XAVIER BEGAUD

Strategies to Extend the Bandwidth of Wideband Antennas Over Artificial Magnetic Conductors

From the two last decades, there has been a growing interest in applying artificial materials, known as Metamaterials to antennas. These materials derive their unique properties, not from their composition but from their structure. They are mostly composed of a periodic arrangement of materials, patterns. This spatial periodicity naturally induces a spectral selectivity. This narrow bandwidth can be used with benefit but is usually cited, in addition to losses, as one of the main limitations for metamaterials applications. The objective of this presentation is to demonstrate that it is possible to design wideband antennas with metamaterials. We are going to focus our attention to those, which can be applied to improve performance in terms of gain and to reduce the thickness of the overall antenna. Designing unidirectional antennas is required on many platforms in order to obtain outward radiation and preserve the interior of any electromagnetic pollution. For this, most common solutions are to place the antenna above a reflector or cavity filled with absorbing materials. The solution with absorbing cavity is simple but half of the radiation is lost and the cavity is sized at a quarter of a wavelength at the lowest operating frequency, which become very bulky for low frequency applications. Another efficient technique is to use a reflector made of a very good electrical conductor to retrieve the radiation lost in the previous solution. This technique is optimal at the middle of the bandwidth where a constructive interference phenomenon occurs by placing the reflector at a quarter wavelength (at center frequency) from the antenna. But this solution is inherently limited bandwidth and can rarely exceed the octave. It therefore appears difficult to design a unidirectional antenna achieving wide bandwidth and good compactness. Nevertheless, reducing the thickness is possible by using an AMC (Artificial Magnetic Conductors) which exhibit the perfect magnetic conductor (PMC) behavior, i.e. no phase shift at reflexion. It then becomes possible to position the antenna closest to this new reflector. The antenna is so unidirectional and thin. However obtaining PMC condition is possible but in a very limited frequency band and generally the AMC has a limited size composed with only few cells who are not all illuminated by a plane wave at normal incidence … In this talk, several strategies to exceed these limitations and keeping the wideband performance of antennas placed above these artificial magnetic conductors will be detailed. The presented results will be compared with the measurements in order to validate the different designs.

Xavier Begaud was born in Chateaudun, France, in 1968. He received a M.S. degree in optics, optoelectronics and microwaves, from Institut National Polytechnique de Grenoble (INPG) in 1992. He received the Ph.D. degree from the University of Rennes in 1996 and the habitation degree from Pierre and Marie Curie University (Paris 6) in 2007. He joined the Télécom Paris in 1998 (formerly Ecole Nationale des Télécommunications, Télécom ParisTech), where he is presently professor. From 2013 to 2017, he was Head of the RF & Microwave group (RFM) at COMELEC Department. He teaches electromagnetics and microwaves in initial training, in continuing education, and in Masters. His research topics in the RF Microwave and Millimeter wave team (RFM²) include theory, conception, modeling, and characterization of wideband, bipolarized, and 3D antennas with special emphasis on numerical methods. Currently, research activities are focused on the design of artificial materials and metamaterials for antennas and radar absorbing materials from GHz to mmWaves. He has published over 250 journal papers, patents, book chapters, and conference articles. He has organized two international conferences (Meta’12 and AES 2012) as the general chairman and edited 2 books.