Mode and characteristic impedance of isosceles triangular waveguide

The mode and characteristic impedance behavior of an isosceles triangular waveguide is found by simulation. There is an interesting transition of the dominant mode as the triangle changes from acute to obtuse, i.e., when the triangle becomes equilateral. When the vertex angle is greater than 43°, triangular waveguides have higher cut-off frequency than that of standard rectangular waveguide with the same-sized base, and they have lower cut-offs when the vertex angle is less than 43°. The characteristic impedance of an isosceles triangular waveguide is close to that of its associated regular rectangular waveguide. These new results offer guidelines for the design, fabrication and applications of the isosceles triangular waveguide.