Abstract: A balanced sub-millimeter wave frequency doubler monolithic microwave integrated circuit(MMIC) was designed based on standard planar Schottky diode process. The nonlinear model of the Schottky diode was established according to both the parasitic parameters, which was extracted from the electromagnetic(EM) model of the diode structure, and the measured intrinsic data. The frequency doubler used balanced topology to get good fundamental suppression, and a three-line coupled balun was designed and integrated with the Schottky diodes on one chip to improve the design accuracy. On chip test results show that when the input frequency varied from 75 GHz to 105 GHz, the frequency doubler chip could get 2.67 dBm peak power under 17 dBm input power. The chip size is only 0.80 mm×0.50 mm.