Fundamental Limits and Design Guidelines for Miniaturizing Ultra-Wideband Antennas

Fundamental physical limitations restrict an antenna´s performance based on its electrical size. These fundamental limits are of the utmost importance, since the minimum size needed to achieve a particular figure of merit can be determined from them. In this paper, the physical limitations of antennas are reviewed in general, with particular emphasis on impedance matching as it relates to ultra-wideband (UWB) antennas (high-pass response). Additionally, the use of antenna miniaturization techniques to approach these limits is discussed. Using a spiral antenna as an example, guidelines are presented for miniaturizing UWB antennas.