Ultra-wide Bandwidth Research Articles

Calibration of Aperture Arrays in Time Domain Using the Simultaneous Perturbation Algorithm

Online calibration is desired in antenna arrays of ultrawide bandwidth. This study proposes a time domain calibration method based on the simultaneous perturbation algorithm. Two objective functions were established: power of the received signal at array output; or combination of power and correlation coefficient between the signal at array output and a target signal. For both criteria, the convergence settings require only two measurements at each iteration. One advantage of the method is that the entire signal operation for calibration is performed in the time domain. This is achieved by resolving the effects of distortion on time delay of each channel, which accounts for both amplitude and phase distortions at different frequencies. Therefore, the proposed method significantly increased the calibration efficiency for ultra-wideband antenna arrays. Since time delay coefficients for calibration associated with array elements were determined independently due to characteristic of the simultaneous perturbation, estimation accuracy of the method is tangential to the number of elements in the array, and is mainly dependent on the convergence conditions. This gives the method an additional distinct advantage for calibrating large-scale antenna arrays with ultrawide bandwidth. An estimation accuracy of 99% on time delay adjustments has been achieved and demonstrated.

An Ultrawideband Dual-Polarized Phased Array Antenna for Sub-3–GHz 5G Applications With a High Polarization Isolation

A dual-polarized ultra-wideband phased array antenna with a wide scanning range and high isolation polarization characteristics is presented in this paper. A tightly coupled dipole with an etched slot is proposed as the element antenna, which has a low active input impedance in a wideband and a wide scanning range. Thus, a simple feed strategy without requiring additional external matching networks and baluns could be adopted for the designed scheme. To obtain a large polarization isolation, a capacitively-loaded cross-shaped metallic wall is proposed. It is also helpful to improve the in-band matching by mitigating the bandwidth-limiting loop mode at lower frequencies and removing the undesirable common-mode resonance. As a demonstration, an array is designed with a 4.1:1 bandwidth (0.69-2.88 GHz) and an active VSWR < 3.4 while scanning up to ±45° in the E-, H-, and D-planes. Its polarization isolation is better than 45 dB at the broadside and 35 dB within most of the bandwidth when scanning to ±45° in the E-/H-planes. Its cross-polarization level is more than 51 dB at broadside and 40 dB in scanning up to ±45° in the E- and H- planes. A dual-polarized 8×8 array prototype (64 ports per polarization) is manufactured and evaluated. Results from the experiment demonstrate good agreement between the measurement and design. The designed antenna is scalable, has a high polarization isolation, a wide scanning range, an ultra-wide bandwidth, and a low cost.

Numerical Method for the Design of Compact Adiabatic Devices with Multiple Parameter Variations

In this study, a numerical method for designing efficient adiabatic devices with multiple structural parameter variations (NAMSP) is developed. This method can be applied to a wide range of devices based on adiabatic mode evolution structures. The numerical design complexity of multiple structural parameter variations will be greatly improved compared to the case of a single parameter variation. Therefore, an efficient domain decomposition scheme was originally introduced into the NAMSP method. The proposed method can help compute compact adiabatic guided-wave shapes for these adiabatic devices with multiple structural parameter variations. Adiabatic devices with multiple structural parameter variations are used to connect different complex waveguides, which are often difficult to design using analytical methods. The design involves tapering the width of the two or more core layers at one time; however, this change in the width typically affects the mode both vertically and horizontally. Our numerical method allows the shape of the width variation for each layer that facilitates compact adiabatic mode transformation to be obtained. The efficiency of the adiabatic device that was designed using the NAMSP method considerably exceeds that obtained using a linear-shaped device. Moreover, our designed adiabatic device enables an ultra-wide operating bandwidth (spans in the wavelength from 1050 nm to 4780 nm).

