Antenna is an
efficient radiator of electoromagnetic energy. (radio waves) into free
space. the same principles apply to both transmitting and receiving antenna
to radiate as much RF power as possible either in all directions
(omnidirectional antenna) or in specified direction (directional antenna).
By contrast the receiving antenna is used to intercept an R F signal
voltage which is sufficiently large, compared to the noise existing within
the receiver's bandwidth.
Frequencies
For example,
at a frequency of 100 MHz (which lies within the FM commercial broadcast
band of 88-108 MHz. The length required for the Hertz antenna is 468/100 =
4.68 feet. Such an antenna would be made from two tin conducting rods, each
2.34 feet long and positioned remote from ground. As practical examples, AM
broadcast stations have antenna systems that radiate vertically polarizerd
waves, whereas Television broadcast stations use horizontal polarization.
The bandwidth of an antenna may be regarded as the frequency range over
which the antenna is expected to perform well.
Field
Strength
For practical
dipole, the value of the radiation resistance is determined by the length:
diameter ratio of each rod and the location of the antenna with regard to
nearby metallic objects and structures. The field strength is therefore
directly proportional to the antenna current and is inversely proportional
to the distance from the transmitting antenna. This relationship is only
true for the radiated field; for the induction field, the field strength is
inversely proportional to the square of the distance. Therefore the
induction field is only important in the immediate vicinity of the antenna.
Electronics
are very good in today's world because most of today's
equipments are made with electronics components. These components are the
most modernized types of components that are used to build these
equipments. Foe example, antennas, transmitters, receivers, satellites,
phones, component sets. radios, televisions, DVD players, computers,
printers, and scanners. For the most part, if it were not for electronics,
communications would not be as efficient as it is today
