Accurate cylindrical near-field measurements on large size conformal antennas

In this paper we describe the cylindrical near-field setup developed for the calibration and testing of large size conformai antenna. The antenna under test considered in this work is a not-rotating array used for SSR (Secondary Surveillance Radar) made by elementary radiators disposed along the 360° in the azimuthal plane producing fan-fixed beam along elevation plane. The electronic scanning is achieved by activating a proper subset of elementary radiators along the ground plane generating antenna patterns related to their individual phase centers generally not coincident with the near-field scanning coordinate system. The mechanical position errors of the antenna under test are increased due to the large dimensions and the payload. The alignment procedure presented here, allows a near-field cylindrical scanning close to the antenna phase center reducing the distortions that can affect the measurements. The improvement is seen in terms of accuracy of the transformed far-field antenna pattern.