Showing papers on "Extremely high frequency published in 2023"

High isolation metamaterial-based dual-band MIMO antenna for 5G millimeter-wave applications

Abstract: This article presents a high-isolation metamaterial-based dual-band multiple-input multiple-output (MIMO) antenna for 5G millimeter-wave communication networks. The proposed antenna is a pentagon-shaped monopole that provides a dual-band response with a wide operating bandwidth at 5G 28/28 bands. The antenna is printed on 0.508-mm-thick Rogers RT5880 substrate of relative permittivity ɛr = 2.2. It exhibits a small physical size of 5.5 × 5.4 × 0.508 mm3, excluding the feeding line. The MIMO system is constructed of two symmetric radiating elements arranged adjacently with the mutual coupling of −18.5 dB at both resonant frequencies. The dual-band metamaterial is designed and placed between the two radiators to reduce the mutual coupling. Embedding a 3 × 1 metamaterial array enhances the isolation to −39 dB and −38 dB at 28 GHz and 38 GHz, respectively. The proposed system is capable of covering both 28/28 5G bands and has the merits of broad bandwidth, low profile, high gain (>5 dB), improved isolation (−38 dB), low envelope correlation coefficient (ECC) (<0.0001) and channel capacity loss (CCL) (<0.05), and high diversity gain (DG) (>9.99 dB). The system performance is verified experimentally with good agreement between the simulated and measured data. These properties demonstrate the system applicability for 5G millimeter-wave communication networks.

Millimeter-Wave On-Chip Bandpass Filter Using Complementary-Broadside-Coupled Structure

Abstract: A new millimeter-wave on-chip bandpass filter (BPF) using complementary-broadside-coupled (CBC) structure is presented. The transmission zeros (TZs) of the proposed BPF are calculated and analyzed through using an LC equivalent circuit. An overall guidance is given for tuning the locations of TZs through changing the physical parameters of the layout or the electrical parameters of the equivalent circuit. To prove the feasibility of the proposed BPF, a prototype with very compact size is designed and fabricated in a commercial 0.13-lm SiGe (Bi)-CMOS technology, whose center frequency and bandwidth are 67 GHz and 44.8%, respectively. Good agreement between simulated and measured results validates the proposed idea.

Wideband Low-Profile Connected Rectangular Ring Dielectric Resonator Antenna Array for Millimeter-Wave Applications

Abstract: A wideband low-profile connected rectangular ring dielectric resonator (DR) antenna (DRA) array is presented for millimeter-wave (mmWave) applications. It consists of four rectangular ring DRA elements. The DRA elements are excited by microstrip feedlines through four slots on the ground plane. A slot mode, the DRA ${\mathrm {TE}}^{\text {y}}_{1\delta 1}$ mode, and the perturbed ${\mathrm {TE}}^{\text {y}}_{3\delta 1}$ mode are simultaneously excited, giving a wideband design. To avoid the alignment problem, the DRAs are connected to their adjacent elements through dielectric arms. It is found that the position of the dielectric arms has significant effects on the antenna performance. To demonstrate the idea, a prototype with a dielectric constant of 20.8 was designed, fabricated, and tested for licensed mmWave bands (24.25–29.5 GHz). A reasonable agreement between the measured and simulated results is observed. The measured 10 dB impedance bandwidth ( $\vert \text{S}_{11}\vert \le - 10$ dB) is 31.6% (22.52–30.97 GHz), with a measured boresight realized gain being higher than 8 dBi from 22.5 to 30 GHz. The measured mutual couplings between the DRA elements of the array are lower than −20 dB in the operating frequency range. Furthermore, our prototype has a low profile of $0.074~\lambda _{0}$ , where $\lambda _{0}$ is the wavelength in air at the center frequency.

