Frequency Diverse Array for Signal Geofencing in Wireless Communications: Does it Work?

Frequency Diverse Array is an advanced antenna technology for clustering received power spatial distribution in specific areas, which has shown significant potential in many applications, including radar or wireless power transfer. In wireless communications, signal geofencing might be beneficial in increasing communication secrecy or reduce interference issues, but system communications through frequency diverse arrays require careful consideration about several design parameters. In this paper, a detailed analysis of the sensitivity of the geofencing effectiveness to the main array parameters is carried out. The analysis covers many aspects of the design, including the selection of the geometrical layout and the number of elements of the array, the frequency increase policy and the frequency offset across the elements and their spacing. The study also discusses the trade-offs between different design choices and provides insights into the performance in terms of focus efficiency and size of the focus area. Results show that bidimensional layouts, e.g., circular or planar, often represent effective solutions, whereas the linear arrangement can be a viable option only in case the frequencies are spread across the elements in a random-like fashion. Frequencies are usually increased according to either a logarithmic or a linear policy. The linear solution in general yields lower performance, but also lower complexity. Frequency offset, number of elements and their spacing represent further project parameters. Finally, a preliminary assessment of the multipath effect on the focus task shows that the performance of frequency diverse arrays can be affected by complex propagation conditions and deserve further investigations.