Design of balanced dual-band filter with reconfigurable center frequencies

A balanced two-pole dual-band filter with reconfigurable center frequencies is constructed in this letter for the first time. By incorporating varactor diodes into the doubly short-ended resonator loaded with two short-ended stubs, flexible tuning capabilities are thus enabled. According to stub-loaded theory, by properly selecting positions of two short-ended stubs on the doubly short-ended resonator, the first differential-mode passband center frequency could be independently manipulated, without affecting the other passband. Besides, source-load coupling is introduced to improve the differential-mode frequency selectivity by creating two finite transmission zeros close to each passband. For validation, a tunable balanced dual-band filter is implemented and good agreement between simulation and measurement results indicates the feasibility of proposed design methodology.