A GaAs Frequency Doubler with 38 dB fundamental rejection from 22 to 40 GHz using a Transformer Balun

A self-biased balanced frequency doubler is presented in gallium arsenide (GaAs) with more than 38 dB fundamental suppression and broad bandwidth from 22 to 40 GHz at its output. The combination of both large bandwidth and excellent harmonic rejection was achieved by applying a transformer balun with a high degree of symmetry and minimal capacitive coupling. The balun alone has a gain and phase imbalance of less than 0.3 dB and 0.7° respectively from 2 to 25 GHz. The conversion gain of the doubler with the balun is -2 to -5 dB across the output frequency range. The highest output power is approximately 8 dBm between 18 and 20 GHz, with 10 dBm input. This work features the highest fundamental rejection across the band compared to the previously reported broadband GaAs doublers, enabled by the excellent balance of the balun.