Abstract:
Natural materials discovered so far do not possess simultaneous negative or
zero value of permittivity and permeability. Metamaterials, however , are
artificial materials which can be designed to have negative or zero values of
permittivity and permeability at a specific frequency. They exhibit phenom ena such as negative index of refraction, sub-wavelength resolution , cloaking
and zero refractive index. They are composed of periodic arrangement of
sub-wavelength metallic inclusions embedded in a host dielectric medium.
The engineering of permittivity and permeability in metamaterials offers a
greater control over wave propagation in them; which is not possible with
natural materials. Therefore, metamaterials have found applications not only
in developing new RF devices but also improving the performance of tradi tional devices. Metamaterials have been extensively applied to enhance the
performance of antennas, including; reducing electrical size, improving band width, minimizing side lobe level and cross polarization,enhancing gain and
directivity of antennas. Metamaterial research has seen explosive growth in
all regions of electromagnetic spectrum from LF to microwave, IR and opti cal frequencies.
This thesis describes the development of a dual-band zero-index metamate rial (ZIM) for purpose of antenna directivity enhancement. This phenomenon
based on Snell’s law of refraction bends the electromagnetic waves towards
normal direction of the interface while passing from a low index medium to a
high index medium. This work explores the design and selection of appropri ate unit cells to construct the dual-band metamaterial superstrate. Nested
capacitively loaded loops are found to be most appropriate for dual-band
operation. The proposed design is fabricated and a printed monopole an tenna is used to demonstrate the gain enhancement ability of dual-band ZIM
superstrate at two frequency bands. The metamaterial superstrate increases
the measured realized gain of printed monopole antenna by 3 dB and 4.3 dB
at 2.4 GHz and 3.5 GHz respectively..
