When considering AP placement, stacking APs vertically is generally not optimal, with the Alta lab AP6 Pro Outdoor being a notable exception designed for such configurations. Always perform a POST installation survey or at least a validation test after installation to ensure optimal performance.
The best placement strategy depends on various factors such as coverage requirements, budget, placement, and aesthetic constraints. For instance, in a two-story home, wall mounting an AP may often be more cost-effective and efficient than installing an additional AP on the upper floor.
In the use case below to cover the perimeter of some building, with the Alta Lab Pro (indoor) , its handing under an overhang (it got IP54 rated ) I would professionally recommend ceiling mounting an omnidirectional antenna like this, so you pick up less interference from farther away. I would also place it closer to the corner, so your client STA has more time to roam seamlessly to the AP in the north side of the building (assuming there is one). But if you want to let the AP radiate as much as possible from the building, wall-mount it.
Here’s a visual example of the Alta Lap AP Pro (indoor) 5Ghz radio, to give you an idea of the antenna patterns in both mounting directions.
Ultimately, both options will work and probably nothing will break. If you have a specific reason to wall mount an omnidirectional antenna or vice versa, just go ahead and do it, as long as you give it some thought before installing it.
Polarization
It’s not always clear from the specification of the AP is dual-polarised. Antennas radiate and receive electromagnetic waves that have a specific orientation, called polarization. Polarization can be horizontal, vertical, or circular. The polarization of an antenna is crucial because maximum signal strength and efficiency are achieved when both the transmitting and receiving antennas have the same polarization
But how the vendor recommends you to place it will mostly give a hint. When a vertically polarized ceiling-mounted antenna communicates with a horizontally polarized client device, there is a polarization mismatch. This mismatch (Because the client STA is almost always horizontally polarised.) leads to a loss of signal strength of approx 3dB. he 3dB figure comes from the general rule that a 45-degree polarization mismatch (common in typical scenarios) causes a 3dB loss. In the case of a completely orthogonal polarization (90-degree mismatch, such as vertical vs. horizontal), the theoretical loss is 20dB. However, in practice, with some device orientations and reflections, the observed loss is typically around 3dB.
Conclusion
In environments such as offices or public spaces, where client devices have mixed or variable orientations, using dual-polarized antennas can significantly enhance performance by minimizing signal loss due to polarization mismatch. Client devices like smartphones, laptops, and tablets are typically horizontally polarized due to how users hold them, while ceiling-mounted antennas are often vertically polarized to effectively cover the area below. This polarization mismatch can result in a signal loss of about 3dB when single-polarized antennas are used. Dual-polarized antennas, however, can transmit and receive both horizontally and vertically polarized signals, thereby ensuring better alignment with the client’s antenna orientation and reducing the potential loss.