RF frontend technology beyond 5G

5G is well known by the use of massive MIMO radios, capable to achieve not only a coverage gain by beamforming, but also a capacity gain by spatial division multiplexing. Phased array systems, the dominant solution for 5G high frequencies, are capable of the former but not the latter. Contrary to common belief, the distinction between a phased array and a massive MIMO radio is not just about the difference between analogue and digital beamforming. It requires fundamental redefinition of RF front-end characteristics. For example, load sensitivity of a power amplifier in a phased array can be characterized by various loading conditions on a Smith chart. How does it look like in a massive MIMO radio, when it transmits multiple uncorrelated beams simultaneously? This talk discusses a few critical technical challenges in RF frontends, beyond 5G systems, and beyond the commonly known challenges such as frequency, power and integration complexity.