Abstract: The traditional Wilkinson power divider needs multiple cascading transmission lines to expand its bandwidth, which increases the difficulty of the design. In this letter, we present a novel wideband power divider using coupled three line microstrip structure. By introducing a quarter wavelength coupled three line microstrip and a single line resonator to the input of the middle conductor of a coupled three line microstrip structure, good performance is achieved over the wide band range. The power divider is analyzed using three line coupler and impedance transformer approach. A prototype power divider is designed and fabricated to demonstrate the performance of the wideband power divider structure. Experiment results show excellent performance in terms of return losses, input to output insertion losses and output to output isolation.