16/6/16

Fast Antenna Diagnosis Algorithm Using

Oblate Spheroidal Non-Uniform Grids

Alexander Gergel

Ph.D. student of

Professor Amir Boag of Electrical Engineering, Physical Electronics Department

Reconstruction of the radiating fields or equivalent currents on a closed surface enclosing a radiating body, also termed source imaging, is a widely used method in antenna diagnostics for estimating inaccuracy of antenna fabrication or localizing antenna malfunction.  The Rayleigh-Sommerfeld (RS) formulation with incoming wave Green function is used in this work to enable the back-propagation from the scalar field measurement on a planar surface.  This method provides a good approximation for the field back-propagated from the measurement plane towards the source, though, due to truncation errors, it is suitable mostly for the metrology of directional arrays or large reflector antennas.  Direct evaluation of the discretized back-propagation RS integral is characterized by a computational complexity (CC) of , where  (  being the radius of the smallest sphere circumscribing the measurement domain and  - the wavenumber).  For radiating surfaces that are very large compared to the wavelength, this computational bottleneck renders this approach unattractive.  Significant reduction of the CC down to  is achieved using a modified version of the multilevel non-uniform grid (MLNG). The MLNG technique is based on a hierarchical divide-and-conquer strategy.  The partial contributions to the field integral by subdomains of the geometry are phase- and amplitude-compensated to allow for their sampling over coarse non-uniform grids.  The partial fields can be reconstructed from their samples via interpolation followed by the phase and amplitude restoration.

In order to choose the most suitable non-uniform sampling scheme, we conduct a study comparing various sampling and interpolation schemes.  As a representative example, a test case parabolic reflector with a localized surface distortion is analyzed.  The ideal reflector surface can be defined analytically in spherical and oblate-spheroidal coordinate systems, thus in both we can provide on-surface 2D grids.  The efficiency of these grids is compared to the regular volumetric MLNG scheme.  The comparison between the source distribution, reconstructed from the simulated measurements, and the desired one is used for the localization of anomalies.  The quality of the localization is measured in terms of location and contrast.  The performance of the proposed algorithm under each of the grid topologies is studied in terms of accuracy, storage requirements, and run-time.

Thursday, June 16, 2016, at 15:00

Room 011, Kitot Building