Dual-passband filters and extended-stopband wide-band bandpass filters based on generalized stub-loaded planar circuits

This paper addresses the application of stub-loaded planar circuits to the realization of dual-band bandpass filters and extended-upper-stopband broad-band bandpass filters with quasi-elliptic transfer function. To this aim, different classes of homogeneous- and stepped-impedance parallel-type open-ended stubs are exploited. Analytical design formulas for the transmission zeros (TZs) generated by these stubs are provided. Furthermore, for experimental-validation purposes, two multipole microstrip prototypes are manufactured and characterized.