W-band ferrite-dielectric image-line field displacement isolators

The authors present the results of theoretical and experimental studies of image-line field displacement isolators operating at W-band (90-100 GHz). Isolators were fabricated using GGG (gadolinium gallium garnet), and GaAs as the dielectric and TT2-111 nickel-zinc ferrite and epitaxial yttrium iron garnet as the nonreciprocal medium. Isolators with S/sub 21/-S/sub 12/ ratios of greater than 20 dB have been designed, fabricated, and tested. The authors present the results of the theoretical analysis of a simplified parallel plane waveguide model of a field displacement isolator. The model gave a clear picture of the forward and reverse propagation characteristics and allowed for the optimization of the design of the isolator. Experimental measurements were carried out on a range of structures utilizing a millimeter-wave vector network analyzer operating at 90-100 GHz.<>