L’ÉLECTROMAGNÉTISME L’ÉLECTROMAGNÉTISME, 150 150-1 U NE SCIENCE EN PLEINE NE SCIENCE EN PLEINE ACTION ACTION ! Analyse et conception d’antennes très large bande en utilisant la théorie des modes caractéristiques Analysis and design of miniaturized extremely wide band antenna using characteristic mode theory Mhamad Hassanein Rabah, Divitha Seetharamdoo, Rafik Adacci, Marion Berbineau Université Lille Nord de France, F-59000, Lille IFSTTAR, COSYS, LEOST, F-59650, Villeneuve d'Ascq Keywords: extremely wide band antenna, characteristic mode theory, miniaturized antenna, spectrum sensing antenna. Mots clés: antenne très large bande, antenne miniature, théorie des modes caractéristiques, antenne pour sondage spectral. Abstract A planar extremely-wide-band antenna is designed and simulated. The proposed antenna is a printed elliptical slotted monopole antenna with a triangular ground plane, fed by semi-ring triple feed followed by a tapered CPW line. The frequencies covered for a VSWR ≤ 2 extends from 0.65 GHz to 12 GHz with stable radiation patterns to guarantee minimal pulse distortion. This configuration has been achieved by analyzing the currents on the antenna by means the characteristic mode theory. Both numerical and experimental results are presented. This miniaturized antenna (largest dimensions of the order of 0.14 λ) is a good candidate for wide band spectrum sensing in the context of cognitive radio applications. Introduction With the diversity of wireless systems, flexibility for operating between different standards is required. Cognitive radio (CR) consist the future system that can propose this flexibility. The federal communications commission (FCC) has defined a cognitive radio as a radio that can change its transmitter parameters based on an interaction with the environment in which it operates. At the hardware level, the implication for future antenna design is the varying degree of reconfiguration and band tuning will be required. CR can have different possible architectures but all of them require a spectrum-sensing unit. In this paper we will focus on the design of a spectrum-sensing antenna used by such systems. The most important challenges for sensing antennas are their dimensions and radiation pattern stability at all the operating frequencies of the communication systems present in the environment [1], [2]. In this paper, a novel design of extremely wideband printed elliptical monopole fed by tapered CPW line is proposed and investigated based on a triple-feed at the bottom of the line [3]. Once a good antenna matching is achieved, obtaining a stable radiation pattern on the whole frequency band can prove to be a challenge. We propose to analyze the current modes on the radiator using the theory of characteristic modes (TCM). Indeed, TCM, developed by Garbacz in 1971 [4] and later refined by Harrington and Mautz [5] has been proposed to analyze radiating modes of any conductive structure and has been used successfully for the design of diverse wire and planar antennas [6]. Here, TCM is used to provide physical insight into the radiating phenomena, thus allowing performance enhancement at particular frequencies where the radiation pattern is distorted. This novel antenna design proposes three significant performance enhancements, namely, miniaturization of total dimensions, the shifting of the lowest operating frequency towards low frequencies and a stable radiation pattern over the frequency band (0.65 GHz – 12 GHz) to ensure that the antenna is a good candidate for CR spectrum sensing applications. 1. Design challenges and optimisation techniques The antenna proposed was inspired by designs for UWB systems. These include various printed antenna with different shapes and enhanced bandwidths. The shapes of the printed antennas can be rectangular [7], triangular-ring [8], circular [9], annular-ring [10], and elliptical [3], [11], [12] . The monopole antenna chosen is an elliptical one since through the variation of its elliptical ratio, a higher degree of freedom is obtained for impedance matching. Since the sensing URSI-France Journées scientifiques 26/27 mars 2013 179