RF or microwave circulators or isolators are devices that usually have three and sometimes four ports. They are used in the design of RF systems, and it is necessary to transmit power from one port to another while isolating the power from the other port.

RF circulators are used as duplexers in many radio frequency applications, allowing simultaneous transmission and reception functions. They are widely used in radio frequency design applications, including radar systems and various professional radio communication systems.

An ideal circulator will transmit all the power from one port to the desired port, but not to any other port. But in fact, there will always be some attenuation in the transmission path, and some signals will always leak to the ports that should be isolated. The key RF circuit design challenge of these devices is to ensure optimal transmission and isolation.

Circulators may use stripline printed circuit board technology (but usually use very low-loss dielectric or PCB materials) and are contained in metal boxes with connectors or other connections to the outside world-some even use surface mount technology. Other circulators may be based on waveguides, and these circulators can be used in RF system design applications that combine waveguide technology. The type and technology of interface required for any given instance will depend on the RF circuit design of the application. As far as its operation is concerned, most RF circulators are based on the use of ferromagnetic materials. There are two main types:

Three-port circulator: The three-port "Y-junction" circulator is based on eliminating waves propagating through two different paths near magnetized materials.

Four-port circulator: A four-port waveguide circulator based on Faraday rotation of waves propagating in magnetized materials. Using this technology, they can route RF signals to four ports.