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Low phase-noise InGaP-GaAs HBT VCOs, utilizing an on-chip 'wide tuning range varactor', have been designed, fabricated, and characterized. The primary design goals were low phase noise, wide continuous frequency tuning and small VCO- gain variation. Two types of varactor were compared, a square varactor and a finger varactor. The square varactor achieves a frequency tuning of 27%, and the finger varactor 21%. The phase noise is typically -100 dBc/Hz at 100 kHz offset frequency. A VCO gain (sensitivity) of 160 MHz/V is obtained with a variation of less than 10%. The power consumption is controlled by the core DC-current and is of the order 50-100 mW.