How RF Circulator Works | How does an RF circulator work

This page describes RF Circulator working operation. It mentions how RF Circulator works along with its terminal diagram.

The non-reciprocal ferrite device which consists of 3 or more ports in which input from port-N will lead to output at N+1 port is known as circulator. The circulator device which operates on radio or microwave frequency is known as RF Circulator. The 3 port circulator is known as Y-Junction Circulator.

Y Junction circulator symbol

The RF circulators are available in waveguide or stripline forms. Based on direction of signal travel in the circulator there are two major types viz. clockwise circulator and anti-clockwise circulator. The figure-1 depicts anti-clockwise circulator.

As shown here signal flows from port 1 to 2, from port-2 to 3 and from port-3 to 1. This means signal input at port-1 will give out signal from port-2 and there should not be any signal output from port-3 and so on. This is due to the fact that insertion loss of circulator is loss from 1 to 2 which is very less (few tenths of a dB). The loss from port-1 to port-3 is known as Isolation which is quite high (about 20 to 25 dB).

RF circulator becomes Isolator when one of its port is loaded with matched impedance. For example, if port 3 in the figure-1 is loaded, then power at port-1 is available at port-2. All the reflections from port-2 will go to load at port-3 and port-1 does not get any reflections back.

Circulators can be used as diplexers and triplexers with the help of appropriate filters at the appropriate ports. As circulators consist of magnets, is should be kept away from ferrous metals. This is due to the fact that close proximity of metals will change frequency response of the circulator.

How RF Circulator Works | RF Circulator Working

rf circulator function

➤The figure-2 depicts use of RF circulator to share single Antenna between transmitter and receiver units. The circulator used here is anti-clockwise one.
➤Let us make arrangement as shown in the figure-2, in which transmitter is connected to port-1, receiver is connected to port-3 and antenna is connected to port-2.
➤Now in this arrangement as circulator is anti-clockwise, any data to be transmitted will traverse from port-1 to port-2 and gets transmitted from antenna.
➤Any data received by antenna interfaced at port-2 gets coupled with port-3 and receiver starts decoding the same.

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