A low-profile 3-D printable metastructure for performance improvement of aperture antennas.

In order to increase the radiation performance of aperture-type antennas, this paper demonstrates a low-profile, planar, single-layer, three-dimensional (3-D) printable metastructure. The proposed hybridized metastructure is highly transparent as it is made out of novel hybrid meta-atoms having transmission coefficient magnitudes greater than - 0.72 dB and fully complies with the near-field phase transformation principle. The hybridized design approach makes the metastructure planar, low-profile, light in weight, and compatible with additive printing technology. For the proof-of-concept, such metastructure is developed and numerically verified to enhance the radiation performance of a resonant cavity antenna (RCA). With the proposed metastructure, the peak directivity of the RCA is improved by 8.6 dBi (from 11.4 dBi to 20 dBi) at the operating frequency of 12.4 GHz. The aperture efficiency and 3-dB directivity bandwidth of the RCA with the metastructure are 41.46% and 16.5%, respectively. Using readily accessible thermoplastics or polymers and copper with cost-effective fused deposition modeling (FDM) 3-D printing technology, the proposed planar hybridized metastructure can be prototyped commercially.

A Wilkinson power divider with harmonic suppression through low-pass filter for GSM and LTE applications.

Conventional Wilkinson power dividers (WPDs) perform satisfactorily near the intended operation frequency. Nonetheless, these WPDs demonstrate subpar performance in the stopband and necessitate a significant physical space. To enhance the existing level of advancement and in order to improve on the current state-of-the-art, a modified WPD is designed and fabricated, demonstrating a significant improvement in stopband and superior isolation between output ports. To improve the stopband and suppress unwanted harmonics, a low-pass filter (LPF) structure is placed in the both branches of the conventional WPD. The proposed modified WPD depicts a wide stopband bandwidth (fSB > 17.25 GHz) from 2.75 to over 20 GHz with an attenuation level of 20 dB, suppressing 2nd to 11th harmonics. According to measured results, the input return loss (|S11|), insertion loss (|S21|) and output isolation (|S32|) at f = 1.8 GHz are better than 33 dB, 3.2 dB and 21 dB, respectively. Indeed, the proposed modified WPD exhibits a magnitude imbalance of 0.00018, a phase imbalance of 1.25 degrees and a group delay of 0.5 ns. The proposed WPD depicts a compact size of 35 mm × 25 mm (0.38 λg × 0.27 λg), where λg is the guided wavelength at f = 1.8 GHz. There is a good agreement between the simulated and measured results. According to the obtained results, the proposed modified WPD shows a desirable performance for modern LTE and GSM communication applications.

Design and fabrication of a Wilkinson power divider with harmonic suppression for LTE and GSM applications.

Conventional Wilkinson power dividers (WPDs) can provide acceptable performance close to the nominal center frequency. However, these WPDs can also exhibit poor out-of-band performance while requiring a large footprint. In order to improve on the current state of the art, a modified microstrip WPD is proposed that exhibits a substantially improved stopband and high isolation. A lowpass filter (LPF) structure is utilized in both branches of the power divider to provide harmonic suppression. According to the obtained results, the input return loss (|S11|), output return loss (|S22|), output insertion loss (|S21|) and isolation (|S32|) are better than 34.2 dB, 26.2 dB, 3.52 dB and 31.2 dB, respectively. The proposed modified WPD has a wide 20 dB stopband (from 2.54 GHz to 13.48 GHz) and filters the second to seventh harmonics with attenuation levels of greater than 20 dB. The proposed WPD has a small size of 33.8 mm × 27 mm (0.42 λg × 0.33 λg), where λg is the guided wavelength at the operating frequency of 1.8 GHz. The WPD has been fabricated and tested and shows good agreement between simulated and measured results and the proposed design has desirable characteristics for LTE and GSM applications.

3D metamaterial ultra-wideband absorber for curved surface.

