Antenna Downtilt: A Practical Overview

Mitigating inter cell interference is one of the top technical challenges that operators have to contend with when managing cellular networks with multiple base stations. This will become increasingly important as we head into the 5G era, as service providers will be looking to densify networks to increase capacity.

In order to densify successfully, base stations have to be able to reuse frequencies within their cellular clusters. Operators must therefore have strict control over each antenna’s radiation pattern. Radiation sprawl will lead to electromagnetic interference, and poor quality communications.

As we explained in a recent technical white paper, one of the most effective ways to prevent radiation sprawl is to direct an antenna’s vertical pattern towards the ground in a process called “downtilt.”

Downtilt can be accomplished using the following methods: 

Mechanical downtilt: This process involves physically adjusting an antenna’s pole-mount brackets, using a digital level set against the back of the antenna to obtain an accurate measurement. This is the easiest and fastest way to control an antenna’s pattern, but the downside is that it will produce an effect called pattern blooming where the signal is reduced more at bore sight and less at angles away from bore sight.

Electrical downtilt: It’s also possible to change an antenna’s radiation pattern by introducing an electrical phase taper inside of a sector antenna array. Electrical downtilt enables a uniform reduction in coverage, as it prevents pattern blooming from occurring. Fixed electrical downtilt antennas have a fixed downtilt whose values cannot be adjusted after design and considers the antenna’s elevation beamwidth among other deployment factors. Antennas can also have variable electrical downtilt that can be changed remotely. Others feature manual electrical downtilt, which is set using a tuning knob when an antenna is installed or by a second tower climb if an adjustment is necessary. The tradeoff, however, is that variable and manual electrical downtilt is typically more expensive and results in reduced antenna gain.

Now that you have a basic understanding of how downtilt works, check out our white paper titled “Downtilt: How to Set It” for a more comprehensive overview of this topic.

You can access this document by clicking here: https://kpperformance.com/Pages/Technical-Articles/White%20Paper%20-%20Downtilt-How%20to%20set%20it.pdf.