Coplanar Stripline Series-Stub With Even Mode Suppression

Coplanar stripline (CPS) series stubs, both the short-circuit and open-circuit terminated stubs, are presented. It is shown that the parasitic even mode (a surface-wave-like mode) on the series stub generates an undesired resonance. An equivalent lattice circuit that describes the desired and undesired modes of the stub is developed. A method to suppress the even mode is presented so the desired series stub characteristics may be obtained.