Three-channel passive circulators may be constructed about antireciprocal twoports whose parameters obey the restriction (Re Y11) (Re Y22) < (Re Y12)2. The characteristics of such circulators are derived in terms of the network parameters of the antireciprocal twoport. Expressions are presented for the required terminations, the driving-point admittances, and the transducer gain of the circulator. Experimental data is presented on circulators constructed about the electromechanical gyrator. The agreement between the calculated and the experimental performance is very good. The electromechanical circulator, an inexpensive and readily fabricated device, has applications in communications and in various instrumentation.