Post dielectric resonator at the junction of three rectangular waveguides: calculations and measurements

The open dielectric or gyromagnetic post resonator on the axis of a radial waveguides or at the junction of three rectangular waveguides, is a standard problem region in microwave engineering. The paper introduces a new exact formulation of the passband frequencies of such a symmetrical three-port junction. It is based on recognising that such passbands coincide with the condition for which the impedance of a symmetric mode of the post numerically coincides with the admittance of certain pairs of degenerate modes. This condition is used to determine the frequencies of the first two passbands of the junction in the vicinities of the TM₁₁₀^m and TM₂₁₀^m degenerate pairs of modes. The dominant symmetric TM₀₁₀^e mode is instrumental in defining each of these passbands. The calculations undertaken here are compatible with existing full wave analysis of the geometry under consideration, finite element calculations and measurements.