Based on the accurate electromagnetic model and an improved equivalent circuit model of Schottky diode, the design and fabrication of a W-band eighth harmonic mixer for broadband operation is presented in this paper. With the analysis of the Schottky diode physical structure, a three-dimensional electromagnetic model and an improved equivalent circuit model up to 180GHz were established. According to the mixing product energy distribution characteristics and bandwidth requirements, broadband RF and LO matching networks were designed, which extend the mixer operation bandwidth to the entire W-band. The measurement result indicates that the conversion loss of the W-band eighth harmonic mixer is less than 28dB in the range of 75～110GHz, and the minimum is 18dB.