Abstract: A broadband Wilkinson power divider with circular micro-strip line structure is presented. Firstly, the design equation is derived based on the analysis of the odd-even mode. Secondly, particle swarm optimization is used to obtain the design parameters of the Wilkinson power divider. This method improves the efficiency and accuracy of the power divider design. The results show that, in the frequency range of 8-12 GHz, the return loss is less than －20 dB, the ports transmission loss is less than 3.4 dB, and the isolation degree is less than －20 dB. The simulation results are in good agreement with the measured results, which verifies the feasibility of this design.