Need help on pattern multiplication with Matlab.

I have an element pattern something like this: g(theta) = I_norm(1) + I_norm(2)*exp(1i*k*d*sin(theta)) + I_norm(3)*exp(-1i*k*d*sin(theta)); %array factor calculation for n=0:N-1 f(theta) = f(theta)+ An*exp(j*n*2*pi*d*(cos(deg2rad(theta))-cos(theta_zero*pi/180))) ; Where N = 7, I am trying to run this with c0=3e8; f=2.4e9; lambda=c0/f; k=2*pi/lambda; d = 1.5*lambda; I_norm(1) = 0.0039 - 0.0030i; I_norm(2) = 0.0008 + 0.0030i; I_norm(3) = 0.0015 + 0.0030i;

I get spikes on polar plot. Can't figure out whats wrong.