Closed-Form Expressions for the Equivalent Circuit Model of Square-Waveguide T-Junctions and Its Application in Ortho-Mode Transducer Design

In this paper, closed-form expressions for the equivalent circuit model of square-waveguide T-junctions are presented. The square-waveguide T-junction is first modeled as a generalized admittance matrix and then reduced to a general five-port network. It is theoretically seen that the general five-port network can be simplified as a combination of a two-port subnetwork and a three-port subnetwork through the mode-matching analysis. Accurate closed-form expressions are derived with proper approximations to calculated the admittance parameters of these two subnetworks. A short-circuited branch ortho-mode transducer is then designed in a circuit simulator using the proposed equivalent circuit model. Measured results exhibit an excellent agreement with those from circuit simulation.