An active single-ended 28-6 GHz MMIC frequency doubler based on a commercial GaAs HEMT process is presented. The presented doubler is broadband and delivers high output power. At 5 dBm input power, the doubler delivers 6 dBm output power. The 3 dB bandwidth is between 48 GHz and 60 GHz. Suppression of the input frequency is better than 23 dB at the design frequency.