System characteristics of quasi-optical power amplifiers

Quasi-optical (QO) amplifiers have advanced to the point where they are competitive with other solid state and vacuum-based power amplifier technologies in the upper microwave and millimeter-wave bands. While still trailing in power-added efficiency, the QO amplifiers have advantages over traditional system architectures because of superior linearity, low noise, high spurious-free dynamic range, and added functionality (e.g., electronic beam steering). These advantages are stated in the present paper through a set of scaling laws that describe the behavior of fundamental amplifier properties versus the number n of elements in the QO array. It is known that the gain and power-added efficiency are scale independent, so that the output power scales as n/sup 1/. Here we find that the white noise figure is scale independent and the 3rd order intercept point increases as n/sup 3/2/. Hence, the spurious-free dynamic range (SFDR) should scale as n/sup 1/.. This makes QO amplifiers attractive as "robust" low-noise amplifiers (LNAs) in traditional superheterodyne receivers. An analysis is carried out to predict the improvement in total SFDR of a superheterodyne receiver having a QO LNA at the front end.