A NFFF approach using spheroidal wave functions in a cylindrical scanning geometry

We develop a Near-field/Far-Field technique to characterize oblong shaped antennas using data acquired in a cylindrical scanning geometry. The approach is based on enclosing the Antenna Under Test in a prolate spheroid and on representing the field on the spheroidal surface using Prolate Spheroidal Wave Functions. We set up an inverse problem to recover the representation coefficients from the measured data through a Singular Value Decomposition (SVD)-based inversion of the operator linking the field on the spheroid to the field on the cylinder. The approach significantly reduces the number of needed expansion coefficients as compared, for example, to a spherical harmonics expansion, positively affecting the problem conditioning. Numerical results are shown.