An RF and Microwave Duplexer is a three-port device that is used to transmit and receive RF signals using the same antenna in a communications system. The Duplexer function like a circulator for low-power applications. A few of the important properties of a Duplexer are:
In this article about RF and Microwave Duplexer, we will cover the following.
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An RF duplexer is a device that allows bi-directional signal transmission over a single path. In radio or Radar communications systems, duplexers permit them to share a common antenna while isolating the receiver from the transmitter.
RF and microwave Duplexer can be designed using lumped components or with micro-strips materials.
In this design, passive components like resistors, capacitors, and Inductors are used for the construction of the band, low, high pass filters, which are part of the diplexer. The duplexer is constructed using two bandpass filters having different band responses but the same characteristics for the receive and transmit path. Filter design concepts like Chebyshev can be used for better isolation between the Tx and Rx paths of the basic circuits.
Microstrip duplexers are designed in a similar way, a RF circulator is designed using the microstrip material. Various design topologies are available for the design and the specification of the duplexers are based on the following substrate specification used in the design.
The frequency of operation and rejection between the Tx and RX path is based on the above specifications and the strength of the magnetic material used for the circulation of the RF signal inside the duplexer. The length of the transmission line to the T-junction of the duplexer can be tuned to obtain the desired RF response.
An RF Duplexer consists of two paths of bandpass filters connected in parallel to a common port. One BPF provides the TX path connecting the transmitter and the antenna, the other provides an RF path connecting between the antenna and the receiver. In a duplexer, there is no direct path exist available between the transmitter and receiver.
Usage of an RF duplexer in an RF circuit has its own advantage and disadvantages as its effect the specification of the entire system.
RF duplexer helps to use the same antenna to transmit and receive the RF signal without interfering with each other. This helps to save space on towers as only a single antenna is used for the Tx & Rx applications.
Due to the insertion loss of the duplexer, the noise figure of the receiver chain may increase which will affect the signal quality. For a better signal, communication system users need to use of receiver with higher sensitivity.
RF duplexer can be calcified mainly as two types
It will work like notch filters in Tx and Rx path with sharp notches for the unwanted frequencies and passes a narrow band of wanted frequencies.
Bandpass duplexers have wide-pass frequency ranges both in Tx and RX path and offer high unwanted band attenuation.
An RF Diplexer is a 3-port passive device consisting of two filters at different frequencies connected to a single communication device, which allows two different devices to share a common channel. Filters like low pass, high pass, or the bandpass can be used for the construction of the diplexers.
An RF Duplexer is a 3-port device that allows two-way communication over a single channel by isolating the transmit chain to the receiver chain by using the control switch. Duplexer allows users to share the same antenna while operating at the nearby or same frequencies. In RF duplexer there is no common path between the receiver and transmitter I.e Port 1 and Port 3 are completely isolated from each other.
RF duplexers have many applications in the RF communication systems as follows.
The process of combining multiple RF signals in the frequency domain often called duplexing, this is done by placing a suitable duplexer with high isolation filter circuitry between the Tx/Rx RF chain and antenna. The process of separating the combined signals into multiple RF signals is called De-multiplexing. A duplexer allows signals from the antenna port to de-multiplex and flow to the respective chains.
In radio communications systems duplexer helps to transfer the different frequency signals with close bands difference over the shared channel in opposite directions.
Duplexer help to connect one antenna to multiple radar systems to transmit and receive signals. This will help to reduce the cost and space needed for multiple large antennas for the multiple radars by sharing the antenna.
Most communication radio repeaters use duplexers and a single antenna to receive and transmit the RF and microwave signals.
Duplexer provides enough isolation between the transmitter and the receiver during the transmitting of the RF signals. The duplexer also avoids the reception of the reflected signal back to the transmitter. For the better protection of the receiver, PIN diode limiters are used in front of the receiver chain after the duplexer.
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There are many parameters like band 1 & 2 frequency, isolation between the bands, power handling need to choose properly for selecting the suitable duplexer for the communication applications. Below are the prime factors which need to consider.
For selecting the suitable duplexer frequency of operation of the lower ( band 1) and higher band (band 2) need to select carefully. It is important to select one which covers perfectly both the bands of the operations to avoid the passing of signal one to another.
For RF signal transmission through the duplexer, it is ideal to select a duplexer that offers higher isolation between the transmitter and the receiver path. If the isolation is the higher signals with even close frequency bands can transmit over the duplexer in opposite direction without interfering with each other.
Power handling for both the Tx and Rx ports should be higher than the expected power flow through it. Different range of power handling capable duplexers is available from different manufactures. Users need to select an RF duplexer as per the design requirement of the system.
Insertion loss created by the duplexer in the chain is one of the prime drawbacks of inserting the duplexer in the RF chain. Designers need to select an RF duplexer with lower insertion loss meeting the frequency bands requirement.
Designers need to select a duplexer that can offer higher return loss, which will help to avoid the RF reflected signal reaching back to the system.
There are 50 ohm and 75-ohm duplexers are available from different manufacturers in the market. The user needs to select a suitable duplexer that matches the source and load impedance to avoid any internal reflection, which may cause to increase in the signal-to-noise ratio in the chain and it causes a reduction in the signal quality.
RF .duplexers are available with different connectors like SMA, N-type, 3.92 connector type, etc with Male and Female connector options from different manufacturers. Designers can select a duplexer with a suitable connector option on the basis of the frequency of operation and the power handling requirement of the system.
An RF diplexer is a passive device that enables to sharing of an antenna between two distinct near frequency bands. Duplexer helps the transmitters and receivers operating on different frequencies to use the common antenna for transmitting and receiving the RF signal.
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