RF Isolator: Working Principle Explained

This page describes the working operation of an RF Isolator, explaining how it functions and providing a terminal diagram.

As we know, the ferrite isolator plays a fundamental role in RF and microwave systems.

Definition: An isolator is a passive ferrite device that allows energy to pass in one direction only and prevents any reflections from traveling in the other direction.

It’s often referred to as the traffic conductor of RF energy, as designed by RF system engineers. It helps in routing the RF signal in the desired direction in RF circuit designs such as RF transceivers, RF Power Amplifiers, RF LNAs, etc.

Let’s understand how an RF isolator works.

An RF isolator is functionally similar to a diode, but unlike a diode, which passes current in one direction only, an isolator passes RF energy in one direction.

When any one port of a 3-port circulator is terminated with 50 Ohms, it becomes an Isolator.

As shown, the device has two ports, namely port-1 and port-2. It allows the signal to pass from port-1 to port-2 with minimal attenuation and from port-2 to port-1 with maximum attenuation.

Moreover, any RF energy that enters from port-2 will be routed towards a matched termination connected to port-3. This energy gets dissipated as heat. Hence, any reflections from port-2 to port-1 are eliminated. This prevents any damage to the signal source or equipment connected to port-1.