Active circulator MMIC in CPW technology using quarter micron InAlAs/InGaAs/InP HFETs

An active coplanar circulator for Q-band operation based on lattice matched InAlAs/InGaAs/InP HFETs has been designed and fabricated. The active devices have a gate-width of W/sub G/=6/spl times/20 /spl mu/m and T-gates with a gate-length of L/sub G/=0.25 /spl mu/m. The circuit is fully passivated, contains all matching and biasing networks on chip and operates under zero volt gate bias. Over the entire frequency range the input reflection of the circulator is better than -15 dB and the isolation between the transmit and the receive path is better than -30 dB which is attributed to the extremely low feedback capacitance of the InP-based HFETs.