Vector network analyzer ferromagnetic resonance spectroscopy (VNA-FMR) isused here to study the different excited modes of sputtered asymmetricalNiFe(13.6 nm)/Ru(dRu)/NiFe(27.2 nm) exchange-coupled films with variable Ru thicknesses. Theobtained results have been compared to those of the symmetricalNiFe(30 nm)/Ru(dRu)/NiFe(30 nm). In both cases, the measurements show the existence of an optic and an acousticprecessional mode. The optic mode was only observed over limited field ranges, especiallyin the symmetrical trilayers. To overcome such a limitation, we developed a new techniquesimilar to the longitudinal FMR, where the bias and the rf field are parallel to eachother and perpendicular to the pinning field. Interestingly, and in contrast to thesymmetrical trilayers, we observed a mode anti-crossing in the dispersion relation ofthe asymmetrical layers that we attributed to the thickness difference betweenthe two NiFe layers. Our experimental results on the effect of the biquadraticcoupling on the mode frequency variations are in good agreement with the theory.