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RF Diplexer vs Triplexer vs Duplexer – What are their Functions and Applications?

Diplexer, triplexer, and duplexer are devices that are commonly used in wireless communication systems and the radar. However, these devices operate differently. For so long, their meanings have been mistaken. This article seeks to distinguish the differences between RF diplexer vs triplexer vs duplexer.

What is an RF Diplexer?

This is a three-port frequency-dependent device that combines or separates signals. A Diplexer is considered a combiner or separator of signals.  It comprises two different fixed tuned bandpass filters with a common port. The diplexer has three terminals which are formed by the output of the two filters (RX and TX).

The passband frequencies of the filter’s determine how the signals used in the common port separates. Also, the signals used in any uncommon port isolates from the uncommon port. These signals then combine at the common port. Diplexers are a type of multiplexer.

On the other hand, duplexers enable a transmitter and receiver operating on different frequencies to share an antenna with less interaction and degradation of various RF signals. A diplexer consists of an antenna port, transmitter port, and a receiver port. This device is commonly used in applications where several modulation methods and carriers function on the same antenna.

In telecommunication systems, an RF diplexer plays a crucial role. For instance, cellular base stations may have limited tower space to accommodate more antennas. Therefore, an RF diplexer can be used in this case.

When choosing a diplexer for an application, there are some things one needs to consider. The specifications of an application determine a lot. The isolation rates, the amount of signal acceptance and rejection are key factors one should consider.

What are the Features of the RF Diplexer?


An RF diplexer comes with a three-port RF filter component which is usually used in multi-band systems. Multi-band systems have an antenna that enables two frequency bands to transmit. Each of these bands can receive and transfer signals. One of the major roles of a Diplexer is to share signals according to their distinct frequencies.

The diplexer has a receiver port that get signals, a transmitter port that transfers signals and an antenna port. Also, there are two filters in a Diplexer. The transmitter port uses one of the filter’s while the other filter is used by the receiver port. The antenna port serves as a point of connection between the two filters and the antenna.

The RF diplexer isolates frequencies and carries them to the appropriate port. It as well prevents unwanted frequencies from going through the two filters. These filters can check the frequencies of signals to reject or accept them. Alternatively, a filter may be available to look for a particular frequency to enable the application to perform a certain function.

It is very possible to customize a diplexer to carry out one specific function. You can customize your diplexer to receive signals only. In this case, a lower performance diplexer is needed. Higher performance diplexers are usually needed for applications like military and aerospace. This type of diplexer will be a perfect option for use in applications that need to transmit and receive signals at the same time. To achieve this, two ports need to be available. 

What are the Design Requirements of RF Diplexers?

For the RF diplexer to offer the necessary functions without restricting the frequencies that should be received and transmitted, it is important to place standard technologies within the diplexer. These technologies include ceramic chips, wavelength diplexer topologies, lumped elements, and planar diplexer topologies. Let’s have a look at some of these technologies.

Planar diplexer

Planar diplexers are very small. These technologies offer great integrability into system components. Due to their smaller sizes, diplexers are much more ideal for more lightweight applications. Also, it is very easy to duplicate planar diplexers and the cost of this device is usually very low.

However, planar diplexer topology has its own issues. One of these issues is that it has lower power handling capabilities compared to waveguide diplexer topology.  Furthermore, planar diplexers have a lower quality factor.

Waveguide Diplexer

The waveguide diplexer is another technology. It features two different bandpass filters and a circulator. One of the benefits of these diplexers is their low insertion losses. Also, they offer high power handling capabilities which need no tuning. Furthermore, they are more selective.

A waveguide diplexer has a big size and as such can be very complex to reproduce. This can be a major concern when designing radar or telecommunication devices. Furthermore, the waveguide diplexer is more expensive. This design type may also experience integrability problems.

What is a Triplexer?


A triplexer is also a type of RF multiplexer. Its functions and operations differ from a Diplexer and duplexer. A 4-port filtering device that divides one major input in three various outputs with a different frequency is a triplexer. This means that a triplexer features three one output port and three input ports.

A triplexer can also be used in a reverse manner. That means it can route signals at three frequencies into one port. With a triplexer, a coaxial cable can easily get into the feed of three different antennas.

This 4-port filter device is bidirectional and it comprises 3 bandpass filters having three separate passband frequencies. You can find a triplexer in wireless transmitter and receiver systems like radar.

A multi-band wireless system with three channels for GPS, WLAN, and GSM/CDMA can make use of a triplexer. One antenna can get the signal and then route different signals to different port. In this manner, a broadband antenna can easily receive three different signals. The isolation of signal between the three ports is a crucial factor to evaluate when choosing a triplexer.

The use of passive techniques in triplexers helps to save cost and as well reduce size. A triplexer provides reduced insertion loss over each path. Also, it provides return loss at all output and input ports. A triplexer finds its use in triple-band devices for smartphones.

What is an RF Duplexer?

