Finite element analysis of high power differential phase shift circulators

An ongoing requirement of the circulator unit used in high power radar systems is to increase the bandwidth and to reduce the insertion loss. The classic broadband arrangement is the 4-port differential phase shift section which uses a rectangular waveguide, loaded with thin transversely-magnetized ferrite slabs. Bias field magnetisation, magnetic losses, high power losses, material temperature performance and geometry all have to be considered in the design process. Bandwidth is restricted by losses, which in turn are associated with bias field inhomogeneity. A magnetostatic finite element solver is used to show how this can be reduced by altering the shape of the ferrite slab cross section. Magnetisation data from the magnetostatic solver is used to construct the microwave tensor permeability. A microwave finite element solver was then employed to calculate differential phase shift in terms of material and experimental parameters. The calculated phase shift compared well with measured data provided by TRAK Microwave