Design of A Tunable Dualband Microstrip Bandstop Filter

In this paper, a microstrip bandstop filter with dual stopbands and tunable function is provided. In order to realize dual stopbands, two shunt-connected coupled lines and T-type transmission line are adopted with parallel connection. Moreover, the bandwidths of dual stopbands can be controlled with opposite sizes by tuning the varactors' voltage. An example of dualband bandstop filter is designed at the central frequency of 2 GHz, and fabricated on the subtract Rogers RO4003C. Moreover, the measured results match well with the theoretical simulation.