We present a fully integrated phase-locked loop tunable from 17.5 GHz to 19.2 GHz fabricated in a 0.25 mum SiGe BiCMOS technology. The measured phase noise is below -110 dBc/Hz at 1 MHz offset over the whole tuning range. Based on an integer-N architecture, the synthesizer consumes 248 mW and occupies a chip area of 2.1 mm including pads. Quadrature outputs at quarter of the oscillator frequency are produced, which are required in a sliding-IF 24 GHz transceiver. Possible applications include wireless LAN as well as satellite communication. The measured phase noise is the lowest among previously published Si-based integrated synthesizers above 12 GHz.