5G/Millimeter-Wave Rectenna Systems for Radio-Frequency Energy Harvesting/Wireless Power Transmission Applications: An overview

Abstract: In this article, we present an overview of the 5G rectifying antenna and its primary elements for applications in millimeter-wave (mm-wave) energy harvesting (EH) and wireless power transmission (WPT). The wide spectrum available for 5G communication bands have attracted significant attention for extensive applications. The power received by the harvesting antenna relies on the size of the antenna. Hence, the realization of antenna and rectenna systems with good efficiency at 5G mm-wave is a challenge. This review article highlights the recent advances in 5G rectenna systems for different applications at the component and structure levels. The primary objectives of the article are 1) to explore the potential advances of mm-wave rectenna systems and the feasibility of their designs to attain desired characteristics and 2) to present a comparative assessment of performance parameters of existing rectenna systems.

Path loss models for outdoor environment—with a focus on rain attenuation impact on short-range millimeter-wave links

Abstract: The deployment of a millimeter wave over a short path is one of the keys to enabling technologies for the next generation of wireless communication systems. Path loss (PL) is the most important parameter to indicate the performance of the mm-wave wireless channel. However, the accuracy and efficiency of each model are limited to characterize path loss for an environment that is different in terms of weather conditions and geographical arrangement from that for which they have been designed. This paper analyzed path loss for accurate signal estimation in Malaysia based on outdoor microcellular at 38GHz on a 300 m path length. The impact of rain attenuation on path loss, path loss exponent (PLE), and shadow fading (SF) have been investigated. This paper also presents two-channel models utilized for simulations in terms of the outdoor Large-Scale Path Loss, the statistical spatial channel model NYUSIM (version 2) developed in 2019 by New York University (NYU) and the 3rd Generation Partnership Project (3GPP) TR 38.900 Release 14 channel mode. Even though the CI and 3GPP models are accurate and suitable in the area where the measurement campaign was carried out in the temperate climate and must need modification for different regions, such as tropical climate. The underestimation can be interpreted because of the difference in AF's attenuation factors (pressure, humidity, temperature, rain rate) calculated by the CI model in the NYUSIM simulations and the attenuation factor (AF) obtained from measurement data. The NYUSIM channel model better estimated the measured data of path loss compared with 3GPP. Thus, the CI model is suitable for outdoor environments.

Millimeter-Wave Bandpass Filters Using On-Chip Dual-Mode Resonators in 0.13-$\mu$m SiGe BiCMOS Technology

Abstract: A novel on-chip dual-mode resonator (OCDMR) is proposed for the design of millimeter-wave (mm-wave) bandpass filters (BPFs). The proposed OCDMR consists of a stub-loaded metallic line and two identical open-end lines, which are extended and bent in opposite directions for coupling to the input and output ports. The two resonant frequencies of OCDMR can be independently adjusted by changing geometric parameters. To clarify the working mechanism of OCDMR, an LC equivalent circuit is constructed to imitate the resonant characteristics of OCDMR, which is calculated and analyzed in detail. Then, using the proposed OCDMRs, three different on-chip mm-wave BPFs with multiple transmission zeros (TZs) are designed and fabricated using 0.13- $\mu$ m SiGe BiCMOS technology. Good agreement between simulations and measurements validates the feasibility of OCDMR for applications in the on-chip mm-wave BPFs.

Five-Band Millimeter-Wave Antenna of Circular/Linear Polarization for Forthcoming Generations of Mobile Handsets

