<< Graphics`PlotField3D`

PlotVectorField3D[{Sin[Pi*x]*Sin[Pi*z], 0, Cos[Pi*x]*Cos[Pi*z]}, {x, 0, 
        1}, {y, 0, 0.5}, {z, 0, 1}]

PlotVectorField3D[{0, Sin[Pi*x]*Sin[Pi*z], 0}, {x, 0, 1}, {y, 0, 0.5}, {
        z, 0, 1}]