Wireless applications have pervasively penetrated the everyday life. They visibly manifest themselves in the omnipresent (mobile) communication devices that are deeply rooted in the present day lifestyle (see the multitude of sound, image and data carrying systems surrounding us). They manifest themselves less visibly, but equally ubiquitously, in weather and traffic monitoring systems, in defence and security technology, etc. They are praised for supporting and facilitating our daily routine and are (in fact, unjustly) blamed for thoroughly invading our privacy. They are instrumental for locating endangered people and for effectively treating diseases and, at the same time, are often cited among the perilous health-hazards.

The present day societal needs exert a lot of pressure on wireless systems for providing increased performance, with a twofold direction presenting the most challenging requirements: on the one hand, the constantly higher channel transmission capacity driven by the (multimedia) wireless data-link systems and, on the other hand, the pattern shaping, often complemented by beam agility, demanded by the high-end radar and space-borne telecommunication application.

The completion of these tasks is extremely complex, with the design of adequate antenna (systems) playing a pivotal role. Although antenna engineering has a long history of achievements, the magnitude of the present demands necessitates, and will still do so in the future, a continuous and sustained effort. The success in this area is indissolubly connected to mastering a broad knowledge arch, having as main pillars the in depth understanding of the pertaining (physical) phenomena and the needed manufacturing and measurement technological utensils.

Recognising these commandments, the International Research Centre for Telecommunications and Radar (IRCTR) has initiated in early 2004 the Wide Band Sparse Element Array Antennas (WiSE) project, a scientific endeavour having a twofold objective: the assembling of a catalogue of (ultra) wide-band radiators that are, preferably, amenable to being incorporated in array antennas and the exploration of the functional possibilities arising from accommodating various radiators on a common aperture, an approach termed as the ‘shared aperture concept’.

Investigations performed over a period of almost 6 years have confirmed some of the initial expectations, while opening new, challenging directions to be pursued. The undertaken research resulted into a multitude of theoretical aspects being elucidated, with solutions concerning the physical implementation of these concepts being also put forward. The performed activities materialised themselves in a sizeable published scientific output and, also, in several concept demonstrators with practical applicability. At the end of this route, IRCTR is firmly anchored on the map of European antenna research and development, with a well established international recognition in the field of non-uniform and/or interleaved array antennas.

The present work offers a retrospect of the project's main achievements, while also assessing their relevance within a wider antenna engineering perspective. The volume touches upon a broad selection of topics, spanning from fundamental electromagnetics up to accounts on the state-of-the-art manufacturing technologies. The included contributions are authored by the WiSE project participants, by the members of the Users' Committee and by representatives of leading European institutes involved in the complex and fascinating antenna research area.

Ioan E. Lager, Massimiliano Simeoni.

Delft, December 22, 2009.