Aspects of the design of millimetric SATCOM LNAs

The development of practical LNAs in this range is subject to a number of difficulties, including: (i) noise parameters, needed to allow the matching circuit to be optimized for low noise, are extremely difficult to measure accurately for millimetric HEMTs; and (ii) the gain of each amplifier stage is low. A high gain LNA requires many expensive stages, and the overall noise figure is degraded by the interstage losses and by the noise of the second and subsequent stages. One approach to the first problem is to generate realistic noise models, permitting extrapolation into the millimetric range of noise parameter data measured at lower frequencies. Recent developments by the authors have enhanced the widely accepted Pospieszalski (1989) model to improve the fit to measured data. A novel approach to the second problem is to adopt a negative resistance, reflection mode amplifier configuration. Recent developments by the authors in the use of this configuration are reviewed