Abstract: A varactor tuned oscillator (10), VCO, operational in the millimeter wave range including frequencies greater than 30 GHz, includes a lumped element active circuit (12) with a negative resistance, a lumped element tuning circuit (16) coupled to the active circuit and providing resonant circuitry in combination therewith, and a VCO output (26) reactively terminated at the fundamental frequency of oscillation and generating a higher order output harmonic at least as high as the second order. The reactive termination at fundamental frequency eliminates the intrinsic diminishing effect on tuning range of resistive loading, to extend tuning range and provide an ultrabroadband VCO. The VCO output (26) is resistively loaded at the higher order harmonic. The output is obtained from the higher order harmonic generated in-situ in the active element (14). Measured performance included continuous tuning from 46 to 66 GHz, a 20 GHz tuning range, with a maximum power output of +6 dBm.