Research On Weather Radar Receiver In X-band

Weather radar is utilized to forecast rain and snow which is the most effective detection equipment to monitor disastrous weather. With the rapid development of radar technology, the demand for the performance of radar is higher. This thesis studies and designs a low noise and large dynamic range receiver applied to the IF coherent Doppler radar at X band. The receiver has characteristics of low-cost, miniaturization, high reliability and is easy to be realized. Therefore, the research on the receiver has an important theoretical significance and practical value.This thesis first introduces the relevant theories of radar receiver, including common receiver structure and technical indicators. The suitable receiver structure and the overall scheme are determined, according to the design requirement of the whole radar. The key parameters of the modules in the receiver are assigned and the devices in the module are selected. The receiver’s operating frequency is from 9320 MHz to 9420 MHz, and the intermediate frequency is 60 MHz. The noise figure is less than 2.5 dB and the dynamic range is larger than 85 dB. The image-rejection ration is more than 30 dB. The receiving system is simulated and analyzed by the Advanced Design System (ADS). The Simulation results demonstrate the feasibility of the system. The theory and design approach of some important circuits inside the receiver such as low noise amplifier, local oscillator frequency source and microstrip filters are described in the thesis. The low noise amplifier is designed in the method of three-stage direct coupled structure, whose noise figure is less than 1.2 dB, and the gain is 27±0.5dB. The local oscillator frequency source is realized by using phase-locked loop (PLL) frequency synthesis technique, the phase noise is less than-100dBc/Hz@1kHz, and spurious rejection is larger than 75 dBc. By using the microstrip structure of parallel coupled, a bandpass filter is realized, the center frequency of which is 9310 MHz and bandwidth is 250 MHz, the insertion loss is less than 3dB, and standing wave is less than 1.3. A bandpass filter is realized based on hairpin structure, whose center frequency is 4000 MHz, bandwidth is 60 MHz, insertion loss is less than 3 dB, and standing wave is less than 1.3.Finally, the whole receiver system was tested after fabricating and debugging. The test results show that the receiver fully achieves the design goals which have higher sensitivity, large dynamic range and better frequency stability.