A 28nm FDSOI CMOS low power VCO working at 40 GHz frequency is presented in this paper. The VCO core only consumes 6mW from a 1 V supply voltage. A wide tuning range of 18.5 % from 38.3 GHz to 46.1 GHz is reached with a tuning voltage from 0 to 1 V. A phase noise higher than -120.5 dBc/Hz at 10 MHz offset has been observed after post-layout simulations. A variable inductance approach has been chosen in order to maintain a sufficiently low phase noise despite significant constraints caused by the advanced technology nodes and the large tuning range needed