What are Metamaterials and How Do They Relate to Antennas?
Metamaterials are an increasingly researched topic, especially where it pertains to modern antenna structures. However, there is a lot of confusion of exactly what metamaterials are and how they are involved in the development of antennas. To put it simply, metamaterials are material and structure combinations that exhibit properties that are otherwise unknown to occur in nature. For instance, a structured material coating a surface can be used to bend light around sharp angle and effectively make an object concealed behind this surface invisible to certain wavelengths of light.
As electromagnetic radiation used in RF, microwave, and millimeter-wave communications and radar is governed by the same physics as light (just at higher frequencies), similar effects can be achieved using structures that react with longer wavelengths of electromagnetic radiation. Where nanoscale metamaterials can be used to create materials with negative refraction indices, millimeter-scale metamaterials can be used to create a variety of phenomena, including a negative magnetic permeability or electric permittivity. The exact effect a metamaterial has depends on the design of the structure and typically only affects electromagnetic radio which the metamaterial structure’s dimensions are a sub-wavelength of.
Hence, using modern fabrication and machining technology, metamaterials can be made using semiconductor fabrication technology, thus affecting millimeter-wave, terahertz, and light frequencies, or with common PCB copper structures, affecting radio and microwave frequencies.
To date, researchers have been able to create 2D metamaterial structures, metasurfaces, and distinct combination structures that have had a variety of results. This includes creating metasurfaces that bend RF and microwave energy around a structure, such as with the light-bending invisibility cloak. Moreover, RF and microwave “lenses” have also been created, that can focus and collimate RF and microwave energy much like an optical lens manipulates light.
More importantly to RF and microwave engineers, metamaterial structures have been created that enable new antenna designs that can vastly improve the performance of these structures compared to traditional antenna designs. Including structures, such as split ring resonators, periodic structures, fractal structures, and other metamaterial structures can be used to design an antenna with much higher gain, wider bandwidths, and with unique antenna patterns. A key note, is that many of these metamaterial enhanced antenna can be fabricated on planar support materials with low-cost electronic circuit manufacturing technology. Hence, these types of antennas can be made relatively inexpensively and can conform to modern flat-panel antenna designs used with array antennas, cellular antennas, DAS, etc.