pls help: wifi turns off when display turns off topic

yesterday i purchased a galaxy tab s 10.5 lte model. i found the wifi automatically turns off when display turns off. i also changed wifi on during sleep settings to always. please help
my phone is not rooted.
settings > Wireless & Networks > WiFi Settings
> advanced>always

above is my current setting , i also changed the options to see whether it works, but result is the same