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Active Radial Transmission Lines as Phased Arrays for Massive MIMO

Two-dimensional active periodic structures arranged to act as radial transmission lines are shown to function as electronically steerable phased arrays. They can be involved in producing multiple narrow radiation beams for massive MIMO. In order to investigate the electromagnetic principles underlying their operation, the presented analysis deals with the limiting case, where the periodic cell size tends to zero, giving rise to a continuous cell distribution. Practical implementations of such structures may use sub-wavelength cell sizes resulting in a considerable reduction of the array dimensions. A possible candidate for the realization of the periodic cells is the well-known microstrip mushroom structure, which has been commonly used in conjunction with the so-called “metamaterials”. Selected simulation results are presented to validate the theoretical analysis.