In this paper a study of some microstrip defected ground structures (DGS) is presented. It is shown that a slot in the ground plane can substantially enhance the electric coupling, or the electric part of a mixed coupling between two resonators, or between a resonator and its external feeding line. The proposed technique avoids the necessity of using very narrow coupling gaps in the design of tight couplings, and thus can relax the fabrication tolerances.

Keywords: Bandpass filter, Defected ground, Cross-couplings, Resonator.