W-Band LFMCW Radar Reflected Power Cancellation Research

With the development of semiconductor technology applied in high frequency, MMW technology has been mature gradually. Millimeter wave precision guidance technology, as terminal guidance technology which takes full advantage of the characteristics of MMW like all weather, automatic track and so on, is widely applied in the modern weapon system. Pulse radar is mainly used, while the CW radar is more suitable for the modern weapon system because of its miniaturization, high resolution, etc. But for the single antenna CW radar, the isolation between transmitter and receiver is not enough, so the power leaking from transmitter is the main problem which limits the application of CW radar, especially when high power signal needed to be transmitted. In order to solve this problem, a lot of methods are proposed in which the RPC(reflected power cancellation) is the most promising. In this paper, a reflected power canceller is designed working in W band, in which all the kinds of modules are accomplished and tested as the primary work to construct the system.The first chapter introduces the characteristics and application of MMW and research situation of the RPC. Then the working principle, advantages and disadvantages of the LFMCW radar are given in chapter two, with kinds of technology to solve the problem of power leakage. Chapter three discusses the basic idea about the RPC, evaluation and conditions of the cancellation. Based on this, the working process of the digital self-adapting close-loop system is discussed and the overall scheme of RPC is put forward. In chapter four, the design processes of modules are given in detail. For the passive circuits modules, mainly about the power divider and coupler, the related theories are introduced and simulation results using HFSS with measuring results are given. Due to the strict requirements of the machining accuracy and roughness of surface, the measuring results are 1.5dB different from the simulation results which are acceptable in W band. The active circuits gives the roles of the modules of LO frequency multiplication chain, transmitter, receiver, feedthrough module and error detecting module in the system. The key components’ related theories and main parameters are briefly introduced, and the designed circuits using Autocad and the fabricated circuits are given with the testing results. Finally the fifth chapter gives the summary and the key points about next work.