  Considering the propagation of fields in the spacetime continuum and the
well-defined features of fields with finite degrees of freedom, the wave
function is expanded in terms of a finite set of basis functions localized in
spacetime. This paper presents the analytic eigenenergies derived for a
confined fundamental fermion-antifermion pair under a linear potential obtained
from the Wilson loop for the non-Abelian Yang-Mills field. The Hamiltonian
matrix of the Dirac equation is analytically diagonalized using basis functions
localized in spacetime. The squared lowest eigenenergy (as a function of the
relativistic quantum number when the rotational energy is large compared to the
composite particle masses) is proportional to the string tension and the
absolute value of the Dirac's relativistic quantum number related to the total
angular momentum, consistent with the expectation.