Abstract: Abstract A compact planar antenna is proposed to operate in five millimeter-wave frequency bands at 28, 51, 55, 59, and 63 GHz. The antenna is designed to produce circular polarization at 28 GHz and linear polarization at the other four frequencies. The 28 GHz frequency band is recommended for long range communications, whereas the other four frequencies are recommended for short range communications due to the atmospheric absorption in this range of the millimeter-wave frequencies and to provide more secure communications. The reasons behind the selection of the specific values of the higher frequency bands (51, 55, 59, and 63 GHz) are (i) to provide enough number of multiple bands at such unlicensed frequency range to be used as alternatives for different applications, (ii) to give about 4 GHz separation between the center frequencies of each band and, (iii) finally, to avoid the operation at 60 GHz, in particular, due to the peak atmospheric absorption of millimeter-wave encountered at this frequency. The antenna is constructed as a square patch surrounded by five parasitic elements that are capacitively coupled to the square patch so as to realize the location of the resonant frequencies of the higher frequency bands. The antenna is fabricated and its performance is experimentally evaluated. The proposed antenna is shown to operate efficiently over the five frequency bands 28, 51, 55, 59, and 63 GHz providing impedance matching bandwidths of 2.0, 0.9, 1.2, 1.1, and 1.6 GHz, respectively. The corresponding values of the maximum gain are 7.0, 6.8, 6.0, 6.0, and 8.0 dBi, respectively. Also, the corresponding radiation efficiencies are 90, 90, 91, 78, and 86%, respectively. The 3 dB-axial ratio bandwidth at 28 GHz is about 1.2 GHz.

Investigation of 5G Wireless Communication with Dust and Sand Storms

Abstract: The demands for higher throughput, data rate, low latency, and capacity in 5G communication systems prompt the use of millimeter-wave frequencies that range from 3–300 GHz with spatial multiplexing and beamforming. To get the maximum benefit from this technology, it’s important to study all the challenges of using mm-wave for 5G and beyond. One of the most important impacts is weather conditions such as humidity, temperature, dust, and sand storms. This study investigates the parameters of the channel model and its statistical behavior with the effect of dust and sand storms. The latter effects can be considered the main challenges these days, especially in middle-eastern countries. A 128 x 128 massive MIMO with URA (uniformly spaced rectangular antenna arrays) uniformly spaced has been considered in the simulation assessment with mm-wave channels operating at 28 GHz and 73GHz are examined by using NYUSIM (New York University Wireless Simulator) software. The simulation results show that the dust increases the attenuation and the path loss when working at higher frequencies compared to the clear weather conditions. Moreover, their effect can be reduced by adapting the transmitted power.

Machine Learning for Millimeter Wave and Terahertz Beam Management: A Survey and Open Challenges

Abstract: Next-generation wireless communication networks will benefit from beamforming gain to utilize higher bandwidths at millimeter wave (mmWave) and terahertz (THz) bands. For high directional gain, a beam management (BM) framework acquires and tracks optimal downlink and uplink beam pairs through exhaustive beam scan. However, for narrower beams at higher carrier frequencies this leads to a huge beam measurement overhead that negatively impacts the beam acquisition and tracking. Moreover, volatility of mmWave and THz channels, user random mobility patterns, and environmental changes further complicate the BM process. Consequently, machine learning (ML) algorithms that can identify and learn complex mobility patterns and track environmental dynamics have been identified as a remedy. In this article, we provide an overview of the existing ML-based mmWave/THz BM and beam tracking techniques. Especially, we highlight key characteristics of an optimal BM and tracking framework. By surveying the recent studies, we identify some open research challenges and provide our recommendations that can serve as a future direction for researchers in this area.

Grey neural network channel estimation and RBFNN hybrid precoding schemes for the multi user millimeter wave massive MIMO

Abstract: The millimeter wave (mm‐wave) multi‐input multi‐output (MIMO) communications are the most promising technology specially developed for next‐generation wireless networks so that the throughput and available spectrum of the network has been massively increased. At base station, it has a large number of antenna arrays with coherent transceiver processing, which helps to increase spectral efficiency. Each antenna in conventional MIMO systems makes use of a single radio‐frequency (RF) chain to boost multiplexing gain. Additionally, due to broader bandwidth, channel frequency is selective and signal‐to‐noise (SNR) is low. A successful channel estimation training phase is thus required. However, the utilization of a huge number of antennas leads to unaffordable hardware costs and excessive power usage. In order to deliver high array gain at a more affordable price, hybrid precoding techniques are applied. Both baseband combinational matrix and baseband precoding matrix must be optimised when transmitter and receiver sides of mm‐wave MIMO systems adopt hybrid precoding architecture. In addition, the combinational matrix and the precoding matrix have to be simulated to obtain the maximum system sum rate. This requires an efficient hybrid precoding approach for generating improved array gain. Therefore, this work uses a novel grey neural network approach for channel estimation and radial basis function neural network (RBFNN) for hybrid precoding. For effective channel estimation, grey wolf optimization (GWO) works in conjunction with artificial neural networks (ANN) to produce optimum results. In mm‐wave MIMO systems, the hybrid precoding RBFNN offers reduced complexity and increased efficiency. As a result, the proposed work adopts neural networks to provide effective channel estimation and hybrid precoding.

