This paper presents both differential receiver and transmitter front-end modules for a 120 GHz phased array transceiver for the use in FMCW radar applications. A Gilbert-cell based vector modulator type I/Q phase shifter is accompanied by integrated LNA / PA in RX / TX channels fabricated with a 0.13µm SiGe BiCMOS technology with fT/fmax of 250/340GHz. Measurements show a 15 dB peak gain with 14 GHz bandwidth for the RX channel consuming 125mW from a 2.5V supply. Furthermore, the designed TX channel achieves a gain of 18 dB with 10.5 GHz bandwidth and an output referred 1dB compression point of 2.7 dBm with 6.4 dBm saturated output power at a power consumption of 225mW. These fully differential core frontends provide continuous 360° phase shift and only occupy an ultra-low area of 0.4mm × 0.25mm allowing a high degree of channel integration.