Harmonic suppression in microstrip multistage coupled-ring bandpass filters using defected ground structures

The introduction of defected ground structures (DGSs) in microwave bandpass filters, based on microstrip coupled-ring resonators to suppress higher harmonics, is investigated. Two topologies based on placing DGS units into and out of the coupled rings are considered and investigated. Harmonic suppression ratios for the second harmonic greater than 20 dB in a flat bandpass filter centered at 2.25 GHz are achieved for both structures. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 351–354, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11214