Jun 25 2009

What Is Antenna Gain?

I didn’t know enough about antenna gain to define it if someone asked me to so I did some research. Gain itself seems to be a tricky term to define, so I’m going to have to explain a few other things along with it.

Antenna gain is basically measure of the effectiveness of a directional antenna as compared to a standard nondirectional antenna.

One of the major parameters used in analyzing the performance of radio frequency (RF) communications links is the amount of transmitter power directed toward an RF receiver.

This power is derived from a combination of:
1 – Transmitter power
2 – The ability of the antenna(s) to direct that power toward an RF receiver(s).

The directivity of the antenna is determined by the antenna design. Directivity is the ability of an antenna to focus energy in a particular direction when transmitting or to receive energy better from a particular direction when receiving. To determine the directivity of an antenna, we need a reference antenna with which to compare our antenna’s performance.

Over the years there have been several different reference antennas used. Today an isotropic radiator is preferred as the standard antenna for comparison. The isotropic antenna transmits equal amounts of power in all directions (like a light bulb).

To increase the directivity of a bulb’s light (the antenna’s energy), similar to a flash light or automobile head lamp in this example, a reflector (antenna) is added behind the bulb. At a distance, in the light beam, the light bulb now appears to be much brighter. The amount that the bulb appears brighter compared to the bulb without a reflector is the directivity of the reflector (antenna).

When the directivity is converted to decibels we call it the antenna gain relative to an isotropic source (dBi). Typically the higher the gain, the more efficient the antenna’s performance, and the farther the range of the antenna will operate. Roughly for every 6 dBi in gain, you double the range of the antenna.

It should be noted that many issues need to be considered when selecting the “best” antenna for the application, and you should discuss any antenna selection with someone knowledgeable in RF radiation and antenna performance.

So a better definition of antenna gain is:
A relative measure of an antenna’s ability to direct or concentrate radio frequency energy in a particular direction or pattern. The measurement is typically measured in dBi (Decibels relative to an isotropic radiator) or in dBd (Decibels relative to a dipole radiator).