A modified parallel-coupled filter structure that improves the upper stopband rejection and response symmetry

A modified parallel-coupled microstrip line filter structure is presented. Using this new structure improves the filter upper stopband rejection by at least 15 dB, and the filter response symmetry is also improved. Compared with the traditional parallel-coupled filter, the modified filter used less space and is easy to lay out owing to its inline structure. Several examples show the performance improvement of the filters fabricated in both low-dielectric-constant (2.55) and high-dielectric-constant (10.2) substrates.< >