01427987IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 53, NO. 5, MAY 2005 1817 Periodically Nonuniform Coupled Microstrip-Line Filters With Harmonic Suppression Using Transmission Zero Reallocation Sheng Sun, Student Member, IEEE, and Lei Zhu, Senior Member, IEEE Abstract―In this paper, the two-port periodically nonuniform coupled microstrip line with nite length is thoroughly studied as an equivalent -inverter network for microstrip bandpass lters with harmonic suppression. Extracted -inverter susceptance is exhibited to vary up and down versus frequency with the null or transmission zero when the coupled length becomes half-wavelength. This transmission zero can be adjusted by varying the periodicity and/or slit depth to suppress the rst spurious harmonic passband of the lter. Fi……