DESIGN OF COMPACT COPLANAR BANDSTOP FILTER COMPOSED ON OPEN-LOOP-RING RESONATOR AND DEFECTED GROUND STRUCTURE (DGS)

Design of a novel compact bandstop filter composed on an open-loop-ring resonator and a defected ground structure (DGS) for coplanar waveguide is proposed and investigated. A simple coplanar open-loop-ring resonator has been designed and tested for the stop-band front 3.9 to 4.3 GHz with tree transmission zeroes inside the stop-band. Two almost symmetrical poles are obtained on both sides of the stop-band. Then the proposed broad band bandstop filter based on the one open-loop-ring resonator has been transformed to the bandstop filter with a narrower stop-band but with improved pass- and stop-band characteristics. It is realized by adding a conventional rectangular DGS slot inside the open-loop-ring. The equivalent circuit model has been proposed to describe the behaviour of the bandstop filters. The improved bandstop filter introduces the stop-band from 3.75 to 5.3 GHz with two transmission zeroes within and more than -20 dB rejection. The total size of the proposed structure is 13.8 x 13.4 mm(2). Both bandstop filters have been fabricated and measured. Measurements are in good agreement with simulation results. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 478-483, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24905