planar CPW fed Yagi uda antenna

hii all,
m simulating a CPW fed planar yagi uda antenna on RT Duroid substrate...can anybody tell me how to get gain value in dBi using HFSS step by step after simulating the structure?

See the below link:
https://www.edaboard.com/thread224374.html

thanks for the reply..but still i have a doubt..in HFSS ver11 gain can be measured in several units as dB, dB10 normalize, dB20 normalize, normalize...so my query is that which one of these units can be used for measuring gain in dBi?

what will be the values of theta and phi for x-z and y-z planes to see the radiation patterns? i am simulating a quasi yagi uda planar antenna on silicon substrate but over the frequency range the gain is coming negative what can be the reason for this? pls help me