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This study introduces an X -band quadrature voltage-controlled oscillator (QVCO) based on two novel techniques: capacitor coupling and sinusoidal current biasing. The proposed QVCO achieves an excellent figure-of-merit (FOM) of 190.5 dBc/Hz. This study analyzes the properties of this QVCO, including its phase noise, oscillation frequency, and amplitude. To generate quadrature phase signals with low phase noise, the proposed design uses two capacitor-coupled LC-tank cores instead of active device-coupled cores. Sinusoidal currents through these capacitors bias the oscillator, increasing oscillation amplitude and reducing the phase noise contribution from cross-coupled transistors compared to existing QVCOs or VCOs biased with a constant current. These two techniques allow the proposed QVCO to achieve at least a theoretical 3 dB phase noise improvement compared to conventional LC-QVCOs. Implemented in a standard 0.18 μm CMOS process, the proposed QVCO had a frequency tuning range of 9.2 ~ 10.4 GHz and a phase noise of -115.7 dBc/Hz@1 MHz from a carrier of 10.4 GHz while consuming 3.6 mW with 1.5 V voltage supply.