Amplitude Balance Research Articles

A 0.6-dB Low Loss and 3–165 GHz Wideband Phase Difference Sub-THz Coupler in 0.18-μm CMOS

In this letter, a new 90° coupler with a symmetric coupled-line structure featuring the use of the tuning multiple floating metals technique is designed, analyzed, and verified for subterahertz (THz) applications; this new coupler was fabricated on the standard Taiwan Semiconductor Manufacturing Company (TSMC) 0.18-μm 1P6M CMOS process. With the proposed structure, the impedances of even and odd modes can be designed individually to simultaneously optimize the performance in terms of insertion loss, phase balance, amplitude balance, isolation, and reflection coefficients. The bandwidths of phase imbalance (± 3°) and amplitude imbalance (± 1 dB) are 162 and 100 GHz, respectively. Reflection coefficients less than -20 dB are reached at 0.2-184 GHz, and isolation higher than 20 dB is from 0.2 to 200 GHz.

Enhancing potential field data using its dip angle

ABSTRACTThe dip angle of a seismic horizon is a commonly used attribute of seismic data. It has the useful property that it is almost independent of the amplitude of the features being analysed. When appropriately rescaled, it can also be a useful edge detector for potential field data. Rescaling is necessary because the gradients of potential field data are not dimensionless. The rescaling also allows the amplitude balancing effect to be controlled, which is useful when poor quality data are being processed. The dip angle of synthetic data and aeromagnetic data from South Africa are analysed and the filter is found to be effective.

Deep-learning for accelerating prestack correlative least-squares reverse time migration

Prestack least-squares reverse time migration based on a correlative objective function denoted as PCLSRTM can retrieve a higher quality image of the subsurface than standard least-squares reverse time migration based on a waveform-matching objective function. However, to invert the optimal migration images of different shots via a gradient-based iteration scheme, PCLSRTM tends to require a huge computational overhead for a large number of reverse time migration (RTM) and reverse time de-migration operators. We introduce a convolutional neural network (CNN) framework to improve the computational efficiency in PCLSRTM. Specifically, the CNN architecture aims to reconstruct the optimal reflection image for a single-shot recording from the standard RTM image. Besides, the migration model can be used as an additional input of CNN architecture. Limited by the absence of true reflectivity of the subsurface as the label data in seismic imaging, we employ the standard PCLSRTM images of a small part of total shot recordings as the labels to train the constructed CNN model. There are two benefits for the well-trained CNN model. On the one hand, it can directly invert a comparable image quality with the PCLSRTM image at a low computational cost, when the migration model does not contain a strong lateral velocity variation. On the other hand, one can use the inverted image from the well-trained CNN model as the initial image of the PCLSRTM approach to accelerate convergence. Through synthetic experiments with the Marmousi-2 and SEG/EAGE salt models and marine field data, it can determine that our approach can build a reflection image with balanced amplitude and good continuity and merely requires about one-ninth to one-fourth of the computational costs of PCLSRTM.

The effect of TRX suspension trainer and BOSU platform after reconstruction of anterior cruciate ligament of the knee joint

Background and Study Aim. The tear of the anterior cruciate ligament of the knee joint is experienced by people of all ages for a variety of reasons. The physiotherapy procedures with different equipment help recover lost functions. The aim of this research was to determine the effect of ‘TRX’ (Total body Resistance eXercise) suspension trainer and platform ‘BOSU’ (Both Sides Utilized) after anterior cruciate ligament of knee joint reconstruction.
 Material and Methods. The study included 20 patients after anterior cruciate ligament reconstruction surgery, 13 women, age (31.7 ± 3.4) and 7 men, age (31.7 ± 3.5) participated in the assessment. The strength of the calf flexors and extensors muscles was assessed by Lovett scale. The range of motion of the knee joint was assessed by goniometer. The static and dynamic body balance was assessed by Fullerton Advanced Balance Scale. The stability of the knee joint was assessed by Lachman test. The statistical data reliability was evaluated using Student's T criterion.
 Results. The data obtained showed that stabilization exercises with ‘TRX’ suspension trainer ant platform ‘BOSU’ have positive effect on knee joint after reconstruction. In the first and second group strength of the calf flexors and extensors muscles, amplitude of knee joint, static and dynamic balance significantly increased (p<0.05). Knee joint stability increased. Comparing both groups’ results, there are no statistically significant difference (p>0.05). 
 Conclusions. Physiotherapy exercises with TRX suspension trainer and platform ‘BOSU’ can help patients to return lost muscles strength, knee joint amplitude, static and dynamic balance and knee joint stability.

