Performance and Stability of Schottky Barrier Mixers

We discuss the performance of a Schottky barrier diode as a mixer when the barrier of the diode is open-circuited at the harmonics 2ωo, 3ωo, etc. of the pump frequency ωo. Such a mixer is shown to be capable of arbitrarily high conversion gain providedωc ηωₒ,where ωc, is the cutoff frequency of the diode and η is a parameter that is typically less than 6.25 and approaches 4 under certain ideal conditions. It is shown that the limit imposed by the series resistance of the diode on the double-sideband noise figure of the mixer is given byFₘ > (1 - η ωₒ ωc)⁻¹.An experiment is described at 1.25 GHz on a room temperature mixer whose double-sideband noise figure Fmas a function of gain has a minimum of about 0.7 dB (for gain less than unity) and a maximum of about 2.3 dB (for high gain).