancellation are deduced in theoretical from the principle of CW radar.The relationship of cancellation ratio and system parameters of receiver is analyzed.The function and main parameters of the microwave components, sub-circuits and theirinfluence on cancellation ratio and closed loop are very detailed analyzed. Based on theanalysis, the cancellation circuit scheme and test program are designed. The finalcancellation ratio after debugging satisfies the design requirements and no other noise is introduced in. Finally, achievements and problems to be further solved in our work aresummarized.