Improving the stopband of the UWB bandpass filter with a novel compact 1-cell CRLHTL geometry with additional nulls

Previously, we suggested the unprecedented design of a very compact UWB bandpass filter, which is based on the 1-cell microstrip Composite Right- and Left-Handed Transmission-line(CRLH-TL)[1]. Though the design result turned out satisfactory in terms of Bandwidth, Insertion Loss, Return Loss, Group Delay variation and so on, it had a narrow stopband beyond the upper passband edge. Therefore, we present the improved design to widen the stopband from ‘10.6 GHz∼12.6 GHz’ to ‘10.6 GHz∼14.6 GHz’ by modifying the original structure to create additional nulls(or poles), and the resultant structure is still as small as ‘guided wavelength( λg )/9.4’.