calculation of mutual coupling coefficient

Zab=η e^(-jkr)/4π ∑_(n=-0.5,0,1,2)〖*{[1/(kr)^(n+1) ] } 〗 *
Cn,0 + Cn,2cos(2Ф) + Cn,4cos (4Ф)
hi ,
i hav to mutual coupling coefficient using ie3d software.The 12 unknown are to be calculated in above formula using software
thanks