This is a glide slope antenna from an aircraft. They are installed in or near the nose cone of an aircraft for the reception of the glide slope signal beams.
The antenna is tuned for 329 to 336 MHz and has an impedance of 50Ω. I have no idea what the center tube is for, the connector on the other side is behind one of the legs with the rubber glands. Sometimes the antenna is missing the center post, perhaps it's only for rigidity.
I'm wondering what type of antenna this is. To me it looks like a folded monopole antenna or something, but I'm not sure. I'd like to know the beam characteristics of it, how to calculate the dimensions, etc. I have no idea how the internal structure of the antenna is, since the connector is one of the legs, so I can only assume the rubber glands isolate the element from the bottom plate. Perhaps it's like an end-driven λ/2 dipole that is folded back or something, I'm really confused and I don't know. But I'm very interested.