Investigation into the design of broadband singly-fed electromagnetically coupled patch (EMCP) antenna elements and arrays for circular polarisation
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The rapid development of satellite and wireless communications pose extraordinary demands on broadband circularly polarised (CP) antenna elements and high-performance antenna arrays. The use of high-dielectric-constant materials as the substrate for the driven layer and a low-dielectric-constant material as superstrate for the radiating patch overcomes the conflict between circuit integration and antenna radiation. The aim of the research presented in this thesis is to design and develop high performance singly-fed microstrip patch antennas and arrays for CP applications. Firstly, we introduce a singly-fed cross-aperture coupled patch antenna and a stacked patch antenna using high and low dielectric materials known as Type-F and Type-E elements, respectively. As the physical structure of the Type-E element is close to the conventional linearly-polarised electromagnetically coupled patch (LP-EMCP) antennas, we have also denoted it as CP-EMCP antenna. The development of CP-EMCP antennas addresses the drawbacks of the cross-aperture patch antenna. A systematic optimisation method is developed for the design of CP-EMCP elements, at which the mean frequencies of the bandwidths can be adjusted in order to achieve a wide overlaid bandwidth. Secondly, we investigate the effects of perturbation on the parasitic patch, layer displacements, material tolerances and superstrate thicknesses on the broadband performance as well as the mutual coupling of the CP-EMCP elements. Both our theoretical and experimental results show that the CP-EMCP elements are robust in performance and have a low mutual coupling. When compared to the conventional stacked EMCP antennas and to the reduced surface-wave antenna, the mutual coupling between CP-EMCP elements is lower which allows the use of small element spacings to avoid grating lobes, which therefore make these elements good candidates for high-performance CP arrays. Following a parametric study on the effect of displacements between stacked patches and the loss consideration of the coplanar feed network printed on high dielectric constant substrates, the modified Type-E elements whose parasitic patch have a zero perturbation are developed for the design of high performance CP arrays. The low mutual coupling allows short feed-lines to connect with the spatially offset elements so as to minimise the feed loss. Consequently, it became possible to develop the novel sequentially rotating feed networks which incorporate the modified elements with a small element spacing of 2/3/λₒ for the 4- and 16-element planar antenna arrays. The results indicate that these arrays have high gain, low axial ratio, high antenna efficiency low sidelobe levels, and wide overlaid bandwidth.
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