A hierarchical SiCnw@SiC aerogel decorated with Ni-capped carbon nanotubes toward high-performance electromagnetic wave absorber

Increasing attention has been paid to the regulation of electromagnetic parameters by reasonable micromorphological design and proper composition to realize high-performance electromagnetic wave absorbers. Herein, a unique hierarchical SiC nanowire-reinforced SiC aerogel decorated with Ni-capped carbon nanotubes (SiCnw@SiC-Ni@CNT) was constructed. The effective synergism between the combination of multiphase magnetic/dielectric materials and the introduction of specific 3D hierarchical microstructures is beneficial for the apparent improvement of multiple dielectric/magnetic losses, electromagnetic scattering effects, and impedance matching capabilities, exhibiting remarkable tunable microwave absorption performance. Accordingly, a strong microwave absorption intensity (RLmin) at 10.24 GHz of −47.75 dB with a loading of 20 wt% and an ultrawide effective absorption bandwidth (EAB, RL < −10 dB) of 8.96 GHz (9.04–18.0 GHz) at only 30 wt% filler loading and thin 2.0 mm thickness are realized. This work provides valuable guidance for the design of multiphase magnetic/dielectric absorbers with hierarchical microstructures and extends the study of advanced microwave absorption materials with the advantages of light weight, minimal thickness, strong RL and broad EAB.

A 345-GHz Sideband-Separating Receiver Prototype With Ultra-Wide Instantaneous Bandwidth

In this paper, we present a sideband-separating (2SB) receiver prototype for operation between 300 and 360 GHz with ultra-wide instantaneous bandwidth. This was achieved using wide bandwidth superconductor–insulator–superconductor (SIS) mixer designs and intermediate frequency (IF) components, including a multi-octave IF hybrid placed outside the cryostat. We tested the prototype with a 3-junction SIS device from the wideband Submillimeter Array (wSMA) high-band receiver, as well as a newly designed 1-junction device. Our measurements demonstrated that the prototype receiver had a usable IF range of 4–13 GHz with the 1-junction device and 4–17 GHz with the 3-junction device. The measured single-sideband noise temperatures were 96±8 K from 312 to 363 GHz with the 1-junction device and 109±14 K from 314 to 367 GHz with the 3-junction device. Over the same frequency range, the image rejection ratio was above 12.3 dB and 11.0 dB for 90% of the data points with the 1-junction and 3-junction devices, respectively. We have identified methods to further enhance the performance of this prototype and we believe that an upgraded receiver can provide a usable IF bandwidth up to 4–20 GHz.

Innovative method of broad banding a helical-TWT

A new method of broad banding a helix TWT is suggested in which, instead of shaping the dispersion characteristics of helical structure by using tapered geometry dielectric helix-support rods, a two-stage dielectric loading is provided by severing the structure in two sections each with a conventional helix supports here typically of wedge cross section. One of the sections was heavily dielectric loaded compared to the other section so that two gain peaks on the frequency scale occur in the former section unlike in latter in which a single gain peak occurs. The structure parameters of the two sections and the beam parameters were so adjusted that the gain peak of lightly loaded section falls between the two gain peaks of the heavily loaded section resulting in ultra-wide bandwidths of the proposed two-stage device. In addition to the well-known Pierce’s gain formula, the basic sheath-helix model of the structure was used in the process of developing this method. Research has been done to investigate whether or not a positive stage speed tightening might help to enhance the display of a broadband helix voyaging wave tube.

Design of a photonic crystal fiber polarization beam splitter with simple structure and ultra-wide bandwidth

A novel polarization beam splitter (PBS) based on dual-core photonic crystal fiber (DC-PCF) is proposed in this work. The proposed DC-PCF PBS contains two kinds of lattices and three kinds of air holes to form the asymmetrical elliptic dual-core structure. By using the full-vector finite element method, the propagation characteristics of the proposed DC-PCF PBS are investigated. The simulation results show that the bandwidth of the proposed DC-PCF PBS can reach to 340 nm, which covers the S + C + L + U communication bands, the shortest splitting length is 1.97 mm, and the maximum extinction ratio appears near wavelength 1550 nm. Moreover, the insertion loss of the proposed DC-PCF PBS is very low. It is believed that the proposed DC-PCF PBS has important applications in the field of all-optical communication and network.

