A thin and short VHF wideband filter using CPW CRLH transmission-line

摘要

This article proposes a thin and short VHF wideband filter. As background information,wireless sensor network modules on power cables and wearable equipmentlikely need placement on cylindrical surfaces and operation in a wide VHF-band.This implies that to meet the aforementioned necessity, wireless components like filtersshould be conformal to curved surfaces and work in a wideband. There occurtwo challenges which are physical flexibility and wideband in VHF. To overcome thedifficulties at once, a coplanar-waveguide composite right/left-handed transmissionline(CPW CRLH-TL) is presented as the flexible printed circuit board (FPCB) structure.The zeroth-order resonator (ZOR) CRLH-TL filter of 0.248×0.025λg formedon the hosting FPCB plane of 0.63×0.26λg, which is not realizable with microstiplines and conventional CPWs. The CRLH filter comprising CPW interdigital linesand two shunt inductors determined for an extremely thin ZOR at 160 MHz providesthe fractional bandwidth of 140% as an unprecedentedly broadband, insertion loss of1.5 dB, and return loss of 16 dB in the measurement which complies with circuit andEM simulations. Besides, when this flexible filter wraps around a cylindrical objectof different curvatures, the wideband performance in the VHF region is robust againstthe bending effect.