With appearance of Raspberry Pi 3 the new wave of hacking begun. This time the attention falls on new WiFi functionality. As wardr states: “It’s not clear why an external antenna is not an option for the Pi 3 ”. Having said that he thought why not including one by himself. He found that there can be two options of including external WiFi antenna. One could be more barbarian – just remove chip antenna and solder it to left top mount pad. This is more messy part as you need to scratch ground plane to make it possible soldering copper mesh.
Another way is more civilized. On the bottom side of Raspberry Pi 3 there is two exposed pads where U.FL connector almost fits. Yet you still need to clear some solder-mask and rotate one zero ohm resistor. By attaching external antenna he was able to get better results.
As you can see the use of U.FL performs best. As always you should know what are you doing when messing with board components. They are tiny and you can permanently damage them with slight move. In other hand, if you want to extend signal power and range of your Raspberry Pi 3 this is one way of doing it.