BSA-OMP: Beam-Split-Aware Orthogonal Matching Pursuit for THz Channel Estimation

Terahertz (THz)-band has been envisioned for the sixth generation wireless networks thanks to its ultra-wide bandwidth and very narrow beamwidth. Nevertheless, THz-band transmission faces several unique challenges, one of which is beam-split which occurs due to the usage of subcarrier-independent analog beamformers and causes the generated beams at different subcarriers split, and point to different directions. Unlike the prior works dealing with beam-split by employing additional complex hardware components, e.g., time-delayer networks, a beam-split-aware orthogonal matching pursuit (BSA-OMP) approach is introduced to efficiently estimate the THz channel and beamformer design without any additional hardware. Specifically, we design a BSA dictionary comprised of beam-split-corrected steering vectors which inherently include the effect of beam-split so that the proposed BSA-OMP solution automatically yields the beam-split-corrected physical channel directions. Numerical results demonstrate the superior performance of BSA-OMP approach against the existing state-of-the-art techniques.

Novel Fine-Tuned Attribute Weighted Naïve Bayes NLoS Classifier for UWB Positioning

In this paper, we propose a novel Fine-Tuned attribute Weighted Naïve Bayes (FT-WNB) classifier to identify the Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) for UltraWide Bandwidth (UWB) signals in an Indoor Positioning System (IPS). The FT-WNB classifier assigns each signal feature a specific weight and fine-tunes its probabilities to address the mismatch between the predicted and actual class. The performance of the FT-WNB classifier is compared with the state-of-the-art Machine Learning (ML) classifiers such as minimum Redundancy Maximum Relevance (mRMR)- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> -Nearest Neighbour (KNN), Support Vector Machine (SVM), Decision Tree (DT), Naïve Bayes (NB), and Neural Network (NN). It is demonstrated that the proposed classifier outperforms other algorithms by achieving a high NLoS classification accuracy of 99.7% with imbalanced data and 99.8% with balanced data. The experimental results indicate that our proposed FT-WNB classifier significantly outperforms the existing state-of-the-art ML methods for LoS and NLoS signals in IPS in the considered scenario.

Self-assembled hollow bowl-shaped metal-organic framework-derived electromagnetic wave absorbers with strong anti-microbiologically influenced corrosion performance

The electromagnetic wave absorbers widely applied to various harsh scenes, especially with anti-corrosion properties have been reported and the focus was at the anti-inorganic corrosion. However, the organic corrosion, such as microbiologically influenced corrosion is also serious and needs to be overcome. Herein, based on the excellent electromagnetic synergy effect, a series of cobalt-based metal-organic framework-derived composites with hollow bowl-shape were synthesized. By modulating the balance between the dielectric and magnetic loss, the minimum reflection loss of − 52.66 dB with matching thickness of 2.7 mm and an ultra-wide effective absorption bandwidth of 6.8 GHz, which covered the whole Ku band, with a thickness of 2.4 mm, were achieved. In addition, the radar cross section values of the composites were simulated and the results verify the excellent absorption performances of the absorbers. Combining the prominent absorption performance, the derived composites exhibited exceptional anti-microbiologically influenced corrosion properties reflected by the electrochemical impedance modulus at 0.01 Hz substantially increasing more than 3 times. Until now, no similar bifunctional materials have been reported, so it is of great significance and emergence to fill this gap, we hope our work can provide a theoretical basis for the following related experimental research.

A compact antipodal vivaldi antenna for modern surveillance systems

ABSTRACT Recent breakthroughs in modern surveillance systems combined with stealth and jamming technologies have led to the development of high-directional and high-gain antennas. This paper presents a compact-sized antipodal Vivaldi antenna (AVA) consisting of an elliptical shaped radiating flare with rectangular slots at the flare edges for modern surveillance systems. The proposed antenna provides improvements in the antenna characteristics, including a higher front-to-back ratio, increased main lobe gain, reduction in the side lobe level (SLL), and lower frequency limit. The results reveal that at 20 GHz, an improved gain of 3.8 dB and a front-to-back ratio of more than 40 dB have been realised. Additionally, in contrast to the antenna without edge slots, the impedance bandwidth, |S11| < −10 dB of 15 GHz, and a reduction in the lower operating frequency by 36.7% have also been achieved. The prototype antenna is developed and tested to verify with simulation results. The proposed antenna with the miniaturised structure may be suitable for surveillance applications in modern radar systems because of its ultrawide fractional bandwidth, high directive gain, and reduced SLL.

