Design of On-Chip Bandpass Filters With Mixed 2-D and 3-D Coupling Structures Using 3-D Glass-Based Advanced Packaging Technology

On-chip bandpass filter (BPF) designs with high out-of-band rejection are proposed by virtue of 3-D glass-based advanced packaging technology. The proposed BPF design employs multiple coupling cells based on a combination of new mixed 2-D and 3-D coupling structures. It can generate multiple transmission zeros (TZs) and transmission poles (TPs). With these generated TZs, the out-of-band rejection of the proposed BPF designs can be greatly improved. The equivalent circuit model is developed and used for theoretical analysis. To prove the concept, two BPFs are designed and fabricated using 3-D glass-based advanced packaging technology. These two fabricated BPFs have center frequencies of 6.55 and 6.2 GHz and fractional bandwidths (FBWs) of 10.69% and 8%, respectively. These two BPFs can achieve insertion losses lower than 2.5 and 2.9 dB, return losses better than 10 and 13 dB, and more than 20-dB rejection up to 16.15 and 17.8 GHz. The sizes of the two BPFs are $2.1\times 2.0\times 0.35$ mm and $2.3\times 4.3\times 0.35$ mm. The simulation and measured results show good consistency.