Resonant Modes and Magnetic Losses in a Ferrite Coaxial Resonator

Abstract

Microwave magnetic losses far enough from the ferrimagnetic resonance are difficult to characterize in a wide frequency range. They are generally measured by the perturbation method in a cavity where a small magnetic sample is centered [1]. The main problem is that magnetic losses are calculated at only one frequency for one cavity size. This method is very difficult to use at low frequencies because it needs a large cavity dimension. Furthermore, the experimental measurement system is difficult to adjust. Therefore, a structure is looked for to characterize out of resonance magnetic losses (Δ Heff ) with good accuracy on a large frequency bandwidth using few ferrite samples (one, if possible). In the case of a ferrite coaxial line, Brodwin and Miller [2] have calculated only the propagation constants of the quasi-TEM mode and Epstein [3] only the general field expressions of any mode. They did not study either the resonant structure or the magnetic losses. In this paper the rigorous analytic field expressions are given for any mode in a coaxial ferrite resonator. Resonant frequencies of these modes are calculated, an experimental study is presented, and good agreement between theory and experiments is seen. Finally, this structure is used for the first time in order to determine magnetic losses.