RF Isolator is a two-port device used in RF circuits to get good isolation for reflected waves back to the input port. Isolators are basically modified versions of circulators.
Circulator
RF Circulator is a three-port device that allows signals to pass from one port to another in a clockwise or anticlockwise direction, depending on how the ferrite material is placed inside the device. The three ports must be separated with 120-degree symmetry to get the desired performance. The construction of the Circulator includes a Y copper junction, ferrite core, and magnet to provide a magnetic field to the ferrite core.
The copper sheet is sandwiched between the ferrite core. Once the signal is applied to port one, it will be passed to port two. In the same way, if the signal is applied to port two, it will pass to port three and from port three to one to port one in the same manner. This phenomenon is achieved by selecting and controlling the properties of the ferrite core, such as magnetic permeability, size, and shape. Signal traveling from port one to port three, port two to port one, and port three to port two will be very low, known as isolation between the ports.
Isolator
The isolator is a two-port device with one input port, one output port, and a terminated port. The basic operation of the Isolator is similar to the Circulator with port three terminated. The input signal is sent from port one and received at port two. The reflection from port two to port one will be very low; this isolation is a major specification of every isolator.
At different operating frequencies, many factors are to be considered during the design and tuning of circulators and isolators. Isolators and circulators can be found in different frequency bands, power ratings, sizes, shapes, operating temperatures, etc. Since the size of modern communication devices reduces continuously, design, manufacturing, and tuning are facing more challenges.
Isolators and Circulators are available from milliwatts power to kilowatt range and few millimeters to few inch sizes. The most commonly available frequency ranges from 10 MHz to 8 GHz. Depending on the application, these devices are available with different connector types and packages.
Applications
- RF test labs and application where signal reflection need to be controlled. The isolator’s main characteristic is blocking the signal from the reverse direction.
- Intermodulation measurement setup. In IMD measurements, reflected signals play a big role in system IMD behavior, limiting system capability.
- RF transmitting devices. In transmission systems, reflected signal create problems for RF engineers, and impedance matching become challenging in antenna design.
- To protect test instruments from signal reflection. Isolator helps to protect expensive pieces of equipment from high-power signal reflection, which causes damage to equipment.
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