alike what proves the algorithm also reconstructs correctly the phase.The mentioned difference of reconstructed phase level could have been caused by an asymmetry in the horns feed network. The detection of this error proves the usefulness of reconstructing the equivalent currents of an antenna since, without this information, the error in the feed network would have been hard to detect.
CONCLUSIONSA complete algorithm for the determination of the equivalent currents, either electric or magnetic, of an antenna from near field measurements has been described. These measurements must be taken, in spherical coordinates, in points placed in such a form that all form a sphere involving the antenna under test. This ensures any lost of information neither any approximation concerning the measurement area like in Cartesian or cylindrical coordinates.The algorithm works well in a real case, as shown in the results section. Both horns have been set right in space and the amplitude as well as the phase of these two horns have been obtained correctly. Furthermore, this last phase reconstruction has been useful to discover an error of the feed system and, by this way, to prove the usefulness of obtaining the equivalent currents of an antenna.In addition to the currents reconstruction, the algorithm also can be used to reconstruct the field at any other distance. This has been shown in the results section, where the field has been calculated again at the measurement distance from the transmission coefficients and the formulas for the field at any distance shown in the spherical wave expansion section. This has been compared with measurements and a correct reconstruction has been concluded.A application of this algorithm could be the currents reconstruction for array antennas, what could help to discover any defective element in the array. Another application could be the feed error detection looking at the reconstructed current. Any disappointment with regard to simulations could help to make modification for the best performance. These, and other applications, prove the usefulness of the algorithm proposed in this paper.
ACKNOWLEDGMENTThis work has been supported by Spanish Ministerio de Educación y Ciencia under FPI research fellowship programme (TEC2004 -04866-C04 -01), cofinanced by the European Social Fund (ESF) REFERENCES 1. P.H. Harms, J.G. Maloney, M.P. Kesler, E.J. Kuster, G.S. Smith, A system for unobtrusive measurement of surface currents, IEEE Trans Antennas Propag 49 (2001), 174 -184
