The local oscillator source is a critical component in modern submillimeter wave instrumentation used for high resolution spectroscopy in the fields of radio astronomy, atmospheric observation and imaging. Existing solid-state sources (e.g. diode multiplier chains, photomixers) can only provide enough output power (μW) to pump cryogenic THz heterodyne detectors and are often bulky and inefficient. The present large international investment in radio astronomy of several planned space missions, e.g. the SWI to Jupiter and the Japanese FIRE instrument, requires stable, room temperature, compact and high efficiency LO sources. Within this project, new material candidates for THz diodes, diode process platforms, innovative circuit topologies and system integration will be explored. The aim of the project is to develop high efficiency heterostructure barrier varactor /Schottky varactor frequency multiplier chains, with good stability operating in the frequency range from 300 GHz up to 3 THz.