A novel Phi-shape defected ground structure (DGS) is proposed in this article. Low-pass filters are designed using the Phi-shape DGS with H shape open stubs line. Single, two-cascaded and three-cascaded U-shape DGS low-pass filters are designed, simulated, fabricated, and measured. The resonant characteristic of the two-cascaded Phi-shape DGS low-pass filter shows its advantages of compact size, high selectivity, low insertion loss, and excellent passband performance. The frequency response of the three-cascaded Phi-shape DGS low-pass filter presents the advantages of compact size, high selectivity, low insertion loss, better passband performance, and high outband suppression. The measured results show a good agreement with the simulated results. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1456-1459, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25968