Bandpass filters utilizing simplified left-handed transmission line structure

In this paper, we propose a new approach to design bandpass filter based on a simplified left-handed transmission line (TL) structure. We demonstrate the filter design by two examples, an ultra-wideband (UWB) bandpass filter with a fractional bandwidth (FBW) of about 110% and a narrow-band bandpass filter centered at 1.8 GHz covering the digital communication system (DCS) band. The main design procedure is to define and realize the parameters of the capacitors and the inductors in the transmission-line unit cell. This novel filter design method described in this paper can be used to achieve any optionally designated passband conveniently. The design has been successfully realized in theory, and verified by both full-wave electromagnetic simulation and microwave circuit simulation. The UWB bandpass filter is also fabricated and measured to demonstrate the performance, which agrees well with the theoretical analysis and simulation.