What is a circulator and how do circulators work

A circulator is a three-port passive device, basically, it is a ferrite device this device will only allow the flow of microwave in only one direction. The ferrite material has unique magnetic properties, circulators can be considered as the oldest microwave ferrite components and its transmission behavior is depended upon its magnetic and geometric parameters. The circulators have a pre-magnetized ferrite body and it would absorb the electromagnetic wave in one direction and transfer it into the other direction without any change. So basically a circulator is a ferrite device that has a multiport junction and in it, a wave can travel from one port to the next in one direction.

What are the functions of circulators?

A circulator is passive equipment that is used in RF and microwave equipment. This device can be used to improve the stability, performance, and reliability of the system. The function of the circulator is to absorb the energy entering the port and to pass it to the next port.

How do circulators work?

The circulator works according to the faraday’s rotation, if we send a wave through the circulator the ferrite rod that has magnetic influence and the wave will be split and it travels through the port. The circulator has three or more ports and in this device, the power will be transmitted from one port to the other. This means that in a circulator that has three-port, the power entering the port1 leaves port 2, port 3 is decoupled and a similar process will take place if the power enters through the other two ports. So each port is connected to one arm of the symmetrical Y junction that is coupled to magnetic biased ferrite material. When one port is terminated then the other ports are isolated in the reverse direction. The circulator would only have less loss while transmitting the signal from one port to the other.


What is the difference between a circulator and an isolator? Can a circulator be used as an isolator?

The working principle of the circulator is similar to the isolator, the circulator can be considered as an isolator with matched termination, it means that in a circulator if one port is terminated then the other ports are isolated in the reverse direction, a circulator won’t do isolation until a port is terminated. The isolator will only allow the signal to pass in one direction and in the other direction it will be attenuated, while the circulator can separate the signal.

What are the advantages of circulators?

We can use circulators to get bidirectional transmission over a single fiber. It is used for applications related to optical sensors because of its isolation properties.

What are the disadvantages of a circulator?

  • It is expensive
  • Circulators are heavy
  • The static magnetic field produced is very high
  • Insertion loss is high too

How to select a circulator?

We must choose a circulator according to some electrical specifications and by checking these specifications we can know if it can be used according to our needs. We must consider certain things while selecting a circulator they are insertion loss, VSWR, power handling, group delay, operating temperature range, and isolation. Power handling is the amount of power that the circulator could pass without and signal distortion and group delay is the time taken by the signal to travel from port 1 to port 2. Insertion loss is the loss of the energy that took place while transferring signals from one port to the other.

What are the applications of circulators?

  • It has applications in radar system
  • It is used in antenna for transmitting and receiving purpose
  • It is used as the coupling element in the amplifiers
  • Duplexers
  • It is used in phase lock injection circuits
  • Test instruments
  • Reflective power handling isolators