Ebook: Antennas for ubiquitous radio services in a wireless information society

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.

A review on the Wide Band Sparse Element Array Antennas (WiSE) project is provided. After describing the general structure of the project and its initial goals, the activities undertaken in the two principal, and the various spin-off and supporting lines of research will be outlined. The most prominent theoretical and applicative achievements will be enumerated, by insisting on the delivered concept demonstrators and scientific output and, at the same time, on the societal impact of the obtained results.

The structural aspects of the mathematics that models wavefield physics in engineering applications are briefly, but rather completely, put in perspective.

The constantly increasing demand of advanced sensors and communications systems aboard of military platforms (ships, UAVs, aircraft, land vehicles, etc.) requires a high number of antennas, covering a very wide frequency spectrum. At the same time, the new platform concepts, dictated by an Integrated Topside Design approach, impose a very high level of structural integration of the antenna systems. The overall platform is designed keeping into account many different parameters including Radar Cross Section (RCS), Electromagnetic Interference (EMI), vulnerability etc. From an antenna system point of view, this translates into the necessity of developing antennas easy to be structurally integrated into different platforms and capable of combining more RF functions into the same aperture. In other words: wide-band active electronically scanned array antennas, preferably in planar printed technology which allows low weight, low profile and low costs. In this contribution, the development of a 6–9 GHz prototype array of dual-polarized connected dipoles is presented and discussed in detail. An analysis of spurious common-mode excitation is carried out and a novel design of a resonance-free connected array is presented.

This paper gives an overview of recent advancements on the design of an innovative sparse array for multibeam satellite applications. Just using a non-uniform placement of the radiators, without resorting to any excitation taper, an array antenna able to satisfy stringent requirements in terms of sidelobe level and beamwidth has been designed. In order to reduced the number of active controls, differently sized sub-arrays, composed of 1, 2 or 3 elementary square array tiles, are used in the design.

An overview on the design of increasingly wider bandwidth radiators that are amenable to being integrated in array configurations is presented. The initial step is represented by moderate bandwidth radiator of the cavity backed patch antennas. The bandwidth characteristics are then substantially increased by combining coplanar waveguide (CPW) feedings and profiled dipoles, the result being radiators with unprecedented performances. This type of radiators are further refined for improving their time-domain adequacy or for ensuring intrinsic filtering properties.

Re-configurability is one of the key features in modern wireless communications. Indeed, the increase of services provided imply an optimized management of the electromagnetic spectrum, along with strong miniaturization in order to allow for the cohabitation of all these services on small handheld devices. Reconfigurable antennas are one possible answer to these challenges. In this paper, we will present designs of reconfigurable antennas and feeding networks using recent technologies, namely MEMS (Micro Electro Mechanical Systems) and Metamaterials.

Active array antennas have very attractive features but are quite complex and expensive. For this reason, they are today considered for space missions essentially when in flight beam reconfigurability or inertialess beam steering is required. However, array antennas may find wider applications in new potential LEO or MEO telecommunication constellations or as a way to generate very large space aperture thanks to digital processing. The paper presents an overview on the European ongoing activities on active phased arrays with a particular emphasis on the main limitations, challenges, possible improvements and opportunities.

This article presents an overview of developments at IMST in the area of antenna front-ends for mobile satellite terminals. Such type of antennas has become a key area of interest because of the ever growing multimedia services provided over wireless links and satellites. Various activities in this area have been conducted in the past, and are on-going. Antenna front-ends for mobile platforms are, in general, complex systems because they have to incorporate special features in order to perform beam steering, and at the same time also be cost-effective. The complexity of the antenna systems, developed at IMST, ranges from small arrays with switch-able elements and partially mechanically and electronically steerable arrays (hybrid systems) to fully electronically steerable arrays. This article examines which kind of user requirements for the three basic mobile platforms (land, maritime and aeronautical) exist, and what kind of impact they have on the design of the front-ends. Latter aspect is critical to achieve a cost-effective design. This is illustrated by examples from past and on-going projects in L-, Ku-, and K/Ka-band. Different concepts are presented and key aspects discussed.

New astronomical science will be enabled by the use of array technology in radio astronomy. Development efforts concentrate on two concepts: aperture arrays and phased array feeds. Key challenges in the front-end development of such systems are the bandwidth, low-noise and stability requirements. A (dense) phased array feed prototype in a 25 m dish of the Westerbork Synthesis Radio Telescope (WSRT) successfully demonstrated the ability to electronically scan the beam about 2 half-power beamwidths in both directions while retaining a high antenna efficiency and low system noise temperature. The final system will lead to a 20× improvement of the WSRT survey speed. The Low Frequency Array (LOFAR) operates in the 15 – 240 MHz band using sparse antenna arrays. The Low-Band Antenna stations (15 – 80 MHz) have a pseudo-random configuration of the antenna elements to smoothen the station beams. Both aperture array and phased array feed technologies are important pathfinders for the next generation radio telescope, the Square Kilometre Array.

The present account reports on the shared aperture antenna concept as an instrument aimed at enhancing the functionality of antenna systems. Non-uniform array antennas implementing, in a concurrent manner, different functionalities are deployed on a common physical area. This concept is adopted to assemble multi-frequency, multi-channel and multi-polarization antenna systems. These applications are illustrated by physical implementations. The advantages introduced by the advocated approach and the challenges that it poses are discussed.