A Cascaded Coupled Resonator Decoupling Network for Mitigating Interference Between Two Radios in Adjacent Frequency Bands

A new microwave device called the cascaded type of coupled resonator decoupling network (C-CRDN) is proposed in this paper. The four-port device can be used to reduce the interference between two radio systems that work in adjacent or even contiguous frequency bands. A C-CRDN is cascaded between the two antennas to be decoupled and the I/O ports of their radio systems, respectively. The coupling matrix of a C-CRDN can be designed to meet the required isolation and return-loss specifications. To prove the concept, a fourth- and sixth-order C-CRDN using coaxial combline cavities are designed, fabricated, and measured according to the characteristics of a testing array that consists of two high-gain sleeve dipoles working in the adjacent time-division long-term evolution and wireless fidelity bands. The measured results have demonstrated that the proposed C-CRDN can effectively mitigate the coexistence interference between the two collocated systems by providing at least 20-dB isolation improvement and enhanced matching performance. The proposed technique is general and can find many applications in heterogeneous wireless systems.