Is there a Wifi booster for the Samsung Galaxy S4?


For the Samsung Galaxy S4 (S4 SGH-1337 AT&T) is there such a device as a portable Wifi booster, range extender that is safe? I’ve heard of external antenna like devices, unfortunately they are not only large and cumbersome, they can run a risk of damaging the phone. Living in California, I go from strong Wifi signals, hotspots etc. to being totally out of range. Any advice would be greatly appreciated!