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Print PageAntenna GAIN
January 2005

How much gain is required?

Antenna performance is primarily established by its gain. Gain must always be measured against a know reference. Unfortunately, there are many "so-called" gain references. Choosing the wrong reference could cost you up to 2.0 dB in performance.

Most commercial antenna suppliers specify gain in dBd (gain over a half-wave dipole). The half-wave dipole is one of the simplest and most efficient antennas. It is relatively easy to construct and has a very predictable radiation pattern similar to that of a donut. This is why most commercial antenna suppliers reference gain to a half-wave dipole.

Another reference, especially at microwave frequencies, is dBi. This term refers to gain over an isotropic radiator, a theoretical antenna that radiates equally well in all directions (such as the Sun). If an antenna is specified in dBi gain, it will appear to have approximately 2.15 dB higher gain than dBd. This may be a nifty way to impress the customer but it does not mean that you get more gain if dBi is the reference.

Beware if the supplier only quotes antenna gain in just "dB". What is the reference? For instance, some mobile antennas are specified in dB gain over a quarter wave whip which is about 0.6 dB less gain than a dipole.

Furthermore, gain influences the type and size of an antenna. The higher the gain, the larger the antenna. Table 1 shows some of the common communication antennas and the approximate gain ranges to expect.

View Antenna Gain Table 1.

As a rule of thumb, doubling the gain (a 3.0 dB increase) will increase the size of an antenna by a factor of 2-3. Properly combining two identical antennas will also increase the gain up to about 3.0 dB over that of a single antenna.

To increase the gain of a 6 foot high unity gain omni by 3 dB, the antenna will height will have to be increased to 12 to 18 feet tall!! Likewise, a Yagi antenna with a 4 foot long boom will have to increase to 8 to 12 feet along with additional elements! Table 2 can be used as a guide to assist in the selection of a Yagi antenna.

To increase the gain of a 6 foot high unity gain omni by 3 dB, the antenna will height will have to be increased to 12 to 18 feet tall!! Likewise, a Yagi antenna with a 4 foot long boom will have to increase to 8 to 12 feet along with additional elements! Table 2 can be used as a guide to assist you. A reminder, increasing gain will decrease your beamwidth.

View Antenna Gain Table 2.

tron Wireless Technologies, Inc. and the author retain the rights to all intellectual property contained herein.
This information should be used as a guideline only to help you in the appropriate selection of an antenna.

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