Following might solve your issue or help you to solve this query.
SELECT Start_Date, End_Date
FROM
(
SELECT calendar_date End_Date, ROW_NUMBER() OVER(ORDER BY calendar_date) RowNum
FROM sys_calendar.CALENDAR
WHERE calendar_date BETWEEN '2013-01-01' AND '2013-12-31'
AND day_of_week = 1 --Sunday
QUALIFY RowNum MOD 2 = 1
) ed
INNER JOIN
(
SELECT calendar_date Start_date, ROW_NUMBER() OVER(ORDER BY calendar_date) RowNum
FROM sys_calendar.CALENDAR
WHERE calendar_date BETWEEN '2013-01-01' AND '2013-12-31'
AND day_of_week = 2 -- Monday
QUALIFY RowNum MOD 2 = 1
) st
ON st.RowNum+2 = ed.rownum
Following might solve your issue or help you to solve this query.