= Antenna =

An antenna is some type of conductor, used to propogate radio signals. This is
done because an electric current in metal induces an electromagnetic field.
This can be transmitted and recieved by an antenna. When the antenna recieves
the signal, an electric current is induced in the antenna due to the
intersection of the electromagnetic radiation in a conductor.

*Polarization* is what orientation the electric field is from an antenna. This
is the same orientation as the conductor of the antenna. To get the best
signal, the sending and recieving signals must be of the same polarization.

Due to how signals propagate through the atmostphere, their polarization
changes dramaticly, and therefore it often doesnt matter what oerientation an
antenna has when working with signals that propogate often (such as HF, see
[[frequency_range]]). This phenomenon is called eliptical polarization.

== Feed line ==

A feed line delivers a signal to the antenna. The ratio of voltage to current
is [[Impedance]]. This is due to the ratio of the physical dimesnions of the
feed point, and the frequency of the signal. They are said to be in _resonance_
when the feed point impedance is all resistance with no reactance.

The feed points impredance is heavily affected by nearby conductors and its
height above ground.

== Gain ==

Gain is concentrating an antenna's radiated signals in a specific direction.
Gain aids in concentrating the antenna in an intended direction. This is done
by creating waves that constructivly add in certain directions, and destruvily
subtract in others.

*Omnidirectional antenna* radiate in all directions, and therefore have an
equal gain in all directions.

*Beam* or *directed antenna* have gain in a single direction, and are great for
communicating in a specific direction.

An *isotropic antenna* is a theoretical antenna that has no gain, because it
radiates equally in all directions. No such antenna exists, and is used for
reference.

Gain is measured in decibels (dB) and is in reference to something, most often
an isotropic antenna (abbr. dBi) or with respect to a dipoles peak gain (abbr.
dBd). The gain is often showns using an azimuthal and elevation diagram,
showing views from the top and side respecivly.