This paper presents a V-band frequency quadrupler in 0.1-µm SiGe BiCMOS technology with 3-dB bandwidth from 44.8 to 57.2 GHz. The circuit employs cascode stacks comprising in-phase class-C common-emitter and anti-phase class-AB cascode devices to obtain current pulses at ×4 frequency. Four such cascodes driven with differential and tunable quadrature increase the 4th harmonic output power while suppressing all other harmonics 22 dB or more. Measurements show >7.4-dBm 4th harmonic output power, and >5.2% power efficiency for the core of the multiplier.