ANTENNA GAIN

Antenna Gain might seem an odd concept.  Many of us think of gain as something that needs amplifiers and batteries or an electrical wall outlet with ac current.  But antenna gain is really a relative measurement between different types of antennas.  An antenna that has "less signal loss" than another is said to have more antenna gain.  So gain for antennas, means in reality, "less loss".

How do we measure antenna gain?  Well, we measure gain relative to something called an isotropic antenna - an antenna that claims to be able to radiate the same amount of power equally in all directions.  There is some question about whether or not someone could make such an antenna in real life, but we use the concept to determine the gain of more normal antennas.

The reason why isotropic antennas do not exist, is that just about any antenna in real life is at least partially a directional antenna.  By that we mean that the power radiating from the antenna is higher in some directions than others.  That is often a good thing by the way.  Note that cellular never needs an isotropic antenna but always could use some form of a directional antenna.  For one reason, there are no people in the sky, so antennas need not radiate there, and there are no people under ground.  Therefore at the very least, cellular antennas should concentrate on the surface of the earth and building height above and below that surface.

Hopefully it makes sense to you, that if an antenna concentrates its power in just the direction it needs then it will be much more powerful and can transmit much further.  The most directional type of antenna is a parabolic type that uses the shape of its dish to concentrate radio waves coming in on a single point, and concentrates outgoing radio waves in a singular beam.  Such antennas are often used for point to point communications, aimed at a specific transmitting point perhaps on a hill top, or even at a satellite.  You can readily see that satellites are far away.  However one other thing about satellites is that they are locked in orbit and therefore in the same place.  One can therefore use a parabolic dish antenna to concentrate a beam to send and receive transmissions.  Such a dish antenna would be said to have very high antenna gain.