Most small , omnidirectional WiFi antennas have an SMA connector, which is the Reverse Polarity version of the SMA connector type for antennas. Most WiFi Access Points come with an SMA female jack, with a removable, small omni-directional antenna connected to the jack.
The removeable antenna can be replaced with an upgrade, and/or re-positioned in a location with line of sight, and thus a much better signal reception: Repositioning the antenna can be accomplished by mounting it high on a wall, roof or tower, and placing the router as high as possible also. Connect the router to the antenna with an RP SMA cable, which is a coaxial cable assembly that has an SMA female connector on one end and an SMA male on the other end. It’s imperative to minimize the length of this cable, by placing the router close to the antenna if possible, because 1dBi of signal gain is lost in each meter of antenna cable. You can power the router with Power Over Ethernet, so that you are not limited by the traditional power cord or location of power outlet.