Dear Zulfikar you can't measure the Directivity in Near Field, because this function D(theta,phi) provide the radiative features in Far Field. Which if you define a direction it provides the directivity parameter Do. However you can arrange the NF Measurement, then you trasform with Fourier the NF in Far Field and finally you can calculation the Directivity paramater. So, I suggest a Measure this parameter directly with Far Field Technique.

Thanks Pasquale for reply.  Is it possible in simulation?

Sure!