On the Projection of Curved AMC Reflectors From Physically Planar Surfaces

We develop a new class of planar low-profile artificial magnetic conductors (AMC) that act as curved magnetic mirrors, i.e., they project the AMC functionality on a curved surface, even though they are geometrically flat. We show that these curved AMCs, despite their thin profile, focus electromagnetic waves similarly to curved metallic reflectors, while, as magnetic mirrors, having a focal region extremely close to their textured surface. An appropriately designed dipole antenna integrated in the focal region of such a curved AMC shows superdirectivity commensurate with a physically curved metallic reflector surrounding the corresponding dipole. These curved AMCs are ideal for new low-profile high-directivity antennas, integrable within standard packaging technologies. We focus our analysis on curved AMCs integrated with dipole antennas embedded on a multi-layer packaging technology for the 60-GHz technology platform. However, the approach is quite general and scalable in frequency. We base our analysis on unit cells composed of metallic spirals, but our approach holds for any other AMC unit cell design. As an application, two packaged 300 μm-thick 60-GHz systems are designed occupying quite small areas, 4.6×3.2 mm² and 4.7×4.5 mm² respectively and obeying typical packaging technology layout rules. The corresponding antenna elements have gains, including return loss, of more than 9 and 10 dBi, respectively. Prototypes have been fabricated and measured indicating excellent agreement with theoretical expectations. Impedance bandwidths are 13-15 GHz, making this technology ideal for broadband, high-directivity 60 GHz radio applications.