Antenna Gain – Directivity, Efficiency and Its Conversion

Antennas are used in this modern communication for transmitting the data and receiving the data through a wired channel or wireless channel. Or in another way, it can be defined as transmitting and receiving the radio waves in all horizontal direction or particular direction. These antennas act as an interface between electric signals and radio signals. Here, electrical signals are forwarded through metal conductors and radio signals are propagating through free space. Heinrich Hertz was the first person to develop an antenna in the year 1886. He has created a dipole antenna and with electric signals, he transmitted and received the signals. Later in the year of 1901, Marconi was the scientist sending the information across the Atlantic region. The antenna parameters are more important. The parameters are directivity (D), antenna gain (G), resolution, patterns, antenna beam area, antenna beam efficiency, antenna efficiency (η). In this article, we will discuss the complete information related to antenna-gain.

What is an Antenna Gain?

We can define the antenna gain as the combination of antenna efficiency and directivity of the antenna, and this depends on these parameters. So these two can be effects the gain of an antenna. Before going to discuss this antenna-gain first, we need to know what is the antenna directivity.

Antenna Directivity

It can be defined as the ratio of maximum radiation intensity of a test antenna to the radiation intensity of an isotropic antenna or reference antenna which is radiating the same power in total. Directivity can be denoted by D.

Directivity of antenna shows, how it able to radiates the energy in one or more specific direction. The radiation pattern of an antenna determines its directivity value.

Then, Directivity D = maximum radiation intensity of a test antenna/radiation intensity of an isotropic antenna. Here, the isotropic antenna is an ideal antenna, which radiates its power equally or uniformly in all direction to space. There is no physical matter of isotropic antenna and it can be taken as a reference antenna only.

In another way, the antenna directivity can be defined as, the ratio of maximum radiation intensity of the test antenna to the average radiation intensity of the test antenna.

Antenna Directivity D = maximum radiation intensity of a test antenna / average radiation intensity of test antenna.

D = Ф (θ, Ф)max/ Фavg
D = Ф (θ, Ф)max/(Wr/4 π)
D= 4 π Ф (θ, Ф)max/Wr

Therefore D= 4 π(maximum radiation intensity)/total radiation power.

Antenna Efficiency

This is the important parameter of an antenna. The efficiency of an antenna is defined as the ratio of power radiated in all directions to the total input power supplied to its terminals. Due to resistance loss in the antenna, the total applied input is not radiated to its targeted direction. Antenna efficiency denoted by ‘η‘. Antenna efficiency can be known in percentages also when it’s multiplied with 100. Usually, the antenna efficiency factor lies between 0 and 1.

                                      Antenna Efficiency η =Power radiated by an antenna/total input

                                            η = Pr/(Pr+Pi) [Pr=radiated power Pi=ohmic losses in the antenna]

Antenna Gain Measurement

Gain mostly calculated in the figure of merit. Here, the gain is denoted by G or power gain Gp. By gain, we can calculate the antenna radiation pattern. “Antenna gain is defined as the ratio between maximum the radiation intensity of a subject antenna in a given direction to the max. the radiation intensity of an isotropic antenna” when the same amount of power is applied to both antennas.

“When directivity converted to decibels we can define it as antenna gain”.

Gain G = Maximum radiation intensity from the subject antenna (Фs) / Maximum radiation intensity from the isotropic antenna (Фi)

The gain of an antenna G = Antenna efficiency * Antenna directivity D

Units for Gain – dB (decibels), dBi (decibels relative to an isotropic antenna), dBd (decibels relative to dipole antenna)

The gain value indicates how much your antenna succeeded while converting the input power into radio waves in a specific direction and how it converts the radio waves into electrical form at the receiver side. Sometimes, the gain is discussed as a function of angle. In this case, the radiation pattern is to be considered.

Antenna Gain Formula

By the gain value, we can know how much amount of signal boosting provided to the input by the antenna.

It helps at the receiver stage, how much power required to reproduce the same transmitted signal from the channel.

Gain of a subject antenna or test antenna Gt = Gi + 10log10 (Pt/Pi)

Where

Gt = Gain of the tested antenna
Gi = Gain of an isotropic antenna
Pt = Power radiated by the test antenna
Pi = Power radiated by the isotropic antenna

Antenna Gain Conversion

Antenna gain is expressed in decibels (dB) because if the gain expressed in regular units like in terms watts in these cases when calculating the received power then the result would be very small i.e., sometimes it will give in exponential form also. It’s hard to consider every time these type of values so, the gain can be expressed in terms of Decibels (dB). 5 dB means 5 times the energy relative to an isotropic antenna in its peak direction of radiation.

The linear units are converted into decibels by following this equation.

Pdb = 10 log10p

Another unit for antenna gain is dBm. It means decibel relative to a milliwatt.

1W = 1000mw = 0dB = 30dBm

dBi is another unit for the gain of an antenna and its decibel of gain relative to an isotropic antenna. dBi means twice the power relative to an isotropic antenna in its peak direction of radiation.

So the gain can be expressed in units of decibels or decibels milli-watt or decibel isotropic antenna. Mostly it’s expressed in decibel (dB) only.

How to Increase Antenna Gain?

The gain of an antenna shows its ability to radiate the signals to channel in any direction. If the gain is more, such an antenna can be transmitted more power to the receiver in one particular direction and it attenuates all other signals from other directions. If antenna radiates the signals equally in all direction means it can be possible by only spherical antenna such is called an isotropic antenna and these do not exist in real times.

If the gain is more always it’s an advantage to the circuit but it only depends on the need. The following methods are useful to increase the gain of an antenna.

They are

• The effective area of the antenna.
• Parabolic reflectors
• Element arrays
• Reflector arrays
• Antenna efficiency
• Directivity.

The antenna is most useful in the field of communication for radiating and receiving the radio waves through an electric form in the channel. There are different types in antenna. Types of the antenna are having a different structure with each of them. As per the need, they have been used and if the gain of the antenna may be low or high i.e., purely dependent on the need only. If the gain is more then it’s capable of radiating the signals in a particular direction to space. If the gain is low then its coverage is wider range. If you observe the daily communication systems we can get more information about the importance of the antenna and antenna gain value.