Entire Bandwidth Research Articles

Broadband high-efficiency plasmonic metalens with negative dispersion characteristic

Controlling the dispersion characteristic of metasurfaces (or metalenses) along a broad bandwidth is of great importance to develop high-performance broadband metadevices. Different from traditional lenses that rely on the material refractive index along the light trajectory, metasurfaces or metalenses provide a new regime of dispersion control via a sub-wavelength metastructure, which is known as negative chromatic dispersion. However, broadband metalenses design with high-performance focusing especially with a reduced device dimension is a significant challenge in society. Here, we design, fabricate, and demonstrate a broadband high-performance diffractive-type plasmonic metalens based on a circular split-ring resonator metasurface with a relative working bandwidth of 28.6%. The metalens thickness is only 0.09λ0 ( λ0 is at the central wavelength), which is much thinner than previous broadband all-dielectric metalenses. The full-wave simulation results show that both high transmissive efficiency above 80% (the maximum is even above 90%) and high average focusing efficiency above 45% (the maximum is 56%) are achieved within the entire working bandwidth of 9–12 GHz. Moreover, an average high numerical aperture of 0.7 ( NA=0.7 ) of high-efficiency microwave metalens is obtained in the simulations. The broadband high-performance metalens is also fabricated and experimental measurements verify its much higher average focusing efficiency of 55% (the maximum is above 65% within the broad bandwidth) and a moderate high NA of 0.6. The proposed plasmonic metalens can facilitate the development of wavelength-dependent broadband diffractive devices and is also meaningful to further studies on arbitrary dispersion control in diffractive optics based on plasmonic metasurfaces.

Bandwidth enhancement of circularly polarised slot global navigation satellite systems antenna using an integrated filter‐antenna approach

Abstract:A technique to enhance the bandwidth of a circularly polarised antenna using the filter‐antenna design approach is presented. The design relies on adding a resonator coupled to the radiation element—an L‐shaped slot antenna in the case of global navigation satellite systems. This change in the feeding structure broadens both the impedance and the axial ratio (AR) bandwidths and allows more design flexibility. Compared with a reference L‐shaped slot antenna with a conventional feed, the proposed antenna design achieves a doubling of the impedance matching bandwidth from 19% to 41% over the frequency range from 1.2 to 1.81 GHz and a wider AR bandwidth from 35% to 44.5% in the range from 1.17 to 1.84 GHz. The AR bandwidth covers the entire impedance bandwidth. The effect of a metal reflector on antenna performance is also investigated and discussed.

Ultra-wideband microwave absorber based on multilayer patterned resistive film

In this work, two ultra-wideband microwave absorbers are proposed. The absorptivity of the proposed original absorber can achieve 90% in a wide bandwidth from 2.41 GHz to 18 GHz at normal incidence. This design has been extended to enhance absorption performance and angular stability by respectively incorporating a high-dielectric substrate and adding metal vias. As a result, the absorptivity of over 90% can be achieved from 0.6 to 18 GHz in transverse magnetic (TM)-incident cases even if the incident angle goes up to 60°, which realizes a relative bandwidth of 153%. While in the transverse electrical (TE) polarization, the absorption of the new absorber performs better than the original one in the entire operational bandwidth. A prototype of the proposed absorber is fabricated and measured, good agreement is obtained between measured and simulated results, indicating the usability of our design in practical electromagnetic wave absorbing scenes.

Advancements in Tunable and Multifunctional Metamaterial Absorbers: A Comprehensive Review of Microwave to Terahertz Frequency Range

Abstract Over the past two decades, metamaterial absorbers have undergone significant advancements, evolving from microwave single-frequency designs to multi-frequency and broadband absorption, extending into the terahertz band. These absorbers have transitioned from unadjustable to adjustable and multifunctional configurations, enabled by the integration of adjustable materials, mechanical structures, and semiconductor devices. This article provides a comprehensive review of the progress achieved in the microwave to terahertz frequency range over the last five years. Key aspects covered include the absorbing mechanism of metamaterials in the microwave frequency band, with absorption efficiencies exceeding 90% for specific frequency ranges. The development of adjustable absorbers allows for frequency tunability within ±10% of the central frequency, while multifunctional absorbers enable concurrent control over absorption and reflection properties. In the terahertz regime, advanced electromagnetic simulations have led to absorber designs with bandwidths exceeding 50% of the central frequency, resulting in absorption efficiencies above 80% over the entire bandwidth. Integration of gallium nitride-based Gallium Nitride High Electron Mobility Transistors (GaN HMET) provides fast switching speeds below 100 nanoseconds, facilitating rapid reconfiguration of absorber functionalities. These advancements in metamaterial absorbers offer promising prospects for intelligent and integrated designs in future applications.

