Mathematical Modeling of Iris-Post Sections for Waveguide Filters, Phase Shifters and Polarizers

Abstract

In this research we carried out mathematical modeling, development and optimization of square waveguide sections with irises and antiphase posts. The presented mathematical model applies scattering and transmission matrices of the structure elements for the calculation of general scattering matrix of the whole waveguide section. Depending on linear polarization type of the fundamental mode the irises are simulated as inductances or capacitances, which are connected in parallel into the equivalent transmission line. Two antiphase posts in a square waveguide are modeled as a parallel resonant circuit in the equivalent transmission line. Using the developed mathematical model the matching characteristics and differential phase shift of square waveguide sections with two irises and two posts were calculated theoretically. In order to check the performance of developed mathematical model the simulations of the same waveguide sections were performed using finite integration technique. Presented waveguide sections can be tuned by changing the length of their posts. Both optimized designs of square waveguide sections with two irises and two posts provide voltage standing wave ratio less than 1.4 for both polarizations. Differential phase shifts of developed polarizer sections are 30°±0.7° and 45°±1.75°. Therefore, suggested new simple mathematical technique for calculation of characteristics of the waveguide sections with irises and antiphase posts can be widely used for the development of new tunable waveguide filters, phase shifters and polarization processing devices.