Design of Microwave GaAs MESFET´s for Broad-Band, Low-Noise Amplifier (Comments)

In the above widely-referenced paper, the empirical formulas for four noise parameters of microwave GaAs FET´s are given. It was assumed that the four noise parameters could be expressed in terms of the equivalent circuit elements by simple formulas (2)-(5) of the subject paper. Four fitting factors in these formulas were determined from the measured values of the noise parameters and the equivalent circuit elements of sample GaAs MESFET´s given in Table II. It is the point of this letter to demonstrate that, in some cases, the measured noise parameters, as well as those determined from the semi-empirical formulas, may not represent the noise of any physical two-port.