  Single-loop cyclic three-level ($\Delta$-type) configuration of chiral
molecules was used for enantio-separation in many theoretical works.
Considering the effect of molecular rotation, this simple single-loop
configuration is generally replaced by a complicated multiple-loop
configuration containing multiple degenerate magnetic sub-levels and the
ability of the enantio-separation methods is suppressed. For chiral asymmetric
top molecules, we propose a scheme to construct a real single-loop
$\Delta$-type configuration with no connections to other states by applying
three microwave fields with appropriate polarization vectors and frequencies.
With our scheme, the previous theoretical proposals for enantio-separation
based on single-loop $\Delta$-type configurations can be experimentally
realized when the molecular rotation is considered.
