Chapter 8Reconfigurable Printed Antennas1
The telecommunication domain in recent years has seen incredible growth. Over the years, downsizing of mobile systems in particular has led to the design of increasingly miniature antennas, responding to severe radio-electric constraints. Nowadays, higher transmission rates and the ever increasing number of wireless communication devices and standards require antennas with the capability to answer to additional features which are often impossible to obtain using conventional radiating structures. Thus, to quickly match to a changing channel frequency (cognitive radio) or random environment, reconfigurable antenna design becomes a necessity. The most commonly desired objectives are generally of course the automatic adjustment of frequency but sometimes, also the real-time correction of radiation pattern or polarization direction.
Research on so-called active antennas, conducted initially in an effort to reduce noise and losses in the transmission lines between the antenna and the RF circuits, have thus migrated over time from a lot of various electronic functions such as frequency mixing, oscillation, modulation [CHA 02], to more recently, frequency, radiation pattern or polarization dynamic reconfiguration. Indeed, many academic and industrial researchers have investigated the possibility of dynamically changing the radio-electric characteristics of an antenna. Solutions have been proposed for many types of radiating ...