A new algorithm based stepped-frequency system about extrapolating near-field to far-field

In order to meet the approximate plane-wave irradiation condition, adequate large field or compact range system is needed for antenna pattern measurement, especially for large size antenna, but an outside testing field site or a compact range system is very expensive. Near-field planar scanning system is another method, however it is time-consuming and only suited for directional antenna. In this paper, a new extrapolating technique by connecting near-distance field with far-field of large-size antenna is set up. If a large size antenna is short in vertical plane, its irradiating field in horizontal plane can be respected as cylinder wave distribution, an ideal aperture as a reference irradiating source is utilized; its width is the maximum size of the tested antenna. In term of the ideal aperture a phase-correction coefficient connected with spherical and plane wave can be deduced, and used to calculate the far-field of the tested antenna. Based stepped-frequency system, a more precise arithmetic of extrapolation can be gained. By theoretical simulation for a simple long antenna, the pattern extrapolated can be obtained correctly. Experimental results of complex antenna show that this new technique makes experiment agree to theory precisely, moreover, it permits the measurement distance to be reduced by 15 percent of the minimum distance of far-field. Also, there is no serious limitation of measurement for antenna in dimension of aperture and depth.