You can create clones of the items in the four weeks and reschedule the cloned items in the next four weeks. The code below illustrates this technique:

DateTime from = calendar1.GetFirstDate();
DateTime to = from.AddDays(28);

ItemCollection items = calendar1.Schedule.GetAllItems(from, to);
if (items.Count == 0)
      return;

foreach (Item item in items)
{
      Appointment copy = item.Clone() as Appointment;
      copy.StartTime += TimeSpan.FromDays(28);
      copy.EndTime += TimeSpan.FromDays(28);
      calendar1.Schedule.Items.Add(copy);
} 

If you want to create a true recurrence based on this pattern, it is going to be more complicated. It could probably be achieved by specifying a daily recurrence pattern, then filtering out all items that do not match by using the ValidateOccurrence event of the Recurrence class.

Let me know if the copy method above works for you.

Regards,
Meppy

I haven't thought about that pattern before, but now that you mention it, it looks like what you need. Use the following code to specify a 28 day recurrence for an item:

Recurrence r = new Recurrence();
r.StartDate = item.StartTime;
r.Pattern = RecurrencePattern.ByTimeInterval;
r.Interval = TimeSpan.FromDays(28);
item.Recurrence = r; 

Regards,
Meppy

No real items are created for recurrences (otherwise infinite recurrences will cause problems). When a particular period of time is being displayed by the control, the recurring items in this period are temporarily generated and displayed. Therefore in your case it might be better to use the cloning technique.

Regards,
Meppy