Fractal geometries are appealing in all applications where miniaturization capabilities are required, ranging from antennas to frequency selective surfaces (FSS) design. Recently, some fractal patches configurations, giving low losses, reduced size, and quite good phase ranges, have been proposed for the design of reflectarray unit cells. This paper reviews existing fractal-based reflectarrays, highlighting their benefits and limitations. Furthermore, a comprehensive analysis of an innovative reflectarray unit cell, using a fractal-shaped fixed-size patch, is presented. The miniaturization capabilities of the Minkowski fractal shape are fully exploited to obtain a compact cell offering quite good phase agility, by leaving unchanged the patch size and acting only on the fractal scaling factor. Experimental validations are fully discussed on a realized 10 GHz0.3λ×0.3λcell. This is subsequently adopted to synthesize various reflectarray prototypes offering single or multiple-beam capabilities over a quite large angular region (up to 50 degrees). Finally, experimental validations on a realized15×15elements prototype are presented to demonstrate the wide angle beam-pointing capabilities as well as a quite large bandwidth of about 6%.

Visible light communication (VLC) builds on the dual use of lightening infrastructure for communication. Even though the advantages of VLC are well known, as emerging communication paradigm, some open issues still need to be addressed in order to rely on it as a robust communication system. First of all, external interference as an extremely varying signal impacting on the reliability of the VLC system needs to be analyzed. In this article, we propose a system where the link conditions (in terms of signal-to-noise-ratio (SNR)) drive the modulation scheme and this procedure is managed through the use of an uplink/channel, to assure a feedback path. The receiver is in charge of choosing the modulation scheme matching the requirement in terms of error rate on the basis of the measured SNR after noise mitigation. The feasibility of the system and its effectiveness are evaluated by designing and implementing a complete bi-directional system. In particular, an uplink channel sending the information regarding the specific selected modulation technique has been implemented and the whole system is based on a fine synchronization approach in order to “track” in real time the most suitable modulation scheme. Experimental results show the effectiveness of a bi-directional system in order to implement an adaptive VLC system able to follow the environmental changes (in terms of interference and noise).

The Universal Software Radio Peripheral USRP NI2920, a software defined transceiver so far mainly used in Software Defined Radio applications, is adopted in this work to design a high resolution L-Band Software Defined Radar system. The enhanced available bandwidth, due to the Gigabit Ethernet interface, is exploited to obtain a higher slant-range resolution with respect to the existing Software Defined Radar implementations. A specific LabVIEW application, performing radar operations, is discussed, and successful validations are presented to demonstrate the accurate target detection capability of the proposed software radar architecture. In particular, outdoor and indoor test are performed by adopting a metal plate as reference structure located at different distances from the designed radar system, and results obtained from the measured echo are successfully processed to accurately reveal the correct target position, with the predicted slant-range resolution equal to 6 m.