This paper presents a series of novel designs for dual-band bandpass filters (BPFs) with excellent in-band and out-band filtering performances. By imbedding the spiral-line resonator into the coupling open-loop structures and adjusting the symmetrical structure, the second-order quad-mode BPFs are designed and then the fourth-order oct-mode dual-band BPFs. The final two designs possess eight resonant modes in the passband and also four/eight transmission zeros in the stopband, achieving a high transition-band selectivity with the roll-off rate over 1000 dB/GHz, broad out-band rejection from 1.5 GHz to 5.3 GHz (lower than 30 dB), and strong isolation between dual bands with the suppression level of 30 dB, operating at 3.2/3.4 GHz and 3.2/3.5 GHz respectively. Measured results agree well with simulations and prove the validity of the asymmetry feeders for multi-transmission-zero characteristics.

本文介绍了一系列具有出色带​​内和带外滤波性能的双带带通滤波器 (BPF) 的新颖设计。通过将螺旋线谐振器嵌入耦合开环结构并调整对称结构，设计了二阶四模BPF，然后设计了四阶八模双频BPF。最后两种设计在通带中具有八个谐振模式，在阻带中具有四个/八个传输零点，实现了高过渡带选择性，滚降率超过 1000 dB/GHz，从 1.5 GHz 到5.3GHz（低于30dB），双频段间强隔离，抑制水平30dB，分别工作在3.2/3.4GHz和3.2/3.5GHz。