Antenna Gain: What It Means and How It Works

Antenna gain indicates how effectively an antenna concentrates radio-frequency energy in a specific direction compared with a reference antenna. It is typically expressed in decibels relative to an isotropic radiator (dBi) and describes antenna performance in wireless communication systems.

The gain of an antenna affects the strength and distribution of a transmitted or received signal. Because it depends on the antenna's directivity and efficiency, gain alone does not describe its full radiation performance.

Antenna Gain Meaning

Antenna gain is the antenna's ability to concentrate RF energy in a particular direction compared with an ideal isotropic antenna.

An isotropic antenna is a theoretical reference that radiates equally in every direction. An antenna with 10 dBi gain concentrates energy more strongly in its main radiation direction than this reference.

Antenna gain does not represent additional transmitter power. The antenna redistributes available RF energy, increasing radiation intensity in some directions while reducing it in others.

This is why high-gain antennas are commonly used for applications where signal energy needs to be concentrated, such as point-to-point wireless links.

What Is the Gain for an Antenna Measured In?

Antenna gain is most commonly specified in dBi. The "i" indicates that the value is referenced to an ideal isotropic radiator.

For example, an antenna rated at 12 dBi has a radiation intensity 12 dB higher in its peak direction than an isotropic reference antenna for the same input power.

Antenna specifications can also use dBd, which references a half-wave dipole. The approximate conversion is:

dBi = dBd + 2.15 dB

Check the reference unit when comparing specifications from different manufacturers.

Antenna Gain and Directivity

Directivity and gain describe related but different properties.

Directivity measures how strongly an antenna concentrates radiation in a particular direction without accounting for losses. Gain includes antenna efficiency, so losses reduce the gain below the theoretical directivity.

The relationship is:

Gain = Directivity × Efficiency

When using decibels:

Gain (dBi) = Directivity (dBi) + 10 log₁₀(Efficiency)

For example, an antenna with 14 dBi directivity and 80% efficiency has approximately 13 dBi gain.

Antenna Peak Gain and Radiation Pattern

Antenna peak gain is the highest gain measured across the antenna's radiation pattern. It normally occurs in the direction of the main radiation lobe.

A directional antenna concentrates energy into a relatively narrow beam, so its peak gain can be substantially higher than the gain measured away from the main beam.

An omnidirectional antenna distributes radiation around the horizontal plane rather than concentrating it into one narrow horizontal direction. Its radiation pattern still varies vertically, so its gain is not identical at every angle.

The radiation pattern therefore provides information that a single peak-gain number cannot show.

Antenna Realized Gain

Antenna realized gain accounts for impedance mismatch in addition to the antenna's radiation characteristics and efficiency.

When the antenna impedance does not match the transmission line, part of the supplied RF power is reflected rather than radiated. Realized gain reflects the effect of this mismatch.

This makes realised gain particularly useful for evaluating practical antenna performance because the measured value accounts for how much input power is effectively available for radiation.

Cable, connector and adapter losses occur outside the antenna itself and should be included separately when calculating the complete RF link budget.

Maximum Antenna Gain and Peak Gain

The maximum antenna gain is generally the highest gain value specified for an antenna under defined frequency and measurement conditions.

The peak gain of antenna can refer to the highest measured gain at a particular frequency or direction. Manufacturers may use these terms differently, so always check the test conditions and frequency in the technical specification.

For example, an antenna may have a maximum gain of 13 dBi at 2.6 GHz while producing lower gain at other frequencies in its operating range.

A maximum value therefore does not mean that the antenna maintains that gain across its entire frequency range.

Maximum Gain of Antenna Across Frequency

The maximum gain of antenna depends on its design and operating frequency. Antenna dimensions, element spacing, impedance matching and radiation characteristics change relative to wavelength as frequency changes.

A broadband antenna can therefore have different gain values at different frequencies.

These values are illustrative; actual performance depends on the antenna design and manufacturer measurements.

When selecting an antenna, the gain at the frequency used by the wireless system is more relevant than the highest number listed in the specification.

Measuring Antenna Gain

Measuring antenna gain requires controlled RF conditions because reflections, nearby objects, cables and other environmental factors can affect the result.

One established method is the gain comparison method. The antenna under test is compared with a calibrated reference antenna, and the difference in received signal levels determines gain.

Anechoic chambers are also used for antenna testing because their RF-absorbing surfaces reduce reflections from walls and surrounding objects. Measurement systems can map the antenna's radiation pattern and determine its gain at different frequencies and angles.

A complete antenna test can measure:

• Peak gain

• Gain across the operating frequency range

• Radiation pattern

• Beamwidth

• Front-to-back ratio

• Polarisation

• Efficiency

• Impedance matching

Measurement conditions matter because gain specifications are meaningful only when the test frequency, setup and reference method are known.

How Antenna Gain Affects Signal Range

Antenna gain can increase signal strength in the antenna's main radiation direction, but gain alone does not determine wireless range. For FPV systems, FPV drone distance also depends on transmitter power, receiver sensitivity, frequency, antenna alignment, interference and environmental conditions. 

