A 7–10 GHz GaN MMIC Active Circulator with Gain

This paper discusses the performance of a MMIC active circulator designed in the WIN Semiconductors NP15-00 GaN-on-SiC process selected for its power handling capabilities. Common-source transistor amplifier nonreciprocal behavior is leveraged to achieve isolation with accompanying gain. To achieve circulation, three amplifiers are cascaded in a loop with ports tapped through couplers. The fabricated circulator chip, 2.7 mm by 3.3 mm in size, is measured under small and large signal conditions. A return loss better than 10 dB is measured between 7 and 10 GHz. In small-signal, the measured 1.2 dB gain peaks at 8 GHz while the isolation remains between 10 and 17 dB from 7–10GHz, a 35% bandwidth. A single branch of the circulator is characterized under large signal conditions. The 1-dB compression point is measured at 15 dBm of input power at 9.5 GHz. The measured large signal gain peaks at 3.7 dB.