the outside world and, in reverse, to the receiver from the out- side world. Antennas have often been the most neglected of the components in a wireless system, yet they really are the most important part of a radio system. The manner in which energy is collected from and distributed into the surrounding air greatly influences the bandwidth efficiency, cost, and service quality of wireless networks. Antenna design is as critical as the prevailing radio conditions. The function of an antenna is to collect or radiate electromagnetic waves. An oscillating electric field from the radio's transmitter is fed to the antenna, creating an oscillating magnetic field. Radio transmission is the propagation of electromag- netic waves through space. The electromagnetic waves create an electric current in the receiving antenna, which is then sent to the radio receiver. Antennas can be designed to handle a wide range of frequencies and power levels. They can also be designed to partially reject interference and signals coming from a direction other than that intended or, on the other hand, to focus energy in a particular direction when transmitting. The first important consideration in antenna selection is gain. Antennas, as passive devices, do not create radio energy; they focus it. Focusing the energy into a narrower beam causes an increase in power, which is referred to as antenna gain. There are two main types of antennas: Omnidirectional-Omnidirectional antennas are used for communicating with mobile stations spread out in all directions. Examples include whip antennas, discone antennas, vertically oriented dipole antennas, and hori- zontal loop antennas. Panel, or directional-Panel, or directional, antennas are designed for high gain and are used to concentrate the signal both vertically and in a specific horizontal sector. Examples include Yagi antennas, parabolic dishes, and patch arrays. Antennas Building Your Own Antenna You can find some interesting photos of all sorts of antennas at www.seattlewireless.net/ AntennaHo