The rapid growth in the field of cellular/mobile communication frequency range, especially in large metropolitan areas has created interference problem requiring special techniques and hardware to deal with it. The Duplexer is useful in such situations. Without Duplexer separate transmit and receive antennas would have to be spaced far enough apart to provide the isolation required between Tx. and Rx. In mobile application providing separate antennas is impractical and hence, Duplexer can be useful in such cases. Duplexer is basically a two channel combining system which allows tuned frequency of either one of the two channel to pass to antenna or vice versa, while offering a specified isolation to other channel. For application requiring high selectivity and low insertion loss, high 'Q' cavities can also be used in specific applications.

AMPL Duplexer series of filters allow simultaneous Tx./Rx. operation to a single common antenna port. The cost and construction of Duplexers varies with the transmit-receive frequency separation (offset) required, power handling capability and ambient RF environmental constraints. For applications in which the offsets are relatively wide, duplexers can be constructed using band pass cavities. This helps in unwanted signal rejection at all frequencies outside intended pass bands, not just duplexer's own transmit frequency. Where the frequency offsets are closer, pass reject cavities are used. It offers benefits of high isolation and low insertion loss but the duplexer generally lacks attenuation at frequencies other than transmit and receive frequencies specified. Some cases both type of cavities may be cascaded for greater duplexer isolation. AMPL Duplexers incorporate materials of similar expansion constants and are made of extruded Aluminium cavities. The temperature cycling assures that Duplexers remain temperature stable. AMPL Duplexers maintain their electrical characteristics over the temperature range -10º to +55ºC. AMPL Duplexers are designed to meet all customer specifications in terms of Electrical and Mechanical parameters. Typical examples are as given in table.