This work proposes a new technique to reduce the phase noise and improve the tuning sensitivity of K-band Voltage-Controlled Oscillators (VCOs) by increasing the quality (Q) factor of the switched resonator. The proposed switched resonator consists of a high Q-factor half-circle inductor in parallel with an improved switched varactor, and operates in four different frequency bands using a single switching voltage pin. The proposed switched resonator introduces one pole before the parallel resonance frequency, which sharpens the skirt characteristics of the scattering parameters of the resonator. The chip is implemented in 0.18 µm CMOS technology, and the proposed VCO operates in four different frequency bands, with a total frequency tuning range of 10.7 %. The first band ranges from 19.4 to 19.84 GHz, the second band ranges from 19.8 to 20.3 GHz, the third band ranges from 20.25 to 20.73 GHz, and the fourth band ranges from 20.7 to 21.3 GHz. The VCO core circuit draws a DC current of 5 mA from a 1.8 V supply and achieves a phase noise of -110.7 @ 1 MHz offset from a 20.25 GHz carrier. This proposed oscillator achieved a Figure of Merit (FoM) of -186.8 dBc/Hz while the FoM taking account of the tuning voltage (FoM T/V) is -181.4 dBc/Hz.