A virtual lossy dielectric model with composite boundary conditions for the analysis of substrate integrated waveguides

A new model for the characterization of substrate integrated waveguides is presented based on the analysis of a non-homogeneous closed waveguide with composite boundary conditions and a section of virtual lossy dielectric. The performance of the closed waveguide simulates the substrate integrated waveguide, once the parameters of the lossy dielectric section are adjusted (width, dielectric permitivity and magnetic permeability). This simple model gives physical insight into the propagation in the substrate integrated waveguide and it is inspired in the different field regions which appear in the open problem. Another important feature of this model is that it allows the characterization of the open substrate structure, including the radiation loss, with an equivalent closed waveguide, where well-known and efficient full-wave methods can be applied. Thus, this model is suited for the accurate analysis and design of devices in substrate integrated waveguide, as it is shown with different structures. The model is able to predict the radiation loss when the structure has large distance between posts. The agreement between measured results and the simulations are also confirmed with a bandpass filter.