High Gain Characteristics Research Articles

Unidirective Miniaturized Ultrawideband Antenna for Sensing Buried Objects in Handheld Ground-Penetrating Radar Systems: A design approach

Ground-penetrating radars (GPR) using ultrawideband (UWB) technology have attracted a lot of research interests worldwide for high-resolution sensing and material characterization. This research contribution, therefore, introduces a miniaturized lightweight UWB antenna with high-gain characteristics for applications in handheld GPR systems. The high-gain antenna is developed to function in the 3.13–11.74-GHz wide frequency range such that it can allow high-resolution sensing of buried targets, such as landmines, metal pipes, and other structures. An elliptical quadrant-shaped UWB monopole radiator with a protuberant ground plane is conceptualized to constitute a highly miniaturized antenna of size 18 × 11 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The standalone UWB antenna realizes an impedance bandwidth of 3.07–11.67 GHz with a peak gain of 2.9 dBi. Next, a single-side copper-coated dielectric substrate as a reflector is placed beneath the antenna to attain a significant gain improvement. The proposed design with a reflector provides an average gain improvement of about 7.1 dB without influencing the original bandwidth. For experimental validation, a prototype is fabricated and characterized. The measured performance reveals close agreement with the simulation with an operating bandwidth of 3.19–11.83 GHz and a maximum gain of approximately 10 dBi at 4.02 GHz.

Enhanced expiratory rebreathing space for high loop gain sleep apnea treatment

The pathophysiology of sleep apnea goes beyond anatomic predisposition to airway collapse and includes additional factors such as arousal threshold and loop gain. High loop gain is a prominent feature in central and complex sleep apnea (with a mixture of obstructive and central features) where relative hypocapnia can lead to respiratory instability and periodic breathing. Existing therapies, including continuous positive airway pressure (CPAP) and adaptive servo-ventilators, often inadequately treat sleep apnea with high loop gain features. Enhanced expiratory rebreathing space (EERS) targets prevention of the hypocapnia that triggers central events in sleep by increasing dead space in amounts less than typical tidal volumes. This is accomplished by covering traditional exhalation ports on positive airway pressure masks and adding small additional tubing with distal exhalation and safety valves. This technique reduces carbon dioxide (CO2) blow-off during arousals and the associated large recovery breaths, typically producing a maximal increase in resting CO2 by 1–2 mmHg, thus increasing the CO2 reserve and making it less likely to encounter the hypocapnic apneic threshold. Typically, the amount of EERS is titrated in response to central events and periodic breathing rather than aiming for a goal CO2 level. Ideally CO2 monitoring is used during titration of EERS and the technique is avoided in the setting of baseline hypercapnia. This method has been used in clinical practice at our sleep center for over 15 years, and retrospective data suggests an excellent safety profile and high rates of successful therapy including in patients who have previously failed CPAP therapy. Limitations include decreased effectiveness in the setting of leak and decreased tolerance of the bulkier circuit. EERS represents a simple, affordable modification of existing positive airway pressure modalities for treatment of central and complex sleep apnea. Areas of future study include randomized controlled trials of the technique and study of use of EERS in combination with adaptive ventilation, and pharmacologic adjuncts targeting high loop gain physiology.

Maximum gain optimization of thulium-doped fiber amplifier based on genetic algorithm for peak gain spectrum at 1800- 2000nm

The optical fiber amplifier doped with rare earth elements has the characteristics of high gain, high doping concentration and short length. Compared with other fiber optic systems, the fiber used is shorter, also known as lumped fiber amplifier. At present, Er, Pr, Tm, Nd and Yb doped fiber amplifiers and lasers are mainly studied more. To further extend the transmission distance, improve the transmission quality and increase the transmission capacity, it is very important for the research of fiber amplifier. In this research, using a two-level structure, we investigate the maximum of the peak gain of the gain spectrum of a thulium-doped broadband fiber amplifier in the 1800-2000 nm wavelength range. Signal gain is inversely proportional to fiber length, doping concentration, and pump power in both the absorption spectrum and the emission spectrum, as shown by the relationship diagram of signal gain with these variables. And through the genetic algorithm data optimization, we get that when the fiber length is 2.2 m, the maximum gain is 42.7 dB.

