A Coupled-Line Isolation Network for the Design of Filtering Power Dividers With Improved Isolation

A coupled-line isolation network is proposed for the design of filtering power dividers. The isolation network functions as the input coupling structures for two bandpass filters (BPFs), and meanwhile isolates the filters to realize a filtering power divider. It can be embedded into various types of BPFs to implement a variety of filtering power dividers. As demonstrated by the theoretical and experimental treatment, the isolation network provides a flexible and effective means of isolating two BPFs and achieving the isolation. Specifically, a fabricated four-pole microstrip filtering power divider achieves 25-dB isolation in the passband centered at 1.96 GHz. In addition, the measured results show that isolation better than 17 dB is achieved from dc to 20 GHz or about 10 times of the midband frequency of the BPFs.