Desarrollo e implantación de un sistema de medida de antenas en cámara anecoica

Abstract

This thesis presents the development and implementation of a measurement system to characterize the radiation pattern of antennas. This system, called anechoic chamber, consists of an enclosure with a metal coating and absorbent material attached to the walls, ceiling and floor, and allows to obtain measurements in the absence of external electromagnetic interference and contributions due to undesired reflections. Besides the above elements, the system consists of other electromechanical and electromagnetic elements, and despite the fact that there is nowadays plenty of information about them, it is not easy to find information on the design process, development and tune-up. This work aims to make a complete study of all elements from which the anechoic chamber is formed, and develop new techniques related to the movement process, control and electromagnetic measuring. The Trajexia Technology from Omron has been used in order to develop different movements to allow planar, cylindrical and spherical exploration. The chamber design allows measurements in the near-field scanning system for planar and cylindrical acquisitions, and near-field and farfield up to 5 meters for spherical scanning. Positioning correction algorithms for different motion axes have been implemented, and they have been the key for a noticeable improvement in the system accuracy. These implemented techniques allow antenna electromagnetic measurements up to 40 GHz. To ease the interaction between the user and the scanning system a graphical interface has been designed as the common link of all the elements installed, allowing to manage the measuring process easily and accurately. The interface has been developed with the Agilent VEE program, which among other things is responsible for the virtualization of the instruments, the configuration of the measurement to be carried out, the synchronization of all the elements of the system and the management of the instrumentation used for the measurements. In order to complete the system a prost-processing software has been developed, which is based on numerical methods that process the near-field measurements and obtain the far-field transformation. These mathematical processes have been designed using Matlab and Fortran, two programming languages which facilitate the computations when large data matrices are involved. The algorithms are implemented through a graphical user interface developed in Java to manage the visualization of the results. It is possible to visualize the antenna radiation pattern, directivity, gain, and S-Parameters, among other type of results. The system described in this work has been verified with different types of antennas and operation frequencies. The results have been compared to electromagnetic simulation results obtained with other anechoic chambers, confirming the correct operation of the system. This system has been part of a large national project in which it has been necessary to characterize the antenna radiation pattern of an Earth observation satellite, demonstrating that the system described in this work is capable of obtaining excellent results for very demanding projects