2012 Volume 9 Issue 7 Pages 718-723
This letter presents a novel microstrip tri-band filter in which a shunt-stub bandpass filter and a dual-band bandstop filter are integrated into a single structure of short length. The two stopbands of the bandstop filter are allocated within the wideband passband of the bandpass filter, resulting in a filter having three passbands. Good return loss is obtained using an optimization routine. This technique has high flexibility on setting the bandwidths and center frequencies of passbands. A prototype filter is designed and fabricated. Good agreements between simulation and measurement in respect of low insertion loss and high isolation are demonstrated.