Closed-form expressions for the equivalent circuit model of H-plane waveguide T-junctions

In this study, the authors present simple and accurate closed-form expressions for the equivalent circuit model of H-plane waveguide T-junctions with a side arm of arbitrary size. The effect of higher-order modes is included through the generalised admittance matrix with proper approximation and simplification. Calculated results agree very well with those from the full-wave mode-matching analysis over the entire single-mode operating band and these expressions exhibit significant improvements compared with those available in the literature. Based on these closed-form expressions, the design of an H-plane diplexer in the circuit level is considered and the initial value of the diplexer can be quickly obtained by circuit optimisation. Results from this circuit model are compared with those from the full-wave simulation and the comparison shows that this circuit model is very suitable for the initial design of diplexers.