Dual-Band Microstrip Bandstop Filter with Multiple Transmission Poles Using Coupled Lines

A novel dual-band microstrip bandstop filter with multiple poles using open/shorted coupled lines is proposed in this paper. Nine transmission poles near the two stopbands can be easily realized by conventional coupled lines and transmission lines. The two center frequencies of the dual-band bandstop filter can be adjusted flexibly by only changing the even/odd-mode of the coupled lines. The planar microstrip dual-band bandstop filter (ϵr = 2.65 and h = 0.5 mm) with nine transmission poles is designed and fabricated. High selectivity and good in-band performances can be achieved in the proposed filter.