We report broadband ferromagnetic resonance measurements based on a coplanar waveguide (CPW) of ultrathin magnetic film structures that comprise in-plane/out-of-plane decoupled layers deposited on nonmagnetic buffer layers of various thickness and diverse sheet resistance values. We show that the excitation of the fundamental mode can be enhanced up to 10 times in the structures deposited on buffer layers with a low sheet resistance compared to what it is in the structures deposited on thin or weakly conducting buffer layers. The results are analyzed in terms of shielding of the electromagnetic field of CPW by the conducting buffer layers. (C(2014 AIP Publishing LLC.