guys, anyone here using external 4G antenna for their B618?

I got problem now where B618 place 1st floor 4G signal strength only middle but WIFI usage at lower floor is excellent. But if i put upstair, 4G signal strength is the best but WIFI signal at lower floor suffer. I got TP-link WA860RE range extender but due to plug location, even the extender can't really receive the good WIFI signal strength.

I'm thinking buy a 4G antenna for the B618 to be used in downstair, so that i can get both best 4G and WIFI signal at downstair.