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Abstract
A planar ultra-wideband (UWB) bandpass filter with widened upper stopband is presented in this paper. The filter is constructed by adopting a novel simplified composite right-/left-handed (SCRLH) transmission line (TL) structure. The fundamental characteristics of the SCRLH TL are first analyzed, and then its corresponding microstrip implementation is utilized to realize the practical UWB bandpass filter. However, thanks to the inherent parasitic effects of the microstrip quasi-lumped elements at high frequency, a spurious passband comes into being around 15.1 GHz. With an aim to broaden the bandwidth of the upper stopband, two embedded open-circuited stubs are introduced in the input and output feeding lines, which can effectively suppress the spurious passband, thus generating a widened upper stopband.