Gain mismatch between simulation and measurement?

[imtiaz369]

This is my radiation pattern at somewhere around 3.5 GHz of my designed Vivaldi antenna. But I want to find out why there is a mismatch around 3dB gain between simulation and measurement. Any idea how I can find out that one?

 

[volker@muehlhaus]

Is your simulated pattern gain or directivity?

In other words, did you include the effect of dielectric loss + conductor loss on antenna efficiency? What is your simulated antenna efficiency?