Reconfigurable Wideband Filtering Balun With Tunable Dual-Notched Bands Using CPW-to-Slot Transition and Varactor-Loaded Shorted-Slot

In this paper, a reconfigurable wideband filtering balun with tunable dual-notched bands is proposed, using coplanar waveguide (CPW)-to-slot transitions and varactor-loaded shorted-slots. The wideband filtering balun consists of a triple-mode slot resonator, two CPW-to-slot transitions, and a CPW short-stub. Three transmission poles are allocated by the triple-mode slot resonator to achieve the wideband operation. To further improve the amplitude- and phase-imbalance responses, two CPW-to-slot transitions are used. Besides, the CPW short-stub is introduced to enhance the passband selectivity. Then, based on the proposed wideband filtering balun, a reconfigurable balun with tunable dual-notched bands is achieved by introducing two pairs of varactor-loaded shorted-slots. The measured results show that the frequency tuning ranges of the dual-notched bands are 1.28-1.58 GHz (21.6%) and 1.89-2.41 GHz (24.2%) with 15-dB rejection, respectively. The proposed filtering balun shows the advantages of wide fractional bandwidth, high selectivity, low insertion loss, and tunable notched band operation.