Ah, I see you're asking for a more specific answer. The Fourier transform of a vector in three-dimensional Euclidean space is a vector in the frequency domain. Specifically, the Fourier transform of a vector r is given by:
F(r)(k) = (1/(2π)^(3/2)) ∫[exp(-i k · x) r(x) dx]
where k is the frequency vector, and the integral is taken over all of three-dimensional space. Is there anything else I can help you with?