W-Band GaN HEMT Frequency Multipliers

This article presents three $W$ -band frequency multiplier monolithically microwave integrated circuits (MMICs) designed in a 40-nm gallium nitride (GaN) on SiC process. Two doublers with fundamental-frequency input from 37.5 to 55 GHz both use two $4\times 37.5\,\,\mu \text{m}$ HEMTs. One is a single-ended topology with a postmultiplication amplifier, while the other is a balanced power-combining topology with a planar Marchand balun adapted to the passives in the MMIC process. The tripler is a balanced configuration for an input fundamental frequency from 25 to 37 GHz. All designs are stable over a wide range of operating conditions. The single-ended, postamplified doubler shows conversion gain from 80 to 85 GHz with a peak gain of 1.5 dB at 10 dBm of input power and 900 mW of dc power. The balanced doubler MMIC has a conversion gain from about 90 to 100 GHz with a peak gain of 3.8 dB at 100 GHz for an input power of 10 dBm and 500 mW of dc power consumption. Both doublers achieve fundamental-frequency suppression above 55 dBc. The results show that a topology that combines the two doubler approaches in GaN should result in simultaneous conversion gain with higher power and improved fundamental-frequency suppression. The tripler measures an output power of 10 ± 1.5 dBm for an input power of 19 dBm from 75 to 110 GHz, with fundamental- and second-harmonic suppressions of 29 and 29.5 dBc, respectively.