Deep learning accelerated discovery of photonic power dividers

Abstract This article applies deep learning-accelerated inverse design algorithms and discovers a spectrum of photonic power dividers with exceptional performance metrics despite the simplicity in the design geometry. The deep learning models exhibit high precisions on the order of 10−6 to 10−8 for both TE and TM polarizations of light. These models enable ultrafast search for an empirically describable subspace that simultaneously satisfy compact footprints, ultralow losses, ultrawide bandwidth, and exceptional robustness against fabrication randomness. We demonstrate a spectrum of devices for silicon photonics with programmable power splitting ratios, excess losses as small as 0.14 dB, to the best of our knowledge, the smallest footprints on the scale of sub-λ 2, and low loss bandwidths covering the whole telecommunication spectrum of O, S, E, C, L and U-bands. The robustness of the devices is statistically checked against the fabrication randomness and are numerically verified using the full three-dimensional finite difference time domain calculation.

Indoor Localization Based on Factor Graphs: A Unified Framework

Indoor localization is of pivotal significance for a wide variety of services in the context of the Internet of Things (IoT). Both ranging-based and fingerprint-based localization techniques are promising for employment in harsh indoor environments. Hence, we propose a unified framework based on factor graphs for ubiquitous high-accuracy indoor localization. Our unified framework efficiently integrates ranging and fingerprinting for striking an appealing accuracy versus deployment cost tradeoff, where the crowdsourcing required for the construction of fingerprinting databases can also be addressed with little human intervention. By intrinsically amalgamating the global grid sampling and the regularized importance-resampling techniques, a nonparametric belief propagation algorithm is proposed for achieving the accurate position estimation at the cost of a moderate computational complexity. For improving the robustness to environmental variations, a likelihood-ratio-based approach is employed to detect ranging outliers. Moreover, a low-complexity serial scheduling scheme defined over factor graphs is designed for real-time localization. We design a hybrid ultrawide bandwidth and Wi-Fi localization system relying on off-the-shelf commercial devices and evaluate the proposed unified framework in a typical office building. Our experimental results show that the proposed algorithm outperforms the existing state-of-the-art methods and it is capable of achieving submeter localization accuracy.

Wide Bandwidth Ratio of 10-to-1 CPW-Fed Whip Antenna With Improved Radiation Patterns

In this communication, a novel compact single whip wideband antenna with an improved omnidirectional wideband antenna is proposed. First, a single whip antenna is designed on a thin flexible printed circuit (FPC) with a tapered coplanar waveguide feed line. This proposed antenna shows a wide impedance matching performance in a frequency range from 194 to 2124 MHz with a bandwidth ratio of 10:1, while a measured return loss is better than 10 dB within the desired passband. The single whip antenna has demonstrated an ultrawide bandwidth with satisfactory radiation properties in the lower frequency band. However, the omnidirectional radiation pattern deteriorated in the higher frequency band. Three whipped antennas are codesigned to form an improved omnidirectional radiation pattern. Finally, the measured performance of the fabricated antenna shows a good agreement with that obtained through simulation results.

Ultralight melamine foam derived metal nanoparticles encapsulated CNTs/porous carbon composite for electromagnetic absorption

Three-dimensional (3D) porous carbon materials have emerged as potential microwave absorption candidates due to their unique advantages of high specific surface area and high porosity. However, much less attention has been paid to enhance the performance by designing microstructures. In this work, metal nanoparticles encapsulated carbon nanotubes/carbonized melamine foam composites were successfully synthesized by a simple chemical and pyrolysis method. The microstructure and microwave absorption properties are investigated, and the magnetic/dielectric loss mechanism is studied furtherly. During the pyrolysis process, metal nanoparticles encapsulated carbon nanotubes in-situ growth on 3D porous carbon derived from melamine foam. The metal component and CNTs morphology could be regulated by changing the precursor concentration and that further tuning the absorption performance. Ascribed to multiple interface reflections, dielectric/magnetic loss, multiple polarization behavior and improved impedance matching, the CNTs/CF-3:0 composite achieves a strong reflection loss (− 75.4 dB at 5.2 GHz) and ultra-wide response bandwidth (4.1–18.0 GHz with RL value over − 10 dB). Such a 3D network framework realizes the low density. These results may generate interest and inspiration for the elaborate design and synthesis of submicron-scale structures of 3D porous carbon-based absorbing materials.

