Showing papers on "Antenna (radio) published in 2020"

Prospective Multiple Antenna Technologies for Beyond 5G

Abstract: Multiple antenna technologies have attracted much research interest for several decades and have gradually made their way into mainstream communication systems. Two main benefits are adaptive beamforming gains and spatial multiplexing, leading to high data rates per user and per cell, especially when large antenna arrays are adopted. Since multiple antenna technology has become a key component of the fifth-generation (5G) networks, it is time for the research community to look for new multiple antenna technologies to meet the immensely higher data rate, reliability, and traffic demands in the beyond 5G era. Radically new approaches are required to achieve orders-of-magnitude improvements in these metrics. There will be large technical challenges, many of which are yet to be identified. In this paper, we survey three new multiple antenna technologies that can play key roles in beyond 5G networks: cell-free massive MIMO, beamspace massive MIMO, and intelligent reflecting surfaces. For each of these technologies, we present the fundamental motivation, key characteristics, recent technical progresses, and provide our perspectives for future research directions. The paper is not meant to be a survey/tutorial of a mature subject, but rather serve as a catalyst to encourage more research and experiments in these multiple antenna technologies.

4-Port MIMO Antenna with Defected Ground Structure for 5G Millimeter Wave Applications

Abstract: We present a 4-port Multiple-Input-Multiple-Output (MIMO) antenna array operating in the mm-wave band for 5G applications. An identical two-element array excited by the feed network based on a T-junction power combiner/divider is introduced in the reported paper. The array elements are rectangular-shaped slotted patch antennas, while the ground plane is made defected with rectangular, circular, and a zigzag-shaped slotted structure to enhance the radiation characteristics of the antenna. To validate the performance, the MIMO structure is fabricated and measured. The simulated and measured results are in good coherence. The proposed structure can operate in a 25.5–29.6 GHz frequency band supporting the impending mm-wave 5G applications. Moreover, the peak gain attained for the operating frequency band is 8.3 dBi. Additionally, to obtain high isolation between antenna elements, the polarization diversity is employed between the adjacent radiators, resulting in a low Envelope Correlation Coefficient (ECC). Other MIMO performance metrics such as the Channel Capacity Loss (CCL), Mean Effective Gain (MEG), and Diversity gain (DG) of the proposed structure are analyzed, and the results indicate the suitability of the design as a potential contender for imminent mm-wave 5G MIMO applications.

Fifth Generation Antennas: A Comprehensive Review of Design and Performance Enhancement Techniques

Abstract: The intensive research in the fifth generation (5G) technology is a clear indication of technological revolution to meet the ever-increasing demand and needs for high speed communication as well as Internet of Thing (IoT) based applications. The timely upgradation in 5G technology standards is released by third generation partnership project (3GPP) which enables the researchers to refine the research objectives and contribute towards the development. The 5G technology will be supported by not only smartphones but also different IoT devices to provide different services like smart building, smart city, and many more which will require a 5G antenna with low latency, low path loss, and stable radiation pattern. This paper provides a comprehensive study of different antenna designs considering various 5G antenna design aspects like compactness, efficiency, isolation, etc. This review paper elaborates the state-of-the-art research on the different types of antennas with their performance enhancement techniques for 5G technology in recent years. Also, this paper precisely covers 5G specifications and categorization of antennas followed by a comparative analysis of different antenna designs. Till now, many 5G antenna designs have been proposed by the different researchers, but an exhaustive review of different types of 5G antenna with their performance enhancement method is not yet done. So, in this paper, we have attempted to explore the different types of 5G antenna designs, their performance enhancement techniques, comparison, and future breakthroughs in a holistic way.

Joint Antenna Selection and Hybrid Beamformer Design Using Unquantized and Quantized Deep Learning Networks

Abstract: In millimeter-wave communications, multiple-input-multiple-output (MIMO) systems use large antenna arrays to achieve high gain and spectral efficiency. These massive MIMO systems employ hybrid beamformers to reduce power consumption associated with fully digital beamforming in large arrays. Further savings in cost and power are possible through the use of subarrays. Unlike prior works that resort to large latency methods such as optimization and greedy search for subarray selection, we propose a deep-learning-based approach in order to overcome the complexity issue without causing significant performance loss. We formulate antenna selection and hybrid beamformer design as a classification/prediction problem for convolutional neural networks (CNNs). For antenna selection, the CNN accepts the channel matrix as input and outputs a subarray with optimal spectral efficiency. The resultant subarray channel matrix is then again fed to a CNN to obtain analog and baseband beamformers. We train the CNNs with several noisy channel matrices that have different channel statistics in order to achieve a robust performance at the network output. Numerical experiments show that our CNN framework provides an order better spectral efficiency and is 10 times faster than the conventional techniques. Further investigations with quantized-CNNs show that the proposed network, saved in no more than 5 bits, is also suited for digital mobile devices.

