“…However, for field propagation, it is necessary to decompose the field into its azimuthal Fourier components, i.e. E(r,) = E(r,n)exp(inçb), (1) where n is the order of Fourier components. Each Fourier component can be propagated independently for a distance L according to the formula: E' (r' ,n) = E(r,n)J(2 zrr' /AL)rdr, (2) where is the wavelength and J, is the Bessel function of nth order.…”