What is RF circulator ?

A circulator is a passive electronic device used in microwave and RF systems to control direction of signal flow between multiple ports. It is commonly used to separate signals and prevent undesired reflections, interference and coupling between different components. The key feature of RF circulator is its ability to detect signals in specific sequence, typically in clockwise or anticlockwise manner through its ports.

In its basic structure, RF circulator consists of three or more ports. These ports are connected to specific signal path and set of non-reciprocal components. The components are ferrite circulators or magneto-optical materials. These components ensure that signals entering the circulator from one port are directed to the next port in predetermined sequence.

Applications of circulator in microwave

There are many applications of circulator in microwave, RF and telecom industry as summarized below.
• It is used as duplexer to share common antenna between transmitter and receiver. This is used in radar systems which helps in preventing leakage of high transmit power into sensitive receiver circuitry.
• It is used as Isolator to protect test equipments from undesired reflections. It helps in protecting circuit elements from reverse signal reflections due to mismatch at junctions, cross junctions, at ports and so on.
• Circulators are used in phased array antenna systems to direct signals to and from individual elements in the array. This ensures efficient use of each element without any interference with neighboring elements.
• They are employed in satellite communication system to separate uplink and downlink signals. This allows efficient use of available bandwidth and prevents interference between uplink and downlink signals.
• Circulators are used in test and measurement setups to direct signals from sources to DUT (Device Under Test) and to separate signals coming from DUT to different test equipments.
• It is used to protect microwave amplifiers from reflected signals to prevent damage to the amplifier.
• The applications of circulators are microwave imaging systems, wireless communication systems, astronomy and radio telescope, MRI systems, military and defense applications and so on.

Circulator as duplexer

The figure-1 depicts RF circulator used as duplexer to use common antenna between transmitter and receiver. The connections are shown in the diagram. Refer working of RF Circulator >>.

Circulator as Isolator & Diplexer

The figure-2 (A) depicts use of RF circulator as isolator. Here one port is terminated to use 3 port circulator as isolator. Here power loss from port-1 to port-2 is less which is known as insertion loss. Power loss from port-2 to port-1 is more which is known as Isolation. Dual port circulators provide more isolation compare to the 3 port circulator mentioned here.

The figure-2 (B) depicts use of RF circulator as Diplexer. It separates two frequency bands from the input frequency band. This is shown in the figure. It uses High Pass Filter at port-2 to separate out desired frequency bands from input frequency band at port-1.

Conclusion : Overall, circulators play crucial role in managing signal flow, reduction of interference and protection of sensitive components in microwave and RF systems across wide range of applications. They enhance overall performance of various communication, radar and testing systems.

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