What type of antenna is this? (glide slope aircraft antenna)
It is better understood as a pair of symmetrical, single-turn loop antennas. Each loop consists of one curved portion, plus the center post. It's mounted so the loops are horizontal, so it's horizontally polarized, and mounted on the nose of an aircraft (sometimes covered by a radome) so it will have a fairly broad, forward-looking radiation pattern.
Grounding the center post helps make the antenna sturdy and invulnerable to lightning or static discharges.
The picture you've shown has a single feed and only uses one loop. The other loop's feedpoint is simply grounded. But the same design can be built in a dual-feed version. I believe that is used to provide redundancy -- i.e., two cables, two receiver front ends, etc -- to reduce the chances of failure at a critical moment in the approach.