Multimode resonator based on composite right-/left-handed transmission line for UWB bandpass filter application

ABSTRACT A new multimode resonator (MMR) using composite right‐/left‐handed transmission line (CRLH TL) is proposed and discussed. The CRLH TL structure is constructed by cascading interdigital coupled microstrip line sections on which short‐ended stepped impedance stubs are loaded. Dispersion characteristic of the transmission line structure is obtained using the Bloch–Floquet theory. The resonator, which has multiresonances electrical behaviors, is especially suitable in ultrawideband (UWB) applications. An UWB filter is presented as an illustration. With transmission zeros introduced at upper stopband, the filter has a sharp skirt performance. In addition, rejection level at lower stopband also gets enhanced due to direct current suppression effects of the multimode resonator. The filter prototype is implemented and measured. The measured results validate the theoretical analysis and show that the filter has a sharp skirt and an out‐of‐band rejection level as good as 38 dB. Meanwhile, return loss is better than 16 dB. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:815–824, 2015.