Research On A Non-Line-of-Sight U/V Broadband Receiver

Wireless communication is one of the most rapidly developing aspects in modern communications; it has been widely applied to various aspects of our daily life. The development and applications of the ultra-short wave radio communication equipment is of vital significance in military and civilian use.This thesis researches on a universal broadband receiver for the Non-Line-of-Sight U/V (225-800MHz) communication, including the argumentation of the system scheme, framework design, design and development of every circuit unit, as well as joint trial of the system. The thesis has some innovations and is characterized as follows:(1) A super heterodyne structure with dual-frequency conversion is used in the receiver to realize wideband receiving. For the selection of the two-stage intermediate frequencies and the gain assignment of each stage, we consider the requirements of optimizing the sensitivity and frequency selectivity, as well as such factors as signal distortion, the mirror-image spurious interference. The thesis involves reasonable design of the system, elaborate selection of the circuit devices of every unit; structure design based on electromagnetic-compatibility, and the circuit manufacture.(2) For the sake of improving dynamic range of the receiver, a three-stage cascaded AGC scheme is employed to realize the automatic gain controlling, which can guarantee the linearity of the whole receiver in a large dynamic range.(3) A scheme of signal strength detection with high precision and a received signal strength indicator(RSSI) based on the scheme is designed and implemented, which can improve the practical usage speciality for the product prototype.After dissertating the detail system framework of the receiver, the thesis describes and analyzes the technical performance and implementation of every function unit, including LNA, frequency synthesizer, fixed-frequency LO, frequency converter, AGC and RSSI. After debugging and testing the system, the thesis has given a lot of test results for various performances and specifications, as well as some analysis and illustration for them. The results show that the successfully developed prototype has reached the expected requirements.