Abstract: It introduces a new type of double radio frequency low noise amplifier circuits with the function of switching between inner and outer antenna using GPS L₁、L₂ band & GLONASS G₁、G₂ band. The low noise amplifier circuit structure was improved, and the amount of restraint outside the band increased obviously, making it have better ability to resist interference. The new type of circuits had the function of switching between inner and outer antenna to avoid the influence of the outer antenna port interface on the signals of the inner antenna. The simulation results show that this new type of double radio frequency low noise amplifier circuits have low noise figure, high gain flatness and the ability of out-of-band rejection. The circuits stability is good. A circuit sample was made, and then the debugging and testing were carried out. The main technical parameters of the measured results are in agreement with the simulation ones. The new type of double radio frequency low noise amplifier circuits have good characteristics. The sample circuit structure is compact, and the occupancy of PCB board area is lesser, which is very suitable for hand-held high precision positioning receivers.

Key words: low noise amplifier circuit；noise figure；out of band rejection；inner and outer antenna switching