Balanced Wideband/Dual-Band BPFs on a Hybrid Multimode Resonator With Intrinsic Common-Mode Rejection

In this paper, a class of balanced wideband and dual-band bandpass filters (BPFs) is proposed and designed on a hybrid multimode resonator. This resonator is composed of two distinctive kinds of transmission lines, i.e., microstrip line and slotline, so it is called a hybrid resonator. On one hand, the resonator itself has the common-mode (CM) rejection as an inherent property by virtue of the hybrid structure; on the other hand, the microstrip/slotline transitions for feeding are avoided because normal microstrip feeding schemes are valid via microstrip lines inside this resonator. As such, the proposed hybrid resonator is largely different from those in the existing balanced BPFs with intrinsic CM rejection. In the traditional one, the resonator is formed by a slotline and it is connected with microstrip/slotline transitions for differential-mode (DM) transmission and CM rejection. What is more valuable, the hybrid resonator can be easily constructed by replacing a portion of then microstrip line in the traditional microstrip resonator with the slotline. Thus, the diversity of the balanced wideband BPFs with intrinsic CM rejection can be extremely enhanced and the balanced dual-mode dual-band BPF can be successfully designed. Two different balanced BPFs under wideband and dual-band operations are finally designed and fabricated to support our theory.