一引言在1～2GHz频率范围内,用室温最佳器件达到的噪声温度(括号内为噪声系数)的典型值是:双极晶体管为120°K(1.5dB),砷化镓场效应晶体管为50°K(0.7dB),参量放大器为40°K(0.6dB)。在许多应用中,特别是在射电天文学中,这些噪声温度限制系统灵敏度,即使需要致冷,也希望有更低的噪声。这是事实,因为灵敏度的其它限制在这个频率 I. INTRODUCTION Typical values ​​for the noise temperature (noise figure in brackets) achieved with the best room temperature device in the frequency range of 1 to 2 GHz are: Bipolar Transistors 120 ° K (1.5 dB), Gallium Arsenide Field Effect Transistors 50 ° K (0.7dB), parametric amplifier 40 ° K (0.6dB). In many applications, especially in radio astronomy, these noise temperatures limit the system sensitivity and even lower noise is desirable, even when refrigeration is required. This is a fact, because of the other limitations of sensitivity at this frequency