Problem with maximum gain of a PIFA antenna

hi sir,
i have designed one PIFA antenna. and iam getting the maximum gain at θ=60deg (3dbi) instead at θ=0deg(-8.5db) . (what i mean in this is if i place the antenna in Y-Z plane at θ=0deg my antenna will recieve the signal at θ=60deg strongly. simillarly if iam keeping my antenna at θ=90deg it will recieve the signal at θ=150deg strongly. ) this is what i mean . and what should i do if i want to recieve the signals in the principle plane at θ=0deg.suggest me