This work presents the first design of an active frequency quadrupler based on GaN HEMTs. It is based on two cascaded frequency doubler stages that allow up-conversion from the S band to the X band, obtaining conversion gain in narrowband without the need for any additional buffer amplifier. A hybrid prototype of the quadrupler provides, at the input fundamental frequency of 2.5 GHz, a measuredfourthharmonic maximum conversion gain of 13.7 dB and an output power of 23.5 dBm, with suppression of both fundamental andsecondharmonic above 14 dBc. To obtain these results, due to its impact in the final quadrupler behavior, a prototype of the higher frequency second stage doubler was designed and manufactured separately to assess its RF performance. The experimental results of this standalone prototype are highly competitive with the current state of the art in frequency doublers at the C band.
Morales-Fernandez et al. (Wed,) studied this question.