We report on a comprehensive study of the interlayer exchange coupling in Co-Feð5 nmÞ=RuðtÞ= Co-Feð8 nmÞ trilayers ðt ¼ 0.8;…; 2.8 nmÞ using broadband ferromagnetic resonance. A systematic frequency dependence of the field separation between the acoustic and optic modes is found, which is caused by different effective magnetizations of the two ferromagnetic layers. Hence, it is shown that the broadband measurements are vital for reducing the systematic error margins in the determination of interlayer exchange coupling using ferromagnetic resonance. We also investigate the temperature dependence of the interlayer exchange coupling and compare our results with existing theories. It is shown that models which take into account the temperature dependence due to thermal excitations of spin waves within the ferromagnetic layers have a considerably better agreement with the experiment than models solely based on spacer and interface contributions to the temperature dependence.