C-band Lna Design

Low noise amplifier, as the key part of a receiver system, Noise figure is a crucial index of a low noise amplifier, It determines the noise and the sensitivity of a receiver system. The C band low noise amplifier designed here works from 4.7 GHz to 6.7 GHz, and has low noise figure and low VSWR, so it shows a very promise market foreground.This thesis introduced the basic theory of the design of low noise amplifier at first, decided the project plan of the C-band LNA, chose the proper transistor, in this issue, we chose the high electronic mobility transistor (HMET), HEMT can fulfill very low noise and high power gain in high frequency, but encapsulation parameters have great influence on the LNA noise performance, so we chose the HEMT chips without encapsulation. The LNA designed in this thesis used two-stage structure, the first stage uses the balance type; connect two branches with 3dB Lange coupler. Then we discussed matching networks at both input and output ports with different design objective to achieve particular performances, then we designed the bias circuit of both stages, and use AutoCAD to design the house, This paper illuminates the processes of the design of the Lange coupler particularly, and introduces the method to extend the work frequency band of the Lange coupler. At last, we use Protel to design the PCB of the LNA, adjusted the circuit till it can fulfill all the performance designed. Finally, the LNA designed in this paper can realize almost all the performances required, testing results show that the LNA can work in 4.7GHz-6.7GHz band, the power gain is greater than 24.5dB, and the noise figure is less than 1.6dB, VSWR at the input port is less than 1.3dB, the gain flatness is less than 1dB through the work frequency band. The tested results prove that the LNA designed can achieve all the requirements of design objective.