Metamaterial-based and Metamaterial-inspired Efficient Electrically Small Antennas: Designs, Simulations and Experiments

The size reduction of state-of-the-art electronic circuits, as well as recent technological advances in fabrication processes, has changed the expectations of antenna designs and their performance in wireless communication and sensor network applications. An inexpensive, easy to build, efficient and electrically-small antenna system would be an ideal fit for many new generation communication and sensor systems. Metamaterials, in general, are artificially fabricated media based on resonant or nonresonant inclusions that can be engineered to obtain unusual electromagnetic (EM) behaviours that can not be readily found in nature. The renewed activity in such artificial materials has attracted interest from different research disciplines and has produced many designs in a wide frequency spectrum including examples from microwave to millimetre-wave to optical structures. The proposed metamaterial based EM applications include subwavelength imaging at microwave and optical frequencies; phase compensated microwave circuit designs; efficient electrically small antennas (EESAs); leaky wave and low-profile antennas; scattering enhancements and mitigation (cloaking); etc. [1-3]. Metamaterials (MTMs) provide one with a design approach to tailor the permittivity and permeability properties of a medium to both positive and negative values for a variety of applications. We have been studying, e.g., [4, 5], the use of MTMs to achieve EESAs We have designed several metamaterial-based antenna systems in which specific metamaterial shells have been used to achieve distributed matching elements that provide a natural reactive and resistive matching. We have also designed MTM-inspired antenna systems [6-8], both planar (2D) and volumetric (3D) and both electric- and magnetic-based, of which some have been fabricated and tested. A comparison of our predictions and the corresponding experimental results for these MTM-inspired systems are in very good agreement. We define an electrically small antenna in free space by the constraint that kre ≤ 1.0, where re is the radius of the smallest sphere that surrounds the antenna system; and an electrically small antenna fed coaxially through a ground plane by the constraint kre ≤ 0.5. The electrically-small limit for a coaxially-fed antenna through a ground plane is then 0 0.08 e r λ