Synthesis and Design of High-Selectivity Wideband Quasi-Elliptic Bandpass Filters Using Multiconductor Transmission Lines

A comprehensive study of high-selectivity filters that employ series multiconductor transmission lines (MTLs) and a shunt MTL is presented. It is shown that this topology is suitable for implementing three- and five-pole bandpass filters having a quasi-elliptic frequency response. An exact synthesis procedure with analytical design equations for achieving equal-ripple passband response as a function of the operating bandwidth is described. To validate the theory, several bandpass filters are designed, fabricated, and measured. The excellent agreement between the measurements and the predicted results validates the proposed procedure as a reliable and quick technique for designing wideband quasi-elliptic bandpass filters.