Facts and illusions with broadband amplifiers for common antenna working

In any broadband system it is likely that a signal transmitted on an adjacent antenna will also appear at the output electrode of an active device in the amplifier. In this situation, either large intermodulation products are produced, or further derating of the amplifier is required. The author formulates this problem. Two possible systems are considered. In a power bank system a common amplifier is used for amplification of all signals. The amplifier must not only be designed for very good linearity, but must also be suitably derated in order to limit generation of intermodulation products. This system is most flexible in operation. An alternative way of common antenna working is to combine a number of broadband, but single frequency amplifiers by means of a type of balanced transformers called hybrids. There is a 3dB power loss each time a signal passes through a hybrid. This lossy combining system is no longer operationally flexible