This paper proposes a three-dimensional metamaterial absorber based on a resistive film patch array to develop a low-cost, lightweight absorber for curved surfaces. An excellent absorption over a large frequency band is achieved through two different yet controllable mechanisms; in the first mechanism, a considerable attenuation in the wave power is achieved via graphite resistive films. The absorption is then intensified through magnetic dipoles created by the surface currents, leading to absorption peaks. The simulation results of the absorber show that a broadband absorption greater than 85% is achieved over 35-400 GHz for both TE and TM polarization waves at normal incidence. The structure has more than 167% and 80% absorption bandwidth above 85% and 90%, respectively. It is shown that the proposed metamaterial absorber is independent of incident wave polarization. In addition, the structure is insensitive to incident angles up to 60° for TE mode and full range angle 90° for TM mode. To describe the physical mechanism of the absorber, E-field, power loss density and surface current distributions on the structure are calculated and shown. Moreover, the oblique incidence absorption efficiency is also explained. This absorber paves the way for practical applications, such as sensing, imaging and stealth technology. In addition, the proposed structure can be extended to terahertz, infrared and optical regions.

Varactor-tuned wideband band-pass filter for 5G NR frequency bands n77, n79 and 5G Wi-Fi.

A wide-band band-pass filter (BPF) using coupled lines, rectangular stubs and Stepped-Impedance Resonators (SIRs) is presented in this paper. The proposed BPF operates over a large pass-band from 3.15 to 6.05 GHz covering 5G New Radio (NR) frequency Bands n77, n79 and 5G Wi-Fi, which includes the G band of US (3.3 to 4.2 GHz), 5G band of Japan (4.4 to 5 GHz) and 5G Wi-Fi (5.15 to 5.85 GHz). The presented filter has a maximum pass-band Insertion-Loss (IL) of 2 dB, a sharp roll-off rate and suppresses all the unwanted harmonics from 4.2 GHz up to 12 GHz with a 15 dB attenuation level. The performance of each section can be analyzed based on lumped-element circuit models. The electrical size of the BPF is 0.258 λg × 0.255 λg, where λg is the guided wavelength at the central frequency. The design accuracy is verified through implementing and testing the final BPF. The pass-band band-width can be controlled by adding the varactor diodes. A good relationship between the band-width and the varactor diodes are extracted by the curve fitting technique.

Introducing a Novel Model-Free Multivariable Adaptive Neural Network Controller for Square MIMO Systems.

In this study, a novel Multivariable Adaptive Neural Network Controller (MANNC) is developed for coupled model-free n-input n-output systems. The learning algorithm of the proposed controller does not rely on the model of a system and uses only the history of the system inputs and outputs. The system is considered as a 'black box' with no pre-knowledge of its internal structure. By online monitoring and possessing the system inputs and outputs, the parameters of the controller are adjusted. Using the accumulated gradient of the system error along with the Lyapunov stability analysis, the weights' adjustment convergence of the controller can be observed, and an optimal training number of the controller can be selected. The Lyapunov stability of the system is checked during the entire weight training process to enable the controller to handle any possible nonlinearities of the system. The effectiveness of the MANNC in controlling nonlinear square multiple-input multiple-output (MIMO) systems is demonstrated via three simulation studies covering the cases of a time-invariant nonlinear MIMO system, a time-variant nonlinear MIMO system, and a hybrid MIMO system, respectively. In each case, the performance of the MANNC is compared with that of a properly selected existing counterpart. Simulation results demonstrate that the proposed MANNC is capable of controlling various types of square MIMO systems with much improved performance over its existing counterpart. The unique properties of the MANNC will make it a suitable candidate for many industrial applications.

Flexible and Transparent Circularly Polarized Patch Antenna for Reliable Unobtrusive Wearable Wireless Communications.

This paper presents a circularly polarized flexible and transparent circular patch antenna suitable for body-worn wireless-communications. Circular polarization is highly beneficial in wearable wireless communications, where antennas, as a key component of the RF front-end, operate in dynamic environments, such as the human body. The demonstrated antenna is realized with highly flexible, robust and transparent conductive-fabric-polymer composite. The performance of the explored flexible-transparent antenna is also compared with its non-transparent counterpart manufactured with non-transparent conductive fabric. This comparison further demonstrates the suitability of the proposed materials for the target unobtrusive wearable applications. Detailed numerical and experimental investigations are explored in this paper to verify the proposed design. Moreover, the compatibility of the antenna in wearable applications is evaluated by testing the performance on a forearm phantom and calculating the specific absorption rate (SAR).

Terahertz beamforming network with a nonuniform contour.

