Reduction of Truncation Errors in Planar, Cylindrical, and Partial Spherical Near-Field Antenna Measurements

Francisco José Cano-Fácila,Sergey Pivnenko,Manuel Sierra-Castañer

doi:10.1155/2012/438727

Abstract

A method to reduce truncation errors in near-field antenna measurements is presented. The method is based on the Gerchberg-Papoulis iterative algorithm used to extrapolate band-limited functions and it is able to extend the valid region of the calculated far-field pattern up to the whole forward hemisphere. The extension of the valid region is achieved by the iterative application of a transformation between two different domains. After each transformation, a filtering process that is based on known information at each domain is applied. The first domain is the spectral domain in which the plane wave spectrum (PWS) is reliable only within a known region. The second domain is the field distribution over the antenna under test (AUT) plane in which the desired field is assumed to be concentrated on the antenna aperture. The method can be applied to any scanning geometry, but in this paper, only the planar, cylindrical, and partial spherical near-field measurements are considered. Several simulation and measurement examples are presented to verify the effectiveness of the method.

Highlights

In many cases, antenna parameters, such as gain, directivity, radiation pattern, side-lobe level, and beamwidth, cannot be determined directly from measurements that are obtained in a far-field range because the distance to the far-field region may be too large
In order to simulate the real behavior of the error, the plane wave spectrum (PWS) obtained from the truncated near-field acquisition is employed
Using this PWS and the spectral reliable region defined by geometrical optics and specified in Table 1, the error curve is as the red dashed line shows

Summary

Introduction

Antenna parameters, such as gain, directivity, radiation pattern, side-lobe level, and beamwidth, cannot be determined directly from measurements that are obtained in a far-field range because the distance to the far-field region may be too large. There are only six coordinate systems that support vector wave functions that satisfy the orthogonality condition, but only three of them (planar, cylindrical, and spherical) are employed because of the simplicity of the required mechanical equipment. These three coordinate systems constitute the classical near-field antenna measurement systems and, the three nearfield techniques are based on the same principle (measurement over a surface in the near-field and transformation to far-field), there are important differences among them. The most accurate antenna patterns are obtained using this last type of acquisition because it is the only measurement setup where

Methods

Results

Conclusion