A device configured for receiving and/or emitting an electromagnetic wave having a free space wavelength λ 0 comprised between 1 mm and 10 m, comprising: - an electronic device configured for receiving or emitting a signal, - a medium of dielectric material, the free space wavelength λ 0 corresponding to a wavelength λ inside said medium, - a plurality of passive resonant elements incorporated inside said medium, each passive resonant element having a first structure comprising at least a first shape and first physical parameters, the first structure being the same for all the passive resonant elements belonging to said plurality of passive resonant elements, each passive resonant element having at least a first resonance frequency (f 1), the plurality of passive resonant elements comprising a frequency band-gap (Δf), two neighbour passive resonant elements belonging to the plurality being spaced apart from each other of a first distance (dl) lower than λ/4, - at least one active resonant element incorporated inside said plurality of passive resonant elements, said active resonant element having a second structure comprising at least a second shape and second physical parameters, said second structure being different from the first structure so that said active resonant element has at least a second resonance frequency (f 2) comprised inside the frequency band-gap (Δf) of said plurality of passive elements, said active resonant element being connected to said electronic device for receiving or emitting a signal having at least a frequency component substantially equal to the second frequency (f 2), characterized in that said active resonant element is spaced apart from a neighbour passive resonant element of a second distance lower than λ/4. - an electronic device configured for receiving or emitting a signal, - a medium of dielectric material, the free space wavelength λ 0 corresponding to a wavelength λ inside said medium, - a plurality of passive resonant elements incorporated inside said medium, each passive resonant element having a first structure comprising at least a first shape and first physical parameters, the first structure being the same for all the passive resonant elements belonging to said plurality of passive resonant elements, each passive resonant element having at least a first resonance frequency (f 1), the plurality of passive resonant elements comprising a frequency band-gap (Δf), two neighbour passive resonant elements belonging to the plurality being spaced apart from each other of a first distance (dl) lower than λ/4, - at least one active resonant element incorporated inside said plurality of passive resonant elements, said active resonant element having a second structure comprising at least a second shape and second physical parameters, said second structure being different from the first structure so that said active resonant element has at least a second resonance frequency (f 2) comprised inside the frequency band-gap (Δf) of said plurality of passive elements, said active resonant element being connected to said electronic device for receiving or emitting a signal having at least a frequency component substantially equal to the second frequency (f 2),