High-Q whispering modes in spherical cavity resonators

This work presents the study of high order modes in spherical cavity resonators. In general there exists mode families, degenerate in frequency, that "whisper" around the spherical surface. We call these Whispering Spherical (WS) mode sets. Each set comprises the well-known Whispering Gallery (WG) mode, which propagates like a ray around the azimuth. Also, we identify a new mode, which we label the Whispering Longitudinal (WL) mode. This mode propagates as a wave front along the longitudinal direction. The rest of the degenerate set propagates like a combination of the WG and WL modes. We show that Transverse Electric WS modes have very high geometric factors. Q-factors as high as 65,000 at 13.3 GHz have been measured at room temperature. These modes introduce the possibility of designing high-Q multipole filters.