A novel 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 the large size antenna is short in vertical plane, its irradiating field in horizontal plane can be respected as cylinder wave distribution. Based on cylinder wave expand theory, the far-field pattern of antenna can be obtained from the whole near-field information of full angular aspect. Taking derivative of the near-field data with respect to frequency in algorithm, the error can be reduced in simplifying formula, and just meet the requirement of stepped-frequency system. The results of simulation and experiments show that the algorithm is precise as well as effective.