Extraordinary-transmission-inspired Bull´s eye antenna for automotive radar

Summary form only given. Leaky wave antennas have been studied since 1940s (C.H. Walter, Traveling Wave Antennas, Peninsula Pub., 1990). They have become a promising type of antenna for applications requiring low-profile antennas such as automotive radars (M. Ettorre, R. Sauleau, L. Le Coq, and F. Bodereau, IEEE Antennas Wirel. Propag. Lett. 9, 859, 2010). Unfortunately, pure broadside radiation cannot be achieved due to the open stopband effect.In this communication we will look at a leaky wave antenna that mimics broadside radiation by combing the radiation of two counter-propagating leakywaves (D. R. Jackson, A. A. Oliner, T. Zhao, and J. T. Williams, Radio Sci., 40, 1, 2005). Although neither of the leaky-waves radiates broadside, the angle of radiation is close enough to normal that the radiation pattern appears as a single beam. The antenna is based on a central resonant slot surrounded by corrugations in the form of Bull´s Eye (M. Beruete, I. Campillo, J. S. Dolado, E. Perea, F. Falcone, and M. Sorolla, IEEE Antennas Wirel. Propag. Lett., 4, 365, 2005), and is originally inspired by the extraordinary optical transmission (F.J. Garcia-Vidal, L. Martin-Moreno, T.W. Ebbesen, and L. Kuipers, Rev. Modern Phys. 82, 729, 2010). The proposed antenna is completely metallic, unlike other leaky wave antennas proposed for millimeter-waves applications. Hence, dielectric losses, that cannot be disregard at these high frequencies, are completely removed, allowing higher gains. We will analysis the effect that the profile of the corrugations has in the radiation characteristics. In particular, we will demonstrate that sinusoidal rather than square corrugations are preferable if high directivity is required. We will link this to the different properties of the leaky-waves supported. Measurements of an all-metallic prototype with 20 sinusoidal corrugations shows at 77 GHz an input reflection coefficient of -20 dB, a 28 dB gain and side lobe level of -21.4 dB, in agreement w- th the numerical modelling.