What is this gigantic dish at Ben Gurion airport?
It is just a design feature, and serves no technical purpose, beyond filtering some light and providing a waterfall feature.


  Safdie designed the roof of the rotunda as an inverted dome, an asymmetric dish floating above the piazza that lets sunlight in and filters the daylight with a special white fabric ceiling.
  source: https://www.bdcnetwork.com/ready-takeoff


and


  Rain falling upon the suspended dome drains towards the center and enters the rotunda through an oculus skylight as a waterfall. In the dry season, a continuous flow of water washes the roof, contributing to the rotunda’s cooling and forming a fountain through the oculus.
  source: https://www.safdiearchitects.com/projects/ben-gurion-intl-airport-airside-terminal


Image, because it looks nice (Same source as second quote above)