  The Klein-Gordon and the Dirac equations with vector and scalar potentials
are investigated under a more general condition, $V_{v}=V_{s} +
\mathrm{const.}$ These isospectral problems are solved in a case of squared
trigonometric potential functions and bound states for either particles or
antiparticles are found. The eigenvalues and eigenfuntions are discussed in
some detail. It is revealed that a spin-0 particle is better localized than a
spin-1/2 particle when they have the same mass and are subject to the same
potentials.
