Inside Wireless: Antenna Gain

Summary

In this video, Tasos from RF Elements explains the concept of antenna gain, focusing on the differences between dBi, dBm, and dB. He clarifies how antenna gain measures signal strength, how decibels work on a logarithmic scale, and why using dBi (isotropic gain) is important for accurate antenna performance comparisons. Tasos also discusses the misinterpretation of peak gain values, highlighting that antenna gain varies with angle and frequency. The video offers valuable insights for anyone looking to better understand the intricacies of antenna gain and how to interpret antenna datasheets correctly.

Takeaways

• 😀 Gain is a measure of how strongly an antenna radiates in any direction, and it is one of the most important antenna parameters.
• 😀 dB (decibel) is a logarithmic unit that helps express large differences in signal strength in a manageable way.
• 😀 A +3 dB change represents a doubling of energy on a linear scale (e.g., 3 dB = 2 units, 6 dB = 4 units, etc.).
• 😀 The dB scale allows for easier comparison of vastly different values by compressing large numbers into smaller ones.
• 😀 30 dB gain means approximately 1000 units, and 45 dB gain equals around 31,622 units, making the logarithmic scale very useful.
• 😀 A change of +15 dB results in 32 times the energy, demonstrating the significant impact of logarithmic scaling on signal strength.
• 😀 dB by itself is a dimensionless unit used when comparing values without a specific reference, while dB with a suffix (dBm, dBi) includes a reference value.
• 😀 dBi (decibels relative to an isotropic antenna) is commonly used to measure antenna gain, comparing it to a theoretical antenna that radiates uniformly in all directions.
• 😀 dBm is used to measure RF power levels, where power is compared to one milliwatt (mW), and common values include 10 dBm for 10 mW, 20 dBm for 100 mW, etc.
• 😀 It’s common to incorrectly refer to antenna gain as a single dB value, but it should be dBi to indicate the comparison with an isotropic antenna.
• 😀 Antenna gain varies depending on the angle and frequency, so it’s misleading to judge an antenna's performance based solely on its peak gain value.

Q & A

What does the gain of an antenna refer to?

The gain of an antenna refers to how strongly the antenna radiates in a particular direction in free space. It is a measure of the antenna's ability to focus its radiated energy.

Why is decibel (dB) used to measure gain instead of linear units?

Decibels (dB) are used because they operate on a logarithmic scale, which is more practical for comparing large differences in power levels. It allows for handling numbers that differ by orders of magnitude in a more manageable way.

What does a +3dB change mean in terms of energy?

A +3dB change means that the energy has doubled. On a logarithmic scale, a 3dB increase represents a doubling of power or intensity.

How does a 30dB gain compare to a 15dB gain in terms of energy?

A 30dB gain is 32 times the energy of a 15dB gain. This is because each 3dB increase corresponds to a doubling of energy, and a difference of 15dB represents 32 times the energy.

What is the significance of dBi in antenna gain measurements?

dBi stands for 'decibels isotropic' and indicates that the antenna's gain is being compared to an ideal isotropic antenna, which radiates equally in all directions. It is a measure of the antenna's efficiency in focusing energy.

What is the difference between dB, dBi, and dBm?

dB is a general measurement of signal strength relative to a reference value, while dBi specifically refers to antenna gain compared to an isotropic antenna. dBm, on the other hand, measures power relative to 1 milliwatt, indicating the power level of a signal in decibels.

What is an isotropic antenna?

An isotropic antenna is a theoretical antenna that radiates energy equally in all directions. It serves as a reference for comparing the gain of real antennas, which focus energy in particular directions.

How is antenna gain typically presented in datasheets?

In datasheets, antenna gain is usually presented as a single number, typically representing the peak gain of the antenna's main lobe at a specific frequency.

Why is it inaccurate to judge an antenna based solely on its peak gain?

It is inaccurate because antenna gain changes with both the angle and frequency. The peak gain may not fully represent the antenna's performance across all angles and frequencies, so it should not be the only factor considered.

How do dBm and dBi relate to each other in RF radios?

dBm is used to measure the power output of RF radios, with power levels referenced to a milliwatt. dBi, however, is used to measure the gain of antennas, which indicates how efficiently they radiate energy compared to an isotropic antenna.