Showing papers on "Linear phase published in 2021"

Second-Order Synchroextracting Transform With Application to Fault Diagnosis

Abstract: Synchrosqueezing transform (SST) is a currently proposed novel postprocessing time–frequency (TF) analysis tool. It has been widely shown that SST is able to improve TF representation. However, so far, how to improve the TF resolution while ensuring the accuracy of signal reconstruction is still an open question, particularly for the vibration signal with time-varying instantaneous frequency (IF) characteristics, due to the fact that the vibration signals of mechanical equipment usually contain many types of noise generated by harsh operating conditions, and the SST will mix these noise into the real signal. Our first contribution is using the Gaussian modulated linear chirp (GMLC) signal model to represent the general nonstationary signals. The GMLC signal model can more accurately represent the time-varying nonstationary signal, compared with the SST signal model composed of linear phase function and constant amplitude. Our second contribution in this work is proposing a method to improve the TF resolution and reconstruction accuracy for nonstationary signals with time-varying IF, which we coined the second-order synchroextracting transform (SET2). In SET2, we apply the GMLC to deduce the nonstationary signal model and then only use the energy at the IF to characterize the TF distribution, which improves the TF while reducing the impact of noise on the real signal.

3-D Printed All-Dielectric Dual-Band Broadband Reflectarray With a Large Frequency Ratio

Abstract: This communication proposes a new all-dielectric broadband dual-band reflectarray with a large frequency ratio using low-cost 3-D printing. In contrast to conventional reflectarrays using metallic resonant cells or dielectric slabs as phasing elements with full metal ground, the proposed design uses air as the phasing element and a stepped dielectric mirror structure as the ground. In this way, the metal ground is removed, which makes the design an all-dielectric one. Taking advantage of the dielectric mirror that only exhibits a bandgap in the predesigned band while allowing electromagnetic (EM) waves to pass through it at the frequency out of the bandgap region, a dual-band reflectarray is obtained. By properly selecting the bandgap frequency of the dielectric mirror, the dual-band frequency ratio is scalable and can be very large. Furthermore, instead of using a metallic or dielectric resonator based on resonance, air layers with linear phase response are adopted as the phasing element. Thus, the reflectarray shows broadband and stable performance over the dual-band. Compared with the state-of-the-art works using printed circuit boards (PCBs) or microfabrication, the proposed design is low cost and lightweight, and can be rapidly prototyped. For proof-of-concept, a prototype operating at $K$ -band and $V$ -band with a frequency ratio of 2.7 is printed and measured.

A novel approach for optimal design of digital FIR filter using grasshopper optimization algorithm

Abstract: The idea behind designing digital filters is to compute the optimal filter coefficients such that the magnitude response of the designed matches the ideal frequency response using optimization algorithms. The proposed work employed a recently proposed swarm-based optimization technique, namely, a grasshopper optimization algorithm (GOA) to design a linear phase finite impulse response (FIR) low pass, high pass, band pass , and band stop filters. This proposed algorithm models the behaviour of grasshoppers while seeking food sources to solve optimization problems. For the designing of the FIR filter, an absolute error difference fitness function is used, which is minimized using GOA to obtain optimal filter coefficients. The performance comparison of the proposed work is done with already existing algorithms such as cuckoo search, particle swarm optimization, artificial bee colony to prove its superiority and consistency. It is found that GOA based filter meets the objective efficiently with reduced ripples in pass band and higher attenuation in stop band with least execution time.

A 60-GHz Variable Gain Phase Shifter With 14.8-dB Gain Tuning Range and 6-Bit Phase Resolution Across −25 °C–110 °C

Abstract: This article presents a 60-GHz variable gain phase shifter (VGPS) with orthogonal phase and gain control technique and linear phase control technique in 65-nm CMOS. Using the orthogonal phase and gain control technique, the proposed VGPS has the ability of gain tuning without extra variable gain block, significantly reducing the size of conventional phased arrays. The linear phase control technique is proposed to greatly improve the accuracy and robustness of phase control against temperature variation. As results, the VGPS achieves 6-bit phase resolution across −25 °C to 110 °C and continuous gain tuning range of 14.8 dB. The measured 3-dB bandwidth is 52–64 GHz. As the gain of VGPS is −22.4 to –dB, the measured root-mean-square (rms) phase errors are 1.3°–3.3°, while the measured rms gain errors are 0.2–0.5 dB in 3-dB bandwidth. Across −25 °C to 110 °C, the variations of rms phase and gain errors are below 1.2° and 0.1 dB, respectively. With supply voltage varying from 1.0 to 1.2 V, the variations of rms phase and gain errors are below 1.1° and 0.2 dB, respectively. During the measurement with different combinations of temperature and supply voltage, no gain and phase calibrations are conducted. The measured input-referred $P_{\mathrm {1\,dB}}$ at the maximum gain state (−7.6 dB) is about −3.8 dBm. The chip consumes 16.4 mA from a 1.1-V voltage supply and the core area of the VGPS is $720\,\,\mu \text {m} \times 560 \,\,\mu \text{m}$ .