Millimeter-Wave Phased Array Antenna Integrated With the Industry Design in 5G/B5G Smartphones

Abstract: In this communication, a dual-polarized millimeter-wave (mmWave) phased array antenna is proposed for the fifth-generation (5G)/B5G smartphones. The configuration of the antenna array is highly integrated with the up-to-date industry design (ID) of ultranarrow side frame, 3-D curved display, and covers, which are widely adopted in flagship smartphones and popular among consumers. The proposed antenna contains a minor portion of slotted metal frame and a cavity-backed antenna module. The air cavity and the multiple slots are employed to enhance the bandwidth. A strip bump is established on the metal frame to meet the ID requirement, which also improves the impedance matching simultaneously. A prototype of the proposed $1\times $ 4 phased array assembled in a smartphone’s metal frame is fabricated and measured. The antenna array achieves a −10 dB impedance bandwidth from 23.2 to 29.7 GHz. At 27.0 GHz, the measured peak gain is greater than 11.2 dBi and the 3 dB scanning angle is larger than 77° for the two polarizations. Finally, the blockage issue of the curved cover is studied. In virtue of high integration with ID, compact size, wide bandwidth, good spatial coverage, and easy assembling, the proposed antenna scheme is promising for 5G/B5G smartphone designs.

Wideband High-Gain Circularly Polarized Substrate Integrated Cavity Antenna Array for Millimeter-Wave Applications

Abstract: A wideband high-gain circularly polarized (CP) substrate integrated cavity (SIC) antenna array is presented for millimeter-wave applications. The proposed antenna element is simply composed of a slot-coupled high-order-mode resonant square SIC and a pair of obliquely placed strip-shaped parasitic patches on the top surface of the SIC. The parasitic patches are used to adjust the aperture electromagnetic field distribution and phase of the two orthogonal resonant modes of TM211 and TM121 in the SIC to achieve a high-gain CP radiation and meanwhile introduce an additional cavity-backed slot-dipole CP radiation to extend axial ratio (AR) bandwidth of the proposed antenna element. By combining the above two high-gain CP radiation mechanisms, a wideband high-gain CP SIC antenna element is achieved. The simulated results of the proposed antenna element show an overlaid bandwidth of 20.36% from 26.20 to 32.14 GHz, while considering the −10 dB reflection coefficient, 3 dB AR, 3 dB gain bandwidths properties, and a maximum right-hand CP gain of 10.53 dBi at 29.40 GHz. On this basis, a wideband high-gain 8 $\times $ 8 CP array fed by a full-corporate substrate integrated waveguide (SIW) network is designed and fabricated. The measured results show that the proposed array has an overlaid bandwidth of 21.72% from 25.85 to 32.15 GHz and a measured gain of up to 26.10 dBic at 29.00 GHz.

