PERIODICALLY LOADED WIDEBAND BANDPASS FILTERS

摘要

A periodically loaded wide-band bandpass filter based on the electromagnetic band-gap (EBG) concept is analyzed and a design methodology is presented. Compact wideband filters with steep transition bands can be designed easily using this novel methodology. Unit cells in the EBG structure are realized by capacitive and inductive loading of a transmission line segment. Two topologies of unit cells with shunt reactive loading and series reactive loading are analyzed. These unit cells are cascaded to realize bandpass filters whose bandwidth depends on the reactive loading of unit cells. Number of unit cells determines the steepness of the band edges of the filter. The main advantage lies in the fact that the size of unit cells can be small because electrical length of transmission line segments in unit cells can be chosen arbitrarily, hence the final filter structure becomes small in size. Filters having different bandwidths are designed and simulated results are depicted. The ripple level in the filter response is minimized by optimizing the characteristic impedances of transmission line segments in unit cells.