A Ku-band voltage-controlled oscillator (VCO) using dual tanks, together with feedback, is proposed and designed by using a 0.18-μm Bipolar compatible Complementary Metal Oxide Semiconductor (BiCMOS) process. A triple-coil transformer is employed to provide strong coupling between the two tanks and simultaneously introduce a transformer-based feedback. The parameters of the transformer are optimized to provide the required inductance ratios and reduce unwanted parasitic. The phase noise improvement for the proposed VCO is analyzed theoretically and verified by circuit and full-wave electromagnetic simulators. A benefit from the strong coupling between the two tanks, the proposed VCO achieves a low phase noise of -117.4 dBc/Hz at 1-MHz offset from an operation frequency of 12.64 GHz with a 4.3-mW power consumption of the VCO core.