Very wideband heterodyne receiver systems are planned for many astronomical applications during the next 5 - 10 years. These extend up to 830 GHz for ground based telescopes and up to 2.7 THz for space and airborne applications. At present the only means to provide sufficient local oscillator power for these submillimeter receivers is the Schottky varactor diode frequency multiplier. Present multipliers operate at up to 1 THz with solid state pump sources, and are largely based on whisker contacted diodes. This paper describes a new generation of varactor multipliers which will be based on planar technology and may extend frequency coverage by a factor of two or more.