d=0.5λ 5 4.5 3.5 3 鱼25 1.5 I WW M 0.5 200-150 -10050 50 100150 200 0 00 -150-100-50 0 50100 150 200-200 -150 -100 -50 0 50 100 150 200 0 1 2 3 4 5  f () -200 -150 -100 -50 0 50 100 150 200 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5  f () d  0.5