the array antenna 210 having a different reception pattern 400 u2032 450 u2032 see fig7 where the height y 2 of the second subset matrix is less than the full height y of the array antenna 210 and the width u00d7 of the second subset matrix is the same as the first in this example the smaller second subset matrix may be exemplary subset matrix 20 see fig1 at process 455 the collected energy re 1 is compared to the collected energy re 2 if collected energy re 2 is greater than collected energy re 1 and re 2 is greater than a predefined threshold then the array antenna 210 is not blocked by an obstacle however if collected energy re 1 is greater or equal to the collected energy re 2 and re 2 is smaller than a predefined threshold then the radar antenna cannot see the ground and is therefore blocked by an obstacle thus in this exemplary embodiment radar energy patterns are transmitted and the directional sensitivity of the element matrix 20 is altered to determine if the radar antenna 210 is blocked by an obstacle as mentioned above in other equivalent embodiments process 415 may also be use where the array antenna 210 is the transmitting antenna and the receiver 241 is used to collect the reflected radar energy patterns in these embodiments the first energy pattern is transmitted using the first subset matrix.