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'. Here we find that the white noise figure is scale independent and the 3rd order intercept point increases as &'\ Hence, the spurious-free dynamic range (SFDR) should scale as n'. 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. !