An isolator/circulator is a three port directional ferrite device in which the signal to the input port (port #1) is directed to the output port (port #2) but a return signal to port #2 is directed to port #3 and isolated from the original input port (port #1). An isolator is a circulator with port #3 terminated in the system characteristic impedance. Power handling capability and isolation are determined by the port #3 load dissipation and VSWR
