Cloak an underground antenna using transformation electromagnetics

We present a scheme to realize a broadband antenna which is hidden under the ground but still possesses radiating performance with steerable beams as its free-space counterpart. This antenna is made invisible via the carpet cloak incorporated with a so-called `virtual boundary´. The cloaking device is empowered to conceal the antenna to external observers while the combined structure operates as a highly directive lens. Conical radiation patterns with steerable beam can be also achieved when the system is fed with an array of line source of radiation at specified positions inside the cavity. The Finite-Difference Time-Domain (FDTD) method is used to numerically verify the device at X-band (8GHz to12GHz). Results demonstrate that external incidences cannot clearly distinguish the antenna system from an empty ground plane. Various radiation patterns are also presented. The device can be implemented based on artificial gradient index materials.