GROWTH IN THE WIRELESS-COMMUNICATIONS industry has fed the demand for more available channels in mobile-communications applications. This trend, in turn, has placed stricter requirements on the phase noise of voltage-controlled oscillators (VCOs). At Korea's Soongsil University, Jaewon Choi and Chulhun Seo have developed a VCO that reduces phase noise without lowering the frequency tuning range. This VCO offers phase noise of 127.5 to 126.33 dBc/Hz at 100 kHz from 5.744 to 5.865 GHz.
To suppress phase noise, a harmonic control circuit is given short impedances for the secondand third-harmonic components. Because phase noise is reduced without a high-Q resonator, the frequency tuning range of the proposed VCO is not reduced. To attain better phase noise, the microstrip square open loop multiple split-ring resonator has been used with the proposed harmonic control circuit. See "Low-Phase Noise VCO Using Output Matching Network Based on Novel Harmonic Control Circuit," Microwave And Optical Technology Letters, August 2009, p. 1838.