A New Technique to Double the Rejectband of a Low-pass Filter by Employing Coupled C-Open-Loop Resonators as Defected Ground Structure (DGS)

In this paper, we proposed two new compact DGS low-pass filters with broad stop-band and low insertion loss in the pass-band. The structures of these new microstrip low-pass filters are simple as they are composed of a pair of DGS- slots and an open-stub. One filter will be realized through the multi-layer method, and the second filter will be realized by cascading. With these configurations, two LPF with compact size, wide reject band and sharp transition from pass to stop-band were realized. The design formulas are derived by using an equivalent-circuit model of coupled DGS resonators. A demonstration filters are designed, fabricated and tested. The experimental results show good agreement with theoretical results and demonstrate that the required characteristics of LPF could be simply obtained through the proposed methods.