Being that it is a Ipad wont factor in, You can just google " Laptop powered wifi boosters "
You will just need to choose between powered "omni directional", and a powered "directional" wifi booster. The difference between the two is the Omni directional will not require you to point it towards the wifi spot. A directional booster will require you to point it in the general area of the wifi spot. The advantage of a directional is that it will give you slightly greater range.
A Key word to note is "powered" , as you don't want to waste your money on non powered antennas. The money spent there could be put toward a more expensive, but a lot more effective powered booster.
Last thing to note is that the booster only requires USB to power it. Some powered boosters will require more power from a electrical jack and that may limit where you choose to connect from.