A microwave or millimetre-wave antenna comprising: a substrate with at least a planar surface; a resonator body formed from an artificial dielectric material; and an excitation structure for exciting the resonator body; wherein the artificial dielectric material comprises: a bulk polymer body, wherein the bulk body has at least a first planar surface and a second planar surface opposed to the first planar surface, a plurality of coupled metal inclusions for increasing an effective permittivity of the bulk body, the metal inclusions extending perpendicularly from the first planar surface, and at least partially through the bulk body toward the second planar surface, wherein the metal inclusions have a height between 2-100% of a thickness of the bulk body, wherein each of the plurality of metal inclusions has a constant cross-section along its height, wherein each of the plurality of metal inclusions has a maximum lateral size in the order of λ 0 10 , where λ 0 is the operating wavelength of the antenna in the bulk body, such that the plurality of metal inclusions do not self-resonate at the operating frequency; wherein the cross-section is window-shaped, rectangular-shaped, triangular-shaped, or hexagonal-shaped; and wherein the resonator body has an effective permittivity at least 5 times that of the bulk body. a substrate with at least a planar surface; a resonator body formed from an artificial dielectric material; and an excitation structure for exciting the resonator body; wherein the artificial dielectric material comprises: a bulk polymer body, wherein the bulk body has at least a first planar surface and a second planar surface opposed to the first planar surface, a plurality of coupled metal inclusions for increasing an effective permittivity of the bulk body, the metal inclusions extending perpendicularly from the first planar surface, and at least partially through the bulk body toward the second planar surface, wherein the metal inclusions have a height between 2-100% of a thickness of the bulk body, wherein each of the plurality of metal inclusions has a constant cross-section along its height, wherein each of the plurality of metal inclusions has a maximum lateral size in the order of λ 0 10 , where λ 0 is the operating wavelength of the antenna in the bulk body, such that the plurality of metal inclusions do not self-resonate at the operating frequency; wherein the cross-section is window-shaped, rectangular-shaped, triangular-shaped, or hexagonal-shaped; and wherein the resonator body has an effective permittivity at least 5 times that of the bulk body. a bulk polymer body, wherein the bulk body has at least a first planar surface and a second planar surface opposed to the first planar surface, a plurality of coupled metal inclusions for increasing an effective permittivity of the bulk body, the metal inclusions extending perpendicularly from the first planar surface, and at least partially through the bulk body toward the second planar surface, wherein the metal inclusions have a height between 2-100% of a thickness of the bulk body, wherein each of the plurality of metal inclusions has a constant cross-section along its height, wherein each of the plurality of metal inclusions has a maximum lateral size in the order of λ 0 10 , where λ 0 is the operating wavelength of the antenna in the bulk body, such that the plurality of metal inclusions do not self-resonate at the operating frequency; wherein the cross-section is window-shaped, rectangular-shaped, triangular-shaped, or hexagonal-shaped; and wherein the resonator body has an effective permittivity at least 5 times that of the bulk body. <EOS>