Dual-Band Bandpass Filters Using 3D Printed Dual-Mode Nested Spherical Resonators

This paper reports on a new class of 3D additively-manufactured dual-band bandpass filters (BPFs). They are based on miniaturized dual-mode nested-spherical resonators which consist of two post-supported metallic spheres that load a hollow spherical cavity and give rise to two independently-controlled resonant modes. The two modes can be exploited for the realization of dual-band BPFs with two independently-controlled bands in terms of frequency and bandwidth. The four transmission zeros (TZs) also can be controlled which give rise to better stopband response. To validate the filter concept, a dual-band BPF was designed, manufactured and measured. It exhibited, two passbands centered at 1.5 GHz and 2.47 GHz with fractional bandwidths (FBWs) of 8.13 and 2.87 %, in-band insertion loss (IL) of 0.14 and 0.39 dB, and effective Q factor (
$Q_{eff}$
) of 1,448 and 2,088 respectively. The measured and simulated results have a good agreement. A low-cost and compact monolithic integration concept enabled by stereolithography apparatus (SLA) additive manufacturing is also demonstrated.