An RF isolator is a specific case of an RF circulator where one of the three ports (usually the reverse port of the reference signal chain) is terminated. RF isolators only allow signal energy to be transmitted in the forward direction of the signal chain, and are heavily "isolated" from any backreflection or noise interference injection. RF Circulator RF isolators are typically passive ferrite devices that are manufactured in such a way that an internal magnetic field within the component directs electromagnetic waves from the incident port in a certain direction that are excited at the nearest port in the direction of travel.
As the name suggests, RF isolators are primarily used to isolate upstream signal chain components, which are usually more sensitive components, from reflections from downstream components. For RF isolators, it is critical to have well-matched terminations in the reverse port to optimize isolation. In the case of a well-matched terminal on the reverse port, most of the reflected reverse signal energy from the output port will be directed to the terminal and dissipated and heated.
RF Isolator, 18 dB Isolation, 2 GHz, 4 GHz, 10 W, N-type female
By simply terminating the reverse port, an RF isolator can be made from an RF circulator. However, factory-designed RF isolators may have better mated terminations and are designed and tested to operate across the entire frequency range and up to specified power levels. Prefabricated RF isolators may also be more compact and plug-and-play than RF isolators made from off-the-shelf RF circulators. The isolation of RF isolators is directly related to the quality of terminal matching.
Key RF isolator characteristics
Frequency range (Hz).
Impedance (ohms).
Insertion loss (dB).
Isolation (dB).
The VSWR forward power handles continuous wave and/or peak (dB).
Reverse power continuous wave and or peak (dB).
Connector type.
Two-section isolator, 40 dB isolation, 11 GHz 18 GHz, 5 W, SMA female
RF isolators can be used to protect any component or part of a signal chain from backreflection, but are most commonly used to protect active components such as transceivers, power amplifiers (PAs), low-noise amplifiers (LNAs), and mixers. It is important to select an RF isolator that meets the requirements of the signal chain, such as frequency range and power. Since RF isolators add a certain amount of insertion loss and their own product reflection (non-ideal VSWR), this must also be considered when selecting an isolator.