Design of lowpass filters using defected ground structure and compensated microstrip line

Abstract—A method to design low-pass filters (LPF) having a de-fected ground structure (DGS) and broadened transmission-line elements is proposed. The previously presented technique for ob-taining a three-stage LPF using DGS by Lim et al. is generalized to propose a method that can be applied in design-pole LPFs for 5. As an example, a five-pole LPF having a DGS is de-signed and measured. Accurate curve-fitting results and the suc-cessive design process to determine the required size of the DGS corresponding to the LPF prototype elements are described. The proposed LPF having a DGS, called a DGS-LPF, includes transmis-sion-line elements with very low impedance instead of open stubs in realizing the required shunt capacitance. Therefore, open stubs, tee- or cross-junction elements, and high-impedance line sections are not required for the proposed LPF, while they all have been es-sential in conventional LPFs. Due to the widely broadened trans-mission-line elements, the size of the DGS-LPF is compact. Index Terms—Defected ground structure (DGS), low-pass filters (LPFs), periodic structures. I