Research On High Isolation Techniques Of Transceiver Front-end In Single Antenna FMCW Radars

With more demanding radar miniaturization and low weight, FMCW radar system especially monostatic radar whose transmitter and receiver share one antenna simultaneously, get more and more attention on the applications of military and civilian. However, design for single antenna continuous wave radar faces a huge challenge that is how to solve Tx leakage problem. Solving the problem can greatly increase detection range of FMCW radars, and thus make it get more extensive application. In the context of this demand, related technology research about how to improve transceiver isolation of monostatic FMCW radar is carryed out in this dissertation.First of all, the existing high isolation techniques are studied, including the spatial isolation by using two antennas, circulator isolation and various cancellation technologies. Further the basic principles of cancellation technology are in-depth analyzed in theory. Based on this, a scheme that combines with high isolation circulator and RF cancellation with digital closed-loop control is proposed in the dissertation. This scheme can greatly improve the isolation between transmitter and receiver of radar. In the scheme, error detection circuit adopts heterodyne architecture. The advantage of this approach is that, compared to tranditional analog technology, it can solve the problem causing by DC offset existing after analog mixers. And more accurate and flexible cancellation control can be obtained by using digital closed-loop control. In order to verify the feasibility of the scheme, an X-band cancellation prototype is designed. According to system requirements, development process of the scheme is introducted firstly. Also the system description is detailed given, and key performances of system are analyzed.Then design of the microwave front-end circuits and metal cavity are detailed described, which is one of the main works. It is in several parts, including RF cancellation module design(feedthrough cancellation circuit and error detection circuit), power amplifier circuir design for transmitter, and cavity design. Design description is elaborated for key component selection, design of passive microwave devices, circuit PCB design, and the cavity structure optimization.At last, a detailed description of the measurement and debugging for microwave circuits are given. Every single circuit module is debugged firstly, and then they are assembled together for measurement. In the measurement, some problems that occur are in-depth analysis, and the solutions are also given. The final measurement results show that in bandwidth of 600 MHz the cancellation part can reach more than 30 dB of cancellation radio. The overall isolation of entire system which combined the cancellation part and circular can achieve up to 70 dB. It meets the system demand. Finally, the dissertation summarys the whole work, and put forward the improvement for the future work.