said by celluser :
why on earth do they need an antenna anywhere near this size for this application? They don't get the cell signal from the MOON!
It's not just distance, it's also signal strength. Cell phones are intentionally low power so they can reuse frequencies in adjacent cells. Crank the power up and you reduce the capacity of the system. Since this system piggybacks on the existing cell towers, they can't change anything. The larger antenna allows for less error correction and it's directional, so it only uses the tower its aimed at.