Design of a Low Loss Wideband Tunable MMIC Active Circulator

In this work, a wideband tunable active circulator MMIC with low transmition loss is presented. This wideband tunable active circulator MMIC uses traveling wave distributed amplifier(TWDA) structure with tunable varactors to achieve the wideband circulator and high isolation. Through modulation the transconduction(g
m
) of each stage, it can enhanced the transmitter (TX) to the receiver (RX) isolation compared with traditional distributed amplifier circulators. By using varactors to adjust phase shift between each stage, which can not only achieve the frequency tuning operation but also mach different antenna impedance wich can also suppress the signal leaking from the TX to the RX. Because of the MMIC active circulator is a power amplifier, the output power can transmit to the antenna port directly, so there has no transmition power loss. The simulation results show that the MMIC active circulator can tunable from 3 GHz to 4.5 GHz, the isolation between TX and RX better than 30-dB over 100 MHz bandwidth. The active circulator MMIC is implemented in 0.25um ED pHENT technology with die area of 2.25 × 1.8mm.