vector form variables in PDE

What is the procedure to specify a dependent variable in PDE interface to be a vector rather than a scalar? In more specific terms, I'm trying to implement the vector wave equation in 3D using the coefficient form PDE. I need to define the dependent variable (u) to be the vector form electric field.
I'm new to the comsol environment and still haven't found this method in the user guide.

Thanks,
Waranatha.