Design of a wideband low noise amplifier

Low noise amplifier (LNA) can effectively amplify the small radio frequency signals, reduce the noise of the whole system, and increase the sensitivity of the receiver. In this paper, the main performance indexes and design methods of the LNA are introduced. The circuit is made up of two stages with ATF-35143, each stage includes two transistors, and the wideband amplifier is designed and simulated by the software Agilent´s ADS. In this design, short microstrip lines are added to the source tone to improve the stability of the circuit by the feedback effect. The capacitance between the two transistors plays the role of blocking DC and improving stability. At last, the designed circuit is fabricated and measured. It shows that, from 3 GHz to 5 GHz, the gain is between 29 dB to 31 dB, the flatness is less than ±1 dB, the noise figure is less than 1.7 dB, the input and output VSWR are less than 2.