Dual-ferrite slot line for broadband, high-nonreciprocity phase shifters

A phase shifting structure that exhibits both broadband operation and high nonreciprocity is presented. This structure comprises a slot line between two oppositely magnetized ferrite substrates. A full-wave spectral-domain analysis is used, where Green´s functions are formulated using a transmission matrix approach. By eliminating the use of relatively thick high-dielectric substrates, a bandwidth of 3:1 and a differential phase of 50°/cm are feasible. The geometry of the present structure can be optimized to increase both the nonreciprocity and the bandwidth. The characteristic impedance of the slot line is presented and shows a strong dependence on the slot width and the state of ferrite magnetization. The addition of thin layers of high-dielectric material increases the differential phase to over 100°/cm without significantly reducing the bandwidth. These layers were found to reduce the variation of characteristic impedance versus the ferrite magnetization