Beginning with the exact Kolmogorov power spectrum for an extended random medium (such as interstellar space), the structure function is first expressed as an inverse Fourier-Bessel transform. An approximate series representation involving fractional powers of the transverse coordinate is then optimized by an equivalent Gaussian expansion up to two terms using the Rayleigh-Ritz technique. The domains of validity as well as the coherence profile of the resulting analytical solution of the two-point electric field correlation function are examined. It is shown that the correlation in both the transverse and longitudinal directions persists over distances up to a few orders of magnitude greater than that for a medium described by a Gaussian structure function.