Semi-experimental characterisation of the 3-port waveguide junction circulator containing a gyromagnetic post resonator

The original 3-port waveguide circulator relies for its operation on a simple gyromagnetic post resonator with top and bottom electric walls and an open magnetic side wall with no variation of the fields along its axis. Its description is a seminal paper in the literature. The purpose of this study is to characterise its first circulation condition (frequency) using a finite-element package and to characterise its second (complex gyrator circuit) experimentally. This is done for one-third-height, half-height and full-height resonator posts. The shortest of these three resonators is compatible with the synthesis of a circulator with an equal ripple degree-2 frequency response with a return loss of 23 dB over a 20 bandwidth. This sort of junction is met in the design of the externally latched junction circulator. This study includes a characterisation of a composite post resonator geometry consisting of an undersized ferrite cylinder surrounded by a dielectric sleeve.