A diplexer is a passive (RF) filter component with three ports, which enables the sharing of a common antenna between two distinct frequency bands. This technology allows transmitters operating on different frequencies to use the same antenna and each band may both transmit and/or receive.
For all multiplexer devices there are two input ports that are multiplexed onto a third port. This allows the signals from the two input ports coexist on the output port without interfering with each other.
A diplexer consists of a three-port RF filter component used in a multiband system. This system has a common antenna that allows the transmission of two frequency bands; each band itself may receive and transmit signals. These signals can use the same common antenna. The job of the diplexer is to sort the signals based on their distinct frequencies.
Within the diplexer, there is a transmitter port to send out signals, a receiver port to gather signals, and an antenna port. The diplexer also has two filters. One of the filters will be attached to the transmitter port, and the other filter will be attached to the receiver port. The third port is simply used as a connection point between the two available filters as well as the antenna. The basic function of the diplexer is to isolate frequencies and send them to the correct port so that a specific function can take place in the rest of the system's application. It also prevents undesired frequencies from passing through the filters.
The two RF filters will accept and reject signals based on their frequencies, or there may be a filter present that will search for a specific frequency so that a certain function can be performed by the application. These filters are called lowpass filters, high pass filters, and bandpass filters.
Technology Design Requirements of RF Diplexers
There are a range of standard technologies that are placed within the RF diplexer so that it provides the desired functions without limiting the desired frequencies that need to be transmitted and received. These technologies consist of wavelength diplexer topologies, planar diplexer topologies, lumped elements, and ceramic chips.
Waveguide Diplexer Topology
One technology is a waveguide diplexer, which has two bandpass filters as well as a circulator. These diplexers offer high quality with low insertion losses. Its power handling capabilities are very high, and it doesn't need to be tuned. They also provide more selectivity.
One thing to take note about when designing a waveguide diplexer is that they can have specific large weight and can be difficult to reproduce, as this can impact the application systems when designing the telecommunications or radar equipment. These types of diplexers also cost more, which could be cost-prohibitive based on the designed system components. There may also be integrability difficulties experienced with this type of design topology.
Planar diplexers are smaller in size than a waveguide diplexer. These topologies provide excellent integrability into system components and come in smaller sizes, which is ideal for more lightweight systems and applications. They are also lower in cost than waveguide diplexers and can be duplicated effectively.
Some of the issues that comes with a planar diplexer topology is that it has much lower power handling capabilities. In addition, the quality factor is usually lower for planar diplexers.
Diplexer RF Capabilities
|Nominal F||Channel||Frequency||Insertion Loss||Rejection||PB Return||Power|
|GHz||GHz||Loss dB||GHz||dB||Loss dB||W|
|2 - 6 - 18||J0||2.0 - 18.0||<10.88||20|
|J1||2.0 - 5.7||<1.0||6.9 - 18.0||>60|
|J2||6.3 - 18.0||<1.0||DC - 5.1||>60|
|J1 / J2||6.0 +/- 60 MHz||<5.0|
|2 - 8 - 18||J0||2.0 - 18.0||<10.88||20|
|J1||2.0 - 7.6||<1.0||9.2 - 18.0||>60|
|J2||8.4 - 18.0||<1.0||DC - 6.8||>60|
|J1 / J2||8.0 +/- 80 MHz||<5.0|
|2 - 12 - 18||J0||2.0 - 18.0||<10.88||20|
|J1||2.0 - 11.4||<1.0||13.8 - 18.0||>60|
|J2||12.6 - 18.0||<1.0||DC - 10.2||>60|
|J1 / J2||12.0 +/- 100 MHz||<5.0|
|2 - 4 - 8||J0||2.0 - 8.0||<10.88||20|
|J1||2.0 - 3.8||<1.0||4.6 - 8.0||>60|
|J2||4.2 - 8.0||<1.0||DC - 3.4||>60|
|J1 / J2||4.0 +/- 40 MHz||<5.0|
|0.1 - 0.7 - 7.5||J0||0.1 - 7.5||<13.74||50|
|J1||0.1 - 0.6||<0.8||0.8 - 7.5||>40|
|J2||0.8 - 7.5||<0.8||0.1 - 0.6||>40|
|0.44 - 0.448 - 0.46||J1||0.44 - 0.444||<1.5||0.456 - 0.46||>40||<12.73||20|
|J2||0.453 - 0.46||<1.5||0.44 - 0.442||>40||<12.73||20|
|0.02 - 0.1 - 2.5||J0||0.25 - 2.5||<13.74||100|
|J1||0.02 - 0.088||<1.0||0.11 - 2.5||>40|
|J2||0.105 - 2.5||<1.0||0.02 - 0.0085||>40|
|0.6 - 2.6 - 6||J0||0.6 - 6.0||<10.88||20|
|J1||0.6 - 2.5||<1.0||3.0 - 6.0||>40|
|2.7 - 6.0||<1.0||0.6 - 2.2||>40|
Using a Custom Diplexer for the Specific Application
A diplexer used in aerospace communications and military radar operations requires it to be designed to handle the changing technologies that are being introduced in these industries. As more frequency signals are being used, the diplexer must be able to handle the transmitted and received frequencies to sort them out based on the decibel level. A failure to do so can lead to either too much frequency rejection or acceptance rates that will render the system application incapable of performing its job efficiently for aerospace and aviation equipment.
In the case of military radar and jamming applications, the diplexers will have multiple functions. They will be used to detect enemy systems in the region based on the detected signal, as well as prevent certain military frequency signals from being detected by enemy forces using jamming techniques. These custom diplexers can help keep military operations secretive as well as protect armed forces when engaged in battle.
There are many things to keep in mind when needing a diplexer to perform a specific application while still meeting manufacturing costs. When considering a diplexer, the amount of signal rejection, acceptance, and isolation rates must be considered. The performance of the diplexer can be customized so that its only function is to receive signals, as a lower performance diplexer will be used in this instance. On the other end of the spectrum, and for many applications involved in aerospace and military industries, higher performance diplexers will be the standard requirement where the diplexer must both receive and transmit signals simultaneously as there needs to be two ports that are present.