You can see some strange big white rectangular hoardings when you are hiking along wilson trail 3, one is facing north east and the other south west. The boards were often tagged as 'former aviation reflector' Many said that it is for aircrafts, during foggy weather, when visibility is low. Common belief is that they bounce back radio waves. Some say it is microwave antenna However, when you think more carefully, the shape of it do not reflect the waves back to aircraft as they should, it is rather a wave spreader than a reflector. What is it? If it is a reflector , it should look like a corner of a square box, or called as corner reflector. It seems to be erected for the Hong Kong airport, likely be the previous Kai Tak airport. It could be part of the transponder system for air traffic control transponder or as special purpose secondary surveillance radar (SSR), or part of the SSR system. The electronics may have been removed after the Kai Tak airport was closed and /or s...