A Theoretical and Numerical Approach for Selecting Miniaturized Antenna Topologies on Magneto-Dielectric Substrates A. Pacini 1 , A. Costanzo 1,2 , D. Masotti 2 1 DEI – “Guglielmo Marconi”; II School of Architecture and Engineering, University of Bologna, Cesena Campus, Italy 2 DEI – “Guglielmo Marconi”; School of Architecture and Engineering, University of Bologna, Bologna, Italy An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared to the wavelength, radiation performances have to be preserved in order to keep the system operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates which allows to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performance are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies. Keywords: Authors should not add keywords, as these will be chosen during the submission process (see http://journals.cambridge.org/data/relatedlink/MRF topics.pdf for the full list) Corresponding author: A. Pacini; email: alex.pacini@ieee.org; phone: +39 3383692711 I INTRODUCTION There are a variety of new application areas in which it is needed to achieve ultra-small wireless systems, such that they can be worn [1], and/or implanted under the tissues [2] (e.g. in the case of biomedical devices). To accomplish this, it is required that the antenna system provides extremely reduced dimensions while preserving the best radiation performance to minimize the power consumption. This is a challenging task since it is well known that for best antenna operation its dimensions need to be proportionally related to 1