The Use of Defected Ground Structures in Designing Microstrip Filters with Enhanced Performance Characteristics

Until recently, microstrip filter designs were being done with full metallic ground-plane present on one side of the substrate. The state-of-the-art, however, changed when deliberately created defects in the ground (called Defected Ground Structures or, simply, DGS) were introduced, to further improve the filter performance. This paper presents four original design examples on low-pass and band-pass filters with and without DGS. Design methodology, optimization details, fabrication details, and experimentally-obtained data are presented, for each of the designs. The prototypes are tested using Rohde and Schwarz ZVA40 Vector Network Analyzer. It is found that the filter performance characteristics like passband ripple, 3-db bandwidth, return loss and stopband rejection show significant improvement when Defected Ground Structures are used in the design.