A broadband resonant cavity antenna using a metamaterial superstrate consisting of two indentical patch arrays
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This thesis presents the research work on the development of a broadband resonant cavity antenna (RCA) using a two-layer metamaterial based superstrate and a wideband patch antenna as a primary source. It is shown that the resonant effect in a metamaterial consisting of two identical patch arrays can be used to design an RCA device for broadband performance. The large radiation bandwidth of 40∼47% with 1-dB-ripple flat band response and the maximum gain of ∼13 dBi have been achieved over the frequency band of 8∼12 GHz. The dimensions of the compact RCA device are 45x45x24 mm3 (or 1.5λx1.5λx0.8λ at 10 GHz). The two-layer metamaterial superstrate is based on an assembled structure using the two liquid crystal polymer (LCP) film substrates each with a printed patch array and separated by an air spacer of 4 mm. This air-based superstrate contributes antenna efficiency; it is lighter and requires less dielectric material. For comparison, the two-layer metamaterial superstrate design is implemented using an FR4 board and it has also been demonstrated to provide similar broadband performance in an RCA device. The Fano resonance effect in the two-layer metamaterial design has been studied. It has been discovered that a sharp resonance can be obtained in such metamaterials when a dielectric spacer is very thin (~100 µm). Analysis of current and electric field distributions shows that the observed electromagnetically induced transparency (EIT) associated with the enhanced transmission originates from the effect of trapped-mode resonance in the two-layer metamaterials. The experimental work was carried out using both FR4 and LCP based dielectric spacers. It is shown that the LCP based metamaterials can also be used as an effective absorber near a design frequency of 10 GHz. A broadband source antenna is based on an optimised coplanar waveguide (CPW) fed and aperture coupled patch antenna design. By exploiting the coupling effects of a triple resonances associated with the CPW structure, the aperture, and the patch element, the broadband patch antenna was obtained and used successfully in the development of the broadband RCA device. Impedance and radiation bandwidths of the practical device are measured to be as large as 41% and 43%, respectively. The new fabrication and assembly methods based on laser micromachining of the PMMA polymer have been developed for a successful construction of metamaterial structures and antenna devices.