Directivity computation by spherical spiral scanning in near field region

A procedure for evaluating the directivity of an antenna under test from near-field measurements on a spherical scanning surface is proposed. It uses a formula in closed form for computing the total radiated power from the knowledge of the radiation intensity samples on the far-field sphere. These last are determined via an efficient probe compensated near-field–far-field transformation technique based on a nonredundant sampling representation of the probe voltage. The samples are collected on a spiral wrapping the near- field spherical surface from pole to pole. With respect to the classical spherical scanning, this innovative way of collecting the data allows the reduction of the time required for the samples acquisition by means of a continuous movement of the positioning systems. The effectiveness of the proposed procedure is assessed by numerical simulations