Monolithically-Integrated 3D Printed Bandpass Filters Using Highly-Miniaturized Dome-Shaped Resonators

A new class of highly-miniaturized 'dome'-shaped 3D bandpass filters (BPFs) are presented. Size reduction is achieved by using: i) capacitively-loaded hemispherical resonators that are significantly smaller than a conventional spherical resonator, ii) stereolithography apparatus (SLA)-based 3D printing facilitating monolithic integration, and by iii) vertically-stacked resonators. A comprehensive design methodology is provided and applied to the realization of high order BPFs. An RF excitation scheme allowing for wideband out-of-band suppression is also proposed. For proof-of-concept validation purposes, a second- and a third-order BPF prototypes operating at 5.8 GHz, and a compact vertically-stacked second-order BPF were designed, manufactured, and tested. The measurement results exhibit the following characteristics: second-order BPF: center frequency f_c = 5.8 GHz, fractional bandwidth (FBW) = 5.5%, effective quality factor (Q_eff) = 890, 20 dB upper stopband suppression up to 10.14 GHz (1.7.3f_c); third-order BPF: f_c = 5.8 GHz, FBW = 6.5%, Q_eff = 1,230, and 20 dB upper stopband suppression up to 10.1 GHz (1.74f_c); vertically-stacked second-order BPF: f_c = 5.9 GHz, FBW = 10.0%, Q_eff = 720, and 20 dB upper stopband suppression up to 8.9 GHz (1.5f_c).