RF Circulator: Advantages and Disadvantages

This page explores the advantages and disadvantages of RF Circulators. It also provides links to various topics related to RF Circulators.

What is a Circulator?

Introduction: A circulator operates based on the non-reciprocal property of ferromagnetic materials. When such materials are placed in a DC magnetic field, electromagnetic wave propagation becomes non-reciprocal. It is a microwave passive device that allows uni-directional propagation of electromagnetic waves, similar to an isolator. It has many applications.

Figure 1 depicts one such application used to share a single common antenna between a transmitter and a receiver.

In this 3-port circulator, the signal travels in uni-directional mode, i.e., from port 1 to 2, and from 2 to 3, and so on. The reverse is not possible. This means a signal fed at the Nth port appears at the (N+1)th port, but not at the (N-1)th port.

As a result, the signal from the transmitter at port 1 can be transmitted via the antenna connected at port 2. Similarly, a signal received at port 2 can be fed to the receiver connected at port 3.

The following are the types of Circulators:

• Four-port circulator and Three-port circulator (based on the number of ports)
• Microstrip circulator
• Strip line circulator
• Waveguide circulator

Benefits or Advantages of Circulators

The following are the benefits or advantages of Circulators:

• It has many applications as it is a lossless and non-reciprocal device.
• The 3-port circulator can be used as an RF isolator by terminating one of its ports.

Drawbacks or Disadvantages of Circulators

The following are the disadvantages of Circulators:

• There is a limit on the power handling capability of the RF circulator. This can be increased by lowering impedance, increasing the intrinsic line width, or increasing substrate thickness.
• Insertion loss between coupled ports depends on various parameters such as copper loss of the strip and ground plane, dielectric loss of input/output strips, and magnetic loss of the ferrite disc. All these should be properly managed in order to achieve minimum insertion loss between the coupled ports.