On the noise resistance of HEMT's for improving the performance of microwave low-noise amplifiers

Among the noise parameters expressed in the reflection coefficient form (F/sub 0/, |/spl Gamma//sub 0/|, //spl Gamma//sub 0/ and r/sub n/), the noise resistance r/sub n/ is of critical importance to the design of low-noise receivers. Very low values of r/sub n/ allow for optimizing the performance of microwave broad-band amplifiers employed in receiver front-ends. We here present a sensitivity analysis performed on typical circuit models of FET's previously characterized in our lab. Such analysis has been aimed at determining the key elements that mostly affect the behavior of r/sub n/ at microwave frequencies. We have also observed how the noise performance may be improved by tuning the value of the input (gate, source) inductances which are responsible of the U-shaped curves typically observed for r/sub n/ in MESFET's and HEMT's.