The relevance of vehicle communications in nextgeneration networks entails the necessity of studying their performance in the framework of upcoming massive architectures. In this regard, a study of the wireless channel between a hybrid massive MIMO base station (BS) and a vehicular platform is proposed. Adequate metrics and methodology are provided for the assessment of such scenarios. The impact of different multiantenna geometries and MIMO architectures in both vehicle and BS is modeled based on a numerical simulation of a realistic urban area. We compare several massive hybrid BS configurations with distinct multi-antenna vehicular rooftop solutions. This paper studies the channel eigenvalues and capacities for sub-6 GHz (3.6 GHz) and millimeter-wave (mmWave) (26 GHz) bands under different propagation conditions. The results suggest that the use of hybrid massive configurations increase the channel capacity by subdividing the massive BS into two or four logical radio channels. It is also shown that the greater available bandwidth at mmWave band can compensate the larger attenuation of radio channels in small size cells. The use of adequate metrics to measure the temporal coherence of the channel is also discussed for the beam switching update.

The emergence of mobile terminals operating at millimeter-wave frequencies necessitates the ability to evaluate the effect the environment, and in particular, users have on their radiation properties. Some studies evaluated the shadowing effects of a hand or an entire body for simple antenna configurations. This letter proposes a method for reliably predicting the performance of different array geometries in the presence of the users when they operate the mobile with one or with two hands. In practice, the way a mobile is operated is varying strongly between users, and hence, it is of great interest to draw a methodology to both numerically and experimentally evaluate any handset design in a large number of use cases in a repeatable manner. The use of numerical models and realistic phantoms allow high repeatability when evaluating the terminal radiation under real use conditions. Both the simulated body and the human phantom are used to study the field scattering from the handset arrays subject to the user interaction, yielding consistent results between them. Results suggest that shadowing by the user's torso usually decreases gain between 20-30 dB close to the region of the user. The user posture largely affects the spherical coverage, particularly for those antennas close to the corners in a two-hand mode.

A switchable multi-antenna architecture for lens-assisted beamsteering in the Ka-band region allocated for 5G communications (24-30 GHz) is proposed. The radiating elements are bow-tie antennas mounted with a 3D printed high-permittivity dielectric lens (ε r = 10). A 5-element array is simulated showing switchable 30° beam steering over a 120° sector with 19 dB maximum gain. Single antenna measurements of a scaled prototype with a Polylactic Acid (PLA) lens (ε r = 2.7) show gains around 11 dB, in agreement with projected performances.

A planar antenna structure based on a folded asymmetrical dipole is presented, whose geometrical parameters are seen to independently determine either the real or the imaginary parts of the complex radiation impedance. This unique feature allows very efficient and wide-band conjugate matching coupling to non-conventional RF sources of arbitrary internal impedance, i.e., small resistance with large and negative reactance. The antenna theoretical framework is developed and an optimized design to match a photodiode is manufactured and measured. The results show a fractional bandwidth of about 20% in the 28 GHz band.