What Is Antenna Gain ?

What Is Antenna Gain ?

And what are “dBi” and “dB” ?

Imagine an antenna that radiates energy equally in all directions, much like a candle. OK, forget the small shadow under the candle and imagine an ideal floating flame. In scientific lingo, this is said to be an “isotropic radiator”, because it has no preference for radiation in any direction …  in other words it has no “directivity”.  An isotropic antenna is said to have “no gain”. “No gain” can be expressed in linear terms like x1 (times 1). That simply means that all directions have the same energy radiation, and are all equal to the average energy radiation. Antenna engineers like logarithmic terms, and we say this no-gain situation is 0 dBi (pronounced “zero dee bee eye”).

Now imagine a mirror beside our candle. Visualize how it would change the light energy distribution, and give the candle directivity. With a mirror, one half of the room would be dark (behind the mirror). The other half of the room would be TWICE as bright, because you can see the real candle PLUS it’s reflection. Mirrors or lenses have the appearance of intensifying energy in some preferred directions by stealing and redirecting energy from disadvantaged directions.

Antennas do the same thing. Mirrors don’t create light, they only divert, direct, or concentrate it in some direction. Antennas don’t create radio energy, they also only divert, direct, or concentrate it in some direction. This is directional feature is called GAIN. Please remember, no new energy is created, it is simply redirected or given directivity. The amount of intensification in a preferred direction is quantified as gain. Thus a mirror can redirect half of the energy from a candle, and make it look twice as bright (i.e. two candles) in some directions (but not all directions). It is said to have a gain of 2x (times two) or doubling.

Want to know how much antenna gain you need? (We get asked that all the time.) … then this article is for you:

Is More Antenna Gain Better?

The Logarithmic dB Scale

Antenna engineers use a logarithmic scale to express this apparent 2x (times two) mirror power doubling as “+3 dBi”. It still means “doubling”. Here are some other examples of ratios or multipliers on the engineering dBi gain log scale.

-10 dBi

One tenth or 10 % (loss)

-6 dBi

One quarter or 25 % (loss)

-3 dBi

One half or 50% (loss)

0 dBi

Same or 100% (no gain/loss)

+1 dBi

12% higher or x 1.12

+2 dBi

58% higher or x 1.58

+3 dBi

100% higher or double

+6 dBi

4x higher or quadruple

+9 dBi

8x higher

+10 dBi

10x higher

+13 dBi

20x higher

+20 dBi

100x higher

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Glossary & Terminology

• Isotropic Radiator: A theoretical point source that radiates energy equally in all directions. It serves as the standard mathematical reference for calculating antenna gain.
• Directivity: The measure of how well an antenna concentrates its radiated power in a specific direction compared to an isotropic radiator. High directivity implies a narrower, more focused beam.
• dBi (Decibels relative to Isotropic): A logarithmic unit of measurement used to express the forward gain of an antenna compared to the theoretical baseline of an isotropic radiator (0 dBi).
• Primary Lobe: The specific portion of an antenna’s radiation pattern that exhibits the highest field strength and greatest directivity. Usually the pointing direction of a directional antenna.

Frequently Asked Questions

Does a higher dBi antenna output more total transmission power? No. An antenna is a passive component and cannot generate power. Higher dBi indicates that the antenna is more highly directive, focusing the transmitter’s existing electrical power into a tighter area rather than distributing it broadly. Total Radiated Power (TRP) remains the same, minus any minor internal insertion losses. It’s like the lens on a 1 Watt bulb flashlight… which becomes brighter in one direction yet still is 1 Watt total power.

What is the difference between gain, directivity, and efficiency? (1) Directivity is a purely geometric measurement that describes how tightly an antenna focuses its radiation pattern compared to an isotropic baseline, assuming the antenna is absolutely perfect with zero internal losses. (2) Radiation efficiency accounts for the physical realities of the hardware, representing the ratio of electrical power actually converted into radio waves versus the power lost as heat due to conductor resistance, dielectric losses, or impedance mismatches. (3) Gain is the practical, real-world performance metric that combines these two concepts. Simply put, directivity dictates the theoretical shape of the beam, efficiency dictates the internal hardware losses, and gain provides the actual, measurable signal boost you will see in the field.

Why would an engineer choose a low-gain antenna over a high-gain antenna? Low-gain antennas (closer to 0 dBi) provide broad, omnidirectional coverage, making them ideal for mobile networks, hand-held radios, or IoT devices where the physical orientation of the receiver is unpredictable. High-gain antennas have narrow beamwidths, which are excellent for fixed point-to-point links but will completely miss target devices that sit outside their specific line of sight. Full article here.

What does a negative dBi value indicate in practical terms? A negative dBi value indicates that the antenna is radiating less in that specific direction than a isotropic radiator. In a directional antenna, this is normal for the “nulls” or the back of the antenna. In an omnidirectional antenna, overall negative dBi values usually point to poor radiation efficiency, meaning the antenna is turning RF energy into heat due to impedance mismatches or poor matching network design rather than successfully radiating it into the air.