How can you measure the gain of an RF antenna?

The gain of an RF antenna is a measure of how well it converts the input power into radiated electromagnetic waves in a given direction. It is an important parameter for evaluating the performance and efficiency of an antenna in wireless communication systems. However, measuring the gain of an RF antenna is not a trivial task, as it involves several factors and methods that need to be considered. In this article, you will learn the basics of RF antenna gain, the different types of gain, and the common techniques for measuring it in the laboratory and in the field.

1 What is RF antenna gain?

RF antenna gain is a dimensionless ratio that compares the intensity of the radiation emitted by an antenna in a specific direction to the intensity of a reference antenna or a hypothetical isotropic antenna. An isotropic antenna is a theoretical antenna that radiates equally in all directions, forming a perfect sphere. The gain of an antenna is usually expressed in decibels (dB) relative to an isotropic antenna (dBi) or a dipole antenna (dBd). A dipole antenna is a simple antenna that consists of two thin metal rods or wires that are fed by a balanced transmission line. The gain of a dipole antenna is 2.15 dBi.

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Omogbai Martins

Incident Management Specialist || Telecommunications Generalist || Engineering Professional || Fiber Optics Specialist || Research and Technical Writing Consultant || RF Optimization (Planning) Engineer
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• Utilize antenna pattern measurements to assess the directional characteristics of the RF antenna and calculate gain based on signal strength in different directions. • Measure the radiation efficiency of the antenna by comparing the power radiated in a specific direction to the power supplied, allowing for the determination of gain. • Perform field strength measurements at various distances from the antenna to quantify the signal strength and calculate gain, considering factors such as transmission power and receiver sensitivity.

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Oleg B. Vorobyev

Physics R&D, Mathematics Tutor at SuperProfs.com
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The gain of an RF antenna can be measured using a pair of known and unknown antennas or a pair of unknown antennas. In the first case, we measure the power supplied for radiation of the known antenna, as well as calculate decrease of power due to propagation of radiation from the known antenna to the unknown. Using the sum of the gain (dB) of the radiating antenna with free space loss, we can calculate power in the unknown antenna, which depends on its gain. If measured power in the unknown antenna exceeds the calculated power, then it has gain. In the case of unknown antennas, their parameters should be same. That allows to reduce the latter case to the case of the known and unknown antennas.

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2 Why is RF antenna gain important?

RF antenna gain is important because it affects the coverage, quality, and reliability of wireless communication systems. A higher gain antenna can transmit and receive signals over longer distances, as it focuses more power in the desired direction and reduces the interference from other directions. However, a higher gain antenna also has a narrower beamwidth, which means that it has a smaller angular range where it can send and receive signals. Therefore, the optimal gain of an antenna depends on the application and the environment. For example, a cellular base station may use a high-gain directional antenna to cover a large area, while a mobile device may use a low-gain omnidirectional antenna to maintain connectivity regardless of its orientation.

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3 How to measure RF antenna gain in the laboratory?

One of the most common methods for measuring RF antenna gain in the laboratory is the two-antenna method. This method involves placing the antenna under test (AUT) and a reference antenna (REF) in an anechoic chamber, which is a shielded room that absorbs or reflects all external and internal electromagnetic waves. The AUT and the REF are connected to a signal generator and a power meter, respectively, through coaxial cables. The signal generator sends a known RF signal to the AUT, which radiates it to the REF. The power meter measures the received power at the REF, which depends on the gain of both antennas and the distance and angle between them. By using a calibrated REF with a known gain, and by varying the distance and angle between the AUT and the REF, the gain of the AUT can be calculated.

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4 How to measure RF antenna gain in the field?

Another common method for measuring RF antenna gain in the field is the three-antenna method. This method involves placing the AUT and two reference antennas (REF1 and REF2) in an open area, away from any obstacles or reflections that may affect the measurements. The AUT, REF1, and REF2 are connected to a signal generator, a power meter, and a spectrum analyzer, respectively, through coaxial cables. The signal generator sends a known RF signal to the AUT, which radiates it to both REF1 and REF2. The power meter and the spectrum analyzer measure the received power at REF1 and REF2, respectively, which depend on the gain of the three antennas and the distance and angle between them. By using two calibrated REFs with known gains, and by varying the distance and angle between the AUT and the REFs, the gain of the AUT can be calculated.

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Naseef Mahmud

I like python, ML and RF.
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Things to consider, 1. use CW tone and not a modulated signal. 2. Polarization of the antennas. 3. Pointing angle , alignment and beam illumination. 4. Line of sight measurements only.

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5 What are the challenges and limitations of measuring RF antenna gain?

Measuring RF antenna gain is not a simple or accurate process, as it involves several challenges and limitations that may introduce errors and uncertainties. For instance, when choosing the reference antenna, it should have a stable and well-known gain over the frequency range and the angular range of interest. However, no real antenna is perfectly isotropic or dipole-like, and its gain may vary due to manufacturing tolerances, environmental conditions, and aging effects. Aligning the antennas in the same polarization and orientation can be difficult to achieve in practice, especially in the field. Moreover, ensuring that the antennas are in the far-field region where the radiation pattern is stable and independent of the distance requires a large space. Lastly, performing measurements in a free-space environment without reflections or interference from other sources may be impossible to achieve in some scenarios.

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Rhys Kissell
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Assessing an antenna's gain involves navigating challenges like environmental reflections from buildings and signal obstructions by terrain. Utilizing anechoic chambers, designed to eliminate external signal interference, and calibrating with reference antennas, such as dipoles or horn antennas, enhances measurement accuracy. Despite potential issues like multipath distortion, this approach reliably provides an idea of an antenna's effectiveness in real-world conditions, assuming a clear day without significant terrestrial or solar weather events, which can variously impact signal propagation.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How can you measure the gain of an RF antenna?

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1 What is RF antenna gain?

2 Why is RF antenna gain important?

3 How to measure RF antenna gain in the laboratory?

4 How to measure RF antenna gain in the field?

5 What are the challenges and limitations of measuring RF antenna gain?

6 Here’s what else to consider

Telecommunications Engineering

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How can you measure the gain of an RF antenna?

1

2

3

4

5

6

1 What is RF antenna gain?

2 Why is RF antenna gain important?

3 How to measure RF antenna gain in the laboratory?

4 How to measure RF antenna gain in the field?

5 What are the challenges and limitations of measuring RF antenna gain?

6 Here’s what else to consider

Telecommunications Engineering

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