Research And Realization On Near Zero-IF RF Front-End Of GNSS Dual-Mode Receiver

GNSS can provide users with high-precision positioning,navigation,timing and other services,which is widely used in the military and civil areas.It is not only the infrastructure of national security and economic,but also an important symbol for the status of modern power and national comprehensive strength.Because of its great significance in politics,economy and military affairs,many countries carry out in-depth research.As an important part of the satellite receiver,the RF front-end is a major research focus.The traditional receiver of single frequency and single mode is inferior to that of multimode and multifrequency in terms of accuracy and applicability.The latter gradually becomes a trend.In the circumstances,this paper focuses on the RF front-end of GNSS dual-mode receiver.This paper mainly aims at designing the RF front-end of GPS/GLONASS dual-mode receiver to achieve dual-mode signals'capture and processing.According to the targets,the whole system is built.The near-zero structure is chosen in project approachment with many structures of RF front-end discussed.Besides,the circuit schematic diagram is drawn and the RF front-end link is simulated.Moreover,orthogonal mixer and multiphase filter are combined to improve the performance of the image frequency rejection.Finally,the circuit design,device selection,PCB drawing,shielding box production are completed.Flowing into the system through the antenna,GPS/GLONASS signals are processed by low noise amplifier(LNA)and splited in two processing channels by power splitter.With the processing of RF filter,RF amplifier,orthogonal mixer,variable gain amplifier,multiphase filter,IF filter,etc.,the central frequency of satellite radio frequency signals is converted into the IF near zero.The project is justfied by system testing.The RF front-end developed in this paper meets the design requirements.Through the quadrature demodulation,GPS/GLONASS signals are respectively transformed into signals of 512 kHz and 140 kHz near zero-IF.The noise figure is as low as 2.5dB,the system gain is as high as 90dB,and the variable gain achieves 31dB.Moreover,the image frequency rejection exceeds 60dB.After frequency conversion,the signals can alleviate the pressure of A/D sampling,and support the receiver in follow-up work.Furthermore,the research and realization on RF front-end of GNSS dual-mode receiver can provide experience and reference for BeiDou Navigation Satellite System.