  The structures of two observed high-spin rotational bands in the doubly-odd
nucleus ${}^{168}$Ta are investigated using the cranked shell model with
pairing correlations treated by a particle-number conserving method, in which
the blocking effects are taken into account exactly. The experimental moments
of inertia and alignments are reproduced very well by the calculations, which
confirms the configuration assignments for these two bands in previous works.
The backbending and upbending mechanisms in these two bands are analyzed in
detail by calculating the occupation probabilities of each orbital close to the
Fermi surface and the contributions of each orbital to the total angular
momentum alignments. The investigation shows that the level crossings in the
first backbending is the neutron $i_{13/2}$ crossing and the in second
upbending is the proton $h_{11/2}$ crossing.