Compact UWB MIMO Antenna for 5G Millimeter-Wave Applications

Abstract: This paper presents a printed multiple-input multiple-output (MIMO) antenna with the advantages of compact size, good MIMO diversity performance and simple geometry for fifth-generation (5G) millimeter-wave (mm-Wave) applications. The antenna offers a novel Ultra-Wide Band (UWB) operation from 25 to 50 GHz, using a Defective Ground Structure (DGS) technology. Firstly, its compact size makes it suitable for integrating different telecommunication devices for various applications, with a prototype fabricated having a total size of 33 mm × 33 mm × 0.233 mm. Second, the mutual coupling between the individual elements severely impacts the diversity properties of the MIMO antenna system. An effective technique of orthogonally positioning the antenna elements to each other increased their isolation; thus, the MIMO system provides the best diversity performance. The performance of the proposed MIMO antenna was investigated in terms of S-parameters and MIMO diversity parameters to ensure its suitability for future 5G mm-Wave applications. Finally, the proposed work was verified by measurements and exhibited a good match between simulated and measured results. It achieves UWB, high isolation, low mutual coupling, and good MIMO diversity performance, making it a good candidate and seamlessly housed in 5G mm-Wave applications.

Relocalization based on millimeter wave radar point cloud for visually degraded environments

Abstract: Simultaneously localization and mapping (SLAM) has been widely used in autonomous mobile systems to fulfill autonomous navigation. Relocalization plays an important role in SLAM for closing the loop and eliminating the drift of pose estimation. Traditional methods mostly rely on LiDAR or camera sensors, which may degrade or even fail in rainy or dusty situations or with large illumination changes. In this article, we explore the use of low‐cost commercial millimeter wave (mmWave) radars and propose a noval mmWave radar point cloud‐based relocalization method. Our method first pre‐processes the radar point cloud and, based on that, achieves fast 3‐DOF pose estimation for the robot. We build a prototype and thoroughly evaluate our method using data sets collected by our platform in four complex environments, including street, park, road, and water surface scenarios. The experimental results show that our method consistently outperforms other baseline methods including the vision‐based counterparts, especially in the visual degraded scenes.

Wideband Circularly Polarized Millimeter-Wave DRA Array for Internet of Things

Abstract: This work proposes a novel millimeter-wave (mm-wave) wideband circularly polarized (CP) antenna array for Internet of Things (IoT) applications. The proposed design addresses the issues of having IoT sensors deployed in remote locations or over large geographical regions. Elliptically shaped dielectric resonator antennas (DRAs) are used as array elements to improve radiation characteristics and achieve circular polarization over a wide impedance bandwidth around 28 GHz. Two different sequential-phase corporate feed networks are studied and compared to obtain wider impedance, 3-dB gain, and axial ratio (AR) bandwidths. Furthermore, a ridge gap waveguide technique based on the low-cost PCB technology is adopted to reduce the transmission losses in the considered sequential-phase feed networks. The proposed mm-wave antenna exhibits an impedance bandwidth of 35% (28.1–40 GHz) and 3-dB gain bandwidth of 19.3% (27.6–33.5 GHz). The achieved 3-dB AR bandwidth is 22.6% (27.5–34.5 GHz). The proposed antenna was fabricated and measured, and good agreement between measured and simulated results was obtained. The reported results show that the suggested wideband CP mm-wave antenna has a lot of promise in preventing polarization mismatch losses between IoT devices and satellites caused by their varying orientations.

A Review of Dielectric Resonator Antenna at Mm-Wave Band

Abstract: This paper is a comprehensive review of the recent literature studies on the developments and applications of millimeter-wave (mm-wave) dielectric resonator antennas (DRAs). Different designs and techniques for linear and circular polarized DRAs are discussed thoroughly. In addition, array and multiple-input multiple-output (MIMO) DRAs operating in the K, Ka, and V bands are illustrated. These applications are highly advantageous on many levels, resulting in the improved performance of the DRA in terms of obtaining a higher gain, lower losses, a higher efficiency, and a lower profile. This work reviews the fundamental research trends in antennas to meet the demands of fifth-generation (5G) communications and beyond. The reviewed studies are scholarly sources which contain measurement-based results. This paper concludes by highlighting the limitations of the studies and the implications for future research.

