Ferrite Device

• Ferrite refers to a category of materials with unusual magnetic properties. A circulator is a type of a ferrite device with three ports.
  
  

Non-Reciprocal

• Circulators are nonreciprocal, which means the energy entering port 1 exits port 2 and energy entering port 2 exits port 3. Similarly, energy entering port 3 exits port 1.
  
  

Circulating Direction

• A circulator can be made to circulate either in a counterclockwise direction or a clockwise direction.
  
  

Duplexer

• Sometimes, a circulator is also called a "duplexer" because it duplexes two signals into one channel. For example, it transmits signals and receives into an antenna.
  
  

Purpose

• Mostly, circulators are used for making antenna interfaces for transmitting and receiving signals. During transmitting, energy flows from port 1 (transmitter) to port 2 (antenna) and during receiving, it flows from port 2 (antenna) to the port 3 (receiver).