An 18-GHz range frequency synthesizer is implemented in 0.13-m SiGe BiCMOS technology as part of a 60-GHz superheterodyne transceiver chipset. It provides for RF channels of 56.5-64 GHz in 500-MHz steps, and features a phase-rotating multi-modulus divider capable of sub-integer division. Output frequency range from the synthesizer is 16.0 to 18.8 GHz, while the enabled RF frequency range is 3.5 times this, or 55.8 to 65.8 GHz. The measured RMS phase noise of the synthesizer is 0.8 (1 MHz to 1 GHz integration), while phase noise at 100-kHz and 10-MHz offsets are 90 and 124 dBc/Hz, respectively. Reference spurs are 69 dBc; sub-integer spurs are 65 dBc; and combined power consumption from 1.2 and 2.7 V is 144 mW.Index Terms-Frequency synthesizer, millimeter-wave, 18 GHz, phase rotator, phase-switched divider, 60 GHz, sub-integer divider, voltage-controlled oscillator.