We present a method to calculate the 2-dimensional complex angular spectrum required to produce a Helmholtz-
Gauss (HzG) beam with an arbitrary intensity profile. Using an iterative Fourier transform algorithm, we find
numerical solutions for several instances of spectra and we reproduce the corresponding beams by encoding the
resulting on a spatial light modulator. We verify the experimental results and compare them to the computer
model of their propagation to excellent agreement. We quantitatively asses the fidelity of the produced beams
and their expected extended propagation properties as HzG beams. Our method can be used to produce an arbitrary beam with the same extended invariance range characteristic of HzG beams.