Hybrid grating bowtie antenna based on metamaterial structures and cavity-backed reflector for high gain wideband applications

Microstrip antenna has attracted many researchers in the applications of wireless communications due to its high performance in terms of high gain, wideband, unidirectional radiation pattern and low cross polarization. This type of antenna can be used to process a function of multimode/multiband operations, high speed data transmission and long-distance communication. There are many techniques adopted to obtain these specifications on the printed microstrip antenna. In this thesis, high gain wideband grating bowtie microstip antenna has been designed. To achieve a unidirectional radiation pattern antenna, an electrical grating bowtie dipole and magnetic half ring dipole have been designed by using grating bowtie dipole, half ring dipole and a cavity backed. The cavity backed has been utilized here for two functions; first to work as an image to the dipoles so that the grating bowtie dipole with its image acts as an electric dipole and the half ring dipole with its image functions as magnetic dipole, in addition to reduce the back lobes. These dipoles were proposed to obtain an equal amplitude and phase in an electric and magnetic current. According to Huygens’ source theory, if the current sources are excited by the same amplitude and phase, unidirectional and low back radiation patterns can be obtained accordingly. However, the results of the bandwidth and gain were still need to be improve. So that a technology of enhancing the gain and bandwidth are required. In order to earn wider bandwidth, a multistage transformer is employed. Which enhance the bandwidth from 9 % (5.3 GHz to 5.8 GHz) to 52.9 % (5 GHz to 8.6 GHz). Whereas, the gain was from 8.4 dB to 14.3 dB. To improve the radiation pattern, a method of pattern radiation improvement is required. Based on Snell’s law, when the antenna loading with structure has a higher reflective index than the substrate reflective index, the energy can be congregate. Metamaterials which have higher reflective index from the substrate have been used. This metamaterial enhances the gain at a bigger scale. The investigation results of the proposed design exhibit a bandwidth of 54.2% from 5 GHz to 8.72 GHz and a stable gain from of 9.5 dBi to 16.7 dBi over the entire frequency band with a total dimension of 76.5 X 140 mm2.

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