Multi-band glass-integrated bandpass filters for new radio (NR) communications

A class of multi-band bandpass filters (BPFs) based on glass-integrated multi-resonant cells (MRCs) are reported. Each MRC comprises multiple in-parallel connected series-type resonators that create passbands in-between transmission zeros (TZs)—located at the resonators’ resonance. The MRCs can be combined in multi-stage configurations to create high-order multi-band transfer functions or used in the RF input and output ports of a conventional transversal multi-band BPF to enhance its selectivity by adding poles and TZs without increasing its size. A compact integration concept using high-Q 3D integrated-passive devices (IPDs) is used for the realization of sub-6-GHz multi-band BPFs. For practical validation purposes: (1) a tri-band BPF with passbands centred at 1.58, 2.07, 2.83 Hz and fractional bandwidths (FBWs): 10.9, 9.06, 10% respectively and in-band insertion loss (IL) between 2 and 2.8 dB and (2) a dual-band BPF with passbands centred at 2 and 2.9 GHz with FBW 14.9% and 16.14% we manufactured and tested.