Broadband unidirectional transverse light scattering in a V-shaped silicon nanoantenna

The efficient manipulation of light-matter interactions in subwavelength all-dielectric nanostructures offers a unique opportunity for the design of novel low-loss visible- and telecom-range nanoantennas for light routing applications. Several studies have achieved longitudinal and transverse light scattering with a proper amplitude and phase balance among the multipole moments excited in dielectric nanoantennas. However, they only involve the interaction between electric dipole, magnetic dipole, and up to the electric quadrupole. Here, we extend and demonstrate a unidirectional transverse light scattering in a V-shaped silicon nanoantenna that involves the balance up to the magnetic quadrupole moment. Based on the long-wavelength approximation and exact multipole decomposition analysis, we find the interference conditions needed for near-unity unidirectional transverse light scattering along with near-zero scattering in the opposite direction. These interference conditions involve relative amplitude and phases of the electromagnetic dipoles and quadrupoles supported by the silicon nanoantenna. The conditions can be applied for the development of either polarization- or wavelength- dependent light routing on a V-shaped silicon and plasmonic nanoantennas.

Direct expansion of Fourier extrapolator for one-way wave equation using Chebyshev polynomials of the second kind

The Fourier method for one-way wave propagation is efficient but potentially inaccurate in complex media. The implicit finite-difference (FD) method can handle arbitrarily complex media, but it can be inefficient in 3D and has limited dip bandwidth. We have adopted a new Fourier method based on the Chebyshev expansion of the second kind. Theoretical analyses and numerical experiments indicate that our method is comprehensively superior to a similar method based on the Chebyshev expansion of the first kind in terms of balanced amplitude and error tolerance. Within the dip bandwidth from 0° to 65°, the fourth-order form of our method has an error tolerance of 2%, which is approximately one-third that of the Chebyshev expansion of the first kind. Our method also is superior to the implicit FD method in several important aspects: effective bandwidth, computational efficiency, numerical dispersion, and two-way splitting error. It can be easily extended from 2D to 3D compared with the FD method and from low orders to high orders compared with the optimized Chebyshev-Fourier method. Our method finds better imaging results of the SEG/EAGE model by providing a well-focused salt dome, flank, and bottom as well as the detailed structures beneath the salt body, compared with the implicit FD method and the Chebyshev expansion of the first kind; meanwhile, our method has fewer imaging artifacts because it can better position the reflectors.

NHF as an Edge Detector of Potential Field Data and Its Application in the Yili Basin

Edge enhancement is a frequently used transformation of potential field data. Its goal is to sharpen the position of the subsurface structures. Here we propose a new method to enhance the edges of the sources causing the potential anomalies called normalized Harris filter (NHF), which is based on the Harris filter and amplitude balance. Three synthetic data sets are used to evaluate the performance of the proposed approach. The presented approach provides a better estimation of the sources’ edges when compared to the other methods. The proposed method is robust to noisy data and can avoid the generation of artificial edges, thereby reducing the ambiguity of interpretation. The testing on real data set from the Yili basin in Northwestern China demonstrates that the new approach highlights several anomalies not shown in the geological map or other methods. The proposed approach also shows the advantages of gradually enhancing the edges of the deep-seated structure. The results demonstrate that the proposed approach may be a better detector in qualitatively determining the edges of sources causing potential field data.

Ultra-Wideband Compact Millimeter-Wave Printed Ridge Gap Waveguide Directional Couplers for 5G Applications

A compact ultra-wideband printed ridge gap waveguide directional couplers for millimeter-wave applications are presented in this paper. A multi-layer coupling technique between two resonant patches is adopted to achieve a wider operating bandwidth with better amplitude and phase balance compared to single-layer technology. For this purpose, a systematic design procedure is deployed to achieve several coupling values in the range of 3-10 dB over a wide frequency bandwidth centered at 30 GHz. A 3-dB hybrid coupler is fabricated and measured, where a bandwidth of 12 GHz (about 38 % fractional bandwidth) from 25 GHz to 37 GHz is achieved. In addition, the phase balance is 90° ± 5° over 38% fractional bandwidth with an amplitude balance of 3.4 ± 0.5 dB over a 26.5% centered at 30 GHz. The proposed couplers with superior characteristics such as compactness, low loss, and low dispersion are considered a good candidate for millimeter-wave applications such as the fifth-generation (5G) wireless communications.

