本文简要评述了近年来在微波低噪声前端放大器设计中被日益广泛应用的噪声量度M的物理意义及其特性。直接应用线性二端口网络的散射参量(S参量)、噪声参量和源反射系数,推导了噪声量度M在史密斯(Smith)圆图上进行图解分析的公式。为按最小噪声量度M_(min)设计微波低噪声前端放大器提供了方便的工具。 This article briefly reviews the physical significance and characteristics of the noise metric M, which is increasingly used in microwave low noise front end amplifiers in recent years. By directly applying the scattering parameter (S-parameter), noise parameter and source reflection coefficient of the linear two-port network, the formula of the noise measure M for graphical analysis on the Smith chart is derived. It provides a convenient tool for designing microwave low-noise front-end amplifier according to the minimum noise measure M_ (min).