On the use of the frequency dependent properties of microwave ferrites in the design of circulators for multiple frequency operation

The conditions for the planar Y-junction circulator to operate within more than one frequency band are studied. Solutions of the circulation conditions are given taking into account the frequency dependent properties of the permeability parameters of the ferrite. It is found that the saturation magnetization and the bias field intensity completely define the circulation frequencies for given resonance modes. A new expression for the loaded Q-value is derived. Finally relations are given for the sensitivities of the circulations with respect to the design parameters.