A Novel Technique to Transform a Fractal LPF to BPF Using a Simple Combination of Defected Ground Structure (DGS) and a Narrow Gap Capacitive

In this paper we present a novel compact band pass microstrip filter employing metal-loaded slots etched in the ground plane (DGS) and a simple capacitive gap on the top. With the proposed technique, a simple transformation from LPF to a corresponding BPF was realized. We also presented, the equivalent circuit of the proposed BPF based on the equivalent circuit model of the DGS, which is derived from the equivalent inductance and capacitance that appeared due to the perturbed ground current in the ground plane due to the presence of the slot. The theory is validated using the commercial full-wave solver CST Microwave Studio and Microwave Office. The new BPF is very compact, and provides sharp transition bands and a wide upper stop-band and improved pass-band response symmetry. Finally, the proposed structure is implemented and the measurement results are found to be in good agreement with the simulation results.