A STUDY OF TUNING CHARACTERISTICS OF GUNN OSCILLATORS

Abstract

A number of analytical techniques are applied to study the driving-point input impedance seen at the gap terminal of a rectangular waveguide mount used for the design of Gunn oscillators. The tuning characteristics of X-band Gunn-effect oscillators with different rectangular waveguide mount structures, e.g., the resonant-cap and conical cap types, have been investigated, based on the theoretical input impedance of the waveguide mount and the equivalent circuit model of the active device. The theoretical analysis of the input impedance of waveguide mount structures was verified with experimental measurements at X-band. A method that enables accurate de-embedding of the relevant parameters from the measured S-parameters was used to determine the required driving-point input impedance of the waveguide mounts. Experiments have been performed to measure the oscillating frequency range of the designed oscillators with different waveguide mount structures. Good agreement between the experimental and theoretical results has been obtained. The investigation shows that oscillators which were designed with conical cap mount structure give wider oscillating frequency tuning range compared with corresponding oscillators built with post and resonant-cap mount structures.