Advantages of Duplexer | disadvantages of Duplexer

This page covers advantages and disadvantages of Duplexer. It mentions RF Duplexer advantages or benefits and RF Duplexer disadvantages or drawbacks. It also describes RF Duplexer basics.

What is RF Duplexer?

The duplexer is a RF device which routes two nearby bands in two different paths. There are two different types of duplexer as per make viz. one using PIN diode switches and the other using circulator. The RF duplexer also uses narrow band filters in order to separate these nearby frequency bands between ports and to achieve good isolation between them.

It isolates transmitter (Tx) while receiving and isolates receiver (Rx) while transmitting. It acts as microwave switch between antenna and Tx/Rx.

RF duplexer

Example application#1 : GSM 900 system
The system uses 890 MHz to 915 MHz for transmit path and 935 MHz to 960 MHz for receive path. The diplexer is used to share the same single antenna between transmitter and receiver for both the frequency bands received over the air. The figure-1 depicts use of 3-port circulator as RF duplexer device. As it operates clockwise, the input at port-1 will lead to output at port-2 and input at port-2 will lead to output at port-3 and so on. As both the frequencies are different, the communication can takes place simultaneously for both the paths.
Example application#2 : LTE system
It is used to separate uplink frequency band (1710-1785 MHz) and downlink frequency band (1805-1880 MHz ) in the transmit and receive directions. This means same antenna can be used for transmitter and receiver in FDD mode.

Following are the common types of duplexers based on design. Each one of them has their respective advantages and disadvantages.
• Branch type duplexer: It uses TR (Transmit-Receive) switch and ATR (Antitransmit-receiver) switch. They are gas-discharge tubes.
• Circulator duplexer: It is three port or four port device which uses circulator for duplexing operation as shown in the figure.
• Balanced duplexer: It is hybrid junction coupled through short-slot. It uses two waveguide sections which are coupled through slots along with TR tubes. TR tube is used to fire and reflect the incident power. It is known as broadband directional coupler.

Benefits or advantages of Duplexer

Following are the benefits or advantages of Duplexer:
➨It helps to share same antenna for both transmit and receive modes. This minimizes space and cost of the wireless system.
➨It makes design of the duplexer very compact due less space.
➨It protects the receiver from high power transmitters by isolation.
➨(Branch duplexer:) Its cost is low.
➨(Circulator duplexer:) They are used in monostatic radar. Refer advantages and disadvantages of RF circulator >>.
➨(Balanced duplexer:) Its power handling capability is higher compare to branch duplexer. Moreover it has higher bandwidth of operation.

Drawbacks or disadvantages of Duplexer

Following are the disadvantages of Duplexer:
➨The noise figure of the receiver increases due to insertion of duplexer in the receiver chain. This is due to insertion loss of the duplexer. Hence appropriate gains and noise figures are used to meet the link budget at receiver.
➨(Branch duplexer:) Bandwidth is limited. Power handling is limited.
➨(Balanced duplexer:) It does not allow simultaneous transmit and receive.

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