A split-ring resonator full/sparse planar array based on Chebyshev polynomial

A planar split-ring resonator (SRR) antenna full/sparse array, fed by a Chebyshev distribution, is proposed in this paper. Following the Yagi principle, the antenna element consists of SRRs and an I-shaped resonator. The inclusion of the I-shaped resonator enhances coupling, resulting in high gain. Additionally, a 14 × 13 Chebyshev planar antenna array, based on corporate feed, allows for a non-uniform amplitude distribution to suppress side lobes. The proposed Chebyshev planar array exhibits high gain characteristics and low side lobe levels (SLL) in both the E- and H-planes. For sidelobes suppression further, by utilizing a genetic algorithm, a planar sparse array is constructed based on the proposed Chebyshev array. The measured gain of the array at 10.1 GHz is 22.4 dBi, with SLL values of −20.4 dB and −17.5 dB in the E- and H-planes, respectively. These results meet the requirements for wireless communication.

High gain metasurface integrated millimeter-wave planar antenna

Abstract A metasurface reflector-backed wideband planar antenna is designed for millimeter-wave (mmWave) applications. A simple meandering structure is used for radiation element design, while the back side consists of a partial ground plane and parasitic elements. The utilization of meander-shaped element led to small antenna dimensions. The partial ground plane is used to achieve wide bandwidth, while the parasitic elements are used to improve the impedance matching toward higher frequency bands. To achieve high gain and directional radiation characteristics, an array of metasurfaces is placed behind the radiating element. It is observed from the simulated results that the proposed antenna system offers 17.72 GHz of impedance bandwidth in the operating range of 22.28–40 GHz, while the measured impedance bandwidth is noted to be 15.8 GHz, ranging from 23 to 38.8 GHz. Furthermore, it is observed that a metasurface-based planar antenna tends to achieve a peak gain of ≈9 dBi in the band of interest.

Perturbation Observation Method-Based Optimization Seeking Control of Soft-Switching and No Backflow Power for LCL Resonant-Type Dual Active Bridge DC–DC Converters

LCL-type resonant dual active bridge (LCL-DAB) DC-DC converters feature high gain, high power density, and low reactive current. To further improve the efficiency, based on the dual-phase shift (DPS) modulation method, the operating characteristics are firstly derived and the design regions of soft-switching and no backflow power are established, and then a perturbation observation method based optimization seeking control of soft-switching and no backflow power is proposed in this paper. In the starting process, the system firstly tracks the reference voltage according to the relationship between the inner and outer phase shift ratio obtained by the first harmonic approximation. Then, the outer phase shift ratio is perturbed based on the characteristics of soft-switching and backflow power, approaching the target phase shift ratio stepwise, while the inner phase shift ratio is calibrated to hold the output voltage. Both H bridges can operate in soft-switching mode, and on this basis, the backflow power was eliminated to the maximum extent. Finally, the simulation and experimental results verified the feasibility and effectiveness of the proposed method.

Topic Mining and Future Trend Exploration in Digital Economy Research

This work proposes a new literature topic clustering analysis framework, based on which the topics of digital-economy-related studies are condensed. First, we calculated the word vector of keywords using the FastText model, and then the keywords were merged according to semantic similarity. A hierarchical clustering method based on the Jaccard coefficient was employed to cluster the domain documents. Finally, the information gain method was applied to estimate the high-gain feature words for each category of topics. Based on the above framework, 23 categories of research topics were formed. We divided these topics into layers of digital technology, convergence innovation and digital governance, and we constructed a three-level digital economy research framework. Thereafter, the current hot spots and frontier trends were derived based on the number and growth rate of the literature. Our study revealed that the research on digital technology, which is the basic layer of the digital economy, has waned. The field related to the integration and innovation of digital technology and the real economy was the current research focus, among which the results with respect to “New Business Forms in the Digital Age”, “Circular Economy” and “Gig Economy” were abundant. The problems of the unbalanced development of the digital economy and digital monopoly have strengthened research on digital governance. Furthermore, research on “Regional Digital Economy”, “Chinese Digital Economy” and “Data Management” is in its initial stage and is a potential area of future research.

