DESIGN OF DIFFERENTIAL WIDEBAND BANDPASS FILTERS WITH MINIATURIZED SIZE BASED ON DUAL-MODE DEFECTED GROUND STRUCTURE

Dual-mode defected ground structure (DGS) is presented to construct differential wideband bandpass filter (WBPF) with very compact size. This proposed DGS is composed of an etched rectangular loop with a central zigzag tapered structure on the bottom surface. Based on this DGS, the filter exhibits adjustable dual-mode resonant characteristics under differential mode (DM) operation and widebandstop filtering characteristics under common-mode (CM) operation. To verify the design concept, one filter to cover the UWB lower-band has been designed, fabricated, and measured. The fabricated differential WBPF demonstrates a DM 3 dB fractional bandwidth of 59% with lower passband insertion loss of 0.52 dB, wider CM suppression better than 10 dB from DC to 11.5 GHz, and very compact size of 0.08 lambda(g)(2), where lambda(g) is the guided wavelength at the center frequency of the DM passband. (C) 2015 Wiley Periodicals, Inc.