Reduced Loss and Prevention of Substrate Modes with a Novel Coplanar Waveguide Based on Gap Waveguide Technology

Abstract: The Gap Waveguide technology utilizes an Artificial Magnetic Conductor (AMC) to prevent the propagation of electromagnetic (EM) waves under certain conditions, resulting in various gap waveguide configurations. In this study, a novel combination of Gap Waveguide technology and the traditional coplanar waveguide (CPW) transmission line is introduced, analyzed, and demonstrated experimentally for the first time. This new line is referred to as GapCPW. Closed-form expressions for its characteristic impedance and effective permittivity are derived using traditional conformal mapping techniques. Eigenmode simulations using finite-element analysis are then performed to assess its low dispersion and loss characteristics. The proposed line demonstrates an effective suppression of the substrate modes in fractional bandwidths up to 90%. In addition, simulations show that a reduction of up to 20% of the dielectric loss can be achieved with respect to the traditional CPW. These features depend on the dimensions of the line. The paper concludes with the fabrication of a prototype and validation of the simulation results in the W band (75–110 GHz).

Regional-Based Object Detection Using Polarization and Fisher Vectors in Passive Millimeter-Wave Imaging

Abstract: Passive millimeter-wave (PMMW) imaging is a powerful approach for detecting hidden objects underneath clothing. The theoretical basis of object detection methods is the contrast of brightness temperature (TB) image. TB differences may be caused by the diversity of material, physical temperature, surface structure, and so on. Existing methods are mainly based on single-polarization and single-pixel processing, which usually generate many discrete pixels of false alarms or missing detections. In this article, we present a regional-based method for hidden object detection using polarization and Fisher vector (FV) features. The necessity of polarization averaging for detection is revealed by theoretical simulation and experimental analyses. Based on the superpixel segmentation of polarization mean image, a modified FV, regional mean FV (RMFV), is created to extract concealed object features. Various imaging experimental data of typical security inspection scenarios are applied to verify the proposed method. The robustness and effectiveness are proved by comparing with several state-of-the-art methods.

Wi-Fi Sensing Based on IEEE 802.11bf

Abstract: Conventionally, Wi-Fi radio signals are widely used for data transmissions in a wireless local area network (WLAN). Recently, it has been an interesting topic to also apply Wi-Fi radio signals to sense the environment where these signals propagate and identify changes associated with certain activities. This technique is referred to as Wi-Fi sensing, and it has been proven effective in a variety of use cases, such as proximity detection, gesture recognition, target counting, and health monitoring. As a result, the IEEE 802.11 working group has formed a new Task Group, 802.11 bf, to develop a new amendment to define necessary PHY and MAC protocols to support Wi-Fi sensing in all spectrum bands, including sub-7 GHz bands (2.4 GHz, 5 GHz, and 6 GHz band), as well as 60 GHz millimeter-wave band. In this article, our primary goal is to identify and describe the basic elements that have been developed in IEEE 802.11 bf to enable Wi-Fi sensing applications in different WLAN scenarios.

Radio SLAM: A Review on Radio-Based Simultaneous Localization and Mapping

Abstract: Simultaneous localization and mapping (SLAM) algorithm has enabled the automation of mobile robots in unknown environments. It enables the robot to navigate through an unknown trajectory by employing sensors that provide measurements to infer the surrounding environment and use this information to localize the robot. Sensor technology plays a key role in defining the quality of measurements as it affects the overall performance of SLAM. While visual sensors, like cameras, can capture rich features of the environment, they, however, fail to work in low-light conditions. On the other hand, radio frequency sensors are invariant to light conditions, however, high-frequency signals such as millimeter wave (mm-wave) are prone to severe channel attenuation, therefore, they are suitable for short-range indoor applications. Despite the high localization accuracy that the mm-wave frequency band has to offer, its shortcomings have limited the amount of research work carried out to enhance the performance of SLAM. Therefore, this paper aims to provide an overview of the recent developments in radio SLAM, with a specific focus on mm-wave enabled localization and SLAM methods. However, some notable research work based on other radio frequency sensors has also been discussed. In addition, we highlight the role of deep learning-based methods for localization and identify some of the key challenges in data-driven implementation.

