Comparing output of one software with another is not a standard process of validation. Remember, Experimental results are the most standard base to match with.  You can also compare with theoretical calculations.

Dear Mr Ali,

I always emphasized to my students that the actual strength of any simulation software depends upon how accurate your models are. In 3D EM simulations, factors like placement and choice of port, type of meshing, type of solver etc all can effect the accuracy of results and no one software is better than others always. The skills of the person play a major role. In nutshell as Mr Donda mentioned comparing results of two software is irrational. The real check is measured results. Again getting closer simulated and measured results from a software once is no certainty that next time you will get best results using the same software. My advice to all young engineers is stick to one software and enhance your knowledge of how results are computed and take care of points which can contribute to errors. Hope it does clarify some of the issues in your mind.   

If your measured results are close enough than no need of that

Validation must always be carried out by means of experiments. 

@Krupali Donda @Irfan Majid @Muhammad Saeed Khan @Armando Fernández Prieto Thank you all for your precious suggestions, it now created a clear picture about validation as expected........ Thank you again actually I was arguing the same but still got confused by that time.

Don't worry, you are more than welcome :).

Gratitude Sir.....