Planar/Waveguide Quasi-Elliptic Linear-Phase Filters Using Mixed Cascaded Frequency-Dependent Triplets With Extracted Pole Sections

Abstract: This article presents two types of planar/waveguide quasi-elliptic linear-phase filters using mixed cascade frequency-dependent triplets (FDTs) and extracted pole sections (EPSs). Specifically, we propose the circuit synthesis and planar/waveguide realization techniques for quasi-elliptic linear-phase filters using the cascaded FDT and EPS. The circuit synthesis for the proposed filters avoids the complex matrix rotation and special scaling procedures compared with the general matrix synthesis and is directly compatible with lumped-element-based integrated circuit design. Besides, it permits cascading of FDTs and singlet sections thus effectively forming the pseudo-elliptic filter with a linear phase. For physical realization, we present new TEM- and TE-mode coupling configurations, and therefore, the mathematical models can be realized in practice with simple and practical structures. Finally, we present the complete design procedures of the planar configuration cascading two FDTs and waveguide structure cascading two EPSs and FDT to validate the theory.

Broadband continuous beam-steering with time-modulated metasurfaces in the near-infrared spectral regime

Abstract: A time-modulated metasurface integrated with indium-tin-oxide (ITO) can dynamically manipulate the scattered light by imparting dispersionless phase discontinuities with 2π span on wavefronts of the generated sidebands. However, maximal frequency conversion efficiency is restricted to a narrow bandwidth at the vicinity of the resonant wavelength due to the dispersive nature of light–matter interactions in such ITO-integrated metasurfaces. Herein, a multiwavelength time-modulated meta-molecule is numerically investigated, which consists of four metal–insulator–metal meta-atoms that are judiciously designed to support four resonant wavelengths at the near-infrared regime. The metasurface platform allows for application of four sets of independent radio-frequency signals to each meta-molecule, which are optimized to excite the output spectra with dominant first-order up-modulated sidebands. Individual modulation of each meta-atom leads to efficient sideband generation at resonant wavelength corresponding to the biased meta-atom. Nevertheless, the conversion efficiency decays rapidly at off-resonant wavelengths. Concurrent modulation of all four meta-atoms within the meta-molecule configuration offers a pathway to simultaneously generate dominant sidebands at all resonant wavelengths while enhancing the frequency conversion efficiency at inter-resonant wavelengths. As the potential application, beam-steering at the up-modulated sideband by both individually and simultaneously biased meta-atoms is demonstrated. It is revealed that simultaneous modulation enables continuous dynamic light deflection over a broad spectrum spanning on 1–1.8 μm, while the steering angle of the wavelengths changes in the range of 34°–85°. Broadband continuous beam-scanning is a non-trivial task that cannot be accomplished by a quasi-static metasurface relying on dispersive resonant phase shift, which hinders simultaneous implementation of linear phase gradients at all incident wavelengths.

Design of Approximately Linear Phase Low Pass IIR Digital Differentiator using Differential Evolution Optimization Algorithm

Abstract: In this paper, a new design approach of approximately linear phase infinite impulse response (IIR) low pass digital differentiator (LPDD) is proposed and studied. The proposed design is based on a transfer function that has a numerator with anti-symmetric coefficients. To better control the magnitude response of the designed LPDD, the differential evolution (DE) optimization algorithm is used to find the coefficients of the transfer function that meets an appropriate pass band and stop band edge frequencies. The use of appropriate pass band and stop band edge frequencies gives the designer of the LPDD direct control on the width of the transition band. The designed LPDD using the proposed approach has approximately linear phase and much better magnitude response than that of the IIR LPDDs designed using other techniques reported in literature. In addition, the designed LPDD using the proposed approach has steeper roll-off magnitude response and narrower transition band than that of designed IIR and high order FIR LPDDs available in the literature.

Reduction of spatio-temporal phase fluctuation in a spatial light modulator using linear phase superimposition

Abstract: Spatio-temporal phase modulation with a phase-only liquid-crystal spatial light modulator (SLM) plays an important role in the optics and photonics community. SLMs are generally affected by either or both spatial and temporal phase fluctuations, depending on driver electronics, thereby reducing the quality of a generated beam. In this study, to reduce phase fluctuations, we present an optical-based linear phase superimposition method with spatial bandpass filtering. We experimentally investigate the method’s effectiveness, particularly for holographic data storage applications. Experimental results show that the presented method is useful in robustly generating phase distributions against fluctuations, regardless of the SLM driving scheme.

