Hello, sorry for this maybe dumb question. I'm thinking in replacing a 15 dbi ombidirectional antena connected lets say to a mikrotik 52 ac (1 wireless channel) as an AP for mobile devices. Disregarding the radiation pattern and angles of coverage wich is obviously different from an omni antenna vs a sector antena

would it be any difference regarding coverage and reliability of wireless mobile clients if i replace the omni 15 dbi antenna by a sector 120 15 dbi antenna?

the question aims to the point that usually the radiation pattern and angle of coverage changes between omni antennas to sector ones to increase the dbi but also i've seen that is usual to find same 15dbi antennas as sector ones, so what would be the advantage of reducing the angle to get the same dbi in this case?

regards

You want to have a certain coverage area for your antenna, so that it has some limited amount of stations in that area.
Sector antennas provide a way to have 3 smaller coverage areas from a single installation point (tower).
Or alternatively, to cover an area from one corner instead of from the middle.

In addition to different coverage patterns, described by @pe1chl, use of sector antennae also reduces interference received from directions not being covered (e.g. because there arent any of your customers).

Many thanks