More on Antennas

A dipole has a uniform or omni-directional radiation patern in one plane and a figure eight pattern in other two planes .This type of antenna can only over cum envoirnmrntal challenges by boosting the power level of signal.Challenges could be mountains, valleys ,buildings,etc.
An antenna is a transducer designed to transmit or recive elecrto-magnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. Antennas are used in systems such as radio and T.V broadcasting, point-to-point radio communication,WLAN, radars, and space stations. Antennas usually work in air or outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances.
Physically, an antenna is an arrangement of conductors that generate a radiating electrnic magnetic feild in response to an applied alternating voltage and the associated alternating electric current, or can be placed in an electromagnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals. Some antenna devices (parabolic antenna,horn antenna) just adapt the free space to another type of antenna.
Thomas A Edison used antennas by 1885. Edison patented his system in US pateint466,972 . Antennas were also used in 1888 by Heinrich Hertz (1857-1894) to prove the existence of elecromagnetic waves predicted by the theory of James Maxwell. Hertz placed the emitter dipole in the focal point of a parabolic reflector. He published his work and installation drawings in Annalen der physik and Cheime (vol. 36, 1889).