Design And Implementation Of Rf Front-end For Anti-Jamming Receivers

The application of satellite navigation technology has penetrated into many fields of national economy. With the development of navigation and positioning technology, network constructing of the"Compass-II"satellite navigation system is developed gradually. In order to meet the demands of military applications and practical requirements of high performance navigation and positioning, smart anti-jamming satellite navigation and positioning system has been a hotspot for study. According to practical need, a RF (radio frequency) front-end for smart anti-jamming receivers is designed and realized in this paper.The design of the receiver system is instructed by RF circuit theory, and analyzed and verified by simulating softwares. The main idea of design is from top to bottom: The system diagram and circuit scheme is established at first. Then technical specifications of each module are decided, and components and layout forms are selected. Through fabricating and adjusting, the study of RF front-end for anti-jamming receivers is accomplished.The development situation of satellite communication technology and satellite navigation industry at home and abroad is introduced, as to clearly define the application background and research direction. The scheme of receiver is selected to be superheterodyne, through comparing the performance indexes, complexity degrees, power consumptions and costs of the receivers commonly adopted, combined with analyzing the size of structure. RF front-end is divided into two parts: down converting channel before anti-jamming processing and up converting channel after digital processing. Component selecting and circuit designing are carried out based on circuit block and related functions. The two-stage LNA (low noise amplifier) in the RF front-end system is applied to provide link gain and suppress NF (noise figure) without saturation distortion or third order intermodulation. Active up converting and passive down converting mixers are adopted to realize frequency conversion, respectively. The dynamic range of IF (intermedium frequency) output signals meets requirement of digital signal processing, and avoid saturation distortion by means of AGC (auto gain control) technology. And with the use of PLL (phase locked loop), LO (local oscillator) and clock signals are generated to frequency converters and baseband processing part, respectively.According to the design scheme, circuit blocks are modeled and link budget is analysized with simulating software Agilent ADS. On basis of size demand of the receiver, signal features and connection locations and types, schematic and PCB (printed circuit board) documents are designed, cavity structure and hardware circuit are fabricated. The measured data of hardware object indicate that VSWR (voltage standing wave ratio) of each port is almost less than 1.5. The total gain of down converting channel is 65dB with 15dB AGC range. NFs of the down converting ports are 0.66dB and 0.89dB. The total gain of up converting channel is -30dB. And 1222MHz LO and 62MHz clock stable signals are generated by PLL. With the analysis of measured results, the testing data meet the specification requirements basically, and the RF front-end is suitable for the anti-jamming satellite navigation and positioning system.