ALOHA TORINO-SYDNEY · Analysis of Low-cost Original Holographic Antenna: Theoretical OveRvIew, NOtes, StudY, DesigN, and EasY Implementation

Analysis of Low-cost Original Holographic Antenna: Theoretical OveRvIew, NOtes, StudY, DesigN, and EasY Implementation

Project context and objectives The main topic of the EU-funded research project 'Analysis of Low-cost Original Holographic Antenna: Theoretical Over-Review, Notes, Study, Design, and Easy Implementation (ALOHA TORINO-SYDNEY)' has been the development of a new kind of holographic antennas (HAs). Holograms are virtual images resulting from the interference of two electromagnetic waves. Such devices were first studied decades ago, but they are still a hot topic given the potential of holographic images for a variety of applications in various frequency ranges, in particular at mm waves and THz. HAs are antennas where the reflecting surface (aperture) is formed by a quasi-periodic conductive metallic pattern on a grounded multi-layer dielectric substrate. Surface waves can propagate along the interface between different media and the hologram is then produced by interference at the air-substrate (top) interface. In the project particular prototypes have been designed, implemented and measured in low-cost microstrip technology at microwave frequencies. The surface consists of a 2D passive periodic and/or quasi-periodic arrangement of unit cells including a width-modulated microstrip line. Planar (Cartesian and polar-grid) as well as conformal (cylindrical) geometries have been considered which enable the coupling of surface and free-space waves leading to interesting EM phenomena, e.g. cloaking. Project results Among the numerous trial products and designs that have been developed, we can mention a prototype device functioning in the microwave K-band of the EM spectrum (18–27 GHz) frequently used in satellite communications. The potentiality this solution offers makes the structure of interest to be employed in different challenging applications, as for example in the forthcoming Square Kilometre Array (SKA) array, 'the world’s largest and most sensitive radio telescope', (visit http://www.skatelescope.org/ for more information). Another demonstrator, consisting of 24 active unit cells each independently tunable and with excellent filtering characteristics, enables a significant size reduction and potentials for use in advanced applications such as the so-called cognitive radios that intelligently and efficiently select wireless communication channels. The millimetre-wave prototyping in GaAs technology of the patent-pending proposed solution is under consideration in collaboration with US universities. Different periodic configurations of a multi-layer reflector screen, covering the Ultra-Wide Band (UWB) range (3.1-10.6 GHz) used in radar tracking applications as well as in wireless communications, have also been prototyped and measured. The phase control of the reflected electromagnetic wave allows realisations of such challenging performances and opens the way for novel solutions for otherwise narrow-band devices, as for example polarisers. These enhanced properties suggest tremendous industrial potential. The various prototypes realised along the project lifetime, and the relevant systems for their measurements, demonstrate new and improved capabilities of HAs with potential applications in a variety of established and emerging fields. Continuing research should enable optimisation of the demonstrators as well as aid development of additional devices. The interest in the different solutions of the project outcome is confirmed by the large number of contacts that the fellow researcher developed with scientists from world-leader institutions and universities. The large number of co-authors with different technical (theoretical, experimental) and disciplinary (electromagnetic, material science) backgrounds clearly reflects the interest of the scientific community in this work. Among the co-authors or collaborators of the fellow, there are: - Dr. T. Bird, President elect for 2013 of the Antennas and Propagation society and EIC for two terms of the Transaction on Antennas and Propagation, -Prof. R. Mittra (PennState University), one of the most renowned and distinguished researchers in the field, -Prof. Y.M.M Antar from the Royal Military College of Canada and Queen's University at Kingston, Canada. It can be concluded that the project has advanced in a very positive way, and the work carried out is of high-level and presents a large number of potential applications.

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