The receiver input is connected to port 3. The transmitter output is applied to port 1 and will pass to port 2, where the antenna is connected.

A duplexer allows the transmitter and receiver in a radio or radar unit to share a common antenna (Fig. The most common application of a circulator is as a duplexer. There is no spacing between actual disk components as shown here. This common construction of a circulator shows a Y strip line, ferrite disks, and magnets. Operation takes place in regions above or below the resonant frequency of the device, where attenuation is minimal.ģ. The circulator is not operated at this frequency. The assembly made up of the Y-junction and the ferrite disks forms a dielectric resonator that has a resonant frequency. This field then interacts with the applied bias magnetic field, causing the signal to rotate in one direction to the next adjacent port. When a signal is applied to one of the ports, an electromagnetic field is set up in the strip line. The axial magnetic field is called the bias. The ferrite material supports and focuses the magnetic field around the Y-junction. The magnets send a strong magnetic field axially through the ferrite disks. Two strong permanent magnets are positioned on either side of the ferrite disks. The Y-junction assembly is then sandwiched between two layers of ferrite material (Fig. The Y-shaped strip line circuit is the heart of the circulator. apart, are commonly terminated with SMA or N-type coaxial connectors.Ģ. ConstructionĪ circulator is typically a Y-shaped section of microstrip or stripline transmission line on a printed circuit board or other dielectric (Fig. This protects or isolates port 1 from port 2 in the reverse direction. If there is a mismatch at port 2, any reflected signal will be passed to port 3 and absorbed by the load. An input signal at port 1 will pass to and exit port 2 if port 2 is properly matched to 50 â¦. If one of the ports is terminated in a resistance equal to the impedance of the port, usually 50 â¦, the circulator becomes an isolator (Fig. Shown are (a) the common schematic symbol of a circulator and (b) the schematic symbol of an isolator. The amount of insertion loss from port to port is typically in the 0.2- to 0.75-dB range.ġ. An input to port 3 will pass to port 1, but not in reverse to port 2. A signal input to port 2 will pass to port 3, but not back to port 1. A signal applied to port 1 will be passed to port 2 with minimum attenuation. How a Circulator Worksįigure 1a shows a circulator, where any port can be an input or an output. The arrow indicates the unidirectional flow any signals from port to port. Figure 1a shows the standard schematic symbol for a circulator. A port is defined as a connection point for either an input signal, output signal, or termination. If you do not allow these cookies, you will experience reduced relevant content.This file type includes high resolution graphics and schematics when applicable.Ĭirculators and isolators are three-port passive electronic devices that help direct the flow of microwave signals in RF equipment and systems.

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Rf isolator