Metantenna: When Metasurface Meets Antenna Again

Abstract: Metasurfaces, composed of 2-D planar arrays of sub-wavelength metallic or dielectric scatterers, have provided unprecedented freedoms in manipulating electromagnetic (EM) waves upon interfaces. The development of metasurface has always been closely related to antennas. On the one hand, metasurface was developed from reflect arrays/transmit arrays that are used as reflectors/lens of antennas, and most fundamental theories of metasurfaces are directly borrowed from antenna array theories; on the other hand, the development of antennas was flourished and expedited by progresses in metasurfaces. Many emerging antenna configurations have been constructed based on unique functional metasurfaces. In this article, we will review briefly the development roadmap of both metasurfaces and metasurface-based antennas, including antenna-inspired metasurfaces, metasurface-assisted antennas, and metasurface antennas. In particular, the recent fusion of metasurface and antenna as metantenna will bring significant impacts on methodologies of functional metasurface, antenna design, and radio-frequency device miniaturization.

Flexible Antennas: A Review.

Abstract: The field of flexible antennas is witnessing an exponential growth due to the demand for wearable devices, Internet of Things (IoT) framework, point of care devices, personalized medicine platform, 5G technology, wireless sensor networks, and communication devices with a smaller form factor to name a few. The choice of non-rigid antennas is application specific and depends on the type of substrate, materials used, processing techniques, antenna performance, and the surrounding environment. There are numerous design innovations, new materials and material properties, intriguing fabrication methods, and niche applications. This review article focuses on the need for flexible antennas, materials, and processes used for fabricating the antennas, various material properties influencing antenna performance, and specific biomedical applications accompanied by the design considerations. After a comprehensive treatment of the above-mentioned topics, the article will focus on inherent challenges and future prospects of flexible antennas. Finally, an insight into the application of flexible antenna on future wireless solutions is discussed.

A Tri-Band Shared-Aperture Antenna for (2.4, 5.2) GHz Wi-Fi Application With MIMO Function and 60 GHz Wi-Gig Application With Beam-Scanning Function

Abstract: This article presents the design and the realization of a tri-band shared-aperture antenna operating at 2.4, 5.2, and 60 GHz. It puts these three bands of antennas within the same radiating aperture and then realizes the Wi-Fi application with MIMO function and the Wi-Gig application with beam-scanning function simultaneously. It consists of two dual-band printed inverted-F antennas (PIFAs) and two SIW leaky wave antennas. By using the structure-reused technology, PIFA for the Wi-Fi application and the SIW antenna for the Wi-Gig application can share the same radiator without adding an extra aperture area. Thus, the ratio of the radiating aperture utilization can be improved greatly. In addition, MIMO technology is also applied to the Wi-Fi antenna design. The envelope correlation coefficients (ECCs) calculated from the simulated and measured data are all lower than 0.04. The measured radiation efficiencies are 74% to 95% and 76% to 95% within these two bands, respectively. Moreover, due to the optimal layout of the whole design, the Wi-Gig antenna can obtain high gain and wide range of beam coverage at the same time. The measured peak gain is 12.29 dBi, and the beam coverage is ±36° from 57 to 64 GHz.

5G mmWave Cooperative Positioning and Mapping Using Multi-Model PHD Filter and Map Fusion

Abstract: 5G millimeter wave (mmWave) signals can enable accurate positioning in vehicular networks when the base station and vehicles are equipped with large antenna arrays. However, radio-based positioning suffers from multipath signals generated by different types of objects in the physical environment. Multipath can be turned into a benefit, by building up a radio map (comprising the number of objects, object type, and object state) and using this map to exploit all available signal paths for positioning. We propose a new method for cooperative vehicle positioning and mapping of the radio environment, comprising a multiple-model probability hypothesis density filter and a map fusion routine, which is able to consider different types of objects and different fields of views. Simulation results demonstrate the performance of the proposed method.

