Dear,

You can check the thesis in the following link:

Design and Development of Multiband Antennas for Portable Devices with MIMO Implementation

http://sdsu-dspace.calstate.edu/handle/10211.3/137804

While working on MIMO, I followed the following link to calculate ECC, MEG etc. parameters.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5298721/pdf/sensors-17-00148.pdf

Write the equations in Output variables section of the HFSS. If you still face any problem, I'll send the step by step procedure along with snapshots to calculate them in ANSYS (HFSS).

FYI

num = (mag(conjg(S(1,1))*S(1,2) + conjg(S(2,1))*S(2,2)))^2

denom1 = (1-mag(S(1,1))^2 - mag(S(2,1))^2)

denom2 = (1-mag(S(2,2))^2 - mag(S(1,2))^2)

ECC = num/(denom1*denom2)

DG = 10*sqrt(1-ECC^2)

TARC = sqrt(((S(1,1)+S(1,2))^2+(S(2,1)+S(2,2))^2)/2)

VSWR_MIMO = (1+TARC)/(1-TARC)

Good Luck !!!

Glad to have your answer.

Thank you,Sir.