Synthesis of Linear-Phase FIR Filters With a Complex Exponential Impulse Response

Abstract: In this paper, a novel recursive realization method with word length reduced is proposed to synthesize linear-phase FIR filters for arbitrary bandwidth. By exploring the sparsity in the frequency domain, it constructs the desired impulse response with few complex exponential series (CES) and very sparse additional coefficients (AC) with equal length. The design problem is formulated as a combinatorial optimization problem by confining the frequencies of CES to a finite dictionary. To reduce the computational complexity at optimization, an iterative algorithm is presented, where appropriate frequencies of CES and zero locations of AC can be quickly determined. Thereafter, an efficient parallel structure is introduced to implement the proposed filter. To verify the performance of the proposed method, MATLAB simulation and Field-programmable gate array (FPGA) implementation are made. It shows that the proposed method requires 18 bits × 23 bits word length while the existing advanced recursive realization method —the piecewise-polynomial-sinusoidal recursive—needs 59 bits × 59 bits for the same filter specifications. Meanwhile, the method can achieve comparable multiplier reduction compared with the state-of-the-art low-complexity techniques but produce a low extra group delay. Moreover, it can realize variable bandedges with a fixed filter structure.

Generation of vector beams using synthetic phase holograms.

Abstract: We discuss a class of synthetic phase holograms (SPHs) applied to the generation of vector fields. Each SPH encodes the transverse components of the vector field, modulated by different linear phase carriers. Such components, which are spatially separated by the carriers, are modulated by appropriate orthogonal polarizations. A final stage that makes the components collinear allows the generation of the vector field. We assess the efficiency and accuracy of the different SPHs, in the task of generating vector fields. The proposal is illustrated by the implementation of vector Bessel beams, which are experimentally generated in a setup based on a phase spatial light modulator.

Time-Domain Short-Pulse Feeding Network for Monopulse Antenna With High Fidelity

Abstract: A monopulse feeding network is proposed for transmitting and receiving time-domain short pulse with high fidelity. The network consists of coplanar waveguides (CPWs), slotlines, microstrip lines, and transitions. Both the sum and the differential performances of the network depend mainly on the transverse structures of these transmission lines rather than their lengths, providing the capability of short-pulse transmission with high fidelity. Moreover, the normalized Euclid distance is employed to characterize and optimize the time-domain performance of the proposed network. A prototype is designed, fabricated, and measured, and linear phase response and stable transmission coefficient are achieved in ultrawide bandwidth. Time-domain performances are evaluated using an input differential Gaussian pulse, with a frequency spectrum of 4–12 GHz. The fidelity between input and output signals is over 0.96, and the amplitude of received signals is nearly the same, showing potential in short-pulse monopulse applications of the network.

Linear Phase Retrieval for Near-Field Measurements with Locally Known Phase Relations

Abstract: A linear and thus convex phase retrieval algorithm for the application in phaseless near-field far-field transformations is presented. The formulation exploits locally known phase relations among sets of measurement samples, which can in practice be acquired with multi-channel receivers. Due to the linearity of the formulation, a reliable phaseless transformation is achieved, which completely avoids the problem of local minima—the Achilles heel of most existing phase retrieval techniques. Furthermore, the necessary number of measurements are kept close to that of fully-coherent antenna measurements. Comparisons with an already existing approach exploiting local phase relations demonstrate the accuracy and reliability for synthetic data.

Temporal Airy–Talbot effect in linear optical potentials

Abstract: We investigate the Airy–Talbot effect of an Airy pulse train in time-dependent linear potentials. The parabolic trajectory of self-imaging depends on both the dispersion sign and the linear potential gradient. By imposing linear phase modulations on the pulse train, the Airy–Talbot effects accompanied with positive and negative refractions are realized. For an input composed of stationary Airy pulses, the self-imaging follows straight lines, and the Airy–Talbot distance can be engineered by varying the linear potential gradient. The effect is also achieved in symmetric linear potentials. The study provides opportunities to control the self-imaging of aperiodic optical fields in time dimension.

A Low-Complexity Linear-Phase Graphic Audio Equalizer Based on IFIR Filters

Abstract: Digital audio equalization is a very common procedure in the acoustic field that allows to improve the listening experience by adjusting the auditory frequency response. The design of graphic equalizers introduces several problems related to the necessity of implementing high performing filters with linear phase, usually characterized by high computational complexity. This paper proposes an innovative linear-phase graphic equalizer based on interpolated finite impulse response (IFIR) filters. IFIR filters seem to be suitable for a graphic equalizer thanks to their properties. In fact, they can reach very narrow transition bands, however with low computational complexity and linear phase, avoiding ripple between adjacent bands. The proposed IFIR equalizer has been compared with some state-of-the-art methods in terms of frequency response, distortion and computational cost. The experimental results have proved the effectiveness of the proposed equalizer, that has shown a considerable reduction on the computational complexity, meanwhile preserving the performances in terms of audio quality.

