Multimode Resonator Based on Composite Right-/Left-Handed Transmission Line for UWB Bandpass Filter Application

摘要

A new multimode resonator (MMR) using composite right-/left-handed transmissionrnline (CRLH TL) is proposed and discussed. The CRLH TL structure is constructedrnby cascading interdigital coupled microstrip line sections on which short-ended steppedrnimpedance stubs are loaded. Dispersion characteristic of the transmission line structure isrnobtained using the Bloch–Floquet theory. The resonator, which has multiresonances electricalrnbehaviors, is especially suitable in ultrawideband (UWB) applications. An UWB filter isrnpresented as an illustration. With transmission zeros introduced at upper stopband, the filterrnhas a sharp skirt performance. In addition, rejection level at lower stopband also getsrnenhanced due to direct current suppression effects of the multimode resonator. The filterrnprototype is implemented and measured. The measured results validate the theoretical analysisrnand show that the filter has a sharp skirt and an out-of-band rejection level as good asrn38 dB. Meanwhile, return loss is better than 16 dB.