Compact Bandstop Filter with Enhanced Stopband Performances Using Defected Ground Structure

A novel compact one-section microstrip bandstop structure is presented, which consists of an open-circuited resonator and a new parallel coupled-line loaded defected ground structure (PCL-DGS). Coupled with the even/odd-mode decomposition of PCL-DGS, it is shown that the etched DGS in the ground plane can significantly increase the coupling of parallel coupled lines and thus enhance the stopband performances. Finally, experimental results of a bandstop filter (BSF) for center frequency at 6.0 GHz show that this BSF has a sharp cutoff frequency response and 3-dB fractional bandwidth is more than 100%. There is good agreement between the simulated and experimental results, which demonstrate the validity of new BSF unit.