Value probability analysis for linear phase estimation in sinusoidal structured-light range imaging.

Abstract: Linear phase estimation is crucial for accuracy of sinusoidal structured-light range imaging. This Letter presents value probability analysis for a continuously differentiable function and shows that the probability of a value of the function is closely related to the derivative of the function. We apply the value probability analysis to the intensity, phase, and intermediate values in sinusoidal structured light, and we show that the probability adjustment of phase is more effective than those of other values for linear phase estimation. The phase probability adjustment is applied to synthetic and real scenarios of sinusoidal structured-light range imaging to show the effectiveness of the presented analysis and adjustment.

An Improved High Frequency Square Wave Injection Permanent Magnet Synchronous Motor sensorless Control

Abstract: In the sensorless control of high-frequency signal injection permanent magnet synchronous motor, rotor position information can be obtained from high frequency response current, So extracting high frequency current is a crucial part. Aiming at the shortcomings of traditional methods of extracting high-frequency currents such as large errors and delays, an improved method is proposed to introduce the equal ripple Chebyshev best approximation finite impulse response filter into the signal extraction. The benefits of this filter include linear phase and maximum error minimization of passband and stopband. High-frequency current can be extracted effectively, the extraction error is minimized, and the interference of harmonic current generated by the inverter is also suppressed. In this paper, a high-frequency square wave is injected into a permanent magnet synchronous motor, and the simulation results showed the effectiveness and superiority of the proposed method.

Radial Velocity Estimation of Ships on Open Sea in the Azimuth Multichannel SAR System

Abstract: The azimuth multichannel synthetic aperture radar (SAR) system can meet the requirements of high resolution and wide swath (HRWS) simultaneously, which overcomes the constraint of the traditional single-channel SAR However, for a moving target illuminated by the azimuth multichannel SAR system, its radial velocity will lead to ambiguous components and mislocation in the image Therefore, the radial velocity estimation plays an important role in improving the image quality and moving target relocation, especially for large ships on the open sea However, as the pulse repetition frequency of a single channel is less than the Doppler spectrum, the traditional velocity estimation methods working in the image domain are out of action This article suggests an idea that the issue of velocity estimation is converted into that of the linear phase errors estimation combining the linear fitting method, and it is assumed that the target has been already detected before applying the velocity estimation algorithms To estimate the linear phase errors, two algorithms operating in the Doppler domain are introduced and compared, namely the subspace-based method and the modified frequency correlation method The advantages of the proposed approaches are free from iteration operation and high accuracy Besides, the effectiveness of the methods is demonstrated via simulation data and GaoFen-3 real data from ultra-fine stripmap mode Finally, this article analyzes the velocity estimation accuracy of the two methods and the influence of channel imbalance through substantial experiments

2D measurements of plasma electron density using coherence imaging with a pixelated phase mask.

Abstract: In this paper, the pixelated phase mask (PPM) method of interferometry is applied to coherence imaging (CI)—a passive, narrowband spectral imaging technique for diagnosing the edge and divertor regions of fusion plasma experiments. Compared to previous CI designs that use a linear phase mask, the PPM method allows for a higher possible spatial resolution. The PPM method is also observed to give a higher instrument contrast (analogous to a more narrow spectrometer instrument function). A single-delay PPM instrument is introduced as well as a multi-delay system that uses a combination of both pixelated and linear phase masks to encode the coherence of the observed radiation at four different interferometer delays simultaneously. The new methods are demonstrated with measurements of electron density ne, via Stark broadening of the Hγ emission line at 434.0 nm, made on the Magnum-PSI linear plasma experiment. A comparison of the Abel-inverted multi-delay CI measurements with Thomson scattering shows agreement across the 3 × 1019 1 × 1020 m−3 only. Accurate and independent interpretation of single-delay CI data at lower ne was not possible due to Doppler broadening and continuum emission.

Improved Classes of CIC Filter Functions: Design and Analysis of the Quantized-Coefficient Errors

Abstract: The paper proposes the use of identical and nonidentical CIC (Cascaded-Integrator-Comb) sections in generating novel classes of selective, highly effective and low complexity filters, for communication systems. The improved classes are described by analytical method in a compact explicit form. Also, analysis of the effects of coefficient quantization is in focus. The quantized-coefficient errors are considered here based on the number of bits and the implementation algorithms.