RF Front End Design Of Anti Jamming System For Satellite Navigation System

With the rapid development of science and technology, satellite navigation technology has widely utilized been in human life. The second-generation of “Compass” satellite navigation system, which is independently developed by China, would achieve global coverage navigation function gradually. Because of the weak signal, frequency disclosure and other reasons of the satellite navigation system, the satellite navigation receivers are easy to be interfered. Thus, it is necessary and meaningful to research the navigation anti-interference technology.In this thesis, structures of the various RF receiver front-end have systematically been analyzed. A four-channel anti-interference RF front-end for satellite navigation system has been designed and fabricated.The current situation and development trend of domestic and foreign satellite navigation system has firstly been introduced. By analyzing a variety of receiver RF front-end structures, as well as combining with the requirements of the task, superheterodyne receiver scheme has been utilized to design a satellite navigation receiver front end. Component selection and circuit design module has been decided according to the specific indicators. Under undistorted conditions, two-cascaded design for the low-noise amplifier of RF front-end has been utilized to increase the system gain and reduce the noise coefficients. By implementing the active mixers down-conversion, gain has been improved and the combination interference can be reduced simultaneously. By implementing an automatic gain control circuit, the sensitivity requirements for the signal processing of the intermediate frequency signal power can be satisfied without introducing the saturation distortion by using an automatic gain control circuit. Phase locked loop(PLL) can be generated by using the local oscillator signal in order to improve the spectral purity as well as effectively suppress spurious.The link, module and improvement has been fulfilled by using the simulation software ADS according to the design scheme. Then, the reasonable PCB layout and the cavity of the entire system can be designed by combining the function of each module, interface and dimension. Measured results of the RF front-end indicate that the VSWR of each channel is less than 1.4; gain of each channel is more than 100 d B; control range of the gain is about 90 d B; noise coefficients of each channel is less than 1.5d B; the amplitude consistency of each channel is less than 0.8 d B; the phase consistency of each channel is less than 10°; a stable local oscillator signal at 1.222 GHz has been generated by PLL circuit. All the indicators have been satisfied. According to the actual system test, the RF front-end can be used in satellite navigation anti-interference systems.