Novel antenna for mobile terminals based on the chassis-antenna coupling

In the miniaturization process of mobile terminals, the antenna plays an important role, since the reduction of its size leads to a degradation of some of the radiation properties (e.g., bandwidth and gain). To avoid this problem, the possibility of considering the whole metallic structure of the terminal as part of the antenna has been proposed (Vainikainen, P. et al., IEEE Trans. Antennas Propag., vol.50, no.10, p.1433-44, 2002). As a result, improved radiation behavior can be obtained. We computed the resonant modes of a chassis structure (Antonino-Daviu, E. et al., AP-SA/URSI Symp., 2004) by means of the theory of characteristic modes, defined by R.F. Harrington and J.R. Mautz (1971), and the effect of the coupling of a small antenna on the characteristic modes (resonant modes) behavior was analyzed as well. As shown by Vainikainen et al., the performance of the antenna-chassis combination has a very clear dependency on the chassis resonance. From our knowledge of the properties of the diverse characteristic modes of the chassis, further work has been carried out to design a chassis-antenna structure with improved radiating properties. The paper illustrates the consistent design procedure followed to obtain the proposed antenna.