Finite-difference time-domain analysis of inset dielectric guide and its application to waveguide transitions

A three-dimensional finite difference time-domain (FDTD) method is used to characterise inset dielectric guide (IDG) and the rectangular waveguide to IDG transition. The propagation constants and characteristic impedances of the fundamental modes are calculated and subsequently used to obtain the S-parameters of the transition. Three different definitions of the characteristic impedance are applied and a simple averaging technique used to compute the power flow along the guide is investigated. The transition is also characterised experimentally and good agreement between measured and numerical results is observed. Further, the finite dimensions of the waveguide flange are investigated for the first time, and are seen to affect results