Antenna blind cone

[1] The concept was encountered as early as the 1950s in low-frequency radio ranges, when it was used to determine when an aircraft was directly over a station.

As the signal may not completely fade away, the aircraft's position could be confirmed by listening for a station location, or "Z", marker.

[2] An Air Route Surveillance Radar (ARSR) is an example of an antenna blind cone.

As the fan antenna is rotated about a vertical axis, it can illuminate targets only if they are 70° or less from the horizontal plane.

Thus, a weather event located very close to and/or directly overhead of the radar site will be mostly situated in the "cone of silence."