All I used was the plot function and I got something pretty sinusoidal
theta = [90, 110, 130, 135, 150, 170, 180, 190, 210, 225, 230, 250, 270, 290, 310,315,330, 350, 365, 370, 390]
I= [0.0030, 0.6240, 1.3060, 1.3320, 0.9610, 0.1900, 0.0160, 0.1970, 1.1250, 1.3480, 1.2900, 0.5660, 0.0030, 0.5750,...
1.6170, 1.6760, 1.0850, 0.1380, 0.0940, 0.2250, 1.2340]
figure
plot(theta,I)
does this not work for you?