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 (F₀, |Γ₀|, /Γ₀ and r _n), the noise resistance r_n is of critical importance to the design of low-noise receivers. Very low values of r _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_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_n in MESFET´s and HEMT´s