Virtual antenna radiation at microwave frequencies using metamaterials is presented. Based on the transformation electromagnetics technique, the media embedding a physical antenna in a ground recess is designed such that the far-zone radiation pattern of a virtual antenna radiating above a flat conducting ground plane is reproduced. The antenna and a limited surrounding space above a ground plane is folded below the ground level, resulting in a physical antenna in a ground recess that is enclosed in transformation media. The electromagnetic specification of the media surrounding the physical antenna at the bottom of the recess is provided by a properly defined coordinate transformation.
A three-step design approach is followed. First, microstrip transmission-line metamaterials for a ground-recessed probe are designed and implemented for virtual source formation above the ground plane. Transmission-line metamaterial unit cell designs for the embedding media are shown. Virtual probe formation is validated using full-wave simulations. Measured field distributions over the fabricated metamaterial-surface for an embedded probe current radiating in a ground recess confirm formation of a virtual line source above the ground plane. As a next step, resonant inclusion-based metamaterials are designed for embedding a two-dimensional electric line source in a ground recess. Metamaterials are fabricated and assembled. Measured field distributions for an effective two-dimensional configuration confirm formation of a virtual line current above the ground plane. As a final extension to a three-dimensional configuration, design, fabrication, and measurement of an embedded monopole antenna in a ground recess is presented. Poorer performance was measured compared with the two-dimensional case. The complexity and material losses associated with resonator-based, negative-index metamaterials for multiple polarizations in three-dimensional applications were identified as main technical challenges