3D skeletal porous nanocage of ternary metallic oxide with excellent electromagnetic wave absorption

With the development of radio technologies, great efforts have been made to manufacture high-performance electromagnetic wave (EMW) absorbers for electronic information security, anti-reconnaissance stealth and human health protection. Reaching both excellent impedance matching and electromagnetic (EM) energy dissipation at the same time is still a challenge for EMW absorption materials. In this study, a 3D skeletal porous nanocage structure made from Co-Fe-Ni ternary metal oxide (CFN-TMO) was designed to simultaneously improve the impedance matching and guarantee sufficient EM energy dissipation of the EMW absorber. The integrity of the 3D skeletal nanocage structure and pore size on the cage wall can be tailored by the calcination temperature to optimize its EMW absorption capability. With a suitable pore size and complete skeleton structure, the best performance of the nanocage reaches a high reflection loss (RL) of −67.2 dB and an ultra-wide effective absorption bandwidth (EAB) of 8.2 GHz. The outstanding EMW absorption performance is mainly attributed to the nanocage structure, which can optimize the impedance matching and trigger multiple reflections of the EMWs. The skeleton constructed with the Co-Fe-Ni ternary metal oxide can improve the EMW dissipation by introducing a large number of interfaces, lattice defects and oxygen vacancies. This work reveals a nanostructure design route for optimizing the impedance matching, which can greatly increase the EMW absorption and provide important guidelines for the design and fabrication of lightweight and high-performance EMW absorption nanomaterials.

Direct-spun CNT textiles for high-performance electromagnetic interference shielding in an ultra-wide bandwidth

Electromagnetic interference (EMI) generated by electronic devices is disruptive to surrounding electronic components and deemed harmful to human beings. As high-speed, miniaturized mobile devices become ubiquitous, developing lightweight, thin, and flexible electromagnetic shielding materials (ESMs) to replace the common metallic ones is of utmost importance. Here we report the development of a high-efficiency standalone ESM made of a self-standing CNT mat (CNTM). This textile is electrically conductive (∼50 × 103 S m−1) and can be post-treated by chemical oxidation or thin copper metalization, increasing the conductivity by ∼10 and ∼1000 times, respectively. CNTMs were tested for shielding effectiveness (SE) in an ultra-wide bandwidth of 30 kHz–70 GHz. Maximal SE of >120 dB was measured for a 30 g m−2 CNTM (<100 μm thickness) at 70 GHz. SE normalized by thickness (SE/t) reached a value of >20,000 dB cm−1 for an HCl-oxidized CNTM. Both SE values are the highest values for non-metal-based ESMs. The CNTMs' experimental EMI shielding behavior corresponds to Schelkunoff's theory which confirms that the CNTM SE is dominated by conductivity-dependent reflection at lower frequencies (<1 GHz) and thickness-dependent absorption at higher frequencies. CNTMs (20 g m−2) were utilized as EMI gaskets and in composite EMI enclosures, tested at 10–50 GHz and 50 MHz-90 GHz, respectively. EMI CNT gaskets reached an SE of 120.9 dB at 50 GHz, surpassing the performance of high-end commercial gaskets (600 g m−2). EMI composite boxes laminated with CNTMs reached an SE of 119.9 dB at 90 GHz, outperforming the non-CNT laminated reference.

