Branch duplexer vs Balanced duplexer vs Circulator duplexer | Difference between Branch duplexer Balanced duplexer Circulator duplexer

This page compares Branch duplexer vs Balanced duplexer vs Circulator duplexer and mentions difference between Branch duplexer, Balanced duplexer and Circulator duplexer. It mentions advantages and disadvantages of Branch, Balanced and Circulator duplexer types.

What is Duplexer?

The duplexer is a device which isolates transmitter while receiving and isolates receiver while transmitting. It functions as microwave switch between antenna and transmitter/receiver.

The functions of duplexer are as follows.
• The single antenna can be shared between transmitter and receiver due to its isolation property.
• It protects receiver from high power transmission of the transmitter part due to isolation.
• It protects receiver from high power transmissions from nearby radars or wireless transmitters.

Following are the common types of duplexers used.
• Branch duplexer
• Balanced duplexer
• Circulator duplexer

Branch duplexer

Branch duplexer block diagram

• The figure-1 depicts block diagram of Branch duplexer. It consists of TR (Transmit-Receive) switch ad ATR (Antitransmit-receive) switch. These are gas discharge tubes.
• When transmitter is in ON state, TR and ATR ionize and as a result firing takes place. TR switch is in short circuit at receiver end and hence transmitter power doe not reach receiver. It acts as open circuit at transmission line and hence it does not reduce or attenuate transmit power.
• ATR placed at λ/4 distance from transmission line functions as short circuit during firing. It functions as open circuit on transmission line and as a result it does not reduce transmit power.
• When transmitter is in OFF state, TR and ATR tubes do not fire. ATR functions as short circuit across transmission line. Moreover it acts as short circuit at λ/4 from receiver. Hence transmitter is disconnected from transmission line. As a result received echo signals will reach the receiver.
• Advantages: Lower cost
• Disadvantages: Limited bandwidth, Limited power handling capability

Balanced duplexer

Balanced duplexer block diagram

• The figure-2 depicts block diagram of Balanced duplexer.
• It consists of two waveguide sections coupled through slots along with narrow walls.
• The TR tube fires and reflects incident power. The energy which is leaked through TR tube goes to dummy load. As a result no energy reaches receiver.
• As TR tube does not fire during reception, the energy from antenna reaches receiver.
• It acts as broadband directional coupler.
• Advantages: It has higher power handling capability compare to branch duplexer. It supports higher bandwidth.

Circulator duplexer

Circulator duplexer block diagram

• The figure-3 depicts block diagram of Circulator duplexer.
• It uses clockwise circulator having four ports for duplexing operation. Here port-4 is terminated. transmitter is connected at port-1, receiver is connected at port-3 and antenna at port-2.
• As it is clockwise, it provides lower attenuation from port-1 to port-2 and from port-2 to port-3 direction. It provides higher attenuation in reverse directions from 2 to 1, 3 to 2, 4 to 3 etc.
• Due to above functionalities, transmitter can easily transmit EM waves to the antenna connected at port-2. It can easily receive EM waves from antenna to the receiver connected at port-3.
• Refer advantages and disadvantages of RF circulator >>.


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