Linear array diagnostic from near-field measurements

The authors present an inversion procedure to obtain the current distribution on a linear array from a near-field measurement. Numerical simulations were performed for a 50-element linear array. Single elements are half-wavelength dipoles spaced 0.75 lambda . The measuring distance is 5 lambda and the frequency 10 GHz. The current distribution is a Taylor (one parameter) of 35 dB, with a Gaussian distributed error of sigma =1 dB and a uniformly distributed error of +or-10 degrees in phase. Three cases have been considered: no filtering of the spectrum, filtering with a Hamming window, and low-pass filtering with a cutoff frequency k´= pi /d. It is shown that from a near-field measurement it is possible to reconstruct the current distribution of a linear array with an error smaller than 0.2 dB in amplitude and 2.5 degrees in phase when filtering is performed according to element spacing. Since the linear arrays may be constituent elements of larger planar arrays, this method makes it possible to check and adjust the intermediate steps of large radiating systems.<>