Multi-Band Filters Based on Coupled-Multi-Line Cells

A class of multi-band bandpass filters (BPFs) based on the in-series cascade connection of coupled-multi-line cells is reported. This cell allows to generate multi-band responses with transmission zeros at both sides of all passbands without cross coupling between resonating nodes. Analytical formulas for the poles and transmission zeros of its associated normalized coupling routing diagram for one-to-four-passband realizations are given. Furthermore, for experimental-validation purposes, a 1.75/1.9-GHz third-order dual-band BPF prototype is manufactured in microstrip technology and characterized.