Design and Synthesis of Ferrite Strip-Line Circulator Based on Enhanced Closed Form Solution and Power Handling Analysis

In this article, Y-junction strip-line circulators are designed using an enhanced closed form solution consisting of unified key equations and a flowchart design, which serves as a direct procedure for designing a ferrite circulator. This design methodology is combined with a 3D EM simulation that allows for the calculation of the saturation magnetization, uniform biasing, and ferrite dimensions needed for a circulator to operate in both modes. In addition, the closed form can be used to calculate the Y-junction parameters and allow the matching network to be calculated and the uniform circulator biasing design ended. Our analysis starts with the ferrite calculation to ensure that it is uniformly biased magnetically, and this is followed by strip-line design, Y-junction matching, and biasing circuit design. Using full-wave electromagnetic (EM), HFSS and magnetostatic (MS), Maxwell3D simulations, several key design parameters such as the saturation magnetization, coupling angle, and various external permanent magnetic biases are investigated. To validate the proposed concept, two strip-line circulators are designed and fabricated for operation in wide-bandwidth and narrow-bandwidth applications. Good agreement is found between the simulated and experimental responses for the S-parameters of the circulators. We also present a semi-analytical analysis of the concept of breakdown, which enables calculation of the peak power and total thermal rise in the strip-line structure. The average power handling capability of a strip-line circulator is studied for the first time. The proposed closed form expressions can also be implemented in various ferrite circulators using different guiding technologies for millimeter-wave applications.