A Single-Stage Charger for LEV Based on Quadratic Buck-Boost AC-DC Converter Topology

A single-stage AC-DC converter, which uses a quadratic buck-boost voltage gain, for LEVs' (Light Electric Vehicles) battery charging is presented in this work. Unlike conventional BCs (Battery Chargers), which employ transformer (low or high frequency) based approaches to charge low voltages LEVs' batteries, the presented charger utilizes transformerless single-stage power architecture. In order to realize desired charging of LEVs and to maintain proper transformerless voltage gain, the presented quadratic buck-boost AC-DC converter ensures high step-down gain characteristics between AC mains and low voltage battery packs. Besides realizing desired battery charging profile, the presented single-stage BC ensures high PQ (Power Quality) indices (low input current distortions and unity power factor operation) at the supply side. Notably, the presented quadratic buck-boost AC-DC converter exhibits an intrinsic power factor correction (PFC) feature at the AC input mains under discontinuous inductor current mode (DICM) operation, thereby, incurring minimum complexities during the control implementation, which further reduces the cost of the charger. The DICM operation facilitates negligible switch turn-on and diode reverse recovery losses, and therefore, ensures an improved conversion efficiency of the BC. Even if, the presented AC-DC converter employs two switching devices, the simultaneous switching of both switches shrinks the cost and complexity of driving circuitry even further. Finally, a comprehensive operational analysis, component selection criteria, and modelling of the presented quadratic buck-boost AC-DC converter-based LEVs BC are carried out and its performance is validated through a test bench set-up in a laboratory environment. Relevant results are presented to validate the efficacy of the presented quadratic buck-boost AC-DC converter for LEVs charging applications.

Research on High Power Fuel Cell DC-DC Based on SiC Devices

With the increasing shortage of traditional energy resources, new energy resources such as fuel cells are widely used. However, the front-end output voltage of new energy power generation systems such as fuel cells is low, which cannot directly supply power to the load. Therefore, an efficient DC converter with a high boost ratio is needed to raise the voltage to the required level. The staggered parallel DC boost converter has the characteristics of small input current ripple and high voltage gain, which is very suitable for low voltage and high current input and high voltage output. Compared with Si Mosfet, SiC Mosfet has better on-state and on-switch characteristics. In this paper, the requirements of fuel cells in DC-DC are analyzed, the characteristics and applications of SiC devices are introduced, and the topology and working principle of DC-DC are studied. By comparing the topology of isolated DC-DC and non-isolated DC-DC, the staggered Boost circuit topology is selected. The advantages and working state of multiple staggered parallel circuits are studied in detail.

A Broadband Fixed-Beam Leaky-Wave Antenna

In point-to-point communication, antennas are often required to radiate a broadband signal in a specific direction. Traditional leaky-wave antennas (LWAs) have the features of low cost and high gain, but also the frequency-beam-scanning property, which is not suitable for this demand. In this paper an LWA with broadband fixed-beam property is designed in millimeter-wave band. The antenna is implemented on a ridge gap waveguide, and a series of microstrip branches are employed as phase delay lines. The working principle of the antenna is elaborated, and the main beam can be designed in any direction (including broadside and inclined angles) by selecting proper lengths for the microstrip branches. Side lobe levels (SLLs) can be reduced by using slots with gradually changed lengths to excite the microstrip branches. Three antennas with main beam directions in 0° and ±25° are designed and measured as verifications. In the experiment, the antennas show stable radiation properties (including beam angles and realized gains) over the band from 25 GHz to 39 GHz (a bandwidth of 43%). This LWA shows potentials in millimeter-wave broadband applications.

