HFSS & CST VS. Measurement results

I have attached the measurement result of a line-fed patch antenna and also the HFSS and CST files of that antenna. The results are quite different. Anybody can help to find the reason?

HFSS:

I don't have now CST and HFSS tools to open attache projects. Could you attach results comparison in PDF? What are dielectric parameters of substrate under 50 Ohm microstrip line?

HI E_M_C,
Under the microstrip line and antenna is air. The results are completely different. Please if you can design in any other software you have.

I have looked at the hfss file, and can can find no immediate problem. Your wave port seems to be in order. I thought I had the problem figured out when I noticed that your 50 ohm microstrip input was almost exactly 1/4 wavelength at your resonant frequency of 1789 MHz. However, when I changed the length, it didn't really do anything useful.
I'll take another look at it tomorrow if I get a chance

I dont have CST.
Please upload the results.

I didn't simulate your structures until now. However, my first impression is: your port (in this case coaxial) is wrongly setup in both cases. Moreover, in CST you draw the airbox which is not needed (by defining open boundary it is already defined).
I'll change the structure to see the results (I'm using HFSS 11.1 and CST 2009).
In the paper, it is written 50 ohm microstrip line. However, if you use air as substrate, 16 mm line will not give you 50 ohm at 1.8GHz frequency. Would you please upload the full paper, so that we know the substrate.

Ok shameemkabir, consider this one: a probe-fed antenna. The CST result is different from measurement. Any idea?