Design of a cylindrical near field system for radar antennas

Abstract

A cylindrical near field measurement system for huge L-band RADAR antennas has been designed, and it is under construction. The cylindrical near field system consists of a 17 meters tower (15.5 meters linear scanning), placed at a distance between 4 and 7 meters from the centre of the RADAR antenna. The RADAR antenna is placed on its azimuth positioner, and the system must allow the measurement of the antenna without stopping the rotation movement, measuring two linear polarizations (horizontal and vertical). The system can work in both transmission and reception. The system must work in an open and windy area. To assure the rectitude of the z-axis, a servo controlled by an optical detector has been implemented. This paper presents the main specifications of the measurement system (mechanical and electrical) and its design process. The paper will explain the acquisition routines (optimised for reducing measurement time without stopping the rotational movement of the RADAR), the control of the motors and RF equipment, the near field to far field transformation software, the algorithms used to compensate some errors (as temperature variations) and, finally, the user friendly environment.