Improved stopband of a compact 1-cell CRLH-TL UWB bandpass filter by forming 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). 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 dasia10.6 GHz~12.6 GHzpsila to dasia10.6 GHz~14.6 GHzpsila by modifying the original structure to create additional nulls(or poles), and the resultant structure is still as small as dasiaguided wavelength( lambda _g )/9.4psila.