The working principle of RF circulator

　　The connection to the RF circulator is usually referred to as a port, and in addition, they are usually numbered as 1, 2, 3, etc.

　　The reason why the RF circulator is named is because it only cycles the power entering one port to the next port. The signal applied to port 1 will be passed to port 2: the signal input to port 2 will be passed to port 3, but will not return to port 1. The input from port 3 will be passed to port 1, but it will not be passed back to port 2

　　An ideal circulator would transfer all power from one port to the desired port, without transferring it to any other port. But in reality, there is always some attenuation in the transmission path, and some signals always leak to the ports that should be isolated. The key RF circuit design challenge for these devices is to ensure optimal transmission and isolation.

　　Circulators may use ribbon printed circuit board technology (but typically use very low loss dielectric or PCB materials) and are included in metal boxes with connectors or other external connections - some even use surface mount technology. Other circulators may be based on waveguides, which can be used for RF system design applications that combine waveguide technology. The type of interface and technology required for any given instance will depend on the RF circuit design of the application. In terms of operation, 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 the magnetized material. Waveguide circulators can be of any type, while more compact devices based on striplines are of the 3-port type.

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

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