In this project, two frequency tripler concepts for the generation of output power in the millimetre-wave range up to 230 GHz have been investigated. Both concepts make use of the advantages of symmetrical devices, whereby the first is based on a HBV (Hetero-Barrier Varactor) monolithically integrated into the rf-circuit on GaAs-substrate whereas the second one uses an ASV (Anti-serial Schottky Varactor) as non-linear device, realised by quasi-monolithic integration on quartz-substrate. By the help of a theoretical model of both structures, design and optimisation criteria for the varactors and the tripler circuits have been deduced and verified experimentally. The results lead to an output power of 10 mW at a frequency of 210 GHz with a conversion efficiency of 13.5% for the HBV and an output power of 15 mW at 228 GHz with a conversion efficiency of 22% for the ASV frequency tripler. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)