Abstract: An aerosol-generating device is provided for heating an aerosol-forming substrate to generate an aerosol, the aerosol-generating device including: an electromagnetic field generator configured to generate radio-frequency (RF) electromagnetic radiation having a predetermined frequency composition; a resonant chamber including a peripheral wall configured to be substantially opaque to RF electromagnetic radiation within the resonant chamber; and a filling arranged within an interior of the resonant chamber so as to circumscribe a substrate cavity defined within the resonant chamber, the substrate cavity being configured to receive the aerosol-forming substrate, the electromagnetic field generator being coupled to the resonant chamber so as to convey the RF electromagnetic radiation generated by the electromagnetic field generator to the resonant chamber, and the filling having a relative permittivity of greater than one.