Master Amplifier Characteristics for Transmission and Reflection Cavities

The noise temperature, band width, and gain modulation characteristics of a transmission maser are obtained as a function of iris coupling for fixed desired gain and other parameters. It is found with the help of a characteristic curve that certain of these characteristics can be optimized at the expense of others. The same functions are compared in the case of a reflection maser. The reflection maser is shown to be superior in most respects, although the same noise temperature may be attained with the transmission maser at a substantial sacrifice in band width and gain modulation. The reflection maser is also limited by the availability of good circulators, while a transmission maser can be made independent of load. A figure of merit for both types of maser amplifiers is obtained. This is Q₀Z, where Q₀ is the unloaded cavity Q; Z is given by ${\text{Z=4πξχ}}_0{\mathrm{-Q}}_0^{\text{−1}}$ ; ξ is the filling factor; and χ₀ is the negative rf susceptibility. When the cavity band width is much less than the susceptibility band width, an auxilliary figure of merit is Z.