An RF duplexer is different from an RF duplexer. The duplexer uses the antenna in a communication system for transmitting and receiving signals. It is a three-port device that acts as a circulator for low-power applications. Also, an RF duplexer enables the transmission bi-directional signal over a single path.

One of the functions of duplexers is that they enable radar communications to share the same antenna while keeping the receiver away from the transmitter. RF duplexer isolates the receiver from the transmitter in order to provide two-way communication over one channel. The path between the receiver and transmitter is not a direct one. Therefore, a duplexer is often considered a circulator. This means that the signal coming from port 1 goes to port 2 while the signal coming from port 2 routes to port 3. In this case, port 1 and port 3 do not meet.

Applications of Duplexer

There are many use cases of duplexers, especially in the RF communication systems. Here are some applications of RF duplexer:


Duplexing entails combining several RF signals in the frequency domain. This involves putting an ideal duplexer that has a high isolation filter circuitry between the antenna and Tx/Rx RF chain.

De-multiplexing occurs when you separate the combined signals into several RF signals.

Receiver protector

When RF signals are transmitting, a duplexer offers isolation between the receiver and the transmitter. Also, the duplexer prevents the reflected signal from going back to the tranitter. Engineers make use of  PIN diode limiters in front of the receiver in order  to protect the receiver.

Radio communications

Duplexers play a major role in radio communication systems. They transmit various frequency signals having close bands difference in opposite directions.

Radio Repeaters

In RF communication, a good number of radio repeaters make use of a single antenna and duplexers for the transmission and reception of RF and microwave signals.

Radar antenna multiplexing

One of the functions of duplexers is that it links an antenna to many radar systems to enable signal transmission and reception. In the long run, this helps in minimizing the space and cost required for multiple radars.

Another important use of an RF duplexer is that it offers protection to the receiver. It prevents high power transmissions from wireless transmitters that are close by.

Difference Between Diplexers and Duplexers

Most times people usually confuse the functions of these two devices. RF duplexers and diplexers are common components you will find in transceiver circuits, receiver, and transmitters for applications like radar and communication systems. Also, other sensing applications make use of RF diplexers and duplexers. Since diplexers sound similar to duplexers, people often interchange them.

Therefore, it is better to clarify the differences between these two components and how they function. The function of an RF diplexer is different from that of a duplexer. Let’s look at the differences in the way these components operate.

A diplexer allows two signal paths to be used on the same transmission line. This 3-port device achieves this by using filters to divide frequency, The filters may be band-pass filters, high pass or low pass filters. With this, it is possible for the same antenna to send and receive two different frequencies. There are factors that determine how a diplexer functions. For instance, the attenuation of the filters must work well with the closeness of the signals.

An RF duplexer is also a 3-port RF device. However, its major role is to share transmitted and received signals from one antenna into two signal paths. This is usually done according to the direction of the signal. A duplexer ensures two-way communication from one antenna since these signals may operate at the same frequency.

One of the use cases of a duplexer is in the radar system. In this application, there is a need to isolate high power transmitter signals from receiver circuitry. However, an RF duplexer has some limitations in how the receive path can be isolated from the transmit path.

What is the Difference between an RF Diplexer vs Triplexer vs Duplexer?

RF Duplexer
RF Duplexer

An RF duplexer considers the signal direction to separate a receive path and a transmit path while a diplexer considers frequency with filters to separate signals. The operations of these two devices are not interchangeable. Therefore, an RF diplexer can’t replace a duplexer. While duplexers are more commonly used in telecommunication systems, diplexers also play a key role in this application.

An RF triplexer is a four-port device with one output port and three input ports. This device is widely applicable in wireless communication systems. A diplexer vs triplexer vs duplexer are a type of RF multiplexer. However, they all differ in terms of their operations and applications. A Triplexer makes use of the passive techniques to reduce size. Also, this device provides ideal isolation when used between ports.

While RF triplexers have one output port and three input ports, RF diplexers have one output port and two input ports.  Also, an RF triplexer is a combinator and a separator. This device separates and combines signals of three frequency bands. In the radar system, a duplexer functions as a connection point between the receiver and transmitter and the antenna.

One of the main benefits of a duplexer is that it can use one antenna to receive and transmit signals. For instance, a duplexer is a great choice when there is one receiver and one transmitter in single channel systems. A triplexer is a better option for multi-channel systems with many receive and transmit channels.

What are the Similarities between RF Diplexer vs Triplexer vs Duplexer?

RF triplexers and diplexers are both RF components that can divide received signals at various frequencies in three or two channels. Also, these components are ideal for combining about three or two signals on the same line.

Triplexers and diplexers are commonly used in applications where there is a need to route signal at several frequencies via various paths. The main similarities between RF diplexer vs triplexer vs duplexer is that they are all RF components.


Diplexers, triplexers, and duplexers are all RF components. These components differ in their functions, mode of operation, and applications. However, people interchange the meaning of these components. Having compared RF diplexer vs triplexer vs duplexer, it is easy to differentiate the functions of these devices.




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