A Portable Very Low Frequency (VLF) Communication System Based on Acoustically Actuated Magnetoelectric Antennas

Abstract: A novel very low frequency (VLF) communication system using one pair of magnetoelectric (ME) antennas has been proposed. The ME antennas are strain-mediated acoustic resonators operating at their electromechanical resonance in the VLF band. The measured near-field radiation pattern reveals ME antennas are equivalent to dipole antennas. The magnetic field radiated by the ME transmitter has been predicted along with distance ranging from 1 mm to 100 km. The measured magnetic field distribution coincided well with the prediction, and the maximum communication distance of 120 m has been achieved. With 80 V driving voltage, the power consumption of the ME transmitter has been measured as 400 mW. Furthermore, the direct antenna modulation (DAM) has also been successfully demonstrated on the ME antennas.

Millimeter-Wave Dual-Polarized Filtering Antenna for 5G Application

Abstract: This article presents a novel dual-polarized millimeter-wave (mm-Wave) patch antenna with bandpass filtering response. The proposed antenna consists of a differential-fed cross-shaped driven patch and four stacked parasitic patches. The combination of the stacked patches and the driven patch can be equivalent to a bandstop filtering circuit for generating a radiation null at the upper band edge. Besides, four additional shorted patches are added beside the cross-shaped driven patch to introduce another radiation null at the lower band edge. Moreover, by embedding a cross-shaped strip between these four stacked patches, the third radiation null is generated to further suppress the upper stopband. As a result, a quasi-elliptic bandpass response is realized without requiring extra filtering circuit. For demonstration, a prototype was fabricated with standard PCB process and measured. The prototype operates in the 5G band (24.25–29.5 GHz) and it has an impedance bandwidth of 20%. The out-of-band gain drops over 15 dB at 23 and 32.5 GHz, respectively, which exhibits high selectivity. These merits make the proposed antenna a good element candidate for the 5G mm-Wave massive MIMO applications to reduce the requirements of the filters in the mm-Wave RF front ends.

ZAIGA: Zhaoshan Long-baseline Atom Interferometer Gravitation Antenna

Abstract: The Zhaoshan long-baseline Atom Interferometer Gravitation Antenna (ZAIGA) is a new type of underground laser-linked interferometer facility, and is currently under construction. It is in the 200-m...

Compact Unidirectional Conformal Antenna Based on Flexible High-Permittivity Custom-Made Substrate for Wearable Wideband Electromagnetic Head Imaging System

Abstract: An approach toward designing and building of a compact, low-profile, wideband, unidirectional, and conformal imaging antenna for electromagnetic (EM) head imaging systems is presented. The approach includes the realization of a custom-made flexible high-permittivity dielectric substrate to achieve a compact sensing antenna. The developed composite substrate is built using silicon-based poly-di-methyl-siloxane (PDMS) matrix and microscale of aluminium oxide (Al2O3) and graphite (G) powders. Al2O3 and G powders are used as fillers with different weight-ratio to manipulate and control the dielectric properties of the substrate for attaining better matched with the human head and reducing antenna’s physical size while keeping the PDMS flexibility feature. Using the custom-made substrate, a compact, wideband, and unidirectional on-body matched antenna for wearable EM head imaging system is realized. The antenna is configured as a multi-slot planar structure with four shorting pins, working as electric and magnetic dipoles at different frequency bands. The measured reflection coefficient (S11) shows an operating frequency band of 1–4.3 GHz. The time-average power density and the amplitude of the received signal inside the MRI-based realistic head phantom demonstrate a unidirectional propagation and high-fidelity factor (FF) of more than 90%. An array of 13 antennas are fabricated and tested on a realistic 3-D head phantom to verify the imaging capability of the proposed antenna. The reconstructed images of different targets inside the head phantom demonstrate the possibility of utilizing the conformal antenna arrays to detect and locate abnormality inside the brain using multistatic delay-multiply-and-sum beamforming algorithm.

A Triple-Band High-Gain Multibeam Ambient RF Energy Harvesting System Utilizing Hybrid Combining

