Inductive irises are applied in modern microwave filters, diplexers, polarizers, and rotators based on waveguides. The article presents an efficient mathematical technique for the analysis of the characteristics of the electromagnetic waves scattered by an inductive iris in a rectangular waveguide. Using the mode-matching technique for the transverse field components, the electromagnetic waves scattering problem was reduced to a set of coupled integral equations, which were then decoupled. Each equation was solved by expanding the electric field in the iris window into a series of basis functions. This procedure was implemented using sets of orthogonal trigonometric basis functions of the aperture field, orthogonal basis functions based on Gegenbauer polynomials with a weighting function of power 1/2, or orthogonal basis functions based on Gegenbauer polynomials with a weighting function of power 2/3. As a result, it became possible to determine the phasors of all modes in each region of the inner volume (before the iris, inside its aperture, and after the iris), along with the complex reflection and transmission coefficients of the fundamental electromagnetic mode TE10. In order to validate the correctness and accuracy of the developed mathematical model, additional calculations by efficient numerical methods (Finite Element Method and Finite-Difference Time-Domain method) and experimental measurements of reflection characteristics were performed for two inductive irises in a standard rectangular waveguide. Measurement setups included a scalar network analyzer or a vector network analyzer, one of two inductive irises, a matching load, and waveguide channels. The experimentally obtained reflection coefficients were in good agreement with those predicted by the developed mathematical model and numerical methods. The developed mathematical model can be widely applied to the analysis of electromagnetic wave scattering by inductive irises in waveguides and to the synthesis of various microwave devices based on these irises.
Piltyay et al. (Mon,) studied this question.