Intermodulation beam spreading in distributed communication systems

In an active multiple-beam distributed communication system, a number of power amplifiers are shared between the different beams, creating the condition of multi-tone operation of the amplifiers. Although the amplifiers are backed up to operate close to the linear region, efficiency considerations require operation in somewhat non-linear region of the input/output curve. The non-linearity results in the creation of undesirable intermodulation components within transmit and receive bands of the communication channels. The coherent radiation of the intermodulation components follow certain beam patterns with special distributions that are different from the main beams in the system. This paper discusses the formation of the intermodulation beams and their spread over the coverage area. The special spread is such that the interferences caused by the intermodulation products occur at reduces values and contribute minimally to the reduction in the system signal to over-all noise and interference ratio. Analysis and measurements are presented and show agreements in predicting the locations and levels of the intermodulation beams.