A device (10) for receiving and/or emitting an electromagnetic wave, comprising a medium (11) of dielectric material, a plurality of passive resonant elements (12) incorporated inside said medium, the plurality of passive resonant elements (12) comprising a frequency band-gap, two neighbor passive resonant elements belonging to the plurality being spaced apart from each other of a first distance lower than λ/4, and at least one active resonant element (13) incorporated inside said plurality, said active resonant element (13) having a second structure different from a first structure of the passive resonant elements (12), so that said active resonant element (13) has at least a second resonance frequency comprised inside the frequency band-gap of said plurality of passive elements (12).