Galaxy s4 MINI DUO - Low Wifi/Antenna problem. DO NOT KNOW ANTENNA LOCATION

[AC Question]

I was reading people tell this same issue as they couldn't use the wifi if wheren't TOO CLOSE the modem. So people told that the problem is the antenna, but my problem is that i DON'T KNOW what im was supposed to fix or clean. Every single image on google shows only and just only the antenna on normal S4, not even mini, or mini duo. i need to know where it is to see if there is a problem