Many RF applications require signal distribution / collection that interconnects over substantial distances using wide bandwidth. Examples of such systems include antenna arrays and signal distribution networks. The main applications are the emerging 5G where bandwidths above 6 GHz are required.
Where bandwidths are low, digital distribution is king, as the signal information content can be maintained over long distances without degradation other than from the original sampling quantization errors. However, when the bandwidth requirement is increased, sampling ADC converters may become impractical for a number of reasons including: limitations of the sample rate, power consumption, and dynamic range.
RF distribution can fill the requirement for such distribution networks with high bandwidths. When signal bandwidths are in the range of 6 GHz (which is used for 5G networks) applications. Sophisticated and complex up-and-down frequency conversion solutions are possible with low loss coaxial lines serving to transport the signals. However, frequency conversion becomes less practical and even impossible for some applications which require massive MIMO antenna arrays, long-distance signal transport, and even wider bandwidths.
RF solutions becomes very difficult to design and implement when there are many distribution points. In some cases, it is simply the sheer weight and girth of all those coax cables that becomes unmanageable. In other cases, frequency conversion adds too many side effects as to preclude the approach altogether. To illustrate: many scientific observatories, 5G and 6G tower infrastructure, ELINT and surveillance systems, multi-use target simulators as well as test ranges cannot use frequency conversion solutions.