A far-field radiation pattern measurement method for eliminating residual reflections by changing distance

In the measurement of antenna radiation patterns, it is necessary to reduce the effects of residual reflected and scattered waves caused by the measurement environment as much as possible so that the radiation characteristics such as the gain and the beam width can be evaluated accurately. In this paper, a new method of measurement for radiation patterns that eliminates reflected waves is proposed. In this method, the radiation pattern is measured while the measurement distance is varied. The measured values are subjected to a Fourier transform with respect to the measurement distance in order to separate and eliminate the reflected and scattered waves. First, a method for separating the direct wave from the reflected wave is presented, together with the analytical relationship between the spacing of the measurement distance (amount of variation) and the effective frequency range of the Fourier spectrum. By means of a model for radiation pattern measurement with one reflected wave from the side wall, the relationship between the reflected wave component remaining in the direct wave and the measurement distance range is studied. For instance, if the measurement distance range is 10 wavelengths and the center of the measurement distance range is 10 wavelengths, the reflected wave component can be suppressed by about 25 dB. Next, by using a radiation pattern experiment using an L band standard-gain horn antenna, it is confirmed that the proposed measurement method is effective for the removal of the reflected wave. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt. 1, 80(10): 10–19, 1997