Research And Design Of Microwave Low Noise Amplifier

In a receiving system such as a base station,a low noise amplifier（LNA）needs to be placed at the front end of the receiver,and its performance will directly affect the performance of the entire receiver system.Generally,the signal received by the antenna is weak.The function of the low noise amplifier is to amplify the received useful signal and reduce the noise interference,so that the system can demodulate the required information data and improve the sensitivity of the receiving system.In this thesis,the low noise amplifier matching network is taken as the research direction,and two related methods are proposed,as follows:（1）In the matching design,the method of joint matching of the lumped element and the microstrip line on the Smith chart is adopted to design a reasonable matching circuit,so that the component value and the microstrip line size are close to the actual value.（2）Adding equal standing wave ratio circles on the basis of the traditional equal noise figure circle and equal gain circle,so the optimal impedance matching point can be selected more intuitively in the same Smith chart for matching network design.In combination with the above method,a narrowband low noise amplifier with a working frequency of 0.8 GHz and a broadband low noise amplifier with a frequency of 0.65 GHz to 1.35 GHz are designed by ADS software,and the design steps are given in detail.In the design process of narrowband low noise amplifier,the effects of source negative feedback and series resistance on the performance of the amplifier are analyzed.The Momentum 3D simulation control in ADS is used to simulate the EM electromagnetic field hybridization of the low noise amplifier,which improves the simulation accuracy and makes the LNA of the simulation design closer to the physical test value.The designed narrowband amplifier noise coefficient NF<0.5dB,gain G>18dB,input and output reflection coefficients S₁₁,S₂₂ are less than-10dB,which meets the requirements of design indicators.Finally,using Altium Designer for PCB drawing,processing into physical objects and testing,and finally analyzing the error of the test results.The broadband amplifier topology designed by the thesis introduces a parallel negative feedback branch,and the theoretical value calculation formula of the parallel feedback resistor is derived.By optimizing the component values and microstrip line size,and then adding a matching network,a broadband low noise amplifier is designed.Its performance index is:operating frequency0.65GHz¹.35GHz,noise figure NF<1.35dB,gain G>12.8dB,The gain flatness is less than 1dB,and the input and output reflection coefficients are less than-10dB.Finally processed into a physical object and tested the results.The successful design of this low-noise amplifier demonstrates the feasibility of designing a low-noise amplifier by combining the impedance of the VSWR with a selected impedance point.At the end of the thesis,the interdigital microstrip coupling line is tried as the matching network of the low noise amplifier.This structure is suitable for use in the S band.The simulation results of the low noise amplifier designed with this structure in the frequency range of 2 GHz to 3 GHz are:NF<2.5 dB,gain G>10 dB,gain flatness less than 1 dB,and input and output reflection coefficients are less than-10dB.Simulation results show that this structure can be used as a matching network for low noise amplifiers.