RF Isolator and Circulator

RF Isolator is a two port device used in RF circuits to get a good isolation for reflected waves back to the input port. Isolators are basically modified version of circulator.

RF Circulator is a three port device which allow signals to pass from one port to another in a clockwise or anticlockwise direction depends 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 and ferrite core and magnet to provide magnetic field to the ferrite core. The copper sheet is sandwiched between the ferrite core. Once the signal is applied to the port one it will be passed to port two. 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 travelling from port one to port three, port two to port one and port three to port two will be very low and is known as isolation between the ports.

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 Circulator with port three is terminated. Input signal is sending from port one and received at port two. The reflection from port two to port one will be very low and this isolation is a major specification of every isolator. At different operating frequency, many factor to be considered during design and tuning of circulators and isolators.

Isolator and circulators can be found in different frequency band, power rating, size, shape and operating temperature etc. Since the size of the modern communication devices reduces continuously, design, manufacturing and tuning are facing more challenges. Isolator 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.These devices are available with different connector types and packages depends on application.

·         RF test labs and application where signal reflection need to be controlled. The main characteristic of the isolator is to block the signal from reverse direction.

·         Intermodulation measurement setup. In IMD measurements, reflected signal play a big role in system IMD behavior which limits the 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 the expensive equipments from high power signal reflection which cause damage to equipments.