Abstract-New phasing element for a wideband microstrip reflectarray is presented. It is formed by a phase-delay line attached to a circular ring loaded with a circular disc microstrip. The structure is enclosed by a circular ring element with a pair of gaps. It is shown that the new phasing element offers a wider bandwidth with an increased phasing range that is useful in reflectarrays phase compensation procedure. Full wave EM simulations are carried out. Good agreement exists between simulation results and measurements by using waveguide simulator method. The mutual coupling effect for a realistic reflectarray configuration with non-identical cells is accounted for by using the perturbation technique.
This paper presents the application of machine learning-based approach toward prediction of path loss for the large intelligent surface-assisted wireless communication in smart radio environment. Two bagging ensemble methods, namely K-nearest neighbor and random forest, are exploited to build the path loss prediction models by using the training dataset. To generate the data samples without having to run measurement campaign, a path loss model is developed owning to the similarity between the large intelligent surface-assisted wireless communication and the reflector antenna system. Simple path loss expression is deduced from the system gain of the reflector antenna system, and it is used to generate the data samples. Simulation results are presented to verify the prediction accuracy of the path loss predictions models. The prediction performances of the trained path loss models are assessed based on the complexity and accuracy metrics, including R 2 score, mean absolute error, and root mean square error. It is demonstrated that the machine learning-based models can provide high prediction accuracy and acceptable complexity. The K-nearest neighbor algorithm outperforms random forest algorithm, and it has smaller prediction errors.
Reconfigurable intelligent surfaces (RISs) have recently attracted attention in the implementation of smart radio environment. In this paper, RISs are realized by the near-field focused antennas (NFF). A near-field channel gain model of RIS-assisted wireless communications is developed for an NFF reflectarray antenna based on the physics and electromagnetic nature of the RISs. The developed model entails the computation of the reflectarray aperture efficiency. Also, it takes into account reflectarray reconfigurablility to cope with varying environment, physical factors like the physical dimensions of the RISs, and the radiation patterns of the unit cells. Moreover, it is characterised by a reduction in the complexity. This model is further used in computing the positioning performance bounds and estimating the RIS optimal beamformer weights. For a validation purpose, the model is simulated by using Matlab software, and the results are compared to the simulation results of a near-field model discussed in literature. The comparison shows a very good agreement. Finally, the reflectarray antenna is thinned to achieve a performance comparable to a fully populated reflectarray antenna case using the full wave 3D electromagnetic solver CST Microwave Studio (CST MWS).
Abstract-The problem of direction-of-arrival (DOA) estimation by using spectral search for a non-uniform planar array is addressed. New search methods for DOA estimation based on piecewise interpolation are proposed.The relationships between these methods and Fourier-Domain (FD) root-MUSIC are discussed. The proposed methods are based on dividing the multiple signal classification (MUSIC) null-spectrum function into a number of equal subintervals. These subintervals are interpolated by using low-degree polynomials. Piecewise interpolation methods based on elementary functions are used to reduce the required computations of MUSIC null-spectrum function.This property reduces the computational complexity compared with line-search methods for DOA estimation. The Cramér Rao Lower Bound (CRB) is used as a benchmark to check the accuracy and validity of the proposed methods.
In this paper, an internal multiband antenna is proposed for LTE-A/WWAN wireless applications in tablet computer. The proposed antenna is configured to have two branch radiators. These two branch radiators are a U-shaped driven monopole and a nonuniform wrapped inverted U-shaped monopole. The impedance bandwidths across dual operating bands are 89.7 MHz and 4185 MHz at the LTE-A/WWAN bands. Various techniques, such as branching and parasitic element are used to enhance the antenna's bandwidth, the matching, and the size of the proposed antenna. The antenna is presented on an area of 50 × 15 mm 2. Experimental results of this antenna show nearly omni-directional coverage and stable gain variation across the LTE-A/WWAN bands.
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