Complex sentence: This combination gives the antenna gain of about 100,000,000 (or 80 db, as normally measured), making the transmitter appear about 100 million times stronger, and a receiver about 100 million times more sensitive, "provided the target is within the beam".
Split into simpler sentences: This combination gives an antenna gain of about 100,000,000 (or 80 db, as normally measured). Thus using such an antenna will make a transmitter appear about 100 million times stronger, and a receiver about 100 million times more sensitive, "provided the target is within the beam".