Recently, defected ground structure (DGS) resonators have been employed to design a low phase noise Voltage-Controlled Oscillator (VCO) for quasi-millimeter wave applications . A few advantages of such VCOs are that a DGS resonator has a higher Q-factor than an on-chip spiral inductor, and it has a higher self-resonance frequency compared to a conventional LC resonator so that a stable inductance value with respect to the frequency can be realized. However, one of its drawbacks is that the tuning range of DGS-based VCOs is limited. In this paper, a method to realize a wide tuning range of DGS-based VCOs has been proposed using two interconnected DGS resonators. As a result, the designed VCO implemented in 0.18-μm 1P6M CMOS technology achieves a 19.8% tuning range with the best phase noise performance of -109.43dBc/Hz at 1-MHz offset frequency in simulations. The experiment result shows that the fabricated VCO has a phase noise of -108.41dBc/Hz at 1-MHz offset frequency with the carrier frequency of 18.51GHz, which exhibits good agreement with the simulation.