RF circulator used as an isolator

　　The transmitted power is transmitted from port 1 to port 2 and to the antenna. Any reflected power will return along the feeder and be transmitted from port 2 to port 3, where it can be absorbed in the load. In this way, the RF power amplifier will be able to operate at high feeder VSWR, but will be protected by a circulator acting as an RF isolator.

　　The load on port 3 needs to provide matching impedance: the isolator needs to match impedance on the port to maintain isolation level with that port.

　　For example, an isolator is connected between a signal generator and a device under test (DUT). If all impedances match, the signal can be freely transmitted to the DUT. If the DUT does not match or is disconnected, a high voltage standing wave ratio (VSWR) will be generated, resulting in a larger reflection signal. The circulator absorbs the signal to protect the usually expensive signal generator.

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The basic circuit components of commonly used control circuits