A 141-GHz quasi-optical heterostructure barrier varactor (HBV) diode frequency tripler is presented. The tripler consists of two slot antennas loaded with FEW diodes and located at the focal plane of a dielectric lens. A quasi-optical high-pass filter is used at the output to improve the conversion efficiency and act as a tuning element for the slot antennas. The tripler demonstrates an effectively isotropic radiated power (EIRP) of 2.24 W at 141 GHz with an input power of 143 mW. The corresponding radiated power is 11.5 mW and the tripler conversion efficiency is about 8%
