Ferrite coupled-line circulator with reduced length

A method to design a circulator based on a ferrite coupled line (FCL) with reduced length is presented. This is achieved by appropriate matching networks. Using ferrite perturbation theory, we derive closed-form expressions for the required matching impedances and the resulting bandwidth of the matched device. Based on this analysis, a realistic design for a stripline FCL circulator is obtained, whose length is shorted by a factor of three. A microstrip FCL circulator with only half of the optimum length is designed and fabricated. Both simulation data and measurement results clearly demonstrate the feasibility of a circulator based on an FCL with reduced length.