L-band GaAs FET amplifier

The low noise figure and high gain of the GaAs FET can by made attractive to below 1 GHz through the addition of lossless feedback in the form of source inductance, thereby reducing the input mismatch and increasing the bandwidth at insignificant expense in noise performance. The application of this concept to low noise amplifier is explored. A simple circuit model, predicting noise and signal performance, is used to derive matching circuits for the amplifier design. A 1 to 2 GHz single stage amplifier, designed on the basis of the modeled results, demonstrates a noise figure less than 1.7 dB, 15 dB gain, and modest SWR across the band. Over narrower bandwidths, a noise figure of less than 1 dB with 15 dB gain and less than 3:1 SWR is demonstrated.