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What is Antenna Gain, and is Higher Always Better?
Estimated 10minutes to finish reading
Let's discuss what antenna gain is and
whether a higher value is always preferable. In reality, it entirely depends on
the application of the antenna. Take a flashlight as an example: if you remove
the reflector, the light will obviously become less intense. However, if you
need an omnidirectional light source to evenly illuminate a room, removing the
reflector to allow the light to spread out uniformly is more appropriate.
Conversely, if the goal is to create a laser, using a lens to focus all the
light from the bulb into a narrow beam is undoubtedly an improvement. But this
concentrated beam is unsuitable for lighting up an entire room.
This phenomenon of concentrating light in a
specific direction is called directivity, and the degree of concentration is
referred to as gain. In the field of antennas, these two concepts behave very
similarly to those of a light source. Imagine an antenna radiating energy uniformly in
all directions like a candle; this is a non-directional isotropic radiator.
Technically, this is defined as 0 dBi, meaning the radiation energy is the same
in every direction.
Now, if you place a mirror next to the
candle, the mirror will alter the distribution of light energy and give the
candle directivity. The mirror will make half of the room darker and the other
half brighter because the light is reflected and concentrated in one direction.
This approach of "stealing" and redirecting energy from less
favorable directions to enhance it in certain directions also applies to antennas.
Therefore, antennas do not generate radio
energy; they merely transfer, guide, or concentrate it in a specific direction.
This directional characteristic is known as gain. A mirror can redirect half of
the candle's energy, making it appear twice as bright in certain
directions—equivalent to two candles. In this case, we say the mirror provides
a gain of 3 dB because it doubles the energy.
It is important to mention that the unit
for measuring antenna gain is the decibel (dB). However, it is typically relative to a reference
antenna. Usually, the radiation intensity of an omnidirectional antenna or a
half-wave dipole antenna with the same input power in a certain direction is
used as the reference value. When using an omnidirectional antenna as the
reference, it is denoted as dBi (i - isotropic), and when using a half - wave
symmetric dipole antenna as the reference, it is denoted as dBd (d - dipole).
From the definition of antenna gain, we can
understand that it refers to the square ratio of the electric field strengths
(i.e., the power ratio) produced by an actual antenna and an ideal radiation
element at the same point in space under the condition of equal input power. It
quantitatively describes the degree to which an antenna concentrates and
radiates the input power.
The gain performance of an antenna in different directions is represented by an antenna gain pattern (or radiation
pattern). The narrower the main lobe and the smaller the side lobes of the
pattern, the higher the gain.
All antennas exhibit a certain degree of
directivity, and the variation in gain across different directions reflects
this directivity. Even omnidirectional antennas have "blind spots" or
"nulls" in their radiation patterns.
After understanding the true meaning of
gain, we can better determine whether more or less gain is preferable for any
specific application. A high - gain antenna, like a flashlight, needs to be
pointed in a specific direction. Although the antenna does not create new radio
frequency energy, its directivity effectively transmits the signal to the
target location.
However, if you want a wireless signal to evenly cover an entire room, you may not need gain or the directivity
it brings. This is because gain essentially "steals" radiation energy
from certain directions to enhance the signal in other directions.
