If you need the SMA from antenna side with the little male center pin you need SMA, not RP-SMA connector like wifi antennas.
You can use the adapter you linked if you don't find the right UHF antenna / SMA connector
The antenna need to be tuned for the frequency use, you cannot use a wifi (2.450Mhz) antenna for Oplink (400-440Mhz).
Same for video antennas running around 5.8GHz.
Antenna gain is mostly around 3dB gain (best case) for omnidirectional radiation.