Predicting Path Loss of an Indoor Environment Using Artificial Intelligence in the 28-GHz Band

Abstract: The propagation of signal and its strength in an indoor area have become crucial in the era of fifth-generation (5G) and beyond-5G communication systems, which use high bandwidth. High millimeter wave (mmWave) frequencies present a high signal loss and low signal strength, particularly during signal propagation in indoor areas. It is considerably difficult to design indoor wireless communication systems through deterministic modeling owing to the complex nature of the construction materials and environmental changes caused by human interactions. This study presents a methodology of data-driven techniques that will be applied to predict path loss using artificial intelligence. The proposed methodology enables the prediction of signal loss in an indoor environment with an accuracy of 97.4%.

A Singly-Fed Dual-Band Aperture-Sharing SIW Cavity-Backed Slot Antenna With Large Frequency Ratio

Abstract: A singly-fed dual-band aperture-sharing slot antenna with a large frequency ratio is investigated, based on the substrate integrated waveguide (SIW) technology. The dual-band antenna consists of a rectangular slotted SIW cavity operating at 40 GHz millimeter-wave (MMW) band and a ring slotted SIW cavity operating at 5.2 GHz microwave (MW) band. Due to the self-shielding effect of the SIW cavity, the two radiating elements can be tightly nested with each other, leading to a compact structure with a high ratio of radiating aperture utilization. The MW and MMW SIW radiating elements are fed via a common microstrip line through two separate slots, and they are excited in the hybrid TMh (120, 210) mode and TMh (230, 320) mode respectively. In order to avoid the signal crosstalk, a transverse stub of half-wavelength (in terms of MMW frequency) is added onto the microstrip feed line to prevent the MMW signal from getting into the MW element, while the MMW element can naturally reject the MW signal for its high-pass characteristics. Consequently, good radiation performance is obtained at both the MW and MMW bands, and moreover, the two bands can be independently adjusted.

A Comprehensive Overview of the Temperature-Dependent Modeling of the High-Power GaN HEMT Technology Using mm-Wave Scattering Parameter Measurements (Invited Paper)

Abstract: The gallium-nitride (GaN) high electron-mobility transistor (HEMT) technology has emerged as an attractive candidate for high-frequency, high-power, and high-temperature applications due to the unique physical characteristics of the GaN material. Over the years, much effort has been spent on measurement-based modeling since accurate models are essential for allowing the use of this advanced transistor technology at its best. The present analysis is focused on the modeling of the scattering (S-) parameter measurements for a 0.25 μm GaN HEMT on silicon carbide (SiC) substrate at extreme operating conditions: a large gate width (i.e., the transistor is based on an interdigitated layout consisting of ten fingers, each with a length of 150 μm, resulting in a total gate periphery of 1.5 mm), a high ambient temperature (i.e., from 35 °C up to 200 °C with a step of 55 °C), a high dissipated power (i.e., 5.1 W at 35 °C), and a high frequency in the millimeter-wave range (i.e., from 200 MHz up to 65 GHz with a step of 200 MHz). Three different modeling approaches are investigated: the equivalent-circuit model, artificial neural networks (ANNs), and gated recurrent units (GRUs). As is shown, each modeling approach has its pros and cons that need to be considered, depending on the target performance and their specifications. This implies that an appropriate selection of the transistor modeling approach should be based on discerning and prioritizing the key features that are indeed the most important for a given application.

