  A method to derive features of modal eigenvalue traces from known and
understood solutions is proposed. It utilizes the concept of subduction from
point group theory to obtain the symmetry properties of a target structure from
those of a structure with a higher order of symmetry. This is applied exemplary
to the analytically known characteristic modes (CMs) of the spherical shell.
{The eigenvalue behavior of a cube in free-space is derived from it
numerically. In this process, formerly crossing eigenvalue traces are found to
split up, forming a macroscopic crossing avoidance (MACA). This finding is used
to explain indentations in eigenvalue traces observed for 3-D structures, which
are of increasing interest in recent literature. The utility of this knowledge
is exemplified through a demonstrator antenna design. Here, the subduction
procedure is used to analytically predict the eigenvalues of a cuboid on a
perfectly electrically conducting plane. The a priori knowledge about the MACA
is used to avoid its negative impact on input matching and the frequency
stability of the far-field patterns, by choosing the dimensions of the antenna
structure so the MACA is outside the target frequency range.
