This chapter provides new insights on antennas, including diversity schemes and UWB applications. It is important to remember that antenna performances are strongly dependent on the electromagnetic properties of the medium in its immediate vicinity. This is a critical point for handset antennas, for example, since the user's hand and body strongly affect the radiation efficiency. Taken together, the total radiated power in the transmission mode and the total radiated sensitivity in the receiving mode provide a general idea of the handset terminal's behaviour in its environment. However, as outlined in Section 5.2, in order to characterise antenna efficiency precisely, it is first necessary to introduce and define such figures of merit as the mean effective gain and the mean effective radiated power, taking the multipath structure of the communication channel into account. For this, measurement techniques must be reproducible. Two of these techniques have been studied in depth. In the first, which is based on the use of a reverberation chamber, multiple reflections on the walls reproduce ideal Rayleigh channels; in the second, the transmitting antenna is placed in an anechoic chamber, allowing the modification of the antenna radiation pattern, due to a phantom that simulates the user's body, to be clearly demonstrated. One of the main factors influencing the measurement results is, of course, the electrical properties of the phantom material. However, both the position of the phantom hand, or in other words, the way a handset is held, and the position of the antenna handset relative to the head are also quite critical. These issues of measurement repeatability and accuracy were widely discussed during the COST 273 Action, with a focus on updating the standardised measurement techniques.
Academic Press, 2006. 218-276 p.