A Dual-Mode SIW Compact Monopulse Comparator for Sum and Difference Multibeam Radar Applications

In this letter, a compact wideband substrate integrated waveguide (SIW) monopulse comparator is proposed. The TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> modes of an SIW transmission line are used to generate in-phase and out-of-phase excitation fields for the sum and difference beams without complex phase shift network. The monopulse comparator can realize maximum 0.4-dB amplitude balance, 3.6° phase balance for both sum and difference ports, and −37.0-dB isolation coefficient within the operating bandwidth of 9.43–10.65 GHz. In addition, to integrate the monopulse comparator with a low-cost beam scanning capability, six monopulse comparators are used as the sources to excite a flat Luneburg lens. The experimental result demonstrates that ±58° beam coverage range with around −20.0-dB null depth and 15.0-dBi gain can be realized. The advantages of the proposed monopulse multibeam antenna, including low profile, low cost, wide beam scanning range, and wide operating bandwidth, make it a very promising solution for low-cost monopulse radar systems.

3-D Least-Squares Reverse Time Migration in Curvilinear-τ Domain

Curvilinear-grid-based least-squares reverse time migration (LSRTM) can produce an accurate image of complex subsurface structures. However, a huge amount of computational cost of LSRTM makes it difficult in real data applications, especially in 3-D cases. We propose a wavefield continuation operator in a new curvilinear- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau $ </tex-math></inline-formula> domain to make the sampling space in the vertical direction to be uniform by stretching and compressing the low- and high-velocity zones, respectively. An objective function based on a conical wave encoding and student’s <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> distribution is constructed to improve the computational efficiency and robustness of LSRTM. The gradient formula is derived based on the objective function, and to correct the unbiased random estimation error, the idea of random optimization is introduced to obtain a weighted gradient. Demigration and adjoint wave equations in the curvilinear- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau $ </tex-math></inline-formula> domain are derived to calculate the synthetic records and the backward-propagated wavefields. Numerical examples on synthetic and field datasets suggest that the proposed 3-D LSRTM method produces better images with a higher signal-to-noise ratio (SNR), more improved resolution, and more balanced amplitude than the conventional 3-D LSRTM and greatly improves the computational efficiency of 3-D LSRTM.

Population, GDP, and Carbon Emissions as Revealed by SNPP-VIIRS Nighttime Light Data in China With Different Scales

Satellite-based artificial nighttime brightness observations are typically considered proxy measures of socioeconomic indicators at large scales, such as population, gross domestic product (GDP), and carbon emissions. However, few studies have explored and compared the correlations between SNPP-VIIRS nighttime light data and socioeconomic indicators from administrative scale to grid scale, and further analyzed the potential mechanisms for the dissimilar correlations at different grid scales. Using regression model, dissimilarity index, and relief amplitude, the quantitative relationship and potential influence mechanism across different scales was investigated in this letter. Results show that the finer the scale is, the lower the correlations between total nighttime lights (NTL) and socioeconomic indicators when comparing 1 km, town, and county scales. The R² values of the NTL-socioeconomic indicator correlations increase sharply with the increase of grid scale at 1&#x2013;10 km scale. The R² values increase volatilely between 10&#x2013;30 km but are relatively stable above 30 km. The differences in R² values may be attributed to the diversity and distribution balance of industrial types and relief amplitude at different scales. This letter provides new insights into estimating and predicting population, GDP, and carbon emissions by using SNPP-VIIRS data.

