Compact Dual wide bandstop filter

Abstract

In this work Dual bandstop filter (DBBSF) using coupled line loaded by a optimum bandstop filter, which consists of stepped impedance resonator. The novel transmission line structure consists of a parallel coupled microstrip line loaded by a modified optimum bandstop filter. The load can be realized by using the uniform characteristic impedance i.e. the total filter can be controlled by using only two characteristic impedances. The wide bandwidth in the stopbands, stopband zero positions can be controlled by using both the coupled line and a shunt stepped impedance open stub (SIOS) unit. Three transmission zeroes in the pass band were created by a mutual coupling between the coupled lines configuration. Design guidelines are derived using loss less transmission line model. The high impedance line required for the series transmission line (TL) sections facilitates convenient meandering that makes the geometry compact. To validate theoretical predictions, a prototype filter operating at two bands 0.74 and 2.2 GHz has been fabricated.