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A voltage-controlled oscillator (VCO) using tunable metamaterial transmission line based on varactor-loaded split-ring resonator (VLSRR) is presented to enhance the tuning range and reduce the phase noise. It is demonstrated that VLSRR coupled to microstrip line can lead to metamaterial transmission line with tuning capability. The negative effective permeability is provided by VLSRR in a narrow band above the resonant frequency. The bias of VLSRR is controlled by the varactor diodes. The square-shaped split ring structure has the large coupling coefficient value, which makes a high Q value, and has reduced the phase noise of VCO. The phase noise of VCO is -110.5 ~ -108.0 dBc/Hz @ 100 kHz in the tuning range, 5.411 ~ 5.857 GHz. The figure of merit (FOM) called power-frequency-tuning-normalized (PFTN) is -6.7 dB.