| Microwave Doppler radar system is being studied and used widely in civil and military field. In civil, this system can be used to traffic speed alarm system and the place where needs auto-sensing control. The system also can be used to weather forecast and detect information of weather objects such as thunderstorms, heavy rain, large-scale. It is also used to detect weapon, plane and naval vessel, and so on. One promising technology, which has been demonstrated to be effective, is microwave Doppler radar system. So the design and research for the system is very import.According to needs of application, it needs to design a system which can detect lows peed moving target. The thesis studies a low cost, simple and compact microwave Doppler radar system which can get good result in the environment of lab. Microwave Doppler radar system has microwave Doppler radar front-end system and send-receive antenna.The send-receive antenna is single antenna which is a 2*2 microstrip antenna array. According to the theoretical formula calculating the size of the antenna, then using HFSS to simulate and observe results. According to the needs of compact and narrow angle antenna, the thesis designs a 2*2 microstrip antenna and achieves the needs of narrow angle antenna through adjusting the distance between two patches. The thesis improves antenna array and gets wide bandwidth to meet qualifications. According to theoretical size, making PCB board, test antenna's center frequency S11 and bandwidth with network analyzer sweep. The thesis debugs and amends the antenna by changing the size of four patch of antenna array. The test results show that the bandwidth is about 500MHz (S11<-10dB) and narrow angle can be achieved in dark room.The thesis uses microstrip circuit to design microwave Doppler radar front-end system. The system contains parallel DRO oscillator, mixer bridge ring, the second sub-power splitter. The thesis designs DRO oscillator according to theory size and test by Spectrum Analyzer. DRO oscillator has the stability frequency output 10.8GHz which not changes by the power supply voltage, and mechanical turning frequency above 100MHz. The thesis designs ring bridge and second sub-mixer splitter according to the theoretical value, then tests the performance of PCB circuit with spectrum analyzer and network analyzer.Finally, the thesis tests the performance of Doppler radar front-end system, and IF mixer output signal with spectrum analyzer. Then integrating Doppler radar front-end system and antenna, testing the whole system, results show that the radar can be used for low-speed moving target detection. |
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