Measurements of a leaky-wave ferrite isolator

A single ferrite/dielectric image line is analyzed using the effective permittivity method adapted for ferrites. E-pq(x) modes are used in association with a transverse bias direction to obtain nonreciprocal behavior. It is shown that the required conditions can be obtained that enable the composite image line to guide in one direction and leak in the other. Thus, the structure behaves as a "leaky-wave isolator." Dispersion diagrams showing this behavior in the frequency range of 14-30 GHz are obtained for a 2 x 2 mm(2) ferrite (type TT1-390) rod with adjacent dielectric loading with epsilonr = 10. The structure is built and the bias is applied externally in a direction transverse to and in the plane of the direction of propagation. The required modes are excited and probed by semirigid coaxial cables mounted on vernier mechanisms. The S-parameters indicating the nonreciprocal behavior in the frequency range expected are shown.