Printed Circuit Board Implementation of N-Way Power Combiner With Isolated Input Ports

A planar implementation of N-way radial power combiners with isolated input ports is presented. While keeping the design simple, the presented combiner can be manufactured solely using printed circuit board technology, and as a result, has a low weight and manufacturing cost. As proof of concept, two power combiners are designed and built. First, a 6-way combiner working at the center frequency of 3.1 GHz with a fractional bandwidth of around 30% was designed. Our measurements of the fabricated combiner showed an input and output return loss of better than 10 dB in a frequency band of 2.65-3.55 GHz where an isolation of higher than 23 dB, amplitude balance of ±0.1 dB, and phase balance of ±1 degree between the input ports were obtained. Then, a simple approach was implemented to widen the frequency band, achieving a fractional bandwidth of 80%. According to our measurements, the wideband combiner has an operating frequency band of 1.35-3.15 GHz, in which an input and output return loss of better than 10 dB with an isolation of higher than 21 dB, amplitude balance of ±0.15 dB, and phase balance of ±1 degree were achieved.

3-D Q-Compensated Image-Domain Least-Squares Reverse Time Migration Through Point Spread Functions

Least-squares reverse time migration (LSRTM) has the potential to retrieve a high-resolution subsurface image. However, the standard acoustic LSRTM approach may produce a blurred image, if directly applying it to attenuated seismic recordings. In this letter, we developed a novel 3D Q-compensated image-domain LSRTM approach, denoted as Q-IDLSRTM. The Hessian matrix in the proposed approach is efficiently estimated from the point spread functions (PSFs) which are calculated by a combination of viscoacoustic Born modeling and reverse time migration (RTM) based on the generalized standard linear solid (GSLS) wave equation. The major advantage of the proposed image-domain inversion is that it is much faster than data-domain inversion. The L1 norm constraint and total variation (TV) regularization are used to produce a sparse solution and maintain the structural continuity of the inverted image. We determine the effectiveness of the proposed approach with a part of the 3D Overthrust model and the resulting images demonstrate the ability of our approach to image subsurface structures with enhanced resolution and balanced amplitude relative to the RTM image and inverted image from the acoustic image-domain LSRTM approach.

A Novel Balanced Frequency Tripler With Improved Power Capacity for Submillimeter-Wave Application

This letter reports on the demonstration of a 204-232-GHz Schottky diode frequency tripler based on the novel balanced configuration, which provides superior power handling to traditional approaches. This tripler adopts a novel balanced configuration, which utilizes a symmetrical circuit to achieve the improved amplitude and phase balance, as well as dc bias without any on-chip capacitor. Thus, this tripler features improved power capacity by multiple diodes and better conversion efficiency. At room temperature, the fabricated tripler exhibits a 22.1% peak conversion efficiency for a nominal input power of around 300-560 mW. This tripler can deliver maximum power of 84.5 mW and 16.2% conversion efficiency for 521-mW input power at 226.8 GHz.

Q least-squares reverse time migration based on the first-order viscoacoustic quasidifferential equations

Seismic wave attenuation caused by subsurface viscoelasticity reduces the quality of migration and the reliability of interpretation. A variety of Q-compensated migration methods have been developed based on the second-order viscoacoustic quasidifferential equations. However, these second-order wave-equation-based methods are difficult to handle with density perturbation and surface topography. In addition, the staggered grid scheme, which has an advantage over the collocated grid scheme because of its reduced numerical dispersion and enhanced stability, works in first-order wave-equation-based methods. We have developed a Q least-squares reverse time migration method based on the first-order viscoacoustic quasidifferential equations by deriving Q-compensated forward-propagated operators, Q-compensated adjoint operators, and Q-attenuated Born modeling operators. In addition, our method using curvilinear grids is available even when the attenuating medium has surface topography and can conduct Q-compensated migration with density perturbation. The results of numerical tests on two synthetic and one field data set indicate that our method improves the imaging quality with iterations and produces better imaging results with clearer structures, higher signal-to-noise ratio, higher resolution, and more balanced amplitude by correcting the energy loss and phase distortion caused by Q attenuation. It also suppresses the scattering and diffracted noise caused by the surface topography.

