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A duplexer is an essential component in modern gadgets using radio communications. It permits duplex communications, which allows bidirectional transmission on a single path. There are many different types of duplexers. An example of a duplexer based on frequency is a wavelength filter, while a duplex based on polarization is an orthomode transducer. In radars, a duplexer based on timing is used. Put simply, when a transmitter and a receiver use the same antenna for communications, an electrical switch is used. This electronic switching system is known as a duplexer. Without a duplexer, signal and frequency interference between the transmitted frequency and the received frequency can damage the receiver.
A duplexer is very important for radio apparatus as it allows the switching of the pathway of the signals toward either the transmitter or the receiver. A duplexer a special type of electronic switch which can open or close very quickly based on the type of signals it handles. In transceiver systems like radars, the transmitter and the receiver often share the same circuitry and components, including the same antenna. If the transmitter and the receiver use the antenna at the same frequency, then the signal interference can almost immediately damage the receiver's components. This is highly undesirable, and so a system had to be developed which would allow the switching between transmitting or receiving modes in the short spans of time between transmitting and receiving. An easy solution for this is a switch that can transfer the signals and switch the pathways quickly with respect to specific transmitted and echo pulses. However, it is not possible for simple mechanical switches to operate so quickly, so electrical switches known as duplexers must be used.