It’s generally agreed that hybrid beamforming, will be the architecture of choice for 5G systems operating at microwave and millimeter wave frequencies. In this architecture, a combination of digital (MIMO) and analog beamforming is employed, to overcome the high path loss and improve the spectral efficiency. A combination of m data streams are split into n RF paths, to form beams in free space, making the total number of antenna elements a product of m × n. The digital streams may be combined in a number of fashions, whether to direct all energy at a single user with high layer MIMO, or to support several users with multiuser MIMO.
In this article, we will work through a simple example of a large-scale antenna array, to examine the optimum technology choice for the millimeter wave radio. Now, drilling into the block diagram of the radio section of the millimeter wave system, we see a classic heterodyne structure connected to a multiplicity of RF paths. In these paths, we employ phase shifters and attenuators to shape the beam.