A Family of Integrated Cascade Multiport Converters for Centralized Equalization Systems: Derivation, Analysis, and Verification

To achieve simultaneous balancing of multiple battery cells, existing centralized equalization methods need to configure multiple converters, which results in large size and high cost that limit the application of such methods. In this article, a systematic approach for deriving integrated cascade multi-port converters (ICMPC) is proposed, and the limitations of existing centralized methods are addressed by the derived family of converters. In the ICMPC-based method, the energy exchange between multiple unbalanced cells and battery string can be realized by configuring only one converter, which greatly improves the power density and cost benefit. Besides, the ICMPC features high voltage gain, high efficiency and easily expandable ports, which further enhances its application potential. In order to better understand the derived converters, the half-bridge based ICMPC with voltage dividing capacitors is thoroughly studied, covering its operation principle, control strategy, parameter selection and soft-switching analysis. Finally, a test prototype for equalizing a battery string consisting of two 7-cell modules is built to validate the theoretical analysis. Also, an in-depth comparative evaluation is carried out to confirm the superiority of the ICMPC-based equalization system.

Design of Microstrip Antenna for Satellite Applications at K-Band

The Abstract-Satellite application's five-band microstrip patch antenna is suggested, and it is modelled using the HFSS studio software. The suggested microstrip patch antenna is constructed using templates that are square and rectangular in shape. The most crucial component of virtually every wireless advanced communication system is the microstrip patch antenna, which is crucial in transforming electrical signals into EM wave signals for electromagnetic transmission. This work develops an antenna that can function in the Ku/k/ku bands at frequencies between 10 GHz and 40 GHz. The majority of antennas for satellite applications are designed to have good wide bandwidth, high gain, and small size characteristics. Adjust and perfect the length using a rectangle and square patch of 4.3-4.4 dielectric constant substrate. Resize and improve the field's length; The microstrip patch antenna is made to operate in several frequency bands, including the ku, k, and ka bands.

1-Bit Hexagonal Meander-Shaped Wideband Electronically Reconfigurable Transmitarray for Satellite Communications

This paper proposes a hexagonal meander-shaped wideband electronically reconfigurable transmitarray (HMRTA) at Ku band for satellite communications and radar applications. The proposed transmitarray offers high gain, low profile, and wideband characteristics with beam-scanning and beam-forming features. The cascaded structure is a low-profile and compact transmitarray. The transmitter (Tx) layer has an angular hexagonal patch with a meandered shape and resonating parasitic patches to enhance the bandwidth. The receiver (Rx) layer comprises a two-part hexagonal receiver patch and a dual ring impedance-matching receiver layer. The current reversal phenomena have executed the 180° phase shift by integrating two diodes in opposite directions. The measured results of a unit cell achieve a minimum insertion loss of 0.86 dB and 0.92 dB for state I and state II. The maximum insertion loss is 2.58 dB from 14.12 GHz to 18.02 GHz and is about 24.83% at 16.5 GHz. The full-wave simulations of a 20 × 20 space-fed reconfigurable transmitarray were performed. Good radiation patterns at all scanning angles of two principal planes are achieved, and the cross-polarization level remains less than −20 dB. The simulated 3 dB gain fluctuation bandwidth of the array is 15.85~18.35 GHz, and the wideband characteristics are verified. The simulation results show that the array can perform beam scanning ±60° in the elevation (y-z) plane and obtain the beam-scanning characteristics for ±60° in the Azimuth (x-z) plane.

