Minimizing dispersion in a TEM waveguide bend by a layered approximation of a graded dielectric lens

We consider compensation of a waveguide bend by a purely dielectric lens, characterized by an inhomogeneous, frequency-independent, isotropic permittivity. If the relative index of refraction of the lens varies inversely as the radius of curvature, then the optical path length through the bend will be independent of the radius, and the bend will support pure TEM waves. Although waveguide structures employing lens materials having the required inhomogeneous permittivity profile are easily conceptualized, constructing them is more problematic. In this paper, we describe an approximation employing coarsely graded layers of dielectric materials of various uniform permittivities. We used this approach to compensate a 90° H-plane bend in a strip transmission line