Nonreciprocal Ferrite Quarter‐wave Plates

This chapter describes a nonreciprocal quarter‐wave plate based on the birefringence displayed by a magnetic insulator with the direct magnetic field intensity perpendicular to the direction of propagation. It includes a description of a number of reciprocal and nonreciprocal phase‐shifters utilizing Faraday rotation and birefringent sections between reciprocal and nonreciprocal quarter‐wave plates. A quarter‐wave plate using a hexagonal ferrite with planar anisotropy is separately described. One possible equivalent circuit of the birefringent or nonreciprocal quarter‐wave plate is a four‐port circulator. Propagation in infinite space or a circular waveguide may be described either in terms of two degenerate orthogonal linearly polarized waves or in terms of two degenerate counterrotating circularly polarized waves. One classic type of reciprocal variable phase‐shifter consists of a reciprocal half‐wave plate between reciprocal quarter‐wave plates. One simple application of the nonreciprocal quarter‐wave plate is in the construction of the switchable circulator polarized antenna.