A link's performance also depends on transmitter power, receiver sensitivity, frequency, propagation losses, cable losses, antenna alignment, polarisation and environmental interference.

A directional high-gain antenna can improve a point-to-point link by concentrating RF energy toward the receiving antenna. The same antenna may be unsuitable for an application requiring broad coverage because its main beam is narrower.

For this reason, evaluate antenna gain alongside the radiation pattern and intended coverage area.

High-Gain and Low-Gain Antennas

Low-gain antennas generally provide broader radiation patterns, making them suitable for applications that require coverage across multiple directions.

High-gain antennas concentrate RF energy more strongly and typically produce narrower beams. They are commonly used for directional communication where the transmitting and receiving antennas can be aligned.

Increasing gain often reduces beamwidth, particularly in directional antenna designs. This creates a trade-off between concentrated signal energy and coverage angle.

The correct gain depends on the required communication distance, coverage area, frequency and antenna position.

How to Choose Antenna Gain

Select antenna gain based on the required radiation pattern rather than choosing the highest available value. Compare FPV antennas by frequency range, gain, radiation pattern, and beamwidth to match the antenna to the RF application. 

Check these specifications together:

1. Operating frequency — The antenna must support the frequencies used by the wireless system.

2. Gain — Check the gain at the actual operating frequency rather than only the maximum advertised value.

3. Radiation pattern — Confirm that the antenna concentrates energy in the required directions.

4. Beamwidth — A narrow beam requires more precise positioning and alignment.

5. Polarisation — The antenna should match the communicating system's polarisation.

6. Impedance — A suitable impedance match reduces reflected RF power.

7. Connector and cable losses — These losses affect the RF power delivered to and from the antenna.

For a point-to-point link, a directional antenna with higher gain may provide the required signal concentration. For broader-area coverage, a lower-gain antenna with a wider radiation pattern may be more appropriate.

Antenna Gain in an RF Link Budget

Antenna gain is one component of an RF link budget. The received signal level depends on transmitted power, antenna gains and propagation losses throughout the communication path. 

A simplified link-budget relationship is:

Received Power = Transmit Power + Transmit Antenna Gain + Receive Antenna Gain − Path Loss − System Losses

All values are normally expressed in dB or dBm.

This calculation shows why you shouldn't consider antenna gain in isolation. Increasing antenna gain can improve the link in the intended direction, but cable losses, poor alignment, interference and propagation conditions can reduce the practical benefit.

Key Points About Antenna Gain

Antenna gain describes how much an antenna concentrates RF energy relative to a reference antenna. It is normally expressed in dBi and varies with frequency and direction.

Peak gain is the highest value in the radiation pattern, while realised gain also accounts for impedance mismatch. Directivity describes directional concentration without including antenna efficiency.

When comparing antennas, consider gain along with frequency range, radiation pattern, beamwidth, efficiency, impedance, and installation conditions. These specifications determine how the antenna will perform in an actual RF system.

FAQs

1. Does antenna gain affect transmit and receive performance?

Yes. Antenna gain affects both transmission and reception because it describes how effectively the antenna concentrates RF energy in a given direction.

2. Why does antenna gain change with frequency?

An antenna's electrical dimensions, impedance and radiation characteristics vary with frequency, so its gain can change across its operating bandwidth.

3. Does higher gain reduce antenna coverage?

Higher gain often produces a narrower radiation pattern, which can reduce coverage outside the antenna's main beam while increasing signal concentration in the intended direction.

4. What is the relationship between antenna gain and beamwidth?

Higher directional gain generally corresponds to a narrower beamwidth because the antenna concentrates RF energy into a smaller angular area.

5. Can two antennas with the same gain perform differently?

Yes. Two antennas with the same gain can have different beamwidths, radiation patterns, polarisation characteristics, efficiency and frequency responses.

6. How does antenna efficiency affect gain?

Lower efficiency reduces gain because some supplied RF power is lost through conductor losses, dielectric losses, and other inefficiencies.

7. Does antenna gain increase transmitter power?

No. Antenna gain does not increase the electrical power the transmitter supplies. It changes how that available RF energy is distributed spatially.

8. Why is antenna alignment important for high-gain antennas?

High-gain directional antennas usually have narrower beams, so small alignment errors can move the receiving antenna outside the strongest part of the radiation pattern.

9. How do cables affect the effective antenna gain?

Cable and connector losses reduce the RF power reaching the antenna or receiver, lowering overall system performance even when the antenna itself has high gain.

10. Can antenna gain be different in different directions?

Yes. Gain varies across the radiation pattern, with the highest value normally occurring in the main lobe and lower values occurring in other directions.

11. Should antenna gain be considered when calculating an RF link budget?

Yes. Transmit and receive antenna gains are key inputs in an RF link budget because they affect the estimated received power alongside transmit power, path loss and system losses.