Abstract: We provide a fully integrated treatment of communication and electromagnetic theories, where the physics of electromagnetic fields when viewed as spacetime processes is directly linked to signal processing, information, and energy transfer in wireless links. Utilizing general and powerful theoretical tools developed in recent researches, such as the antenna current Green's function, energy localization in spacetime, the cross-correlation Green's functions, the infinitesimal dipole model (IDM) techniques in machine learning, and electromagnetic neural networks, we explicate how information capacity, correlation, and energy transfer are influenced by taking into account the full physical content of EM fields as spacetime signals in concrete applications, including spectral efficiency enhancement, diversity gain optimization, engineering MIMO channels using metasurfaces, mutual coupling and dispersion management in large and complex arrays. Various case studies in massive MIMO, 5G, and Future Antennas are introduced to illustrate the main advantages and novel new applications in a pedagogically illuminating manner.
