Gain antenna measurement using single cut near field measurements

Some antennas require rapid validation at a reduced measurement distance while maintaining sufficient accuracy in the determination of pertinent antenna parameters such as gain. In particular, for cellular base station antennas in production phase the measurement time can be a limitation. In these cases, a rapid check of the radiation performance in the two main planes is sufficient. Other examples are phase arrays with high degree of steering that would require considerable measurement time for characterizing all steering positions. This paper presents a near-field antenna test procedure providing single or double main plane patterns including the gain. The procedure is applicable to antennas, with separable excitation in the two main planes. The test set-up is based on an azimuth positioner and near to far-field transformation based on expansion in cylindrical modes. The paper shows results for gain measurements. Near to far-field transformation is performed using the cylindrical modes expansion assuming a zero-height cylinder. This allows the use of a FFT in the calculation of the far field pattern including probe correction. In the case of gain, the near to far-field transformation factor is calculated for bore sight direction, taking advantage of the separable excitation properties of the antenna. This factor is used in the gain calculation by comparison technique.