Test Zone Performance Enhancement in Anechoic Chambers Using Two - Level GTD Principles

摘要

The primary purpose of a chamber for Far-Field (FF) antenna measurements is to create a test zone surrounding the AUT, where the electric field is to be as uniform as possible, and multiple reflections are kept to a minimum. It is well known, that typical rectangular anechoic chambers for Far-Field (FF) antenna measurements are subject to increased reflectivity from specular regions on the side walls, floor and ceiling. The reflectivity further increases if a larger test zone and, consequently, longer source antenna/AUT separation is required. The alternative to a rectangular chamber, which can be implemented to reduce the reflectivity, could be a chamber with a shaped interior, where the side walls are to be shaped based on GTD/GO principles so that the reflections are diverted out of the test zone. Even more reflectivity suppression is expected, if, in addition, wedge absorbers are used throughout the specular region or entire wall with a smoothly varied wedge orientation chosen according to GTD principles. The combination of two approaches constitutes a chamber design method termed a "Two - Level GTD". The chamber shape and wedge orientation for delivering reduced reflectivity in the test zone are not unique. According to a "Two - Level GTD" a plurality of solutions exists and can be practically implemented. Freedom in choosing these parameters can be utilized to satisfy the additional requirements for the chamber design to reduce RCS clutter and/or secondary reflections in the chamber. In this paper the method validity is confirmed based on comparison of various chamber designs performed using 3D EM analysis tools.