Tunable distributed harmonic voltage controlled oscillator for generating second and third harmonic microwave signals. The oscillator comprises a plurality of gain cells in a parallel configuration. Each gain cell comprises a bottom n-MOSFET  and a top n-MOSFET, each of gate length 0.18µm. The drain of each bottom n-MOSFET is connected to the gate of the respective top n-MOSFET. The drain  of each top n-MOSFET is connected to a drain transmission line  and the gate  of each bottom n-MOSFET is connected to a gate transmission line . The drain transmission line comprises a CPW  at each end thereof and a CPW  between every two drains. The gate transmission line comprises a CPW  at each end thereof and a CPW  between every two gates. The output end of the drain transmission line is connected to the input end  of the gate transmission line through a feed back path . The body of each bottom n-MOSFET and top n-MOSFET is connected to a body bias voltage  and the source of each bottom n-MOSFET and top n-MOSFET is earthed. The input end of the drain transmission line is connected to an input voltage . The output end of the gate transmission line is connected to a frequency collector . A peeking inductor  is connected across the gate and drain of each bottom n-MOSFET. The length of each of the end CPWs in the drain transmission line and gate transmission line is half the length of the CPW between every two drains and gates, respectively. When the inductance of each peeking inductor is 2 to 2.25nH, the oscillator generates a high frequency second harmonic microwave signal with a high power output. When the inductance of each peeking inductor is 1 to 1.1 nH the oscillator generates a high frequency third harmonic microwave signal with a high power output. When the inductance of each peeking inductor is 1.25 nH the oscillator generates high frequency second and third harmonic microwave signals with a high power output .