rectangular combline

Hello Everybody
I have to design a Combline filter using Slabline Rectangular bars.
There are many programs for the design using Round Rods.
I need the equation which relates the coupling to the spacing between resonators.
Regards
Moti Attias

Both Eagleware and Ansoft (Designer) have design software that you might consider.

As an alternative you can use the ? Microwave Filters, Impedance Matching Networks and Coupling Structures? GL Matthei, L Young, EMT Jones, it is an excellent book for filter design.

Hello Everybody
Eaglware has only round rods
I have tried WASP-NET simulation program and the simulation is fine. very good results.
Regards
Moti Attias