Help!!! How to enable Create Array Command in Ansys HFSS

Hi Guys,
According to the Ansys Help guide, the Create Array Command (in the context menu of model in the project tree) is automatically enabled when Master and Slave boundaries are assigned. Well I have assigned master and slave boundaries to my unit cell and the command is still disabled. Kindly help me out. I would like to create 1D array as shown in the attached picture. Also I will appreciate more explanation of the U and V vectors. Kindly find my unit cell model attached.

Thanks in anticipation

Hi Guys,
I have been able to create the array but I haven't fully understand the U and V vectors and still need the explanation or a reference to an explanation.

Thanks