The Determination of the Highest Mode Expansion Coefficients N for Spherical Near-Far Measurement

Abstract

The far field of antenna can be divided into direct measurement and indirect one.Obtaining the far-field radiation patterns by the near-field measurement is indirect measurement, which has a advantage of all-weather and short-distance. Spherical near-field measurement is applicable for any kind of antennas,which can obtain omnidirectional radiation characteristics precisely.This method expresses the measured antenna as the finite terms of spherical wave function superposition. However,it becomes a challenge to calculate the highest order N of the antenna expansion coefficients. Until now, an experimental formula only has been given. In order to further enhance the accuracy of N, firstly, this paper calculate the weighted coefficients, by using the theory of the near-field to near-field (NF-NF) transformation. Then, based on the agreement between the source domain and field domain for different N,then,which can be determined. Finally, we obtain the far-field radiation by spherical near-far measurement.The experimental results show that it can improve efficiency of the near-field to far-field (NF-NF) transformation heavily,which confirms the validation and accuracy of the thought in this paper.Therefore, with the development of communication, radar and other technologies, and the antenna as an essential factor, this study can better solve the accuracy and efficiency of antenna the near-field to far-field (NF-NF) transformation, and then better apply to the antenna test and diagnosis.