Low Discrepancy Sparse Phased Array Antennas

Sparse arrays have grating lobes in the far field pattern due to the large spacing of elements residing in a rectangular or triangular grid. Random element spacing removes the grating lobes but produces large variations in element density across the aperture. In fact, some areas are so dense that the elements overlap. This paper introduces a low discrepancy sequence (LDS) for generating the element locations in sparse planar arrays without grating lobes. This nonrandom alternative finds an element layout that reduces the grating lobes while keeping the elements far enough apart for practical construction. Our studies consider uniform sparse LDS arrays with 86% less elements than a fully populated array, and numerical results are presented that show these sampling techniques are capable of completely removing the grating lobes of sparse arrays. We present the mathematical formulation for implementing an LDS generated element lattice for sparse planar arrays, and present numerical results on their performance. Multiple array configurations are studied, and we show that these LDS techniques are not impacted by the type/shape of the planar array. Moreover, in comparison between the LDS techniques, we show that the Poisson disk sampling technique outperforms all other approaches and is the recommended LDS technique for sparse arrays.

An extended family of perforated submicrometer hollow or core-shell plasmonic particles as antireflective synthetic brochosomes

We investigated different biomimetic structures inspired by natural brochosome powders which appear on the bodies and wings of leafhoppers (insects from the Cicadellidae family). All structures we analyzed are roughly spherical, with diameters 200 nm to 1000 nm, with a core and a shell made of different materials and the core perforated with subwavelength holes with diameters of the order of tens of nanometers. We extended the range of possible designs, geometries and materials of synthetic brochosomes, inspired by their natural counterparts found as powders secreted by various species of leafhoppers. We performed simulation of the optical properties of the structures using the finite element method. We found out that our approach ensures the design of highly efficient omnidirectional ultra-antireflective diffractive powders with subwavelength apertures. The reflectivity of 600 nm diameter holey spheres does not exceed 0.02% in 500-600 nm range. We showed that planar arrays of plasmonic-based artificial brochosomes exhibit a rich optical behavior, including effective refractive index below unity and even below zero at longer wavelengths. Such metamaterial-like behavior contributes to the multifunctionality of our synthetic brochosomes which can already serve as antireflective, superhydrophobic and highly porous structures controllable by design. This kind of versatility shows potentials for numerous practical uses. A major part of the novel functionalities stems from the use of nanocomposites containing free-electron conductors (plasmonic materials). Thus we arrived at a toolbox for the design of highly customizable antireflective layers. Potential fields of use include photodetectors, photoelectrochemistry, photocatalysis and general microoptoelectromechanical (MOEMS) systems.

Medium-Sized Highly Coupled Planar Arrays with Maximum Aperture Efficiency

This paper presents a technique to design strongly coupled planar arrays with very high aperture efficiency. The key innovation is that, based on an irregular 2 × 1 array, very compact medium-sized arrays of size 2 × 2, 2 × 4, and 2 × 6 are constructed with very strong and constructive mutual coupling between the elements. In this way, a maximum aperture efficiency is reached for a given footprint of the array. The occupied space of the antenna in comparison with conventional linear patch arrays is studied. A prototype 2 × 4 array operating around 5.8 GHz is designed, fabricated, built, and measured. The results show a large bandwidth of 20% and a very high aperture efficiency of 100%, which is the largest found in the literature for similarly sized arrays. These results are important in view of the future Internet of Things, where small and medium-sized arrays are planned to be mounted on numerous devices where a very limited physical area is available.

Broad Coverage Precoding for 3D Massive MIMO with Huge Uniform Planar Arrays

In this paper, we propose a novel broad coverage precoder design for three-dimensional (3D) massive multi-input multi-output (MIMO) equipped with huge uniform planar arrays (UPAs). The desired two-dimensional (2D) angle power spectrum is assumed to be separable. We use the per-antenna constant power constraint and the semi-unitary constraint which are widely used in the literature. For normal broad coverage precoder design, the dimension of the optimization space is the product of the number of antennas at the base station (BS) and the number of transmit streams. With the proposed method, the design of the high-dimensional precoding matrices is reduced to that of a set of low-dimensional orthonormal vectors, and of a pair of low-dimensional vectors. The dimensions of the vectors in the set and the pair are the number of antennas per column and per row of the UPA, respectively. We then use optimization methods to generate the set of orthonormal vectors and the pair of vectors, respectively. Finally, simulation results show that the proposed broad coverage precoding matrices achieve nearly the same performance as the normal broad coverage precoder with much lower computational complexity.

Two-Dimensional Nanoplatelet Superlattices Overcoming Light Outcoupling Efficiency Limit in Perovskite Quantum Dot Light-Emitting Diodes

Quantum dot (QD) light-emitting diodes (LEDs) are emerging as one of the most promising candidates for next-generation displays. However, their intrinsic light outcoupling efficiency remains considerably lower than the organic counterpart, because it is not yet possible to control the transition-dipole-moment (TDM) orientation in QD solids at device level. Here, using the colloidal lead halide perovskite nanoplatelets (NPLs) as a model system, we report a directed self-assembly approach to form the two-dimensional superlattices (2DSLs) with the out-of-plane vector perpendicular to the substrate plane. The ligand and substrate engineering yields close-packed planar arrays with the side faces linked to each other. Emission polarization in individual NPLs rescales the radiation from horizontal and vertical transition dipoles, effectively resulting in preferentially horizontal TDM orientation. Based on the emissive thin films comprised of stacks of 2D superlattices, we demonstrate an enhanced ratio of horizontal dipole as revealed by 2D k-space spectroscopy. Our optimized single-junction QD LEDs showed peak external quantum efficiency of up to 24% and power efficiency exceeding 110 lm W-1, comparable to state-of-the-art organic LEDs.

Ka-band planar slotted waveguide array based on groove gap waveguide technology with a glide-symmetric holey metasurface

The design of a planar slot array in groove gap waveguide technology implemented by glide-symmetric holes as Electromagnetic Band Gap structure is here presented. Despite the advantages of using holes instead of pins in terms of manufacturing simplicity and cost,the larger size of the holes compared to pins needs to be considered when designing slot arrays without grating lobes. A 1 to 4 corporate feed network is designed using this technology as well. Corrugations are included to further reduce the grating lobes. Experimental results support the viability of the proposed concept for designing glide-symmetric planar arrays of any size.