Abstract: Overcoming the challenge of battery recharging and replacement in industry Internet-of-Things (IoT) applications is considered by proposing the design of a triple-band high-gain multibeam ambient radio frequency (RF) energy harvesting system utilizing hybrid combining. The novelty of the design is that it simultaneously exploits frequency, space, and polarization to maximize the harvested RF energy. Wideband hybrid combining is proposed, which enables the harvesting of energy at low RF power densities while maintaining the wide frequency and space coverage necessary for ambient RF energy harvesting. The antenna design consisting of 16-ports has an average area per port of $0.3\lambda \times 0.3\lambda$ (where $\lambda$ is the freespace wavelength at 1.8 GHz) and is demonstrated to achieve a wide relative bandwidth of 38.5% covering the GSM-1800, UMTS-2100, and WiFi frequency bands. Hybrid combining of the 16-port antenna provides multiple antenna beams each with up to 11 dBi antenna gain and these provide broad beam coverage. The design for the rectifiers, using multistub impedance matching, is also provided and these are shown to be efficient over the frequency bands of interest. Measurements in an anechoic chamber demonstrate that the proposed energy harvesting system can provide an output dc voltage of more than 755 mV, an output dc power of more than $-$ 6.4 dBm and RF-to-dc efficiencies greater than 40% when the power density is more than 1400 $\mu \mathrm{W}/\mathrm{m}^{2}$ . It is also shown that the proposed system can provide output dc power of 80 $\mu \mathrm{W}$ and 7.3 $\mu \mathrm{W}$ in real outdoor and indoor ambient environments, respectively.

Beyond 5G Wireless Localization with Reconfigurable Intelligent Surfaces

Abstract: 5G radio positioning exploits information in both angle and delay, by virtue of increased bandwidth and large antenna arrays. When large arrays are embedded in surfaces, they can passively steer electromagnetic waves in preferred directions of space. Reconfigurable intelligent surfaces (RIS), which are seen as a transformative 'beyond 5G' technology, can thus control the physical propagation environment. Whereas such RIS have been mainly intended for communication purposes so far, we herein state and analyze a RIS-aided downlink positioning problem from the Fisher Information perspective. Then, based on this analysis, we propose a two-step optimization scheme that selects the best RIS combination to be activated and controls the phases of their constituting elements so as to improve positioning performance. Preliminary simulation results show coverage and accuracy gains in comparison with natural scattering, while pointing out limitations in terms of low signal to noise ratio (SNR) and inter-path interference.

Metamaterial-Inspired Antenna Array for Application in Microwave Breast Imaging Systems for Tumor Detection

Abstract: This paper presents a study of a planar antenna-array inspired by the metamaterial concept where the resonant elements have sub-wavelength dimensions for application in microwave medical imaging systems for detecting tumors in biological tissues. The proposed antenna consists of square-shaped concentric-rings which are connected to a central patch through a common feedline. The array structure comprises several antennas that are arranged to surround the sample breast model. One antenna at a time in the array is used in transmission-mode while others are in receive-mode. The antenna array operates over 2–12 GHz amply covering the frequency range of existing microwave imaging systems. Measured results show that compared to a standard patch antenna array the proposed array with identical dimensions exhibits an average radiation gain and efficiency improvement of 4.8 dBi and 18%, respectively. The average reflection-coefficient of the array over its operating range is better than S11 ≤ −20 dB making it highly receptive to weak signals and minimizing the distortion encountered with the transmission of short duration pulse-trains. Moreover, the proposed antenna-array exhibits high-isolation on average of 30dB between radiators. This means that antennas in the array (i) can be closely spaced to accommodate more radiators to achieve higher-resolution imaging scans, and (ii) the imagining scans can be done over a wider frequency range to ascertain better contrast in electrical parameters between malignant tumor-tissue and the surrounding normal breast-tissue to facilitate the detection of breast-tumor. It is found that short wavelength gives better resolution. In this experimental study a standard biomedical breast model that mimics a real-human breast in terms of dielectric and optical properties was used to demonstrate the viability of the proposed antenna over a standard patch antenna in the detection and the localization of tumor. These results are encouraging for clinical trials and further refinement of the antenna-array.

Large Intelligent Surface Assisted Wireless Communications With Spatial Modulation and Antenna Selection

Abstract: Novel communication technology based on large intelligent surface (LIS) [1] has arisen recently, with the aim to enhance the signal quality at the receiver In this paper, a practical structure of LIS-based spatial modulation (LIS-SM) is proposed, in order to utilize both transmit and receive antenna indices Meanwhile, the theoretical average bit error rate (ABER) performance bound of the developed LIS-SM scheme is investigated For the sake of achieving further spatial diversity gain, we extend its employment to the antenna selection (AS) scenario, and a low-complexity selection algorithm is designed on the basis of minimum squared Euclidian distance and signal-to-leakage-and-noise ratio as well as the idea of greedy elimination algorithm Performance analysis shows that AS-aided LIS-SM is more robust in terms of ABER compared with conventional LIS-SM Moreover, complexity analysis also depicts that the proposed fast selection algorithm achieves much lower complexity yet a comparable ABER performance, compared to the traditional exhaustive search

