We present a dual-polarized connected array of slots with an artificial dielectric layer (ADL) radome for mobile communication applications operating in the sub-6 GHz and the upper 6 GHz bands of 5G. The radiating slots are combined with two interchangeable ADL radomes with different thicknesses, targeting the bands 6-8 and 2-8 GHz, respectively. This highlights the main property of the ADL radome, which realizes an impedance transformer whose bandwidth is proportional to the height of the structure. Moreover, the ADL anisotropy allows for wide scanning, up to 60° in the main planes for both radomes, without scan blindness. An $8\,\, \times \,\, 8$ prototype array has been manufactured and tested with the two ADL radomes. The measured results of the active voltage standing wave ratio (VSWR) and the radiation patterns are reported to validate the design.

We present a study on beam coupling in radiating structures that support multiple simultaneous beams. The formation of multiple beams is relevant in modern wireless communication applications when diverse data streams can be sent from a single transmitter to users located in different directions. General expressions are provided that relate the coupling between radiated beams to the associated current distributions on the radiating aperture. When expanding the currents in terms of basis functions, the beam coupling can be also written in terms of coupling contributions due to each pair of basis functions. The analysis is applied to antenna arrays with different levels of mutual coupling between the array elements. More specifically, arrays of resonant elements, characterized by very low mutual coupling, are compared with arrays of connected elements, which are strongly coupled. We show that, even for a very high level of mutual coupling between individual array elements, it is possible to obtain orthogonal beams if the total current distributions associated with the beams are uncoupled.

The number of independent links that can be hosted by an antenna platform for Line-of-Sight (LoS) communications is limited by its physical size and the interference between the beams associated with different users. For large-size platforms, the interference can be reduced by compromising the aperture efficiency, and this trade-off is the metric to quantify the effective use of the platform. This metric fails for antenna platforms that are not electrically large, for which the aperture efficiency is no longer a useful parameter. Here we resort to the concept of the Observable Field, related to the maximum theoretical directivity, to estimate the potential number of independent links supported by moderate-size platforms. This allows the introduction of coupling coefficients between the beams associated with the observable portion of the incident field and the beams associated with the receiving antennas. These coefficients are bounded to unity for any platform dimension, unlike the aperture efficiency, and they are maximized when the antenna pattern is equal to the pattern predicted by the Observable Field. Accordingly, selecting beams dictated by the Observable Field constitutes a benchmark for the effective use of the volume. Any antenna design can be compared to this benchmark to assess its merits.