Ka-band MMIC power amplifier in GaN HFET technology

We report the development of Ka-band GaN MMIC power amplifiers in CPW and microstrip topologies. This is, to the best of our knowledge, the first demonstration of millimeter wave MMIC's in GaN technology. The single stage CPW MMIC utilizes four 2/spl times/100 /spl mu/m wide GaN HFET's whilst four 4/spl times/60 /spl mu/m wide HFET's with individual through substrate source vias were used for the microstrip MMIC's. The CPW amplifier has a gain peak of 8 dB at 33 GHz with 4 GHz bandwidth while the microstrip amplifier has a peak gain of 9 dB at 27 GHz and gain higher than 8 dB over the 2.45 GHz to 33 GHz frequency range. The saturated CW output power of the amplifiers measured into a 50 /spl Omega/ system at 33 GHz was, respectively, 1.6 W for the microstrip MMIC. The corresponding power density of 2.3 W per mm of gate periphery for the microstrip MMIC is by a factor of 4 higher than that of a typical GaAs pHEMT MMIC at this frequency. Microstrip MMIC performance was further improved through external output impedance matching, resulting in power levels of up to 2.8 W (27% associated PAE) and peak PAE's of up to 36.2% (1.2 W associated power).