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In this paper, a novel coupled-line tunable Wilkinson power divider with perfect port match and isolation in a continuously tunable passband is presented. The proposed tunable power divider consists of an isolation resistor, two coupled lines, and two types of varactors. By providing these varactors with suitable bias voltages, the operating frequency of the proposed power divider can be flexibly changed as desired. Meanwhile, perfect port match and isolation are maintained at all tunable operating frequencies. After applying the even-odd mode analysis method, the closed-form equations of the design parameters are derived to illuminate the effects on the minimum and maximum operating frequencies. These equations exhibit that the proposed power divider has a wide frequency tuning range and a high tunability (more than 110% in ideal conditions). Owing to the limitation of manufacturing process, a microstrip power divider with a tunable frequency of 0.54–1.41 GHz (89.23%) is designed and simulated based on the provided closed-form equations. The measured results show a frequency tuning range from 0.56 to 1.39 GHz (85.13%) with a more than 20-dB return loss and isolation in the entire tuning range, agreeing well with the simulation results.