A novel filter for three-phase power factor correction voltage feedback loop under heavy DC voltage ripple condition

THD and the amplitude balance of three-phase input current are an important index for the performance of three-phase power factor correction (PFC). In general, when the hardware and the load of three-phase PFC are confirmed, the THD and amplitude balance of three-phase input current mainly depend on voltage and current feedback loop of PFC. Firstly, this paper designs the traditional voltage and current feedback loop for three-phase PFC according to traditional small signal theory. Secondly, this paper studies the designing difficulty of large dc voltage ripple for PFC voltage controller and puts forward a new dc voltage ripple filter which can eliminate the ac component of sampling dc bus voltage. Finally, this paper proposes a novel filter with dc voltage ripple frequency adaption function to copy with the frequency variety of the voltage ripple caused by the change of the output inverter frequency. With the help of the proposed algorithm the distortion of three-phase 3 input current reference decreases rapidly, therefore, the low THD and good amplitude balance of three phase input current will be achieved.

Microstrip hybrid wideband 10 dB coupler

In this paper, the design, simulation, optimization and testing of a Microstrip Hybrid 10 dB Wideband Coupler was done. The aim of the project was to introduce a new coupler design and to achieve stable operation for as wide bandwidth as possible. For this proposed design simulated results are as follows: 3.8 GHz Bandwidth and Coupling Amplitude balance of 1 dB across it. Coupler is then produced using LPKF ProtoMat 104s machine and it is tested with Vector Network Analyzer at Istanbul Technical University.

Least-squares reverse-time migration with sparsity constraints

Abstract Least-squares reverse-time migration (RTM) works with an inverse operation, rather than an adjoint operation in a conventional RTM, and thus produces an image with a higher resolution and more balanced amplitude than the conventional RTM image. However, least-squares RTM introduces two side effects: sidelobes around reflectors and high-wavenumber migration artifacts. These side effects are caused mainly by the limited bandwidth of seismic data, the limited coverage of receiver arrays and the inaccuracy of the modeling kernel. To mitigate these side effects and to further boost resolution, we employed two sparsity constraints in the least-squares inversion operation, namely the Cauchy and L1-norm constraints. For solving the Cauchy-constrained least-squares RTM, we used a preconditioned nonlinear conjugate-gradient method. For solving the L1-norm constrained least-squares RTM, we modified the iterative soft thresholding method. While adopting these two solution methods, the Cauchy-constrained least-squares RTM converged faster than the L1-norm constrained least-squares RTM. Application examples with synthetic data and laboratory modeling data demonstrated that the constrained least-squares RTM methods can mitigate the side effects and promote image resolution.

Load-tolerant external matching unit based on a wideband hybrid coupler for the ICRH system of DTT

In the first phase of the Divertor Tokamak Test Facility (DTT), the goal of coupling a RF power of 3 MW to the plasma will be reached with a single ICRH module constituted by 4 generators, 2 or 4 External Matching Units (EMU) and 2 antennas. The operation with high levels of RF power into ELMy H-mode plasmas requires a robust and reliable Load-Tolerant EMU. Currently the most appropriate solution, ensuring a VSWR at the generators under the safety threshold of 1.5:1, will be based on a Wideband 2-section coaxial Hybrid Coupler operating in the frequency range of 60−90 MHz. HFSS and CST-MS simulation software was used for the optimization of the characteristic impedances and lengths of the transversal and longitudinal branches aimed to achieve excellent performance (amplitude and phase balance at the output ports, and low reflection at the input port) over the entire frequency range. The analysis has been carried out for Zo = 50 Ω and 30 Ω coaxial transmission lines in terms of S-parameters and electric field. Several good solutions with an amplitude imbalance about ±0.25 dB and a return loss lower than −20 dB in a large part of the frequency range will be presented. Then a simulation of the overall (end-to-end) EMU (Wideband Hybrid Coupler with shifter, stub and service stub in each of the 2 output branches) exploiting a suitable circuital solver of Ansys Electronics tool of HFSS, has been implemented. The resilience of the EMU has been tested determining the VSWR in input and the amplitude balance at the outputs for a typical resistive and reactive loading variation occurring during ELMs at f = 75 MHz and compared with the results at 65 MHz and 85 MHz.

A Terahertz 3dB Waveguide Power Divider with 90° Phase Shifter Integrated

A 3dB power divider is designed based on E-plane waveguide directional coupler and self-compensating waveguide phase shifter. This power divider was implemented with a center frequency at 110GHz. Simulation results show that amplitude balance within ±0.3dB and phase balance within +0.5/-1.2 degrees, and isolation is better than -15 dB from 100 to 120 GHz. It has good performance in-band flatness and bandwidth is 18%. It can be used in terahertz communication system.