Senin, 04 Juli 2011

Antenna diplexer

Antenna diplexer
A brief overview, a tutorial on the basics of antenna or RF diplexer diplexer used for purposes including enabling a single RF antenna for use by several transmitters .

An antenna or RF diplexer diplexer is a unit in a single application can be used to allow more than one transmitter to operate on a single RF antenna. Sometimes these units can be called antenna duplexers. Typically an antenna diplexer will allow the transmitter to a different frequency operation using the same antenna. In other applications, an antenna diplexer can be used to allow a single antenna to be used for transmission on one frequency band and receiving on other bands.

Antenna diplexers find many uses. In one common example of an antenna or RF diplexer diplexer used in cellular base station to allow it to send and receive simultaneously. The diplexer antenna allows the system to use the same antenna while preventing the transmitted signal from reaching the receiver and the input block. In other applications diplexer may be used by broadcast stations transmitting at different frequencies at the same time using the same antenna. Use of diplexer allows a single antenna to be used, while preventing the output of a transmitter which fed back into the other output.

Diplexers small antennas can be used in a domestic environment to enable multiple signals to run along a single feeder. In one application may allow a single feeder to be used for television and VHF FM radio reception, or to allow television signals from terrestrial and satellite voice box low (LNB) to pass on the same lead. This RF diplexers are usually relatively low cost as not nearly as demanding specifications that are used for professional installation of the RF diplexer.

Basic concept of antenna diplexer

There are a number of ways to implement the RF diplexers. They all involve the use of filters. In this way the path to a different transmitter and receiver can be separated according to the frequency they use. The easiest way to implement the diplexer is to use low pass and high pass filter despite the band-pass filter can be used. In this way diplexer routes all signals at frequencies below the cut-off frequency of low pass filter to one port, and all signals above the cut-off frequency high pass filter to another port. Also here are the street from between two long-distance from the filter. All the signals that can pass through low pass filter in the diplexer will not be able to pass through a high pass filter and vice versa.

A further feature of the RF diplexer instead of allowing the impedance seen by the receiver or transmitter to remain constant, although the load is connected to another port. If the filter is not present and the three cable ports in parallel, both the antenna and the two transmitter / receiver will see the correct impedance port.

Filter RF diplexer requirements

When designing an antenna diplexer number of parameters should be considered. One is the level of isolation required between the port for high and low frequency transmitter / receiver. If the diplexer must be used purely to receive, then the need for high levels of insulation is not so high. Even the filter provides a relatively simple isolation sufficient to ensure that each recipient sees the proper impedance and input signals are routed to the right without losing sight. Even the level of 10 dB of isolation would be sufficient for many installations. For diplexers are used to divide and combine TV and VHF FM radio with a single line, te level of isolation may be very low.

The next case is when the diplexer that will be used for transmission only. It will be necessary to ensure that the level of power transferred back to the second transmitter is small. Power is fed to the output of the transmitter in this way can cause intermodulation products that may radiate and cause interference. It is also important to ensure that the transmitter to see the true impedance, and that the presence of a second transmitter does not affect the impedance seen by the first. Usually the level of isolation between the transmitter port 60-90 dB may be required.

The last case is where one of the ports used for transmission, and the other for receiving simultaneously. In this case a very high level of insulation needed to ensure that a minimum level of transmitter power reaches the receiver. If high levels of the signal transmitter reaches the receiver, it will be desensitised prevent proper reception of the signal needed. Levels over 100 dB isolation is usually required for this application.

Band pass filter

In some cases the band pass filter can be used. It can be used where a relatively narrow bandwidth required for one or both of the transmitter / receiver port. Sometimes a resonant circuit which is very high T can be used. Using this approach a high degree of rejection can be achieved. Often repeater stations that receive and transmit on one channel on another simultaneously using diplexers which utilizes this approach.


Although the antenna diplexers mainly used in specialized applications, which enables a single RF antenna for use by more than one transmitter or receiver, they remain an essential element of many installations. For example, cellular technology will be much different if they can not be used and the RF antennas for cellular base stations will be much more complicated. Similarly, antenna diplexers are used in many broadcast applications allow a single large RF antenna for use by more than one transmitter.

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