Improving the Stopband of the UWB BandPass Filter with a Novel Compact 1-Cell CRLH-TL 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 similar to 12.6 GHz' to '10.6 GHz similar to 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(lambda g)/9.4'.