TABLE OF CONTENTS Thomas F. Eibert
Universit t Stuttgart
John L. Volakis
The Ohio State University
Antennas are key components of any wireless communication system.1 ,2 They are the devices that allow for the transfer of a signal (in a wired system) to waves that, in turn, propagate through space and can be received by another antenna. The receiving antenna is responsible for the reciprocal process, i.e., that of turning an electromagnetic wave into a signal or voltage at its terminals that can subsequently be processed by the receiver. The receiving and transmitting functionalities of the antenna structure itself are fully characterized by Maxwell's equations and are fairly well understood.3 The dipole antenna (a straight wire, fed at the center by a two-wire transmission line) was the first antenna ever used and is also one of the best understood.1 ,2 For effective reception and transmission, it must be approximately ?/2 long ( ? = wavelength) at the frequency of operation (or multiples of this length). Thus, it must be fairly long (or high) when used at low frequencies ( ? = 1 m at 300 MHz), and even at higher frequencies (UHF and greater), its protruding nature makes it quite undesirable. Further, its low gain (2.15 dB), lack of directionality, and extremely narrow bandwidth make it even less attractive.
