DESIGN AND ANALYSIS OF LOW PROFILE CIRCULARLY POLARIZED ANTENNAS

In the last decade, mobile communication has spread widely and become an essential tool in every day’s life. A tremendous increase in the demand of small Personal Mobile Devices (PMD) has been observed with wide model ranges and applications. This necessitates the design of low profile and compact antennas that can be accommodated in the smaller PMD sizes. This thesis focuses on designing low profile Circularly Polarised (CP) antennas that can be incorporated with these devices. Two types of circularly polarised antennas have been considered; Dielectric Resonator Antennas (DRA) and planar open loop antennas backed by an Artificial Magnetic Conductor (AMC) ground plane. The Elliptical DRA has been considered owing to the simplicity of achieving CP radiation compared to a cylindrical DRA. Several EDRAs have been designed employing a simple conformal strip excitation mechanism. The designed antennas include single and dual band, as well as a wideband CP DRAs. In addition, a low profile elliptical dielectric resonator antenna has been designed using a dielectric constant of ε_r=25. Extremely lower profile CP loop antennas have been designed by incorporating the Artificial Magnetic Conductor (AMC) as a ground plane. Two excitation mechanisms have been employed; the Co-Planar waveguide and the vertical probe feed. A total antenna’s thickness of λ_o⁄48 has been achieved for the probe-fed loop antenna compared to λ_o⁄21.2 that has been reported in the literature and incorporated the square patch AMC. Two artificial magnetic conductor surfaces have been designed; the traditional square patch and a novel AMC. The novel AMC has reduced the antenna’s size by ~28% compared to other antennas, incorporated the square patch AMC given the same thickness using a 4×4 unit cells’ grid. Additionally, a reduction of ~45% has been achieved using a 3×3 grid of the novel unit cell with sufficient matching and axial ratio bandwidths. Furthermore, a CP loop antenna backed by the novel AMC out-performs an identical counterpart placed above the traditional square patches AMC with simulated axial ratio bandwidth of ~10%. Moreover, two dual band AMCs are presented, that are suitable for the L1 and L2 GPS bands. Once more, a pronounced size reduction of ~42% has been attained using the novel dual band AMC unit cells compared to the double square dual band AMC. Several prototypes have been fabricated with close agreement between simulated and measured results. Some results have been verified using another commercial software, HFSS.