This paper presents a terahertz beamforming network based on a nonlocal lens with a 2D beam-scanning demonstration through leaky-wave antennas. The proposed design methodology is novel, to the best of our knowledge, in the aspect of using unconventional optimization parameters to significantly reduce the phase error associated with this class of beamformers. In this approach, a nonuniform contour defined by Fourier series expansion is used as a new optimization parameter to significantly decrease the phase error over a larger scan-angle than that in the previous works. The proposed system is a good candidate for industrial and security applications such as automotive radar sensors and electromagnetic THz imaging, thanks to its extensive 2D scanning range: -68∘ to 0° in the elevation plane and -45∘ to +45∘ in the azimuth plane over the frequency range of 140-180 GHz.

MIMO Antenna System for Modern 5G Handheld Devices with Healthcare and High Rate Delivery.

In this work, a new prototype of the eight-element MIMO antenna system for 5G communications, internet of things, and networks has been proposed. This system is based on an H-shaped monopole antenna system that offers 200 MHz bandwidth ranges between 3.4-3.6 GHz, and the isolation between any two elements is well below -12 dB without using any decoupling structure. The proposed system is designed on a commercially available 0.8 mm-thick FR4 substrate. One side of the chassis is used to place the radiating elements, while the copper from the other side is being removed to avoid short-circuiting with other components and devices. This also enables space for other systems, sub-systems, and components. A prototype is fabricated and excellent agreement is observed between the experimental and the computed results. It was found that ECC is 0.2 for any two radiating elements which is consistent with the desirable standards, and channel capacity is 38 bps/Hz which is 2.9 times higher than 4 × 4 MIMO configuration. In addition, single hand mode and dual hand mode analysis are conducted to understand the operation of the system under such operations and to identify losses and/or changes in the key performance parameters. Based on the results, the proposed antenna system will find its applications in modern 5G handheld devices and internet of things with healthcare and high rate delivery. Besides that, its design simplicity will make it applicable for mass production to be used in industrial demands.

All-metal wideband metasurface for near-field transformation of medium-to-high gain electromagnetic sources.

Electromagnetic (EM) metasurfaces are essential in a wide range of EM engineering applications, from incorporated into antenna designs to separate devices like radome. Near-field manipulators are a class of metasurfaces engineered to tailor an EM source's radiation patterns by manipulating its near-field components. They can be made of all-dielectric, hybrid, or all-metal materials; however, simultaneously delivering a set of desired specifications by an all-metal structure is more challenging due to limitations of a substrate-less configuration. The existing near-field phase manipulators have at least one of the following limitations; expensive dielectric-based prototyping, subject to ray tracing approximation and conditions, narrowband performance, costly manufacturing, and polarization dependence. In contrast, we propose an all-metal wideband phase correcting structure (AWPCS) with none of these limitations and is designed based on the relative phase error extracted by post-processing the actual near-field distributions of any EM sources. Hence, it is applicable to any antennas, including those that cannot be accurately analyzed with ray-tracing, particularly for near-field analysis. To experimentally verify the wideband performance of the AWPCS, a shortened horn antenna with a large apex angle and a non-uniform near-field phase distribution is used as an EM source for the AWPCS. The measured results verify a significant improvement in the antenna's aperture phase distribution in a large frequency band of 25%.

Artificial Intelligence and COVID-19: Deep Learning Approaches for Diagnosis and Treatment.

COVID-19 outbreak has put the whole world in an unprecedented difficult situation bringing life around the world to a frightening halt and claiming thousands of lives. Due to COVID-19's spread in 212 countries and territories and increasing numbers of infected cases and death tolls mounting to 5,212,172 and 334,915 (as of May 22 2020), it remains a real threat to the public health system. This paper renders a response to combat the virus through Artificial Intelligence (AI). Some Deep Learning (DL) methods have been illustrated to reach this goal, including Generative Adversarial Networks (GANs), Extreme Learning Machine (ELM), and Long/Short Term Memory (LSTM). It delineates an integrated bioinformatics approach in which different aspects of information from a continuum of structured and unstructured data sources are put together to form the user-friendly platforms for physicians and researchers. The main advantage of these AI-based platforms is to accelerate the process of diagnosis and treatment of the COVID-19 disease. The most recent related publications and medical reports were investigated with the purpose of choosing inputs and targets of the network that could facilitate reaching a reliable Artificial Neural Network-based tool for challenges associated with COVID-19. Furthermore, there are some specific inputs for each platform, including various forms of the data, such as clinical data and medical imaging which can improve the performance of the introduced approaches toward the best responses in practical applications.