Comments on "Analysis of nonreciprocal coupled image lines" [with reply]

For the original article see ibid., vol.35, no.7, p.629-35, 1987. D.B. Sillars and L.E. Davis showed that nonreciprocal effects are present in a homogeneous waveguiding structure containing a gyromagnetic medium biased in the direction of propagation. The commenter points out that E. Jansen and C. Schieblich (ibid., vol.35, no.4, p.470-1, 1987) have previously shown that any longitudinally biased structure showing reflection symmetry with respect to its midplane is reciprocal. The structure in the Sillars and Davis paper is considered to fall into this category, because a homogeneous structure is symmetrical with respect to any plane perpendicular to the direction of propagation. In a reply, D.B. Sillars and L.E. Davis point out that nonreciprocal effects have been observed experimentally on coupled image lines loaded with a ferrite slab which is magnetized longitudinally just above saturation. Since the applied magnetic field was small, the behavior has been analyzed using approximations. The possibilities of higher-order modes and mode conversion have deliberately been neglected. This approximate approach has yielded dimensions that are similar to those used experimentally. A full-wave analysis of the open coupled structure is required to obtain a more precise description of the behavior and design information.<>