The main research objective of SILIKA is to develop innovative integrated antenna systems for future 5G base stations operating at millimeter-wave (mm-wave) frequencies utilizing highly-integrated and cost-effective silicon (Bi-) CMOS technologies. These antenna systems will rely on the use of multi-antenna massive MIMO concepts in which the number of individual antenna elements in the base station is much larger than the number of users (M>>K). In state-of-the-art phased arrays, only a limited number of identical antenna beams are used, usually operating in a single frequency band. Multi-antenna massive MIMO systems, however, can generate multiple beams, each with different shape operating at different frequencies, using polarization agility and adaptive waveforms. Multi-element antenna systems are expected to increase the energy efficiency of future base stations, while achieving high data rates with in-door and out-door coverage both for line-of-sight and non-line-of-sight propagation conditions, by sending out many independent data streams to simultaneously serve many users. The proposed design methods in SILIKA aim at synthesizing energy-efficient multi-beam array antennas, while minimizing the effects of electromagnetic mutual coupling between the array antenna elements, i.e. de-correlating them.
Large-scale array antenna systems for 5G wireless infrastructure call for novel electronic beamforming approaches. These system-wide beamformers combine analog and digital beamforming in an optimal manner; they employ specific antenna elements, power distribution networks, integrated microwave electronics, adaptive digital beamforming and waveform algorithms. Regarding electronic beamforming, we focus on large apertures, but reduce the number of active antennas to the minimum required by employing
- Sparse Irregular Arrays (SIAs), where each antenna element sees all users all the time, hence providing full coverage,
- Quasi-optically beamformed array antennas such as Focal Line Arrays (FLAs) and Focal Plane Arrays (FPAs), where each antenna element sees multiple users, albeit a smaller subgroup of users within a sector of the total coverage area.
In both concepts, each active array element will consist of a silicon integrated circuit (IC) with integrated antenna radiator. The two configurations comply with the multi-user scenario and offer the advantage that signal distortion and noise effects are reduced by the averaging effect due to the large number of active antenna elements. Another advantage of SIAs and FLAs as compared to traditional dense-arrays is that they can provide a solution for the stringent thermal requirements for air-cooled antenna systems. Although both concepts serve different use-cases, w.r.t. in-door and out-door applications, they require the same enabling technology in terms of radiating elements, integrated electronics, packaging and signal processing.
 Rusek, Fredrik, et.al.. “Scaling up MIMO: Opportunities and challenges with very large arrays.” Signal Processing Magazine, IEEE -30, no. 1, 2013 and Gustavsson, Ulf, et al.. “On the impact of hardware impairments on massive MIMO.” InGlobecom Workshops, IEEE, 2014.
 We will use the words “beamforming” and “beamformer” in a generic way to mean also transmission to non-line-of-sight users, where optimal transmission may not form focused beams.