Novel defected ground structures (DGSs) have been investigated to achieve improved low-pass filter (LPF) properties. A chronological development in designs ranging from conventional square-patterned photonic-bandgap structure (PBGS) and conventional dumbbell-shaped DGS to proposed novel nonuniform DGS has been investigated theoretically and experimentally using computer-aided design (CAD) tools. It can be seen that the proposed novel DGS having Chebyshev distribution provides excellent performances in terms of ripples in the passband, 10-dB return-loss bandwidth (RL-BW), and 20-dB rejection bandwidth, as compared to conventional DGSs and PBGSs. Thus, a perturbed surface below a standard 50Ω microstrip transmission line provides LPF characteristics. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.