A Dual-Polarized Shared-Aperture Antenna With Conical Radiation Patterns and High Gain for 5G Millimeter-Wave Ceiling Communications

A dual-polarized (DP) antenna with a conical radiation pattern and high gain characteristics is proposed. It is mainly comprised of a horizontally polarized (HP) array, a vertically polarized (VP) element, a fence, and a feeding network. In the HP direction, a rotatable stacked substrate-integrated waveguide (SIW)-to-coaxial-to-SIW transition (SCST) is meticulously designed to yield omnidirectional radiation with low gain variations and low transmission loss. As for the VP direction, two orthogonal substrates that are arranged above the VP radiating element act as a holder to fix the director, resulting in gain enhancement. Here, the VP element is placed in the center of the HP array to share the aperture for size reduction. Moreover, the top-hat-shaped metal fence collaborates with the large-size ground plane to yield dual conical beams with high gain in DP directions. From the measured results, the HP direction has exhibited desirable bandwidth of 11.4% (24.8–27.8 GHz) with a peak gain of 11.6 dBi, and the VP direction has demonstrated wider bandwidth of 13.7% (24.5–28.1 GHz) with a corresponding gain up to 8.1 dBi. Notably, low gain variations of ±0.65 and ±0.8 dBi are also realized for the HP and VP directions, respectively. Therefore, a DP antenna with high-gain conical beams and low gain variations can be obtained for the fifth-generation (5G) millimeter-wave (MMW) ceiling communications.

A Compact Mu-Near-Zero Metamaterial Integrated Wideband High-Gain MIMO Antenna for 5G New Radio Applications.

This article demonstrates a compact wideband four-port multiple-input-multiple-output (MIMO) antenna system integrated with a wideband metamaterial (MM) to reach high gain for sub-6 GHz new radio (NR) 5G communication. The four antennas of the proposed MIMO system are orthogonally positioned to the adjacent antennas with a short interelement edge-to-edge distance (0.19λmin at 3.25 GHz), confirming compact size and wideband characteristics 55.2% (3.25-5.6 GHz). Each MIMO system component consists of a fractal slotted unique patch with a transmission feed line and a metal post-encased defected ground structure (DGS). The designed MIMO system is realized on a low-cost FR-4 printed material with a miniature size of 0.65λmin × 0.65λmin × 0.02λmin. A 6 × 6 array of double U-shaped resonator-based unique mu-near-zero (MNZ) wideband metamaterial reflector (MMR) is employed below the MIMO antenna with a 0.14λmin air gap, improving the gain by 2.8 dBi and manipulating the MIMO beam direction by 60°. The designed petite MIMO system with a MM reflector proposes a high peak gain of 7.1 dBi in comparison to recent relevant antennas with high isolation of 35 dB in the n77/n78/n79 bands. In addition, the proposed wideband MMR improves the MIMO diversity and radiation characteristics with an average total efficiency of 68% over the desired bands. The stated MIMO antenna system has an outstanding envelope correlation coefficient (ECC) of <0.045, a greater diversity gain (DG) of near 10 dB (>9.96 dB), a low channel capacity loss (CCL) of <0.35 b/s/Hz and excellent multiplexing efficiency (ME) of higher than -1.4 dB. The proposed MIMO concept is confirmed by fabricating and testing the developed MIMO structure. In contrast to the recent relevant works, the proposed antenna is compact in size, while maintaining high gain and wideband characteristics, with strong MIMO performance. Thus, the proposed concept could be a potential approach to the 5G MIMO antenna system.

A Design of Similar High-gain and Dual-band Frequency/Polarization Reconfigurable Antenna for ISM Band Applications

This paper proposes a frequency/polarization reconfigurable antenna (RA) incorporating Frequency Selective Surface (FSS) to achieve dual-band and similar high-gain characteristics. The proposed RA-FSS design using 4 PIN Diodes can produce reconfigurability between circular polarization (CP) at 1.8 GHz and linear polarization (LP) at 2.45 GHz. The fabricated prototype shows good CP performance at 1.8 GHz while the measured peak broadside gains are about 7.2 dBi at 1.8 GHz and 8.5 dBi at 2.45 GHz when PIN diode ON and OFF, respectively.

