New uniaxial-ferrite millimeter-wave junction circulators

The authors report on progress in the development of millimeter-wave junction circulators for the band near 31 GHz, incorporating the technique of exploiting the high effective internal magnetic anisotropy field of barium and strontium magnetoplumbites (hexagonal ferrites) to eliminate the external permanent magnet requirement. Microstrip and waveguide three-port junction versions have been built and evaluated, exhibiting good isolation and insertion loss performance, and requiring no magnet. Design considerations include the magnetic material parameters of remanent magnetization, anisotropy, coercive field, resistivity, and shape-dependent demagnetizing effects, as well as microstrip and waveguide junction circuit geometries, dissipative effects, temperature stability, and influences of coax-microstrip transducers.<>