Mathematica understands this, so perhaps Alpha does as well. Note that this is a cylindrcal surface of infinite extent in z, so we need to truncate it somwhere, or the plot won't fit in the observable universe. ;-)
ContourPlot3D[x^2 + 4 y^2 == 4, {x, -3, 3}, {y, -3, 3}, {z, -5, 5}]