English: A microwave ferrite circulator used as an isolator. The circulator is the top device, shaped like a "T" with three connectors (ports) to attach to coaxial cable lines carrying radio waves. It has the property that a radio signal entering any port only comes out of the port clockwise of it. In this example the bottom port is attached to a matched resistive "dummy load" (labeled "Dummy"), which absorbs power. So radio power entering the righthand port (labeled Eingang, "Input") will come out of the lefthand port (labeled Ausgang, "Output"), but radio power entering the lefthand port is absorbed by the load. This device is used to prevent any radio power reflected from the load attached to the lefthand port from returning to the source.