Evaluation of Gain Measurement Method for Long Antenna Using Synthetic Aperture Antenna

A cellular base station antenna has a narrow beam width in the vertical plane because the length of the antenna is more than 10 λ. While generally long distance measurements are needed to measure the antenna with high accuracy, some measurement methods in a short-range anechoic chamber have been used. The compact range method [1-2] and near-far field transformation method [3-6] are very popular. However, since additional equipment, which is large or expensive, is needed to employ these methods, it is difficult to measure the far-field pattern of an antenna compared to conventional pattern measurement methods in an anechoic chamber. In order to overcome these problems, a far-field measurement method has been proposed for long antennas using a conventional pattern measurement system when the measurement distance is not sufficient in an anechoic chamber [7]. Since a source antenna is treated as a synthetic aperture array antenna in this method, a virtual quasi-plane wave is generated around the antenna under the test (AUT) to obtain the far-field pattern. It is found that the far-field can easily be obtained in a short range chamber without additional equipment. In this paper, the principle of the proposed method that applies the synthetic aperture antenna technique is described to obtain the antenna gain, and experimental results are shown to clarify the validity.