Intuition behind ambiguity of direction using linear array
Consider a linear array of sensors aligned in a North-South direction. This array cannot distinguish between a signal arriving from the East versus a signal arriving from the West. Either signal will arrive at all of the sensors at the same time. Now consider what happens if there are two parallel arrays designated A and B with array A to the West of array B.  A signal arriving from the East will reach the sensors in array B before the sensors in array A.  Similarly a signal arriving from the West will reach the sensors in array A before those in array B. Thus the directional ambiguity no longer exists.