Design and Analysis of 24-GHz Active Isolator and Quasi-Circulator

In this paper, a new topology using the common-source amplifier, which is a unilateral component and the directional coupler, is proposed to realize an isolator without ferrite. The theory and the design procedures are presented. The performance of this isolator is comparable to those of the ferrite isolators, except for the bandwidth. The 1-dB compression point of output power (OP_1dB) of the insertion loss is high due to the passive nature of the directional coupler, but the reverse isolation deteriorates with the increasing input power. The proposed 24-GHz monolithic microwave integrated circuit isolator is developed in TSMC 180-nm CMOS. Based on the proposed isolators, a quasi-circulator is designed and fabricated. Both the isolator and quasi-circulator have better OP_1dB of the insertion loss than reported active isolators and quasi-circulators.