球面近远场和远近场变换算法

天线的远场对于研究天线辐射特性具有重大意义,近场测量技术因其能够避免直接测量远场而得到广泛应用,该技术采用近远场变换获得远场,然而,检验该远场的准确性也是很重要的.为了解决此类问题,文中以球面近场测量为例,提供了一种解决方案.该方案主要探讨了球面波模式展开理论,该理论是实现球面近远场变换算法的关键,其将待测天线在空间建立的场展开成球面波函数之和,天线的加权系数既包含了远场信息也包含了近场信息.因此,不仅能够利用近场测量信息获得远场辐射特性,同样能够利用远场辐射特性反推得到近场处电场,这样就能检验由近远场变换算法得到的远场是否准确.文中首先推算得到了近远场变换公式,随后进一步推算得到远近场变换的公式,最后将本文算法计算结果与FEKO测量结果进行比较,二者吻合良好,从而证实了本文两种算法的有效性.

The algorithm of near-far and far-near transformation for spherical surface

The far-field of antenna is very important for studying the radiation characteristics of antenna, and the near-field measurement techniques which can obtain far-field by near-field to far-field transformation are widely applied because the techniques can avoid direct measurement of far-field, however, it is also very important to exam the accuracy of the far-field. To solve this problem, the spherical near-field measurement is taken as an example in this paper, in which we propose a method that mainly discusses spherical wave mode expansion theory which is key to implementing the spherical near-field to far-field transformation. The theory can develop the field in the space which is built by the antenna expanding into the sum of spherical wave functions. The weighting coefficient of the antenna includes both the information of far-field and near-field. Therefore, not only the far-field radiation characteristics can be obtained from near-field measurement information, but also the electric field of near-field can be obtained from far-field measurement information, as a result, which can test the accuracy of far-filed obtained by near-far to far-field transformation. The formula of near-field to far-field transformation is deduced, and then the far-field to near-field transformation formula is further deduced. The simulated result using the FEKO simulation software and calculated result obtained by the proposed algorithms are presented, and show very good agreement, which confirms the validation and efficiency of the algorithms.