Optimum performance of parametric diodes at S-band

It is shown that a Fourier expansion of the inverse of the barrier capacitance describes the potential noise performance of a semiconductor parametric diode better than the commonly used expansion of the capacitance itself. The Fourier coefficients are evaluated for point-contact and graded-junction diodes. Experiments carried out on diodes in two different amplifiers have given results in good agreement with the theoretical analysis over a wide range of pump power. Germanium, silicon and gallium-arsenide diodes all showed clearly defined pumping conditions for optimum noiseperformance. The theoretical analysis suggests a definition of a simple static figure of merit (an extension of Uhlir´s cut-off frequency) which is sasily measurable at microwave frequencies. The noise performance expected from this figure of merit agrees well with the minimum noise temperatures measured for germanium and gallium-arsenide diodes in a degenerate amplifier at 2.4Gc/s. For silicon diodes the measured noise was higher than predicted by the simple theory, owing to the eerious influence of an anomalous reverse current.