Monolithically-Integrated Quarter-Spherical Bandstop Filters

This paper discusses a unique design and integration concept for high-quality factor (Q) monolithically-integrated 3D bandstop filters (BSFs) using quarter-spherical resonators. Monolithic integration is facilitated by: i) stereolithography apparatus (SLA) 3D printing and ii) EM design methodologies focused on the realization of a self-supported geometry. A coaxial excitation scheme is proposed to facilitate utilization in connectorized RF systems. For proof-of-concept validation purposes, two BSF prototypes were designed, manufactured, and tested. They include a two-resonator BSF configuration with center frequency (f(cen)): 11.9 GHz, 3-dB rejection fractional bandwidth (BW): 4.5%, maximum stopband rejection: 61 dB and a four-resonator BSF with f(cen): 11.8 GHz, 3-dB rejection bandwidth (BW): 4%, maximum stopband rejection: 85 dB.