3-D printed highly selective dual-band filter based on hemispherical cavity resonators (HCRs)

Abstract This paper proposes a highly selective dual-band bandpass filter (BPF) utilizing hemispherical resonators and an in-band transmission zeros (TZs) method. For obtaining high isolation between two passbands, a compound resonator topology is realized by arranging six hemispherical cavity resonators (HCRs) in a two-by-two vertical configuration, and then three TZs between the passbands are introduced. The filter selectivity is further optimized through elaborately placing three metal pillars in the cavity, and then one TZ in the lower stopband and two in the upper stopband are generated. Notably, the size of the HCR is reduced by about 50% compared to the conventional spherical resonator. To validate the design, a dual-band filter is 3D printed, which operates at 9.1 and 9.77 GHz with bandwidths of 210 and 200 MHz, respectively. The measured results show good agreement with the simulated ones.