This paper analyzes and demonstrates the use of coupled-LC tanks to enlarge the locking range (LR) of millimeter-wave (mm-wave) subharmonically injection-locked oscillators. Design guidelines are derived from a simplified analysis. Different techniques are proposed to tune the coupled-LC tank. A mm-wave subharmonically injection-locked quadrature voltage-controlled oscillator in 40-nm CMOS verifies the proposed approach. The LR is larger than 2 GHz over a 55-63-GHz tuning range. An on-chip envelope detector facilitates the tuning of the coupled-LC tank. The phase noise and the quadrature-phase imbalance are uniform over almost the whole LR.