Sub-6 GHz Dual-Band 8 × 8 MIMO Antenna for 5G Smartphones

Abstract: In this letter, a dual-band 8x8 MIMO antenna that operates in the sub-6 GHz spectrum for future 5G multiple-input multiple-output (MIMO) smartphone applications is presented. The design consists of a fully grounded plane with closely spaced orthogonal pairs of antennas placed symmetrically along the long edges and on the corners of the smartphone. The orthogonal pairs are connected by a 7.8 mm short neutral line for mutual coupling reduction at both bands. Each antenna element consists of a folded monopole with dimensions 17.85 x 5mm2 and can operate in 3100-3850 MHz for the low band and 4800-6000 MHz for the high band ([S11] ˂ -10dB). The fabricated antenna prototype is tested and offers good performance in terms of Envelope Correlation Coefficient (ECC), Mean Effective Gain (MEG), total efficiency and channel capacity. Finally, the user effects on the antenna and the Specific Absorption Rate (SAR) are also presented.

Characterization of Metasurface Lens Antenna for Sub-6 GHz Dual-Polarization Full-Dimension Massive MIMO and Multibeam Systems

Abstract: A metasurface lens antenna fed by a planar $8\times8$ dual polarized antenna array is proposed and characterized for full-dimensional massive multiple-input multiple-output (MIMO) and multibeam systems at sub-6 GHz bands. The lightweight multilayer metasurface structure consisting of Jerusalem cross elements is used for a planar lens design. The lens antenna with the size of $10\lambda _{0} \times 10\lambda _{0} \times 5\lambda _{0}$ is fed by an $8\times8$ dual-polarized stacked patch array to operate over the range from 5.17 to 6.10 GHz, where $\lambda _{0}$ is the free-space operating wavelength at the center frequency of 5.6 GHz. This article shows the scanning range of ±25° with a maximum gain of 22.4 dBi and the gain variation of 3.3 dB at 5.6 GHz. Beam coverage performance, pattern envelope correlation coefficient, and port isolation properties demonstrate its full-dimension access capability of the antenna. Besides, the multibeam antenna system with high-gain coverage is achieved by beams operating at the same frequencies, while the frequency division multiplexing can be realized for the isolated beams. The proposed metasurface lens antenna, featuring lightweight, compactness, and low cost compared to a 3-D dielectric lens and low-complexity compared to the array scenarios, can be an alternative for fifth-generation (5G) sub-6 GHz frequency bands.

An Aperture-Sharing Array for (3.5, 28) GHz Terminals With Steerable Beam in Millimeter-Wave Band

Abstract: The integration of the sub-6 GHz and millimeter-wave (mmWave) antennas has become an important issue for the next-generation wireless communication. For the mmWave band, adaptive beam steering is required to solve the path loss and coverage range problems. In this communication, an aperture-sharing technique is developed, so that a four-unit linear 28 GHz array and a 3.5 GHz dipole antenna can be integrated and the same aperture can be shared. The SIW is utilized to enable the integration and maintain the radiation of both antennas, without mutual interference. By adopting a separate feeding network, each mmWave array unit is independently excited, so that a beam steerable in the E-plane can be synthesized in the mmWave band. A prototype is fabricated with a compact size owing to the shared aperture. The measured results show good radiation characteristics and broad 10 dB impedance bandwidth exceeding 20% in both bands. Furthermore, the mmWave beam steering is obtained with a stable gain level. The proposed dual-frequency antenna is suitable for some terminal applications in the next-generation wireless networks.

Electrically-driven Yagi-Uda antennas for light

Abstract: Yagi-Uda antennas are a key technology for efficiently transmitting information from point to point using radio waves. Since higher frequencies allow higher bandwidths and smaller footprints, a strong incentive exists to shrink Yagi-Uda antennas down to the optical regime. Here we demonstrate electrically-driven Yagi-Uda antennas for light with wavelength-scale footprints that exhibit large directionalities with forward-to-backward ratios of up to 9.1 dB. Light generation is achieved via antenna-enhanced inelastic tunneling of electrons over the antenna feed gap. We obtain reproducible tunnel gaps by means of feedback-controlled dielectrophoresis, which precisely places single surface-passivated gold nanoparticles in the antenna gap. The resulting antennas perform equivalent to radio-frequency antennas and combined with waveguiding layers even outperform RF designs. This work paves the way for optical on-chip data communication that is not restricted by Joule heating but also for advanced light management in nanoscale sensing and metrology as well as light emitting devices. Nanoantennas have been developed to direct light, but most still rely on laboratory scale light sources. Here, the authors demonstrate electrically-driven directional emission in the optical frequency range using a nanogap in conjunction with a Yagi-Uda antenna nanostructure.