Novel versatile topologies and design optimization of wide-bandstop frequency selective surfaces for X-band, Ku-band and millimeter-wave applications

Abstract: Abstract Novel designs of frequency selective surface (FSS) are presented for wideband applications in X, Ku and mmWave (millimeter Wave) bands. Two identical metallic layers of FSS are imprinted on both sides of the RO4003 substrate. The geometry parameters are optimized to maximize the bandstop at the specified in-band maximum transmission level of −10 dB; satisfaction of the latter condition is enforced through appropriate formulation and handling of the design constraints. The proposed structure is versatile and can be readily re-designed for various operating bands. For the sake of illustration, two instances of the FSS were developed. Design 1 exhibits broad bandstop of 9.8 GHz at the X- and Ku-bands, whereas the bandstop of Design 2 is 33.5 GHz at the mmWave band. The two FSS unit cell designs share the same base topology, but specific dimensions are adjusted to operate within the lower and the higher bands, respectively. The unit cell is symmetrical, therefore, ensures an excellent resonance stability performance with respect to different polarizations (TE and TM) and incidence angles. For proof of concept only FSS Design 1 is fabricated and measured in an anechoic chamber. The simulated and measured results exhibit good agreement. Extensive benchmarking against state-of-the-art FSS designs from the literature corroborates the advantages of the proposed topology in terms of design novelty, topological versatility, compact size, and wide bandstop response as compared to the previously available designs.

Short-Range Transmission using OAM-Carrying Waves Generated by Uniform Circular Arrays

Abstract: The orbital angular momentum (OAM or vortex) waves are expected to provide ten-fold and larger increases in wireless data rates, required for short-range communications within the beyond 5G and 6G concept of all-connected life and industry. We address the specifics of short-range communications employing OAM-carrying waves generated by small uniform circular arrays (UCAs) at lower, i.e., 10 GHz, transmission frequencies. Comparing the link budgets obtained using (i) asymptotic analytical formulas, (ii) numerical electromagnetic simulations, and (iii) measurements on two pairs of manufactured prototypes comprising 8 microstrip-patch-element UCAs, we point out the limitations of simplified models which do not account for various effects, such as coupling, parasitic radiation, and insertion loss. The observed effects are expected to be relevant at millimeter-wave frequencies as well.

Communication Compact Dual-Band Hybrid Dielectric Resonator Antenna for 5G Millimeter-Wave Applications

Abstract: In this communication, a new kind of dual-band hybrid dielectric resonator antenna (DRA) with its array design and extended dual-polarized version is presented for fifth generation (5G) millimeter-wave (mm-Wave) applications. The hybrid antenna that integrates three types of resonators of strip, slot, and DRA can generate four resonances in 28 and 39 GHz frequency bands. In this design, the strip and slot modes are used to cover the lower frequency band of 26.41–30.42 GHz, while the TE111 and TE131 modes of the DRA are employed to cover the upper frequency band of 36.05–40.88 GHz. It shows that the 5G mm-Wave bands of n257 and n260 can be covered simultaneously. It should be mentioned that our proposed hybrid antenna has a compact size of $0.34\lambda _{01} \times 0.36\lambda _{01} \times 0.1\lambda _{01}$ ( $\lambda _{01}$ means the free-space wavelength at 28 GHz). Based on the compact size of the antenna element, a $1 \times $ 5 antenna array with the capability of beam steering is designed and simulated. Wide steering angles of ±50° and ±40° can be obtained at 28 and 39 GHz frequency bands, respectively. Furthermore, an extended dual-polarized antenna configuration is also described and measured that provides similar two-port impedance and radiation performance with the single-port counterpart.

Wideband Circularly Polarized Millimeter Wave Hemispherical Dielectric Resonator Antenna

Abstract: A novel approach is proposed to design a circularly polarized (CP) hemispherical dielectric resonator antenna (DRA) with a wide axial ratio (AR) bandwidth by incorporating an additional dielectric substrate between the antenna and the ground plane. This is in addition to the lower feeding substrate that is located between the ground plane on one side and the feeding microstrip line on the other side. Adding another substrate on top of the ground plane provided an additional degree of freedom in the design that facilitated the achievement of ab 18% AR bandwidth. In addition, an integrated hemispherical DRA and perforated substrate configuration was utilized to achieve optimum effective substrate permittivity and overcome the DRA alignment and assembly challenges while maintaining the achieved wide CP bandwidth. A close agreement was achieved between measurements and simulations.