Fast electromagnetic analysis of an X-band power injection coupler of dielectric-loaded accelerator using a novel transmission line model

In this paper, a novel transmission line model of a dielectric-loaded waveguide is introduced and employed to analyze a non-uniform dielectric-loaded coupler. In this method, a dielectric-loaded waveguide is equaled by a fully dielectric-filled waveguide with the same phase constant, power flow, and dissipated powers in the dielectric part and wall of the waveguide. This leads to a set of four non-linear equations. Four unknown variables of the filled-waveguide including the real and imaginary parts of dielectric permittivity, inner radius, and conductivity of the metal body of the waveguide can be obtained by solving the equation system. To investigate the validity of the new model, an X-band tapered dielectric-loaded coupler is considered and its scattering matrix parameters are obtained by a full-wave electromagnetic (EM) software. By segmentation of the coupler structure into a large number of uniform dielectric-loaded tubes and using the proposed transmission line model for every section, the whole structure can be considered as a series of transmission lines. Then, by calculating the total transmission matrix of the coupler, the scattering matrix parameters are achieved. It is shown that there is an acceptable agreement between the total behavior of the analytical and simulation results. Moreover, the fast proposed method with a combination of optimization algorithms can provide an initial point of design for further more accurate full-wave optimizations to reduce the total time of the optimization process.