Orthogonally Polarized Dual Antenna Pair With High Isolation and Balanced High Performance for 5G MIMO Smartphone

Abstract: For the first time, zero-ground-clearance dual antenna pair with high isolation and balanced high performance is proposed. A T-shaped monopole intersects with a T-shaped slot that is etched on a large ground edge, constituting the CPW-fed dual antenna pair. By exploiting the odd and even modes of the CPW structure, two orthogonal characteristic modes including the in-phase current and monopole modes can be excited, generating high port isolation. Both modes are unbalanced mode, which means that the ground currents can be fully excited, so the two antennas are with balanced high performance. A sub-6 GHz antenna pair that occupies a footprint of $15\times 7$ mm2 ( $0.18\,\,\lambda \,\times 0.08\,\,\lambda$ ) is analyzed and the simulated results show an isolation of better than −24 dB and an envelope correlation coefficient (ECC) of lower than 0.0016, −6 dB bandwidths of 230 and 240 MHz, and average efficiencies of 57.9% and 57.4%. A four-antenna multiple-input multiple-output (MIMO) array is fabricated and measured to verify the feasibility. The measured isolations and ECCs of the two modes are, respectively, better than −20.0 dB and 0.04, −6 dB bandwidths are 230 MHz/240 MHz and 220 MHz/230 MHz, and average efficiencies are 54.5%/50.2% and 49.9%/48.6%. The proposed dual antenna pair exhibits a great potential for 5G MIMO smartphone application.

Miniaturization of a Dual-Band Wearable Antenna for WBAN Applications

Abstract: A planar, compact, dual-band antenna on a semiflexible substrate is proposed for 2.45/5.85 GHz wireless body-area network applications. The proposed antenna is comprised of an I-shaped monopole embedded with an inverted L-shaped slit and an inductive meander line on the front side of the substrate, which excites the higher resonant mode at 5.85 GHz. On the backside, an inverted U-shaped stripline embedded with another inductive meander line is attached to the ground plane to excite the lower resonant mode at 2.45 GHz. The key to the miniaturization procedure is increasing the inductance and the capacitance by loading the inductive meander lines and slit line. The overall size of the proposed antenna is 0.15λ × 0.1λ × 0.004λ at 2.45 GHz. The measured results of the proposed antenna show the impedance bandwidths of 5.7% (2.4–2.54 GHz) and 3.78% (5.72–5.94 GHz) and the maximum peak gains of 2.1 dBi and 3.5 dBi, respectively. The simulated specific absorption rate values satisfy both the U.S. and EUR standards of under 1 g average and under 10 g average, respectively.

A Survey of Performance Enhancement Techniques of Antipodal Vivaldi Antenna

Abstract: The increasing proliferation of advanced devices for UWB, 5G communication, micrometer-wave, and millimeter-wave communication demands an antenna which can handle huge data rates, provides high gain and stable radiation pattern as a panacea of most of the current wireless communication problems. Many different antenna designs have been proposed by the researchers but, Antipodal Vivaldi Antenna (AVA) has drawn the attention of most of the researchers because of its high gain, wide bandwidth, less radiation loss, and stable radiation pattern. Different methods are presented to make AVA more compact while maintaining the performance of an antenna to an acceptable level. These different methods are substrate choice, flare shape, slots, and feeding connectors. Also, AVA performance can be enhanced by incorporating corrugation, dielectric lens, patch in between two flares of AVA, balanced AVA (BAVA), metamaterial, computational intelligence (CI), and AVA array. The AVA performance enhancement techniques modify the electrical and physical properties of an antenna which in turn improves its performance. A large number of performance enhancement methods of AVA design have been proposed, however, no comprehensive study exists to categorize these performance enhancement techniques and outline their concepts, advantages, disadvantages, and applications. So, in this paper, we have attempted to outline all methods available for enhancing and optimizing the parameters of AVA. Additionally, to validate some of the important performance enhancement methods, they are incorporated in the basic conventional AVA design and further simulation results are obtained for the same which are in line with the surveyed literature. Each method is explained in detail by incorporating its key points, merits, and demerits. Moreover, illustrations from the literature are given to demonstrate improvement in the parameters as a result of applying a particular performance enhancement technique.

