Dual-path fourth-order microstrip coupled lines filter for wideband applications

A novel fourth order coupled lines filter topology is presented based on two parallel paths containing quarter-wavelength coupled lines. Three identical coupled lines are combined in series in each path to form a ring structure. This configuration leads to the compactness of a highly selective filter. The proposed filter is designed for wideband applications whose center is at 3 GHz with a fractional bandwidth around 41.9%. The filter is designed on a 1.6-mm-thick FR4 substrate with dielectric constant, ε_r = 4.1. Filter simulations are proposed throughout the paper to validate the idea.