Simulation of two monopole antenna

Hello, i succed to simulate two monopole antenna in hfss but i dont understand the simulation results because i m beginner in hfss:

1. The difference betwen S11, S22; S21 and S12;
2. i would like to visualise the horizontaal Gain so i clik in create far field report ;radiation patern but i found this fig

   

   but in my cas i want just one curve.
3. i would like to know if i can know the value of these paramters
   
   • the distance between transmitting and receiving antennas;
   • the maximum directivities of the transmitting antenna and receiving antenna;
   • the distance between the image of the transmitting antenna and receiving antenna.
   • the value of S11,S12,S22
   
   from the hfss simulation .

Thanks in advance

it is jst simulation resul and not measred; my goal is to understand the phenommena of antenna ..
it is not possile to get only the gain of antenna?

RF books will teach you about S-parameter. Guillermo Gonzalez, "Microwave Transistor Amplifiers, Analysis and Design, 2nd. Ed.", Prentice Hall, New Jersey is the best book i came across in this subject matter.



this i think involve friis equation. i dont know if hfss has it because im not familiar with the software