A Novel 1 Bit Wide-Angle Beam Scanning Reconfigurable Transmitarray Antenna Using an Equivalent Magnetic Dipole Element

Abstract: A novel 1 bit reconfigurable transmitarray antenna (RTA) using an equivalent magnetic dipole element for wide-angle beam scanning at Ku -band is presented. The RTA element consists of a rectangular patch and a side-shorted patch with an equivalent magnetic dipole radiation. A 1 bit phase difference is achieved by controlling two p-i-n diodes on the side-shorted patch based on the current reversal mechanism. The half-power beamwidth of the presented antenna element is 142° in E-plane, which is significantly larger than other conventional elements. A RTA prototype with $16\times16$ elements is designed, fabricated, and tested. The measured results show good beam scanning capabilities of the 1 bit RTA. The measured gain in the broadside direction is 21.4 dBi, and the scan gain loss is 3.6 dB for the 60° scanned beam in E-plane.

Dual Band Notched Orthogonal 4-Element MIMO Antenna With Isolation for UWB Applications

Abstract: A Novel dual notched 4-element MIMO (Multi-Input-Multi-Output) antenna with gap sleeves and H-slot is proposed and fabricated for UWB (ultra wide-band) applications. The proposed antenna is CPW (Co-Planar Waveguide) fed and consists of four orthogonal elements with good isolation. It has low profile and small dimensions of 80 × 80 × 1.6 mm 3 . The proposed MIMO antenna achieved an impedance bandwidth (S11 <; -10$ dB) from 2.1GHz - 20GHz with notches from 3.3GHz - 4.1GHz and 8.2GHz - 8.6GHz frequency bands. These achieved notches can filter the interference of WiMAX(3.3GHz - 3.7GHz), and military/radar applications band (8.2GHz - 8.6GHz). Mutual coupling among the elements is also below -25dB. The performance parameters of proposed MIMO antenna are relatively good with very low ECC (Envelop Correlation Coefficient) less than 0.02 except at notches and DG (Diversity Gain) nearly 10. Peak gain of 5.8dB is achieved by the proposed antenna and the radiation efficiency is also above 80% except at notches.The computer-generated and experimental results are in accord and therefore, the proposed four element MIMO antenna can be suggested as a suitable aspirant for UWB applications with stop bands for WiMAX and military/radar applications.

Multistage Collaborative Machine Learning and its Application to Antenna Modeling and Optimization

Abstract: A multistage collaborative machine learning (MS-CoML) method that can be applied to efficient multiobjective antenna modeling and optimization is proposed. Machine learning methods, including single-output Gaussian process regression (SOGPR) and symmetric and asymmetric multioutput GPR (MOGPR) methods, are introduced to collaboratively build highly accurate multitask surrogate models for antennas. Variable-fidelity electromagnetic (EM) models are simulated, with their responses utilized to build separate MOGPR surrogate models. By combining the three machine-learning methods in a multistage framework, mappings between the same and different responses of the EM models with variable fidelity are learned, therein helping to substantially reduce the computational effort under a negligible loss of predictive power. Three antenna designs aiming at single-band, broadband, and multiband applications are selected as examples. And, for illustrating the applicability and superiority of the proposed MS-CoML method, a reference point-based multiobjective antenna optimization algorithm is used to optimize these three antennas. Simulation results show that using the MS-CoML method can significantly reduce the total optimization time without compromising modeling accuracy and optimized performance.

Efficient Wireless Power Transfer System With a Miniaturized Quad-Band Implantable Antenna for Deep-Body Multitasking Implants

