What does the gain of an antenna NOT tell you?

Mobile networks are complex systems with multiple contributing elements. One of the main challenges for operators is balancing equipment, software, and services. This balance is crucial to make sure users have the best possible experience with their mobile services.

In pursuit of this goal, the Service Providers technical teams focus on network planning, evaluations, and rigorous testing to select the optimal equipment for their networks. Among these essential components is the passive antenna, the familiar white or gray panel on towers that delivers the signals enabling mobile phones to connect.

So… Let's explore this intriguing question: If the mission is to elevate service quality while ensuring users enjoy good and clear signals, faster speeds, and seamless connectivity, why do we often place so much emphasis on antenna gain as the primary measure of success?

The gain value in antenna datasheets only relates to a specific direction, focusing on a particular spot in the cell where there might not even be much traffic. This opens a world of possibilities to consider other factors that could enhance network performance even further.

Despite factual evidence, we often overlook critical factors that significantly impact customers' main goal: improving service for end users. At Ericsson Antenna System, our research and development efforts are dedicated to understanding how different antenna parameters enhance network performance. Beam efficiency, in particular,  is a valuable indicator of an antenna's potential performance.

Some customers wonder if higher beam efficiency always translates to more gain. The answer is no, and I'd like to clarify, from a simplified perspective, a few key concepts and their differences.  

1. Beam efficiency

Very concisely, and focusing only on the horizontal plane, beam efficiency (measured in percentage - %) is (1) the radiated energy in the sector divided by (2) the total energy radiated by the antenna. But here, it is important to highlight, the definition of sector. Generally speaking, we refer to a 120-degree sector that goes from -60 to +60 degrees starting from the beams main direction of radiation.

Optimizing Antenna Beam Efficiency: Enhancing SINR, RSRP, and network performance by maximizing signal concentration within targeted sectors

In this image where a horizontal section of the radiation pattern of an antenna is seen as an example, the entire area of the sector indicated in blue that overlaps with the antenna beam (red) contributes to the beam efficiency. In turn, all the energy that is outside this zone acts as an interferer in the adjacent sectors. The tests we have done show us that the higher the concentration of energy (signal) in this space, the greater the contribution to network performance, sustaining improvements in signal-to-interference plus noise ratio (SINR), high-grade modulation, power received from the reference signal (SINR,  Reference Signal Received Power, or RSRP), carrier aggregation, which clearly result in a better end-user experience.

In addition, a higher quality signal reception allows us to appreciate a reduction in the transmission power of mobile phones, giving more battery life of the equipment to the user and reducing uplink interference in the network.

2. Gain

Gain, in a practical sense, is defined as directivity minus losses. Gain is important, as it is the measurement that tells you how effectively the antenna radiates the power it receives in a specific direction.

And remember, directivity is the ratio of the intensity of radiation in a specific direction (the direction of maximum intensity) to the intensity of radiation averaged in all directions. In other words, it is achieved by dividing the maximum radiation intensity by the average radiation intensity, and is expressed in dBi.

And I want to highlight this part of a specific direction, because it has a great influence on our evaluation of an antenna. Let's look at the graph for a better explanation.

Measuring antenna gain: Understanding beam behavior across 120-degree sectors for enhanced service and user experience

In this graph the green arrow indicates the specific direction in which the gain is measured, notice how of the entire 120 degree sector that we saw in graph 1, this point represents only a small part, and it does not provide too much information about the behavior that this beam is really having when you evaluate the entire sector,  where you effectively want to improve the service and where a greater number of users are concentrated.

3. Half power beamwidth (HPBW)

An additional concept I'd like to clarify is Half Power Beamwidth (HPBW), which is an angle, measured in degrees. The amplitude of this angle is determined by the magnitude of the radiation power and monopolizes the region to which the radiation power decreases by 50% (or 3 dB) compared to the maximum power of the main beam.

In this graph we can see marked in green a horizontal HPBW of about 65 degrees, which is a common design criteria for passive antennas in tri-sector site configurations.

Understanding Horizontal HPBW: Typical 65-degree beamwidth design for passive antennas in tri-sector site configurations

In summary, we have learned that:

1. When we talk about profit, we are referring to a specific point in the sector.
2. When we talk about H-HPBW we are referring to an angle within the sector.
3. The sector is defined by 120 degrees (-60 to +60) from the main beam.
4. Beam efficiency measures the percentage of energy radiated in the sector with respect to the total energy radiated.

The studies and tests that Ericsson continuously performs to improve the design of its antennas and maximize the performance and performance of the network, show that the focus on beam efficiency is going in the right direction.

Comparative analysis of antenna patterns: Balancing gain, beam efficiency, Horizontal HPBW, and 120-degree sector coverage

And finally, here I show a graph where you can see all the concepts together:

1. The blue pattern represents an antenna that has better gain, but worse beam efficiency. (radiates less energy in the sector).
2. The red pattern represents an antenna that has lower gain, but better beam efficiency (it radiates more energy in the sector).
3. The angle bounded by the green lines represents the horizontal HPBW.
4. The opening marked by the purple lines represents the 120-degree sector.

Here it is clearly observed how the blue antenna, although it has better gain, has worse beam efficiency, with a lower proportion of its beam in desired parts within the sector and more energy radiated in unwanted areas. When comparing these patterns, the red pattern antenna does  indeed result in better performance, but many times we are attracted to choose the blue  one just because it has better gain! We must evolve our antenna evaluation criteria and focus on the impact on the network rather than individual specifications.

Read more

• Learn more about trio net antennas and design. 
• Watch our on-demand webcast with ABI Research: How Antennas Drive Higher Throughput and Energy Efficiency in 5G Networks
• Watch our on-demand webcast with Light Reading: The Future of Programmable Networks: Highlighting the Latest RAN Product Innovations
• Find out more about the benefits of Ericsson Antenna System. 
• Read the press release announcing our new wave of radio, antenna and RAN Connect products to advance high-performing programmable networks.
• Explore the seven tenets of a modern antenna strategy.