Terminology » RF Components » Diplexer vs. Duplexer: Key Differences and Applications Explained

Diplexer vs. Duplexer: Key Differences and Applications Explained

rf communication diplexer duplexer wireless system frequency

Diplexers and duplexers are two critical components used in RF communication systems. They are often confused, but they serve different purposes. Both devices manage multiple frequency bands and improve signal transmission efficiency, but their applications and designs vary significantly. Understanding the key difference between a diplexer and a duplexer is essential for selecting the right component in wireless communication setups.

This article delves into their functionality, structure, and use cases, providing a clear comparison to help you distinguish between the two.

Diplexer Definition

A diplexer separates two different frequency bands in the receive path and combines them in the transmit path. These frequency bands are usually wide apart in the frequency domain for a diplexer to work satisfactorily. It’s often referred to as an RF power combiner/divider with the added functionality of filtering. Broadband filters are used to pass appropriate bands at the Tx and Rx paths.

Example of Diplexer:

A diplexer is used to separate/combine frequency bands of GSM900 and DCS 1800 systems. It is also used in the multiband design of mobile handsets with multiple technologies like GSM, CDMA, and LTE.

As shown in the figure, a diplexer multiplexes and demultiplexes wide frequency bands with an appropriate difference. The figure shows L and H bands at the S port.

RF diplexer

As shown in the figure, there are two RF ports in a diplexer other than the output port. A triplexer will have 3 ports other than one output port.

Duplexer Definition

A duplexer allows the use of a single antenna by both the transmitter and receiver parts of a single device or two devices. In other words, a duplexer couples the transmitter and receiver to the antenna while producing isolation between the transmitter and receiver. There are two types of duplexers: one using PIN diode switches and the other using circulators.

Both transmit and receive paths usually have frequency bands very near each other, hence narrowband filters are used to separate these frequencies. A duplexer is often referred to as a 3-port RF circulator. Duplexers are of two types: using PIN diode switches and using circulators.

RF duplexer

Example of Duplexer:

It separates uplink (890-915MHz, Uplink-UL) and downlink (935-960MHz, Downlink-DL) frequency bands in the GSM900 system.

Difference between Diplexer and Duplexer

Let us summarize and compare diplexers vs. duplexers:

A diplexer is a three-port passive device that permits sharing of a common channel between two devices operating in different bands. As mentioned above, both GSM900 and DCS1800 can make use of a single communication path and antenna using different frequency bands. Two separate filters help them perform this task.
A duplexer is also a three-port device that permits sharing of a single antenna by two systems operating in very near bands. As mentioned above, both uplink and downlink bands of a single device are being separated by a duplexer using a circulator-like structure.

These terms are not interchangeable. They are designed for very different purposes.

The following table highlights the difference between diplexers and duplexers.

Specifications	Diplexer	Duplexer
What is it?	It consists of a set of filters which allows separate processing of signals with widely differing frequencies. It separates two different bands in the receive path and combines them in the transmit path.	It consists of two filters (of bandpass type) which allows simultaneous transmission and reception within the same band and using the same antenna.
Direction of operation	It usually operates with signals flowing in the same direction.	It usually operates with signals flowing both ways at the antenna.
Separation of bands	Operates on wide apart frequency bands	Frequency bands of Tx and Rx path are very nearer
Tx-Rx Isolation	50 to 60 dB	90 to 95 dB
Examples/Applications	Smart phones use LC diplexers, other examples of diplexers are antenna splitters, DSL splitters, speaker crossover networks	Smart phones use SAW duplexers

Conclusion

In summary, diplexers and duplexers play unique roles in RF systems by enabling efficient frequency management and simultaneous signal transmission. A diplexer separates or combines different frequency bands, while a duplexer enables simultaneous transmission and reception on the same antenna by isolating the transmit and receive paths. Choosing between a diplexer and a duplexer depends on the specific requirements of the RF system, such as the need for frequency separation or simultaneous two-way communication. Understanding these differences ensures optimal performance and reduced interference in wireless communication networks.

Diplexer and Duplexer Manufacturers

Diplexer, duplexer, and triplexer devices are widely used for test and measurement of wireless modules compliant with standards such as WLAN, WiMAX, GSM, CDMA, and LTE, etc.

The following are popular manufacturers of diplexer and duplexer devices: