Surface diagnosis of large reflector antennas using microwave holographic metrology: An iterative approach


  • Y. Rahmat-Samii


Recent investigations have shown that it is quite possible to accurately characterize the surface profile of large reflectors using microwave holographic techniques. In these techniques the complex (amplitude and phase) far-field pattern of the antenna is measured first. The surface profile is then constructed using the Fourier transform relationship which exists between the far field and a function related to the induced surface current. In this paper the concept of the Fourier transform relationship is first investigated to demonstrate that it is, in general, a summation of many Fourier transforms. However, for large reflectors with small beam widths, only the first term of the series has the major contribution. Furthermore, an iterative scheme is described to analytically/numerically continue the far-field pattern outside the measurement window. This, then, results in an improved resolution of the surface map data and, in particular, reduces the amplitude artifacts outside the boundary of the reflector. A novel and efficient simulation model has been developed to properly evaluate the accuracy of the technique in recovering the simulated surface errors. Finally, results of a recent measurement are summarized.