Meta-materials are man-made materials that derive their novel wave-interaction and propagation properties from embedded (artificial) resonance structures. The Split Ring Structure (SRS) is just a renowned metallic metamaterial that provided the first artificial negative m system. A mushroom structure with a metallic planar pattern and a flat metal sheet interconnected through metallic vias is also a metamaterial with simultaneously negative e and m can have high impedance and an absolute gap in the surface wave spectrum at the same time and thus can serve as good ground planes.
The physics is governed by a series of intrinsic magnetic resonances and can be well described by an effective medium of frequency-dependent permeability. An antenna placed directly on the top surface of this composite shows significantly enhanced forward radiation at those in-phase reflecting frequencies. Different metallic planar patterns can be adopted in such a structure and some amazing physical properties can be achieved. For example, a quasiperiodic structure was adopted and we realized a directive emission on such a planar structure theoretically and experimentally. Preliminary theoretical calculations indicate that the directional emission can just be realized using effective negative m substrates mixed with disjoint patches of negative e. We will design experimentally realizable structures and verify the concept experimentally. Some other unconventional geometries are under research to get novel properties. Finite difference time domain (FDTD) method is the main tool in the simulation and it provides perfect agreement with experiment and reveals the underlying physics well.