“low gain antennas with a Vertical of 55 and 28 degrees”
that’s a bad choice to put this kind of antennas at 12m above ground.
55° = you must put at least 30° tilt
28° = you must put at least 17° tilt
With less tilt than that, there is going to be overshooting and cell resurgence !
i recommend you choose another antenna to install up there. The gain doesn’t really matter : you can always decrease the power of the BTS to obtain (in the end) a total EIRP of about 40dBm or 45dBm.
“Also what I am thiking of is a great tilt may cause a wider cell which may increase the overlap between the other neighbouring cells.”
I don’t understand this sentence ! If you increase the tilt, the antenna will point more towards the ground. Therefore increasedowntilt = reduce the cell range = reduce the overlap with neighbors.
However, the cell you’re putting is a micro cell, it means that it will be totally overlaid by an umbrella cell.
The overlap with the umbrella cell is 100%, whichever is the downtilt you choose for the microcell.
Last thing : reduce the power will not work as good as increasing the downtilt. The priority is to put a high downtilt, to compensate for the high height.