Abstract: Passive operation and battery-charging of deep-body implants can be insured through wireless power transfer (WPT) technologies. However, the power transfer efficiency (PTE) is constrained by device miniaturization and implantation depth. This study proposes a complete WPT system consisting of a patterned WPT transmitter (Tx), an efficient rectifier, and an antenna integrated with the system. The WPT Tx had a size of 6 cm $\times$ 6 cm and was optimized to focus the power on the deep-tissue implants at 1470 MHz. The voltage doubler was optimized at 1470 MHz, had a small size of 5 mm $\times$ 10 mm, and exhibited a high radio frequency (RF)-to-direct current (dc) conversion efficiency of 90% at 2-dBm RF input power. Moreover, the implantable antenna occupies a small volume of 8.43 mm3 and supports quad-band operations: telemetry at 403 and 915 MHz, WPT at the midfield band of 1470 MHz, and control signaling at 2.4 GHz. First, the fabricated prototypes were measured individually in minced pork, in the American Society for Testing and Materials (ASTM) model, and in the saline-filled 3-D head phantom. While operating collectively as an integrated system, the PTE of the system was measured. Additionally, to enhance the PTE of the WPT system, a high-dielectric matching layer ( $\varepsilon _{r} = 78$ ) was used between the WPT Tx and the phantom. Furthermore, to demonstrate the PTE of the WPT system, the voltage doubler was integrated with the implantable antenna, encapsulated in a 3-D-printed capsule endoscope, and its PTE was measured in a saline solution and minced pork. Finally, the compliance of the WPT system with the human safety standards was analyzed and found that the system solely satisfied the safety limits. It is evident from the experimental results that the system can transfer 6.7-mW power to millimeter-sized implants located 5-cm deep in tissues.

Optically Transparent Subarray Antenna Based on Solar Panel for CubeSat Application

Abstract: This article focuses on the design of a transparent circularly polarized (CP) antenna subarray integrating with Cube satellite’s (CubeSat’s) solar panels. The subarray antenna employs two techniques including the Fabry–Perot cavity (FPC) and sequential rotation-feeding network. These techniques are used to generate CP along with a high level of directivity over a broad bandwidth. The main aim here is to propose a multifunctional antenna with the high radiation properties and the capability of power harvesting, simultaneously. To harvest power using a solar panel, the transparency requirement should be satisfied. Hence, the proposed design is sputtered with the thin layer of indium–tin–oxide (ITO) with a thickness of 200 nm. However, it seems to be sacrificed a large amount of conductivity at the frequency band of interest (x-band). Correspondingly, the performance of conductivity and transparency for both the materials of ITO and copper (Cu) as coated on the proposed design is determined. Alternatively, as an optically transparent conductor (OTC), a combination of both coating layers, including ITO and Cu with thicknesses of 200 and 5 nm, respectively, is applied. In the scattering point of view, the proposed design is also capable of suppressing the radar cross-section (RCS) for the space missions with the aim of space-based observations.

High-Gain On-Chip Antenna Design on Silicon Layer With Aperture Excitation for Terahertz Applications

Abstract: This letter investigates the feasibility of designing a high gain on-chip antenna on silicon technology for subterahertz applications over a wide-frequency range. High gain is achieved by exciting the antenna using an aperture fed mechanism to couple electromagnetics energy from a metal slot line, which is sandwiched between the silicon and polycarbonate substrates, to a 15-element array comprising circular and rectangular radiation patches fabricated on the top surface of the polycarbonate layer. An open ended microstrip line, which is orthogonal to the metal slot-line, is implemented on the underside of the silicon substrate. When the open ended microstrip line is excited it couples the signal to the metal slot-line which is subsequently coupled and radiated by the patch array. Measured results show the proposed on-chip antenna exhibits a reflection coefficient of less than −10 dB across 0.290–0.316 THz with a highest gain and radiation efficiency of 11.71 dBi and 70.8%, respectively, occurred at 0.3 THz. The antenna has a narrow stopband between 0.292 and 0.294 THz. The physical size of the presented subterahertz on-chip antenna is 20 × 3.5 × 0.126 mm3.

A Compact Single-Layer Wideband Microstrip Antenna With Filtering Performance

Abstract: A compact single-layer filtering microstrip antenna with diverse characteristics of low profile, high gain, wide band, and high selectivity is proposed in this letter. Simple structure as it is, the presented antenna mainly consists of a rectangle driven patch, four parasitic strips, a pair of symbiotic strips, and a set of shorting pins. By attaching four parasitic strips to the original rectangular patch antenna, an additional resonance can be excited while the high-band edge selectivity is greatly improved due to the formation of a radiation null outside. Then, two symbiotic strips are embedded on both sides of the driven patch, which in turn creates an extra resonance mode and a lower-band radiation null. The set of shorting pins are applied to further improve operating and filtering response. Finally, the use of two parasitic patches can effectively improve the level of impedance bandwidth (IBW) and upper-band suppression. To verify this design, the corresponding antenna is fabricated and tested. The measured and simulated results are highly consistent, which reveals that it owns a wide IBW of 20.1% (2.19–2.68 GHz) with three resonance points, a higher average gain larger than 9.5 dBi, and a flat radiation efficiency above 88% in-band. The suppression level of the out-of-band gain on both sides can reach 14.5 dB.