A Novel and Compact Bandstop Filter with Folded Microstrip/CPW Hybrid Structure

Abstract

A novel and compact circuit configuration for narrowband bandstop filter (BSF) is proposed. The distinct filtering characteristics of this new type of transmission line filter are investigated theoretically and experimentally. The presented filter consists of hybrid microstrip/coplanar waveguide (CPW) transmission-line units with a pair of uniformly shunt microstrip stubs. At the bottom of substrate material, two identical CPW short-circuited resonators and an open-circuited CPW resonator are broadside-coupled to the top microstrip main transmission lines, respectively. To reduce the size of the filter, the folded microstrip/CPW composite elements and parallel stubs have been applied to layout. A demonstrator with approximately 16.7% fractional bandwidth at a mid-stopband frequency of 6 GHz is developed and presented. The proposed filter is successfully realized in theory and verified by full-wave electromagnetic simulation and experiment. Simulated and measured results are in excellent agreement.