What is this radar-like thing?
It is a wind tee; it serves the same function as a wind sock. It is designed to resemble an airplane from the air so that pilots overflying the field can more easily determine in which direction they should land. The top of the "T" is the front of the airplane and represents the direction in which an airplane should land.

When the wind hits the vertical tail surface it weathervanes. The tail points in the direction that the wind is blowing.

Unlike the wind sock, the wind tee does not provide wind speed information, only wind and landing direction.