Design of Dual Band-Reject Filter based on Short-Circuited Parallel Coupled Lines Structure at S-Band

Abstract

This paper presents a simple design of dual-band reject filter based on parallel coupled lines structure. Parallel coupled lines structure is a four-port network. A dual-band shunt resonator using this structure is obtained by short-circuiting two opposite ports to ground and connecting one of the two remaining ports to a transmission line in shunt. The fourth port is an open circuit. This modified parallel coupled lines structure has been connected with a high impedance transmission line to obtain the narrow dual band reject filter. Theoretical analysis has been performed in order to obtain the resonant frequencies. The numerical simulations have been performed and these results have been verified by the full-wave electromagnetic simulations for an S-band dual band reject filter with rejecting frequencies at 2.5 GHz and 3.5 GHz. The control over the band rejection frequencies is obtained by selecting the parameters of the parallel coupled lines in terms of gaps, widths, and lengths.