The expression of G(r,r???) used for this work is definedin Ref. 16 in terms of a double series of vector wave functions in spherical coordinates:[10]where l, m are the expansion indices, Xl,m is a vector spherical harmonic 13, k is the complexwave number, r is the radial coordinate and jl is a spherical Bessel function of order l.We started by defining a complete basis set of surface current mode