An approach to modifying bias in a circulator to prevent higher order modes that involves the use of features positioned near the ferrite material of the circulator. The ferrite bias in the perimeter of the ferrite material is modified by the adjacent features such that higher order modes cannot be sustained. The features may include scallops that create a non-uniform magnetic field towards the perimeter of the ferrite while leaving the field near-uniform in the center where the fundamental circulator mode primarily resides. Alternatively, slots may be placed in the magnetically conductive housing bottom in the region of the edge of the ferrite material to prevent higher order modes.