ABSTRACT
Heterodyne receivers are an important component of most high-frequency communications systems and other receivers. In its simplest form, a receiver consists of a mixer being pumped by a local oscillator with an associated intermediate frequency (IF) circuit. At lower frequencies, a variety of local oscillator sources are available, but as the desired frequency of operation increases the local oscillator source options become more limited. The “lower frequencies” limit has increased with time. Early transistor oscillators were available in the MHz and low GHz range. Two terminal transit time devices such as impact ionization avalanche transit time (IMPATT) and Gunn diodes were developed for operation in X and Ka band in the early 1970s. However, higher frequency heterodyne receivers were needed for a variety of communications and science applications, so alternative local oscillator sources were needed. One option was vacuum tubes. A variety of vacuum tubes such as klystrons and backward wave oscillators grew out of the radar effort during World War II. These devices were able to produce large amounts of power over most of the desired frequency range. However they were large, bulky, and expensive, and suffered from modest lifetimes. They were also difficult to use in small science packages for space applications.
