The Suppression Of The Transimitted Leakage And Phase Noise In FMCW Radar

FMCW radar has attractive features like low cost and low power requirement, which is finding applications in such diverse fields as naval tactical navigation radars, smart ammunition sensors and automotive radars. Furthermore, the mono-static structure, which uses a single antenna as transmitter and receiver simultaneously, will result in an even more compact system. One of the greatest challenges in designing continuous-wave mono-static radar is sufficient isolation between the transmitter and the receiver. In pulse radar, it is easily achieved by time gating. In continuous wave radar, transmission and reception are simultaneous and it is necessary to detect target returns of a pico-watt or less in the presence of leakage signal from circulator and reflected signal from antenna mismatch. It can result in two serious problems. One problem is the transmitter noise sidebands can swamp out valid targets. The other one is power leaking into the receiver can desensitize the receiver. The phase noises of the transmitted power leaking into the receiver will fall into the same frequency band of the radar video signal and cannot be filtered out. Thus the dynamic ranges of conventional FMCW radars are limited.The thesis focuses on the analysis and research of the transmitted leakage, including the principle of cancellation and the schemes of reflected power cancellation. On this basis, an improved scheme is proposed, namely the adaptive cancellation system. Specific work completed is as follows:The thesis describes the related-knowledge of FMCW, including the advantages and disadvantages of FMCW radar, some applications and the principle of FMCW radar. On this basis, some simulations are made in MATLAB, including continuous signal and four target echoes. For transmitted leakage, an in-depth analysis is made, including ways to signal leakage, the principle and the echo power of antenna reflection. The influence of the leakage noise on receiver performance is analyzed.Secondly, the technology solutions of reflected power canceller are analyzed, including analog and digital solutions for cancellation. On this basis, the advantages and disadvantages of these two schemes are analyzed. Meanwhile, the cancellation performance of reflected power canceller is analyzed, including the depth of cancellation, the bandwidth of cancellation and the evaluation of cancellation performance.Finally, an improved scheme using adaptive LMS algorithm is proposed. Based on this, the LMS algorithm is firstly introduced, and the structure of adaptive cancellation system is studied theoretically. Further, the weighting coefficients, the signal to interference ratio(the ratio of the leakage signal to the noise) and the ratio of the signal to noise of the system are analyzed. Meanwhile, in MATLAB the system simulations are made, including system simulation only with a leakage signal, the simulation system including a noise, the system simulation including the target echo, the simulation including the two leakage signals, the simulation system with local oscillator including noise, and the simulation system with the three target signals. In addition, the effect of the step size to the system is analyzed and simulations are made.