Dependence of the noise resistance of microwave FET´s from the device characteristics

The noise parameters F₀, Γ₀ and r_n are a complete representation of the noise performance of any linear twoport. We focus upon r_n which is a measure of the noise figure degradation when the source reflection coefficient departs from the optimum value Γ₀. In the present paper, the behaviour of r_n is analysed as a function of the main elements of the noisy electrical model which reproduces the device performance. Such a study is aimed at evidencing the factors which allow for decreasing either the values and the frequency-dependence of r_n . By optimizing r_n, great improvements can be obtained in the performance of broad-band microwave low-noise amplifiers