SAW Duplexer basics | SAW Duplexer working principle

This page covers SAW Duplexer basics and describes SAW Duplexer working principle and application. It mentions example application note of use of SAW duplexer in RF transceiver system.

The duplexer is a device which separates two frequency bands which are closer to each other. It uses narrow band filters to perform filtering of respective bands.
Refer Diplexer versus Duplexer>>.

It is a 3-port device. The major application of duplexer is to share same RF antenna between transmitter and receiver. This is shown in the figure-1 below. As it can be used for simultaneous trasmission and reception of the frequency bands, it is especially used in FDD duplex type of wireless system e.g. LTE, UMTS etc.

SAW Duplexer

SAW duplexer works based on generation of acoustic waves from electrical signal. The generation of mechanical energy (e.g. SAW) from electrical energy and vice versa is accomplished by the use of piezo-electric substrate material. It uses inter-digital transducers (IDTs) and gratings in its construction.

SAW generation

SAW devices use piezo-electric effect of materials such as quartz, lithium tantalate, lithium niobate, and lanthanum gallium silicate for conversion of acoustic waves to electrical signals and vice versa. The figure-2 depicts generation of Surface Acoustic Waves.

SAW Duplexer Working Principle

SAW Duplexer frequency response

The figure-3 mentions frequency response of the duplexer. There are two frequency bands shown in the figure. As shown when there is low attenuation in one band curve, there is very high attenuation for the other curve. This allows separation of two frequency bands easily using SAW duplexer.

The SAW duplexer works based on surface acoustic wave propagation>> principle. It allows bidirectional communication over single path as explained above.

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