Analysis of a compact circular TE0,1 - rectangular TE0,2 waveguide mode converter

An analysis method for a three section mode transformer that converts a TE_0,1 circular waveguide mode to a TE_0,2 rectangular waveguide mode will be presented. Experimental results for this taper were earlier published in [1]. The middle section is a cylinder with a wall radius defined by r_wall = a(1 + epsicos(2thetas)), where a is the radius of the circular guide and e is a design parameter. This cylinder is connected on either side to a circular waveguide and a rectangular waveguide section respectively, through tapered waveguide sections. In this analysis we used a perturbation technique where the rectangular waveguide section´s wall radius is treated as a Fourier series expansion with a, the fundamental radius and e the perturbation parameter. By applying the proper boundary conditions we optimize the taper dimensions to minimize conversion into spurious modes.