TABLE OF CONTENTS This section introduces the fundamental antenna parameters for the context of mobile communications. Some of the terms have been used already in previous chapters, but their formal introduction is given context in this chapter. The basic antenna elements the dipole and loop are discussed both to fix ideas and to demonstrate design considerations for compact antennas.
Antenna elements are often categorised from the basis of the antenna's construction: hence the terms wire antennas, slot antennas, patch antennas, aperture (e.g. horn) antennas, etc. Other categorisations reflect a physics approach: electric source antennas, magnetic source antennas, etc., or some engineering parameter type; for example: low , medium or high gain antennas. Here, we are mostly interested in compact and relatively simple elements, although the mounting, often on a complicated platform such as a handheld terminal, can inadvertently make the antenna appear complicated.
The directivity of an antenna is classically defined in a single direction corresponding to the direction of maximum power radiation:
The directivity is thus a function only of the 3D shape of the radiation pattern. It is a measure of how directional the antenna beam is, referenced to an isotropic (perfectly spherical) pattern. The principle of reciprocity for antennas states that the receiver and transmitter can be interchanged between the two antennas of a link, and this implies that the transmit pattern and the receive patterns are the same.
In classical antenna treatments, it is conventional to denote...
