Super compact and ultra-wideband bandpass filter with a wide upper stopband based on a SCRLH transmission-line unit-cell and two lumped capacitors

Abstract

ABSTRACTThis paper presents a simplified composite right/left-handed trans-mission-line (SCRLH-TL) unit-cell, which is primarily consisted of a rectangular ring with two grounded vias. Superposing this unit-cell onto a high–low–high step-impedance resonator (SIR) leads to a novel SCRLH-TL multiple-mode resonator (SCRLH-TL MMR). By combining the SCRLH-TL MMR with a cross-shaped defected ground structure (DGS) and using a broadside coupling approach with two lumped capacitors, a highly compact and ultra-wideband bandpass filter was carefully designed and fully investigated. The filter was fabricated by using a conventional PCB process with the substrate of FR4. The measured 3-dB passband ranges from 2.55 through 11.75 GHz with the fractional bandwidth (FBW) of about 129%. The filter exhibits a high selectivity with steep skirt property, and has a wide upper stopband. Its total dimension, including the rectangular substrate with feed lines, occupies only 13.5 mm × 6.0 mm, which is found with the smallest size in comparison to those recently published in the literature.