TECHSHIP IS A GLOBAL SUPPLIER OF WIRELESS COMPONENTS
I have an antenna with linear polarization. How shall I place the module?
The general rule is to place the module in the same direction as the sender/receiver antenna. If the antenna your antenna is communicating with has a horizontal antenna, place it horizontal. If the antenna is a vertical antenna, place it vertical. This can be an issue, since you might not know how the other antenna is placed.
The other rule is that if the antenna is close to the ground, place it horizontal. This will allow the radiated waves to travel across the ground, instead of getting caught in it.