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 (S), - 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 (S) 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 (d2) lower than λ/4. - an electronic device configured for receiving or emitting a signal (S), - 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 (S) having at least a frequency component substantially equal to the second frequency (f 2 ), <EOS>