characterisitic impedance can be plotted using the same modal values,but this time you will be choosing z-parameters and then you plot IM and Re values of the Z-parameters.
Another point why do we not have half wavelength dipole rather than something less than half a wavelength. at half wavelength we see some reactance as well,inorder to minimize the reactance to zero we use a value less than that of the actual half wavelegth.
small tip,actually two
use more number of points in the sweep, you will see a smoothly curved plots
radiation patterns.i see you have an habit of having a scale of 0 to 180 in phi. its a good practice to have a scale of 0 to 360 degrees in both theta and phi plane. you will all the lobes minor major and side. and the step value make it 1 as well in radiation pattern for smoother curves.
Regards