A hybrid Balanced Frequency Doubler working up-converting from 2.45 to 4.9 GHz using packaged GaN HEMTs and with no amplification stage, was designed and its performance validated with measurements. The design procedure is detailed, including a brief study of the HEMT optimum bias point. Moore space filling curves are used in the design of the input hybrid coupler, to reduce its size at the fundamental frequency. A maximum measured conversion gain of 11.5 dB with a second harmonic output power of 26.3 dBm was obtained, while fundamental and third harmonic suppression exceeds 40 dBc.