A high resolution prism-grating panoramic imaging spectrometer based on occultation observations

Occultation observation is an important technique for shadow region detection and a significant complement to the illuminated region detection method. This technology will significantly reduce the impact of background light pollution and provide clearer occultation signals. In order to achieve high-resolution all-round detection in the shadow region, this paper introduces a proposal for a prism-grating panoramic imaging spectrometer based on occultation observations. It utilizes a panoramic annular lens to enable 360-degree occultation observations within the shadow region, combines a grating for spectral separation to obtain spectral information, and achieves an overall straight-line design for the system by adjusting the prism-grating surface's deflection angle. This paper, by analyzing the non-uniformity of light rays from different fields of view after dispersion by the grating, obtains the coordinate information of the spectrum on the image plane, significantly improving the accuracy of subsequent spectral calibration. The design results indicate that the optical system of this imaging spectrometer achieves a spectral resolution of 0.67 nm in the wavelength range of 365–770 nm. At a Nyquist frequency of 37.04lp/mm, the MTF across the entire bandwidth exceeds 0.6. The RMS of the point spread function is less than 9 μm across the full field of view, and aberration correction is excellent. This imaging spectrometer utilizes stellar occultations to achieve real-time 360-degree observations in the shadow region, and at the same time obtains total information on atmospheric components and contour information that varies with occultation height. This scheme offers a more comprehensive information for scientists in related fields.

A Survey on Beamspace Millimeter-wave Massive Mimo Systems: An Overview of Open Issues, Challenges, and Future Research Trends

Abstract: The channel sparsity is exploited by transforming the channel into an angular domain from the spatial domain at millimeter wave frequencies in Beamspace Multiple-Input Multiple-Output (B-MIMO) systems. Every beam in B-MIMO corresponds to an individual radio frequency (RF) chain, and thus, beam selection techniques can reduce the RF hardware complexity. RF chain limitation is needed for an ideal beamspace precoding scheme to attain good system performance across the entire bandwidth. New methods of beamspace channel estimation with a small amount of estimation error and low computational complexity are challenging in the beam domain due to the larger antenna arrays deployed. A novel beamspace processing technique to improve the direction of arrival estimation performance for different array configurations with improvement in system performance is desired in a 5G system. A detailed review of the B-MIMO system with its architecture and various beam selection techniques is presented in this paper. The scope of the work is elaborated by incorporating various existing beamspace precoding and channel estimation methods. The paper also presents various beamspace processing schemes for parameter estimation with a focus on the direction of arrival estimation performance.

Small Size Broadband Printed Antenna for 5G Applications Covering 28 GHz / 38 GHz and 60 GHz Bands

This work offers the radiation insight of a compact modified monopole rectangular printed antenna suitable for 5G applications. A Double copper cladded RT Duroid 5880 material sheet with dimensions 4.4×5.0×0.5mm3 is chosen as the base substrate in the offered design with a loss tangent of 0.004 and a dielectric constant of 2.2. In the provided strategy lower-left corner of a rectangular printed antenna is made in the form of a smooth circular curve. After extensive simulation, a circular slot with an elliptical patch is incorporated into this monopole antenna. The designed antenna parameters are adjusted to cover the impedance bandwidth from 21.7 GHz to more than 70.0 GHz. Three resonances at 28.0 GHz, 38.1 GHz and 60.2 GHz were observed in three bands allocated for 5G communication applications. The efficiency and gain values found sustained in the entire bandwidth range. Stable and desired radiation patterns at all three resonant frequencies 28/38/60 GHz prove the suitability of this antenna for recent 5G applications.

