This paper describes a highly-integrated 122 GHz system-on-chip radar sensor in a SiGe BiCMOS technology. The chip includes a radar transceiver and two on-chip antennas utilizing a novel antenna design approach that allows the use of the localized backside etching technique without compromising the mechanical stability of the chip. The implemented double folded dipole antenna achieves an antenna gain of 6 dBi with a radiation efficiency of 54%. The transceiver is equipped with a 61 GHz VCO that is complemented with a frequency doubler to generate the transmit signal. The receive path includes an LNA, a 90 degree coupler, two passive subharmonic mixers and variable gain amplifiers. Radar measurements with static as well as moving targets were done to show the applicability of the developed system.