Shaping and Slotting High-Q Spherical Resonators for Suppression of Higher Order Modes

This paper proposes two methods to improve the spurious-free stopband range for high-quality-factor spherical resonators and a new family of shaped spherical resonators are presented. Geometrical shaping of the proposed resonators is realized by symmetrically squeezing a spherical cavity and further opening a rectangular slot in each squeezed area. The higher order modes of the resonator are first tuned spectrally farther away from the dominant mode by the squeezing, and then are suppressed by the slotting. X-band resonator prototypes are designed, and 3-D printed by using a metallic selective laser melting technique. Quality factors of the fabricated resonators are further improved by vibration grinding process. The experiment validates effective suppression of the first higher order mode and indicates potential applications of the proposed resonators in bandpass filters to extend the spurious-free stopband bandwidths.