RADITEK INC. Circulator and Isolator Primer

A circulator is a three port device. It is essentially a passive device, but can exhibit some characteristics that make it almost behave as if it were active. An isolator is a two port device having an input and an output, it is simply a circulator whose third port has been terminated.

Circulators and Isolators provide unique transmission paths, allowing RF energy to pass in one direction with little (insertion) loss, but with high loss (isolation) in the other direction.

Isolators and circulators can exist as Stripline, Coaxial, Microstrip, or Waveguide type, and can be rated for powers from milliwatts to Megawatts. Raditek can provide superb stripline isolators to 18GHz, Microstrip ones to 60 GHz. Coaxial to 50Ghz and Waveguide to 110GHz.

A typical use of a circulator would be as a duplexer, connecting a transmitter to Port 1, antenna to port 2 and receiver to port 3. This provides simultaneous transmission and reception of signals.

A very common use for isolators is at the output of a power amplifier. Forward power is passed with a minimal insertion loss. Reverse power resulting from disconnect at the output (removing the connection to antenna), will (with no isolator installed) flow back to the output FET/LDMOS etc. and likely damage or destroy it/them. With the isolator installed, any reflected power will flow into the isolator’s load and be safely dissipated as heat (as long as the load is rated to handle the power, and is properly heat sunk, so that the load temperature stays <100C).

Typical parameters could be 0.25dB insertion loss, 22dB isolation and VSWR on the ports of 1.2:1 over a 5% percentage bandwidth.

The Raditek isolators and circulators are believed to have the best performance in the marketplace, within constraints and compromises of physical size, power, and RF performance.