Design and simulation of a novel miniaturized printed antenna with ultra-wideband and high gain for millimeter-wave wireless applications

The goal of this work is to create a new patch antenna array with a standard gain, broadband, unidirectional radiation pattern, and high efficiency, making it a viable contender for millimeter-wave wireless applications. This study begins with a simple single-patch antenna that has four key components to provide effective matching and a wide impedance bandwidth: elliptical lateral edges, vertical stubs, slots expressed in concavity, and notches. The ground plane was defect-free, and the patch was printed on a Rogers RT5880 substrate. The performance of the proposed antenna can be improved using array topologies of 1×2 and 2×2 patches, for which a corporate feed network was built for excitation. The suggested 2×2 array antenna with a compact size of 18x16.1 mm2 achieved a gain of 13.8 dB, 92% efficiency, a return loss of-34.8 dB, and an ultra-wide bandwidth of 12.2 GHz (ranging from 39.9 to 52.1GHz) at a resonant frequency of 43.2. It’s a novel compact 2×2 array antenna appropriate for miniature devices is suggested using CST studio software, which gathers all qualities together, including high-gain, radiation efficiency, and ultra-wideband. The planned antenna operating frequency range runs from 27 to 58 GHz, which encompasses multiple frequency bands, such as V, Q, and Ka.

Ultra-Wideband Dual-Polarized Base-Station Antenna With Stable Radiation Pattern

This communication presents an ultrawideband dual-polarized antenna consisting of a main radiator, parasitic elements, and a ground plane. The main radiator is composed of two pairs of dual dipoles, which are cross-arranged and fed by coplanar-strip lines in order to achieve <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm \mathrm{45}^{\circ }$ </tex-math></inline-formula> dual-polarization within a wide frequency band. Parasitic elements, including a circular patch and four pairs of dipole strips, are employed for improving the radiation performance in high frequencies, which is very essential for stabilizing the radiation pattern over the entire bandwidth. The proposed antenna can cover the frequency range from 1.7 to 5.1 GHz for both polarizations, corresponding to an ultrawide bandwidth of 100%. The gain and half-power beamwidth (HPBW) are very stable within the entire bandwidth, which are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.2~\pm ~0.7$ </tex-math></inline-formula> dBi and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{65}^{\circ }\pm \mathrm{5}^{\circ }$ </tex-math></inline-formula> , respectively. The measured results agree well with simulated ones, indicating that the proposed antenna is a very promising candidate for the future base-station communication system.

A Low-Loss Impedance Transformer-Less Fish-Tail-Shaped MS-to-WG Transition for K-/Ka-/Q-/U-Band Applications

This paper presents a low-loss, high-transmission, broadside-coupled, transverse, reciprocal, two-port, and nature-inspired Ka-band transition design to move the electromagnetic energy of a rectangular waveguide (RWG) to the microstrip (MS) line. The proposed transition is simple in structure, with an excellent insertion loss, S12/S21, (IL) near −0.40 dB and return loss, S11/S22, of &lt;−21 dB, while the VSWR value is very close to one. Thus, this transition is an outstanding candidate for MIC/MMIC-based millimeter wave, military, and RADAR applications, as well as in wireless and satellite communications as a compatible connector. This transition also provides a bandwidth of 21.50 GHz (23.52–45.0 GHz) for the abovementioned microwave applications, at a &lt;−10 dB return loss (RL). The proposed transition model also exhibits a −15 dB absolute bandwidth of 27.06–23.44 GHz, with an insertion loss &lt; −0.60 dB. Due to a return loss of &lt;−15 dB over an ultra-wide bandwidth, the proposed transition is not only a good candidate for full Ka-band (26–40 GHz) applications but also covers applications for K-band from 23.74 GHz to 26.0 GHz, Q-band applications from 33.0 to 45.0 GHz, and U-band applications from 40.0 GHz to 45 GHz, with approximately 97% power transmission between the transmission lines and only 3% power reflections. The impedance matching at the designed frequency between the RWG and MS line is achieved by flaring one end of the MS line inside the RWG in a fishtail shape, without the need for a quarter-wave/tapered/exponential/Binomial, or multi-section Chebyshev transformer. The main goal of this research was to design a multi-section impedance-transformer-free, simple, and easy-to-fabricate MS line, to share electromagnetic (EM) energy between an MS line and RWG in 30 GHz satellite applications and 30 GHz high-frequency applications, for interconnects screen printed on an organic substrate for flexible, wearable, textile conformal antennas. This work also presents an exact RLC electrical equivalence model of the MS line (fishtail) to RWG transition at 30 GHz. The novelty of this work is that the proposed transition can be used for four microwave bands of electromagnetic energy transmission, with extremely low reflection, and with a compact, simple-design MS line, and simple RWG.