Spatially-coded Fourier ptychography: flexible and detachable coded thin films for quantitative phase imaging with uniform phase transfer characteristics.

Fourier ptychography (FP) is an enabling imaging technique that produces high-resolution complex-valued images with extended field coverages. However, when FP images a phase object with any specific spatial frequency, the captured images contain only constant values, rendering the recovery of the corresponding linear phase ramp impossible. This challenge is not unique to FP but also affects other common microscopy techniques -- a rather counterintuitive outcome given their widespread use in phase imaging. The underlying issue originates from the non-uniform phase transfer characteristic inherent in microscope systems, which impedes the conversion of object wavefields into discernible intensity variations. To address this challenge, we present spatially-coded Fourier ptychography (scFP), a new method that synergizes FP with spatial-domain coded detection for true quantitative phase imaging. In scFP, a flexible and detachable coded thin film is attached atop the image sensor in a regular FP setup. The spatial modulation of this thin film ensures a uniform phase response across the entire synthetic bandwidth. It improves reconstruction quality and corrects refractive index underestimation issues prevalent in conventional FP and related tomographic implementations. The inclusion of the coded thin film further adds a new dimension of measurement diversity in the spatial domain. The development of scFP is expected to catalyse new research directions and applications for phase imaging, emphasizing the need for true quantitative accuracy with uniform frequency response.

Three‐element ultrawideband MIMO antenna based on shared‐radiator structures with high efficiency and gain

AbstractThis letter presents a novel three‐port ultrawideband (UWB) multi‐input‐multi‐output (MIMO) antenna that covers the sub‐6 GHz (between 1.7 and 6 GHz) frequency band for wireless device applications. The proposed antenna consists of two parts: a dipole and two centrosymmetric slot antennas with shared structures. The radiating arm of the dipole can be reused as the large slot ground without increasing the size. The novel circular slot antenna etched on the radiator and circular microstrip feed line are designed to achieve wide impedance bandwidth. Meanwhile, four chamfers are loaded at the corners of the dipole to further optimize the impedance match in the whole frequency band. The physical dimension of the proposed three‐port MIMO antenna is 70 × 45 × 0.762 mm3. Experimental results validate that the reflection coefficient remains lower than −12 dB and the port isolation is better than 12 dB in the entire operational bandwidth without any decoupling network. The measured average peak gains are up to 5.6 dBi for all three ports, accompanied by a radiation efficiency of 90% across the frequency spectrum. With the advantages of simple design, high gain and high radiation efficiency, the proposed three‐element MIMO antenna design is well‐suited for implementation in UWB applications.

A Capacitive-Feedback Amplifier with 0.1% THD and 1.18 μVrms Noise for ECG Recording

This paper presents an amplifier with low noise, high gain, low power consumption, and high linearity for electrocardiogram (ECG) recording. The core of this design is a chopper-stabilized capacitive-feedback operational transconductance amplifier (OTA). The proposed OTA has a two-stage structure, with the first stage using a combination of current reuse and cascode techniques to obtain a large gain at low power and the second stage operating in Class A state for better linearity. The amplifier additionally uses a DC servo loop (DSL) to improve the rejection of DC offsets. The amplifier is implemented in a standard 0.13 μm CMOS process, consuming 1.647 μA current from the supply voltage of 1.5 V and occupying an area of 0.97 mm2. The amplifier has a 0.5 Hz to 6.1 kHz bandwidth and 59.7 dB gain while having no less than a 65 dB common-mode rejection ratio (CMRR). The amplifier’s total harmonic distortion (THD) is less than 0.1% at 800 mVpp output. The amplifier can provide a noise level of 1.18 μVrms in the 0.5 Hz to 500 Hz bandwidth that the ECG signal is interested in and has 3.38 μVrms input-referred noise (IRN) over the entire bandwidth, so its noise efficiency factor (NEF) is 2.13.

