Active quasi-circulator realisation with gain elements and slow-wave couplers

A microstrip active quasi-circulator is presented using two generic amplifier blocks and two power couplers. The power couplers are parallel-coupled lines with a slow-wave structure in order to improve the isolation between ports of the quasi-circulator. A detailed analytic design procedure is presented for the slow-wave couplers based on the capacitive coupling modelling approach for coupled transmission lines. Experimental results show that the quasi-circulator has an insertion loss between 1 and -2 dB, a return loss better than 11 dB at each of the ports and an isolation better than 20 dB from 1.0 to 3.0 GHz. The input 1 dB compression point is 14 dB m at 2.4 GHz.