A 1.32 to 1.89 GHz Diplexer/Filtering-Switch for Reconfigurable FDD/TDD Operations

Time division duplexing (TDD) and frequency division duplexing (FDD) are two typical duplexing techniques in modern wireless systems. Adopting appropriate duplexing mode in specific scenarios can effectively improve the communication efficiency. In this paper, a novel reconfigurable diplexer/filtering-switch (RDFS) for reconfigurable TDD/FDD operations is presented. It is constructed by seven varactor loaded half-wavelength microstrip resonators. Common resonator technique is adopted to divide the seven resonators into two signal channels, while the controllable mixed electromagnetic coupling (CMEC) technique is employed for inter-stage couplings. With the proposed methods, not only the intrinsic reconfigurable diplexer and filtering-switching functions can be easily achieved, multiple transmission zeros are also introduced to improve the channel isolation in FDD operation and stopband suppression in TDD operation. A circuit prototype with a tunable center frequency covering 1.32-1.89 GHz is designed, fabricated and measured to validate the proposed method. Good agreement between the simulated and measured results can be observed.