  In this paper we present a simple and effective method, based on appropriate
superpositions of Bessel-Gauss beams, which in the Fresnel regime is able to
describe in analytic form the 3D evolution of important waves as Bessel beams,
plane waves, gaussian beams, Bessel-Gauss beams, when truncated by finite
apertures. One of the byproducts of our mathematical method is that one can get
in few seconds, or minutes, high-precision results which normally require quite
long times of numerical simulation. The method works in Electromagnetism
(Optics, Microwaves,...), as well as in Acoustics.
  OCIS codes: (999.9999) Non-diffracting waves; (260.1960) Diffraction theory;
(070.7545) Wave propagation; (070.0070) Fourier optics and signal processing;
(200.0200) Optics in computing; (050.1120) Apertures; (070.1060)
Acousto-optical signal processing; (280.0280) Remote sensing and sensors;
(050.1755) Computational electromagnetic methods.
