A 140 GHz doubler based on Schottky varistor is described. It applies quartz substrate microstrip circuits embedded in rectangular waveguide. Four Schottky junctions are paralleled together to receive higher driving signal power. Exact 3-D diode model, wideband power coupling and wideband impedance matching structure are used to improve the precision of simulation. Measured results indicate that under the input signal of 65 GHz-75 GHz, 20 dBm, the doubler output frequency can reach 130 GHz-150 GHz, output power is 3.3 dBm-8.0 dBm, and conversion loss is 11.7 dB-16.3 dB. The maximum output power of 140 GHz doubler is 11.2 dBm/136 GHz, when driven with maximum input power 23 dBm-24 dBm. This device is suitable for the application of 140 GHz imaging radar