A 21.4-GHz 1.1-V regulator-stabilized voltage-controlled oscillator (VCO) with a dual-transformer configuration and a 115% frequency-range dynamic divider-both based on 0.18-μm SiGe BiCMOS technology-were developed. As for the VCO, the combination of two types of transformers, which exhibit high input impedance and capacitive-input impedance, respectively, provides both wide frequency-tuning range and low phase noise. The measured phase noise of the VCO at a 1-MHz offset frequency is - 109 dBc/Hz with 11.1-mW dc power dissipation (including the regulator). The figure of merit of the VCO is -192 dBc/Hz, which is the best value among 20-GHz-class silicon-based VCOs (to the best of the authors' knowledge). As for the divider, a two-stage single-balanced mixer reduces dc power and increases operation frequency range. The measured operation frequency of the divider is from 7 to 26 GHz while dissipating only 1.15-mW dc power and occupying a small area (0.004 mm2). These performance results indicate that the proposed VCO and the divider are suitable for low-power transceivers of quasi-millimeter-wave wireless communication systems.