coupling k between 2 1/4λ microstrip resonators

Interdigital filters compose of many 1/4λ microstrip resonators,one short end and one open end.how to calculate the coupling coefficients between them with HFSS or other 3D EM simulators?
thanks.

you can search in the help
use designer or @ds is better for microstrip

"Microstrip filters for RF and Microwave Applications" by jia sheng hong (chapter eight)

here u will get all the required info.