Question about Netgear AirCard 790

How exactly does this device work. If I buy(delivered) from a card Sim of the operator Yallo, it I achet who is 21mbts / 8mbts. How with this card I can reach the 300mbts max that gives me device this? How does it work? Improve or increase the performance of the antènes added to the product? How are antènes compatible with this product? Improve, from the antènes added to the product or increase you he performance? How are antènes compatible with this product?