Apparatus for scanning and measuring the near-field radiation of an antenna

Apparatus for measuring the near-field radiation of an antenna such that its far-field radiation characteristics can be determined is described. The invention utilizes the principle of the Foucault pendulum. It uses a bob attached to a long pendulum arm that is free to rotate. Rotation of the earth causes an apparent rotation of the swing plane of the pendulum with a period of T = 24/sin (latitude). By attaching a field sensing probe to the pendulum bob and mounting the antenna under the Foucault pendulum, the entire antenna aperture can be scanned without moving the antenna. The motion of the probe covers part of an external sphere centered at the pivot point of the pendulum and having a radius equal to the length of the pendulum. Appropriate transformation of the measured near-field data gives the far-field radiation pattern.