Common mode currents on antenna feeders usually occur when feeding a symmetric radiator through an asymmetric line, or when the ground plane is electrically small. Such currents may have magnitudes comparable to the feed currents and therefore have a major impact on the total radiated field. For antenna radiation measurements, both assessment and reduction of the common mode currents on antenna feeders are crucial. Techniques to discriminate antenna and feeder radiation are mainly needed for design and optimization purposes. Antenna gain measurements in a multipath site can be performed by using the distance averaging method. In this paper, we show that the distance averaging technique can be applied to reduce the effect of common mode currents for measuring the field radiated by symmetrical antennas. Two measuring configurations are proposed depending on the number of symmetry degrees of the antenna under test, and a differential approach for extracting the field created by the common mode currents was also developed. The experimental validation was performed by measuring a simple wire dipole and a log-periodic dipole array (LPDA) with a small square loop as a probe, both on the feeder side and on the feeder free side.

中文翻译：

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辐射测量中天线馈线上共模电流的评估和降低影响。

天线馈线上的共模电流通常在通过非对称线馈入对称辐射器或接地平面较小时发生。这样的电流可能具有与馈电电流相当的幅度，因此对总辐射场具有重大影响。对于天线辐射测量，评估和降低天线馈线上的共模电流都至关重要。出于设计和优化目的，主要需要区分天线和馈线辐射的技术。可以使用距离平均方法在多径站点中进行天线增益测量。在本文中，我们表明可以使用距离平均技术来减少共模电流对对称天线辐射场的影响。根据被测天线的对称度数，提出了两种测量配置，并且还开发了一种用于提取由共模电流产生的磁场的差分方法。通过在馈线侧和无馈线侧上测量一个简单的线偶极子和一个带有小方形环作为对数的对数周期偶极子阵列（LPDA）来进行实验验证。