  Quantum interference effects in rings provide suitable means for controlling
spin at mesoscopic scales. Here we apply such a control mechanism to the
spin-dependent transport in a ballistic quasi one dimensional ring patterned in
two dimensional electron gases (2DEGs). The study is essentially based on the
{\it natural} spin-orbit (SO) interactions, one arising from the laterally
confining electric field {($\beta$ term) and the other due to to the
quantum-well potential that confines electrons in the 2DEG (conventional Rashba
SO interaction or $\alpha$ term).} We focus on single-channel transport and
solve analytically the spin polarization of the current. As an important
consequence of the presence of spin splitting, we find the occurrence of spin
dependent current oscillations.
  We analyze %the effects of disorder by discussing the transport in the
presence of one non-magnetic obstacle in the ring. We demonstrate that a spin
polarized current can be induced when an unpolarized charge current is injected
in the ring, by focusing on the central role that the presence of the obstacle
plays.