A Variable Fractional Delay Filter Based True-Time-Delay Array Architecture for Wideband Beamforming

True-time delay (TTD) units are critical in Wideband Large-Scale Antenna Systems (LSASs) for resolving beam squint and frequency selective fading. In this paper, we propose a TTD array architecture for wideband beamforming that addresses the challenges posed by LSASs by utilizing variable fractional delay (VFD) filters and time delay estimations (TDEs). This study introduces a convex optimization problem to develop a novel method for designing VFD filters that can achieve high precision time delay resolution while maintaining an acceptable frequency response peak error. Using these VFD filters, we present a TDE approach with Newton-Raphson iteration update that corrects the difference in arrival time between sensors. Due to the implementation of VFD filters and fast TDE modules, the new architecture can complete beam steering and tracking in 10 ms with MATLAB simulation. Furthermore, an example was designed to demonstrate that the proposed architecture is capable of producing precise beam pointing while maintaining the bit error rate (BER) that is extremely close to the theoretical curve over the entire bandwidth.

Four‐port MIMO Vivaldi antenna for access points

AbstractIn this article, a 4‐port multiple input, multiple output (MIMO) antenna array is presented, based on a Vivaldi design for nonplanar applications like access points above 6 GHz. The antenna is configured with four Vivaldi antennas arranged orthogonally, one to each other, to increase the electromagnetic isolation among elements. The Vivaldi element is fed with a microstrip with an integrated balun in only one arm, and each arm is set in an antipodal position to the other, giving an easy‐to‐design and build prototype, with no complicated feeding techniques. Each antenna plane has dimensions of 90 × 40 mm2. The array presents a bandwidth from 5.3 GHz to beyond 20 GHz, with electromagnetic isolation above 20 dB, an envelope correlation coefficient below 0.001 for the entire bandwidth, giving a diversity gain around 20 dB, and a total active reflection coefficient below −10 dB from 7 to 20 dB, fulfilling the metrics for MIMO applications.

Design And Simulation of a Hexagonal High-Gain MIMO Patch Antenna For 5G Applications

View of the technological evolution and the problems encountered by the world, researchers are obliged to find solutions, particularly researchers in the field of antennas. This article has been devoted to the design and study of a hexagonal dual-band MIMO patch antenna for Satellite and 5G applications. Several parameters have been studied, we can quote among other things the gain, the bandwidth, the radiation diagram, the directivity, and the distribution of the electric field E. To achieve these studies and find optimal solutions, several designs have been made like the design of a simple hexagonal patch antenna, and, in the end, the proposed antenna is a MIMO with a hexagonal shape and 2 feeding ports. The proposed antenna operates at 25 GHz as the central frequency. The obtained ECC (envelope correlation coefficient) value is less than 0.006 for the entire operating bandwidth, which satisfies the standard value criteria of less than 0.5 and indicates minimal isolation between the antenna arrays. The values of the gain and the maximum directivity of the antenna obtained are respectively 8.12 dB and 8.37 dB, which gives us an efficiency of the antenna at 97.01% with high isolation > 25 dB. The results are found to be sufficient for the device to be used for mm-wave 5G MIMO applications. Additional MIMO performance metrics, such as the channel capacity loss (CCL), diversity gain (DG), and total active reflection coefficient (TARC), are evaluated. All this work has been done using HFSS 15 as software.

A Compact Slotted UWB Antenna Based on Characteristics Mode Theory for Wireless Applications

The development of electronic systems and wireless communication has led to a proportional increase in data traffic over time. One potential solution for alleviating data congestion is to augment the bandwidth capacity. This study presents a novel asymmetric circular slotted semi-circle-shaped monopole antenna design using a defective ground structure. The extended ultrawide bandwidth is achieved by implementing a design where the semi-circle radiator is etched in a specific asymmetric circular slot. This involves etching a circle with a radius of 1.25 mm at the center of the radiator, as well as a succession of circles with a radius of 0.75 mm along the edges of the radiator. In addition, the ground plane is situated at a lower elevation and features a U-shaped truncation that has been etched onto its surface. The expansion of the impedance bandwidth can be accomplished by making adjustments to the radiator and ground plane. The UWB antenna under consideration possesses a geometric configuration of 21.6 × 20.8 × 1.6 mm3 and the antenna is fabricated using an FR-4 glass epoxy substrate. The UWB antenna operates throughout the frequency range of 2.2–16.5 GHz, exhibiting a gain of at least 3.45 dBi across the entire impedance bandwidth and the maximum peak gain of 9.57 dBi achieved at the mid-resonance frequency of 10.5 GHz. The investigation of the antenna’s physical properties is conducted utilizing characteristic mode analysis. The investigation also includes an analysis of the time-domain characteristics, revealing that the group delay was found to be less than 1 ns across the operational frequency range. The predicted and measured findings demonstrate consistency and confirm that the suggested antenna is suitable for electronic systems and wireless applications.

