[1] Relatively simple and accurate closed form Uniform Geometrical Theory of Diffraction (UTD) solutions are obtained for describing the radiated and surface wave fields, respectively, which are excited by sources near or on thin, planar, canonical twodimensional (2-D) double positive/double negative (DPS/DNG) material discontinuities. Unlike most previous works, which analyze the plane wave scattering by such DPS structures via the Wiener-Hopf (W-H) or Maliuzhinets methods, the present development can also treat problems of the radiation by and coupling between antennas near or on finite material coatings on large metallic platforms. The latter is made possible mainly through the introduction of important higher-order UTD slope diffraction terms which are developed here in addition to first-order UTD. The present solutions are simpler to use because, in part, they do not contain the complicated split functions of the W-H solutions nor the complex Maliuzhinets functions. Unlike the latter methods based on approximate boundary conditions, the present solutions, which are developed via a heuristic spectral synthesis approach, recover the proper local plane wave Fresnel reflection and transmission coefficients and surface wave constants of the DPS/DNG material. They also include the presence of backward surface waves in DNG media. Besides being asymptotic solutions of the wave equation, the present UTD diffracted fields satisfy reciprocity, the radiation condition, boundary conditions on the conductor, and the Karp-Karal lemma which dictates that the first-order UTD space waves vanish on a material interface.Citation: Lertwiriyaprapa, T., P. H. Pathak, and J. L. Volakis (2007), A Uniform Geometrical Theory of Diffraction for predicting fields of sources near or on thin planar positive/negative material discontinuities, Radio Sci., 42, RS6S18,
This research proposed an S-shaped metasurface (MTS)-based wideband circularly polarized (CP) patch antenna for C-band uplink frequency spectrum. The proposed MTS-based CP patch antenna was of low profile and fabricated on three substrate layers: upper, middle, and lower. The upper substrate contained 4 × 4 periodic S-shaped MTS elements, the middle substrate functioned as ground plane with a rectangular-shaped slot at the center, and the lower substrate contained a coplanar waveguide with microstrip and ground. The S-shaped MTS elements converted linearly polarized (LP) into CP wave. Simulations were performed, and an antenna prototype was fabricated and experiments carried out. The measured impedance bandwidth and axial ratio bandwidth (ARBW) at the center frequency of 5.9 GHz were 43.22% (4.05 -6.6 GHz) and 22% (5.3 -6.6 GHz), respectively, rendering the proposed antenna suitable for satellite communication applications. The proposed antenna achieved the maximum gain of 6.16 dBic at 5.6 GHz. The novelty of this research lies in the use of S-shaped MTS elements to efficiently convert LP into CP wave and achieve wider ARBW for the C-band uplink spectrum.
A two-dimensional (2-D) discrete dielectric lens antenna is designed to radiate fan-shaped multi-beam patterns for gain stability in beam switching. The target is to minimize adjacent-beam overlapping transition regions and provide sufficient and similar gains for all field angles when the antenna is employed in a mobile device. This design starts with a conventional 2-D Luneburg lens antenna, and distorts its dielectric permittivity and the sizes of discrete dielectric rings to defocus the pencil beam patterns into shaped ones with a relatively flat pattern for uniform field distribution. The design is realistically implemented at 38 GHz with both simulation and measurement results shown to validate the concept. Successful validation of feasibility in beam synthesis is achieved. Fabrication discrepancy to result in slight radiation degradation is also discussed. INDEX TERMS Genetic algorithm, Luneburg lens antenna, multi-beam radiation, pattern synthesis.
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