In this paper, we present an injection locked oscillator operating at 81GHz and intended for automotive radar applications. The topology of the voltage controlled oscillator (VCO) is based on a push-push topology suitable for millimeter wave applications. The synthesis technique is based on a synchronization throw an external sub-harmonic signal. The reference signal, around 8GHz, is converted before being injected into the oscillator by inductive coupling. We describe in this work, the details of this synchronization technique. The synthesizer is implemented in a 0.13μm SiGe BiCMOS technology from STMicroelectronics. The synchronized oscillator exhibits a maximum locking range of 3GHz from 81GHz to 84GHz and a phase noise around -108dBc/Hz at 10MHz from the carrier frequency. The 1.1mm² circuit chip consumes 60mA under 1.8V supply.