High-Gain All-Metal 3-D Printed Lens–Horn Antenna for Millimeter-Wave Applications

In this letter, a high-gain all-metal lens–horn antenna for millimeter-wave applications is proposed. Unlike the conventional metal lens horn, the proposed lens horn can theoretically achieve an arbitrary focal-to-diameter (F/D) ratio, which can further shorten the length of the horn antenna. Considering the design difficulty of the feed, in practice, the F/D ratio generally needs to be greater than 0.4. To further reduce the overall height of the antenna, the lens can be kept at a certain thickness according to the Fresnel lens principle. To demonstrate the proposed theory, a lens–horn antenna with an F/D ratio of 0.7 and an aperture area of π×93.75 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is designed, fabricated, and tested. In order to reduce the processing costs and difficulties, the antenna is processed by metal 3-D printed technology. The test results indicate that the antenna achieves a peak gain of 30.8 dBi and 3-dB gain bandwidth of 22.5% (28.4–34.5 GHz). The length of the proposed antenna can be reduced by about 68% compared with the horn antennas without lenses. The proposed antenna has the characteristics of high gain, compact structure, and low cost, which is suitable for high-power millimeter-wave applications.

A Single-Switch Continuous Input Current Buck–Boost Converter With Noninverted Output Voltage

In this article, a single-switch continuous input current (CIC) buck–boost converter with noninverted output voltage is proposed. The proposed converter utilizes capacitor and inductor along with three diodes in conjunction with a quadratic boost converter to adopt its CIC feature. The features of high voltage gain, single active power switch, less ripple CIC, and noninverted output voltage make the proposed converter suitable for renewable and industrial applications. In addition, it provides a wide operating voltage gain with optimum component count, which is higher than the conventional buck–boost converter. Furthermore, it has low voltage stress across the power switch with comparable converters. To elevate the importance of the proposed converter, a detailed comparison analysis has been carried out considering voltage stress, voltage gain, effectiveness index, and component count. The operating principle and steady-state analysis in continuous conduction mode and discontinuous conduction mode of the proposed converter are discussed in detail. To validate the theoretical analysis and performance of the proposed converter, a prototype has been developed and tested in laboratory.

A Hollow-Waveguide-Fed Planar Wideband Patch Antenna Array for Terahertz Communications

This article presents a design of terahertz (THz) patch antenna array with high gain and wideband features. The proposed array consists of eight subarrays printed on a single-layer high-frequency laminate and a power distribution network realized by a hollow waveguide made from a copper block. The simulated results show that the subarray can achieve an impedance bandwidth of 37% for the reflection coefficient < −10 dB with a peak gain of 15.2 dBi at 155 GHz. The 1-to-8 hollow-waveguide network has a simulated reflection coefficient below −14 dB and a simulated transmission loss smaller than 0.4 dB. A parametric analysis is implemented to determine the range of key parameters of the subarray and find out fabrication tolerance of the array at such high frequency. The measured results show that the proposed array achieves the reflection coefficient below −10 dB from 150 to 205 GHz. The measured 3-dB gain bandwidth of the proposed antenna array is 19.7% with a maximum gain of 21.9 dBi. These performances ensure that the proposed array is a promising candidate for THz communications.

X-Band Active Phased Array Antenna Using Dual-Port Waveguide for High-Power Microwave Applications

An X-band active phased array horn antenna with high power capacity and high peak power is proposed in this paper. At the horn aperture, the baffles are loaded to suppress higher-order modes and eliminate blind spots during beam scanning. Straight walls are added to improve impedance matching. Considering that the peak power that T/R modules can provide is very limited, the proposal of a dual-port waveguide breaks through the bottleneck of the power capacity of a single-port input for the first time. The proposed curved dual-port waveguide is used to connect the horn antenna and the T/R module, which is verified to improve the power capacity of the overall internal structure. Simulated and measured results show that VSWR ≤ 2 in the frequency range of 7.5–8.5 GHz. There is no grating lobe in the ±10° scanning range and the maximum gain drop does not exceed 0.4 dB. The power capacity of the proposed HPM array is 56.34 MW. The phased array antenna has the characteristics of flexible scanning, small size, and high gain, and can be applied in high-power microwave systems.