A Hybrid FETD-GSM Algorithm for Broadband Full-Wave Modeling of Resonant Waveguide Devices

An efficient hybrid algorithm that combines the finite-element time-domain (FETD) method with the generalized scattering matrix (GSM) technique is proposed to characterize the properties of wave propagation in highly resonant waveguide devices. To alleviate the problem of an extremely large number of time steps required for a highly resonant device, the algorithm first divides the device into several less resonant or resonant-free subdomains to reduce the number of time steps and the computational complexity of the FETD solver. The subdomain interfaces, which are assumed to be homogeneous, are modeled with an accurate waveguide port boundary condition (WPBC) to absorb any impinging waveguide modes. Each subdomain is then represented by a broadband GSM, which is computed by the fast Fourier transform of the FETD solutions. Finally, the subdomain GSMs are cascaded to form the global GSM of the original resonant device. The formulation and implementation of the FETD method with the WPBC, its required general waveguide modal analysis, and the cascading of GSMs are discussed in detail. Three numerical examples are presented to demonstrate the accuracy and efficiency of the proposed hybrid algorithm.