Phase-only control of antenna sum and shaped patterns through nullperturbation

Satisfactory sum or shaped antenna radiation patterns can often be synthesized by modifying just the phase distribution of an initial excitation by an arbitrary amplitude distribution. As examples, we calculate linear and circular apertures with uniform, Taylor, or cosine-section amplitude distributions, affording symmetric sum patterns with low sidelobe levels or symmetric shaped patterns with low ripple and sidelobe levels; linear aperture distributions, affording patterns with low sidelobe levels on one side of the beam; and planar arrays, with uniform or cosine-section amplitude distributions affording φ-symmetric or elongated-oval footprints     

Arbitrary footprint patterns obtained by circular apertures

The proposed quasi-analytical method undertakes the shaping of a desired footprint as a composition of several /spl phi/-symmetric circular Taylor patterns exhibiting flat-topped beams. The final pattern is obtained after sampling the obtained circular aperture for circular grid planar arrays. A square and a rectangular footprint pattern, both radiated by a planar array with 1246 elements, demonstrate the performance of the technique.     

Dye‐Doped Polyhedral Oligomeric Silsesquioxane (POSS)‐Modified Polymeric Matrices for Highly Efficient and Photostable Solid‐State Lasers

Here, the design, synthesis, and characterization of laser nanomaterials based on dye‐doped methyl methacrylate (MMA) crosslinked with octa(propyl‐methacrylate) polyhedral oligomeric silsesquioxane (8MMAPOSS) is reported in relation to their composition and structure. The influence of the silicon content on the laser action of the dye pyrromethene 567 (PM567) is analyzed in a systematic way by increasing the weight proportion of POSS from 1 to 50%. The influence of the inorganic network structure is studied by replacing the 8MMAPOSS comonomer by both the monofunctionalized heptaisobutyl‐methacryl‐POSS (1MMAPOSS), which defines the nanostructured linear network with the POSS cages appearing as pendant groups of the polymeric chains, and also by a new 8‐hydrogenated POSS incorporated as additive to the polymeric matrices. The new materials exhibit enhanced thermal, optical, and mechanical properties with respect to the pure organic polymers. The organization of the molecular units in these nanomaterials is studied through a structural analysis by solid‐state NMR. The domain size of the dispersed phase assures a homogeneous distribution of POSS into the polymer, thus, a continuous phase corresponding to the organic matrix incorporates these nanometer‐sized POSS crosslinkers at a molecular level, in agreement with the transparency of the samples. The silicon–oxygen core framework has to be covalently bonded into the polymer backbone instead of being a simple additive and both the silica content and crosslinked degree exhibit a critical influence on the laser action.     

Synthesis and Biophysical Study of Disassembling Nanohybrid Bioconjugates with a Cubic Octasilsesquioxane Core

Polyhedral oligosilsesquioxanes (POSS) have recently attracted attention as scaffolds for the synthesis of multivalent bioconjugates. The synthesis of glycosyl‐octasilsesquioxanes (glyco‐POSS) using a copper(I)‐catalyzed azide‐alkyne 1,3‐dipolar cycloaddition approach is reported. The problems associated with the use of bases or aqueous media in their preparation are investigated and a comprehensive study of the multivalent interaction between the mannosyl‐octasilsesquioxanes and a model lectin, concanavalin A (Con A), using an array of complementary biophysical techniques is presented. The possibility to modulate the half‐life of POSS conjugates in aqueous solution and the low toxicity of their constituent monomeric organosilanes offers an advantage over other scaffolds in vivo, preventing bioaccumulation and saturation of complementary receptors (lectins). Despite the hydrolysis in water, the octamannosyl‐POSS studied shows a 50‐fold higher binding affinity to Con A than methyl α‐D ‐mannopyranoside. These experiments suggest that the novel glyco‐POSS are attractive compounds for in vivo applications that require multivalent display of glycans.     

Phase-only synthesis of continuous linear aperture distributionpatterns with asymmetric side lobes

A method for synthesising linear aperture distribution patterns with different side lobe levels (SLLs) on both sides of the main beam is proposed. This phase-only control method was applied to a Taylor distribution as well as to a uniform amplitude distribution and achieved differences in the SLL on both sides of the main beam as great as 23 dB, improving on a previous procedure that had achieved a gap of little more than 10 dB     

Multiple-pattern linear antenna arrays with single prefixedamplitude distributions: modified Woodward-Lawson synthesis

The authors describe the design of linear antenna arrays that generate multiple radiation patterns by switching between different excitation phase distributions while maintaining a constant pre-established amplitude distribution. Examples are given of antennas with uniform or Gaussian amplitude distributions that, depending on their phase distribution, generate a sum pattern, a flat-topped beam or a cosec-squared pattern     

Synthesis of antenna patterns of circular arc arrays

A new method is described for the synthesis of antenna patterns of circular are arrays. The method is based on the application of the simulated annealing technique to achieve the excitations of elements for a desired radiation pattern. Design specifications include sidelobe level, beamwidth, control of nulls, and other parameters such as the dynamic range of excitations     

Synthesis of non-/spl phi/-symmetric patterns from circular arrays

A new method for synthesising non-/spl phi/-symmetric patterns radiated by planar antenna arrays with circular boundary is presented. The described synthesis procedure uses the modified Taylor expressions, but turning aside their inherent /spl phi/-symmetry, to provide good non-/spl phi/-symmetric patterns.     

Beam reconfiguration of linear arrays using parasitic elements

An innovative method for linear arrays beam reconfiguration is presented. This pattern reconfigurability is achieved by a mechanical displacement of a parasitic array located in front of an active one. Two worked examples that use parallel dipoles are presented.     

Arbitrary footprint patterns from planar arrays with complexexcitations

Elliott and Stern's (1990) method for synthesising shaped patterns using a circular or elliptical planar aperture or array with a complex excitation distribution is generalised to allow the synthesis of footprints of arbitrary shape. The use of complex excitations allows a given footprint to be synthesised using a smaller array than with real excitations. The procedure is illustrated by synthesising a square footprint using an array with a rectangular grid