We have studied the energy spectrum and magnetotransport of a parabolic one
-dimensional channel in the presence of periodic modulations in both magnet
ic field and the electrostatic potential. The periodic modulations change t
he sub-band energy-wave-vector relation and produce mini-gaps at specific w
ave-vectors. The gaps exist even if there is only modulation in the magneti
c field. For the cases where the two kinds of modulation are in phase or ou
t of phase, we give the explicit expressions for the values of the gaps. In
the ballistic transport regime, the conductance-is expected to remain quan
tized and to evolve in a simple manner as a function of the Fermi energy. S
tarting from linear response theory, the transport properties are studied n
umerically, taking into account the impurity scattering. Calculations relat
ed to magnetic field modulation show that a series of cusps in the conducta
nce are produced, whose magnitude depends strongly on the degree of impurit
y scattering. The structure of these cusps can be explained in terms of the
energy band structure.