ISP Wireless - Antenna Alignment for Outdoor Wireless Links

This article will provide the best practices for antenna alignment, as well as basic steps to align in both Point to Point (PtP) & Point to Multi-Point (PtMP) scenarios.

Introduction & Best Practices

Having a perfectly aligned link is crucial for a well-performing link. Without proper alignment, less-than-desirable throughput, high latency, and/or stability issues can occur. By following the steps outlined in this article, you can better maximize link performance. Listed below are some best practices for antenna alignment: 

• Always plan your outdoor link using the UISP Design Center, to ensure that the products you're using will successfully link with strong signals & speeds.
• Conduct a site survey at the planned install site to determine where your antennas will be installed. Choose locations where obstructions (ex. rooftop, chimney, walls, poles, other antennas) will not cause signals to bounce/reflect between link ends.
• Most new Ubiquiti radios (besides airMAX M-series) feature a short-range, Bluetooth management radio for easy setup. Download UISP Mobile (available for iOS and Android) to set up each device.
• Configure & set up the initial link in your workspace, not in the field. Once the link is connected, then move to deploy the devices outside.
• Especially in PtP scenarios, working with a partner is often necessary to make fine-tune adjustments at each side of the link. Only attempt to align one side of the link at a time, changing vertical & horizontal angles in small steps until you reach the peak signal on each side.
• Higher frequency radios (ex. 11GHz, 24GHz, 60GHz) require much more precision & attention to properly align. Some devices ship with precision mounting kits (PAKs) included.
• Align antennas to match the signals estimated in UISP Design Center. If after some time aligning, you cannot achieve these signals, or there is a discrepancy in signals across MIMO chains greater than 2-3 dB, then you may be aligned to the antenna's side lobe, or have one or more Fresnel Zone obstruction between link ends.

The image below provides some example locations (good, bad & best) for airFiber 5GHz (AF-5/AF-5U) devices, and the following recommendations can, generally speaking, be applied to other devices/antennas as well:

• For best performance, install as high up as possible, with a line of sight free from obstructions.
• Installed 1 m (3.3 ft) below the highest point of the structure to reduce the risk of a lightning strike.
• When the device must be installed above a metallic surface like a corrugated flat roof or water tower, then you should ensure that the device is not located more than 3 m (10 feet) above the metal/reflective surface.
• What is generally true for cellular installations is true for fixed wireless antennas.
• Mount the antenna where it can see no reflections in the near field, such as perimeter mounting on a water tower/structure (best), mounting near the edge of the top of a structure, or mounting on an elevated mast or tower.
• Radios that are mounted anywhere near the surface of a roof or the top of a water tower can be significantly affected by reflections, especially at higher frequencies (ex. 24GHz, 60GHz). Full-duplex capable devices like AF-5 & AF-24 (when configured with FDD, Frequency Division Duplexing mode) are even more susceptible to problems related to the deployment environment than half-duplex radios (which use TDD, Time Division Duplexing mode).

Steps to Align in PtMP Deployment

Step 1: Ensure the plan is viable with our link planner.

• Visit UISP Design Center and select the AP location and desired Station locations.
• Set the real height of each location.
  • airLink does not account for trees, buildings, or other obstructions; only ground elevation. If deployment is in a wooded area, the obstructions will have to be judged by sight, either by looking at the satellite imagery or by going on site.
  • For PtMP deployments, the AP is generally higher, Stations will be closer to the ground.
• Select the antennas that will be used at each location.
• Select the total EIRP that you are allowed to use. 
• Change the channel width until the desired capacity is reached.

If the signals are not close to -50, consider using higher gain antennas.

Step 2: Install the Access Point.

• For longer links, it can be easier to use satellite imagery to pick out a landmark that is visible from the AP location and point the AP in that direction.
• Be mindful of the tilt. It is very easy to point the AP too far up or down. Most sector antennas have a 2-degree electrical down-tilt already.

Step 3:  Install the Station or Stations.

• Find a high ground high above all reflective surfaces to mount the Client's CPE.
  • Never install and point a CPE across the surface of a roof.
  • Be sure to install the antenna two or three meters above the ground.
• Point the CPE in the general direction of the AP, then log into it.
  • Once logged in, open the scan list and select the AP's SSID. 
  • Once the connection has been established, open the alignment tool and start very slowly panning the antenna from the left to the right, keeping in mind the best signal that appears. Once the signal starts dropping dramatically, pan back from right to left until the signal starts dropping again. Pan one more time from left to right and stop once again at the best signal seen so far.
  • Repeat for elevation.
• The signals should now match the expected signal from airView.

Step 4: After several CPEs have been installed, go back to the AP and adjust the alignment as needed.

Steps to Align in PtP Deployment

1. Use UISP Design Center to find landmarks near both ends of the link for the installers to aim at.
2. Mount the Access Point and Station radios with installers at both sides.
3. Have both installers use the previously found landmarks to establish a link. This can take quite a while depending on the experience of the installers. Each installer may need to change the azimuth and elevation a few degrees at a time in order to establish the initial link. Be sure only one antenna is being moved at a time!
4. Open up the alignment tool in the airOS WebUI and have one installer slowly adjust the azimuth on one antenna until the signal gets better, and then it begins to worsen.
5. Once you notice you're losing signal, start backing up the azimuth until you reach the peak signal.
6. Repeat step 5 for the elevation.
7. Do the same for the second installer: have the second installer slowly adjust the azimuth on one antenna until you see the signal improve, then get worse again, then again for elevation.