Insights into the Near-Field Characteristics of mm-wave Massive MIMO Arrays using EM Lagrangian Density and Poynting Vector

In this paper, we use the concept of EM Lagrangian density and Poynting vector magnitude to probe into the near-field region of MMIMO (massive MIMO) antenna arrays and reveal interesting insights. Adopting an IDM (infinitesimal dipole model) based methodology, we evaluate the spatial distribution of normalized EM Lagrangian density and Poynting vector magnitude around a MMIMO array modelled as URA (uniform rectangular array) of electrically small dipoles. The use of IDM ensures the effects of element polarization and radiation pattern are taken into account (unlike the isotropic source based modelling), while the computational complexity associated with full-wave analysis of MMIMO arrays is substantially reduced. The numerical results show that the spatial maps of normalized EM Lagrangian density can provide an useful phase-less alternative for identifying the transition from reactive to radiating NF region of MMIMO arrays. The EM Lagrangian density and Poynting vector magnitude plots further highlight the redistribution of high reactive energy density regions around MMIMO arrays, and illustrate crucial aspects like NF beam-depth.