I think you'd be best creating a basic calendar in your QV document. If you check the QlikView example docs loaded I think there is one there already, if not I'll dig out an example from here.
You basically build a calendar from a min to max date, for each date in that you define a week number:
WEEK(date) as WEEK
Then I would suggest an inline load (something like the below). Alternatively do the inline load before as a mapping load an map the period field into the calendar as you build it.
LOAD * INLINE [
I hope that helps.