  We offer a general treatment of electromagnetically induced transparency
(EIT) in a five level system consisting of four metastable ground states. Two
additional RF/microwave fields coherently couple the two ground states of the
standard EIT $\Lambda$ atom to a pair of additional hyperfine states in the
ground state manifold, generating two sets of dressed states that interact via
the probe and control lasers, which couple to the electronic excited state.
These new hyperfine dressed states manifest themselves in the linear optical
susceptibility of the probe as new resonances in addition to the Autler-Townes
doublet characteristic of EIT. In particular, we show that the existence of two
new narrow resonances, whose width are limited only by ground state
decoherence, appear inside the normal EIT transparency window. We show that by
controlling the intensity of these RF/microwave fields, one can engineer both
the position and width of these narrow resonances and thereby exercise
additional control over both the dispersion and group velocity of the probe.
