Effect of DC Biasing on RF Performance of X-Band LNA

R. Lakshmanan and A.T. Kalghatgi (India)


DC Biasing, GaAsFET, HEMT, Low Noise Amplifier, Noise Figure, Gain.


Low Noise Amplifier (LNA) is an essential block for any RF & microwave front-end receivers. In this paper effect of dc biasing on the RF performance of GaAsFET based LNA operating at X-Band frequency range is discussed. The LNA developed, as part of the study, is a three-stage amplifier; the first stage design offers low noise match to achieve low noise figure and the second & third stages are simultaneously matched to obtain good VSWR and gain. The LNA uses Super Low Noise HEMT and general purpose GaAsFETs. The circuit is designed using Micro-striplines and optimized using the RF CAD tool. The LNA is realized using PTFE soft substrate with the dielectric constant of 10. The LNA gives a gain of around 30dB and Noise Figure of less than 1.8 dB over 10% bandwidth @ X-Band with the normal operating bias conditions. As part of the study, the dc biasing conditions of all the three stages are independently varied and the effect of the same on the overall performance of LNA is analyzed. It is concluded that the dc biasing conditions of the individual stages can be tuned to derive the best performance of LNA on Noise Figure, Gain, Input Return Loss and Output Return Loss.

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