A Pick‐and‐Place Technology Enabled, Mechanically Programmable, Spiral Optical Waveguides Integrated Hybrid Circuits from Four Extremely Pseudo‐Plastic Organic Crystals for Visible Spectral Band Tunability

AbstractIn the field of silicon photonics, highly compact and miniature high‐density circuits are achieved by precisely shaping millimeter‐long waveguides into spiral configurations. Organic photonics, on the other hand, takes advantage of mechanically flexible crystal spiral waveguides (SWs) within organic photonic circuits. These SWs offer versatility, enabling precise control over light paths and mechanical programmability. This study introduces an innovative pick‐and‐place technique for constructing various organic spiral waveguides (OSWs) with different geometries, such as Cornu, Archimedean, elliptical, rectangular, four‐sided polygons, and three‐sided polygons. Additionally, this method allows for the creation of optically reprogrammable photonic circuits. Custom‐synthesized flexible crystals are used, including blue‐emitting (Z)−3‐(4‐(9H‐carbazol‐9‐yl)phenyl)−2‐(3,5‐bis(trifluoromethyl)phenyl)acrylonitrile (Cz‐2CF3), green‐emitting (E)−1‐(((5‐bromopyridin‐2‐yl)imino)methyl)naphthalene‐2‐ol (BPyIN), cyan‐emitting 9,10‐dibromo anthracene (DBA), and red‐emitting 4,7‐bis(4‐octylthiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (BTD). Systematically integrating a Cz‐2CF3 OSW (with two ports for optical signal routing in clockwise/counterclockwise directions) with DBA and BTD waveguides produces multi‐color hybrid photonic circuits with customizable optical functions, tailored to specific design needs. The number of output ports can be dynamically adjusted through mechanical programming by coupling crystals tip‐to‐tip when replacing the DBA waveguide with a BPyIN waveguide using the pick‐and‐place technology. This mechanically programmable hybrid spiral photonic circuit seamlessly operates across the entire visible spectral bandwidth, making it valuable for various applications, including high‐fidelity sensing, spectrometer components, and intelligent circuitry.

An Inverted Doherty Power Amplifier Insensitive to Load Variation With an Embedded Impedance Sensor in Its Output Power-Combining Network

This article presents an inverted Doherty power amplifier (IDPA) made load insensitive up to 2:1 voltage standing wave ratio (VSWR) across its fractional bandwidth with a very compact wideband impedance sensor embedded in its output power-combining network (OPCN). To correct for load variation, a low-loss tunable resonator (TR) is used to ensure ohmic loads to the main and peaking stages at the center frequency of operation. At off-center frequencies, TR is used to present an ohmic load for the main stage, while a digitally adjustable phase shifter is used to (re)align the main and peaking stage’s current summation in the OPCN. For ohmic load deviations, the main and peaking stage supply voltages and input drives are adjusted to maintain the ideal Doherty’s output power and efficiency profile related to nominal 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Omega}$</tex-math> </inline-formula> loading across the bandwidth. To implement the control of the formerly mentioned technique, a wideband impedance sensor is proposed, which uses the orthogonality of incident and reflected waves and requires only four peak detectors. As proof of principle, a prototype 850–950-MHz IDPA featuring the proposed correction technique, the impedance sensor, and the control loop has been implemented as a printed circuit board (PCB) demonstrator. Measurement results show that the IDPA can maintain constant output power with a tolerance of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\pm}$</tex-math> </inline-formula> 0.2 dB while improving the drain efficiency and linearity across the entire fractional bandwidth (11 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\%}$</tex-math> </inline-formula> ) for a VSWR range of 2:1.

