Dual-Band Ferrite Circulators Operating on Weak Field Conditions: Design Methodology and Bandwidths' Improvement

This article presents the principle of coupling fundamental and upper eigenmodes of a ferrite cavity for demonstrating a dual-band stripline circulator. The weak field operation is used for increasing circulation bandwidths and choosing the ratio between the two circulation central frequencies. Indeed, an eigenmode study is presented which identifies parameters that influence the working frequencies and the circulation direction, which can be either the same between the first and the second bands (unidirectional circulator) or different (bidirectional circulator). Two prototypes of dual-band circulators (uni- and bidirectional) have been designed and their measurements validate the developed methodology based on modal analyses.