Very Compact Stacked LC Resonator-Based Bandpass Filters With a Novel Approach to Tune the Transmission Zeros

This letter presents very compact stacked LC resonator structures and their coupling and excitation techniques for designing the bandpass filters operating in the 3.5 GHz WiMAX band. Using a coupled stacked LC-resonator structure not only greatly reduces the overall size but also can create multiple transmission zeros to enhance roll-off rate or desired stopband rejection for the designed bandpass filters. Furthermore, this letter develops a simple technique of etching a rectangular C-shaped slot in the bottom ground plane to flexibly adjust the transmission-zero frequencies without changing the size and shape of the filter.