Rainbow link beamforming technology and relevant analysis

In the 5G era, millimeter wave has been mentioned as an important position. Millimeter wave has some problems that cannot be ignored: the free space path loss and atmospheric attenuation. To overcome these problems, millimeter wave systems rely on beamforming to overcome losses. Traditional techniques utilize phase antenna arrays for beamforming, which can cause delays in the time consumption and beam scheduling, and due to limited beams, this technology can only be connected to a limited number of devices, and each transmission occupies the entire bandwidth. This paper introduces a new technology called rainbow link, which is implemented by a new true time delay (TTD) array structure. This technology can achieve the allocation of different subcarriers to a large number of users in the corresponding beamforming direction. Users only need to select appropriate frequency resources. In this work, we calculate the performance of rainbow link with different parameters, and our results show that given 1 GHz bandwidth using 64 element antenna arrays, a rainbow-link cell achieves 1ms latency and 0.6M symbols per second with 0.03 active user rate.

Design and Optimization of a Compact Super-Wideband MIMO Antenna with High Isolation and Gain for 5G Applications

This paper presents a super-wideband multiple-input multiple-output (SWB MIMO) antenna with low profile, low mutual coupling, high gain, and compact size for microwave and millimeter-wave (mm-wave) fifth-generation (5G) applications. A single antenna is a simple elliptical-square shape with a small physical size of 20 × 20 × 0.787 mm3. The combination of both square and elliptical shapes results in an exceptionally broad impedance bandwidth spanning from 3.4 to 70 GHz. Antenna dimensions are optimized using the trust-region algorithm to enhance its impedance bandwidth and maintain the gain within a predefined limit across the entire band. For that purpose, regularized merit function is defined, which permits to control both the single antenna reflection response and gain. Subsequently, the SWB MIMO system is constructed with four radiators arranged orthogonally. This arrangement results in high isolation, better than 20 dB, over a frequency band from 3.4 to 70 GHz band. Further, the system achieves an average gain of approximately 7 dB below 45 GHz and a maximum gain equal to 12 dB for 70 GHz. The system exhibits excellent diversity performance throughout the entire bandwidth, as evidenced by the low envelope correlation coefficient (ECC) (&lt;3 × 10−3), total active reflection coefficient (TARC) (≤−10 dB), and channel capacity loss (CCL) (&lt;0.3 bit/s/Hz) metrics, as well as the high diversity gain (DG) of approximately 10 dB. Experimental validation of the developed SWB MIMO demonstrates a good matching between the measurements and simulations.

A Tunable Dielectric Resonator Oscillator with Phase-Locked Loop Stabilization for THz Time Domain Spectroscopy Systems

Precision microwave measurement systems require highly stable oscillators with both excellent long-term and short-term stability. Compared to components used in laboratory instruments, dielectric resonator oscillators (DRO) offer low phase noise with greatly reduced mechanical complexity. To further enhance performance, phase-locked loop (PLL) stabilization can be used to eliminate drift and provide precise frequency control. In this work, the design of a low-cost DRO concept is presented and its performance is evaluated through simulations and measurements. An open-loop phase noise of −107.2 dBc/Hz at 10 kHz offset frequency and 12.8 GHz output frequency is demonstrated. Drift and phase noise are reduced by a PLL, so that a very low jitter of under 29.6 fs is achieved over the entire operating bandwidth.

OVERLOAD AND TRAFFIC MANAGEMENT OF MESSAGE SOURCES WITH DIFFERENT PRIORITY OF SERVICE

The scheme of dynamic management of traffic and activity of message sources with different priority of service is considered. The scheme is built on the basis of the neuroprognostic analysis model and the gradient descent method. For prediction and early detection of overload, the apparatus of the general theory of sensitivity with indirect feedback and control of activity of message sources is used. The control algorithm is started at the bottleneck of the network node. It uses a recursive prediction approach where the neural network output is referred to as many steps as defined by a given prediction horizon. Traffic with a higher priority is served without delay using the entire available bandwidth. Low-priority traffic will use the remaining bandwidth not used by higher-priority traffic. An algorithm for estimating the maximum available bandwidth of a communication node for traffic with a low service priority has been developed. This approach makes it possible to improve the efficiency of channel use without affecting the quality of service for high-priority traffic.