Microwave Photonics for Remote Sensing: from Basic Concepts to High-Level Functionalities

In the last decades, photonic technologies have been increasingly proposed for microwave and millimeter-wave applications, opening the way to the development of a new field of research known as Microwave Photonics. The hybridization of the microwave world with photonics has demonstrated a beneficial impact on both communications and remote sensing. 5G radio access networks, as well as the next-coming generation of distributed, multistatic radars, are expected to massively leverage on photonic techniques for the generation, distribution, processing, and acquisition of microwave signals. This is due to the advantages brought about by photonics in terms of system transparency to the employed frequency or waveform, low losses, electromagnetic interference immunity, high signal stability. In particular, the inherent coherence guaranteed by photonics will enable next-future multiple input-multiple output radars with enhanced performance. In this paper, we expose in detail some of the most widely employed functions on RF signals obtained with photonic techniques, highlighting the achievable performance that help overcoming some limitations of classical electronic technologies. Finally, two recently implemented microwave photonics systems are described, i.e., a multiple input-multiple output radar and a RF spectrum scanner, showing with practical examples all the potential of microwave photonics systems.