Application: Radar cross-section. A small radar is used to measure the radar cross-section of a small airplane as part of the certification process. The radar transmits 100 W at 6 GHz. The antenna has a gain of 20 and is. placed 100 m from the airplane (in the far field) so that the plane is in the direction of maximum antenna directivity. The received power at the radar's antenna is 100 nW. If propagation is in free space and there are no losses in the antenna, calculate the radar cross section of the airplane.