Showing papers on "Linear phase published in 2016"

Phase mixing versus nonlinear advection in drift-kinetic plasma turbulence

Abstract: A scaling theory of long-wavelength electrostatic turbulence in a magnetised, weakly collisional plasma (e.g. drift-wave turbulence driven by ion temperature gradients) is proposed, with account taken both of the nonlinear advection of the perturbed particle distribution by fluctuating flows and of its phase mixing, which is caused by the streaming of the particles along the mean magnetic field and, in a linear problem, would lead to Landau damping. It is found that it is possible to construct a consistent theory in which very little free energy leaks into high velocity moments of the distribution function, rendering the turbulent cascade in the energetically relevant part of the wavenumber space essentially fluid-like. The velocity-space spectra of free energy expressed in terms of Hermite-moment orders are steep power laws and so the free-energy content of the phase space does not diverge at infinitesimal collisionality (while it does for a linear problem); collisional heating due to long-wavelength perturbations vanishes in this limit (also in contrast with the linear problem, in which it occurs at the finite rate equal to the Landau damping rate). The ability of the free energy to stay in the low velocity moments of the distribution function is facilitated by the ‘anti-phase-mixing’ effect, whose presence in the nonlinear system is due to the stochastic version of the plasma echo (the advecting velocity couples the phase-mixing and anti-phase-mixing perturbations). The partitioning of the wavenumber space between the (energetically dominant) region where this is the case and the region where linear phase mixing wins its competition with nonlinear advection is governed by the ‘critical balance’ between linear and nonlinear time scales (which for high Hermite moments splits into two thresholds, one demarcating the wavenumber region where phase mixing predominates, the other where plasma echo does).

An Improved Grid-Voltage Feedforward Strategy for High-Power Three-Phase Grid-Connected Inverters Based on the Simplified Repetitive Predictor

Abstract: When faced with distorted grid voltage, more harmonics will appear in the output currents of the grid-connected inverters. The grid-voltage feedforward strategy, as the most direct solution to compensate the harmonics, however, is seriously affected by the errors in the grid-voltage feedforward loop, such as delays. This issue is more significant for high-power inverters, where the switching frequency is relatively low (< 5 kHz), and the grid-interface inductance is small (< 0.5 mH). The errors mainly include the signal distortion caused by the conditioning circuits, the control delay of the digital controller, and the zero-order hold (ZOH) characteristic of pulse width modulation (PWM). In this paper, several improvements have been made to reduce the signal distortion and compensate the delays. A second-order Butterworth low-pass filter in the conditioning circuit is carefully designed with the maximum flat magnitude response and the almost linear phase response to avoid distorting the measured grid voltage. Furthermore, based on the conventional repetitive predictor, an open-loop simplified repetitive predictor is proposed to compensate the delays in the grid-voltage feedforward loop. Three predictive steps are achieved by the open-loop simplified repetitive predictor to compensate the delays: one step for the delay caused by the conditioning circuit, the second step for the control delay of the digital controller, and the third step for the ZOH characteristic of PWM. The effectiveness of the improved grid-voltage feedforward strategy are experimentally validated on a 250-kVA solar power generation system, where the current harmonics are effectively attenuated. In addition, the inverter starting current is suppressed.

Wideband Folded Reflectarray Using Novel Elements With High Orthogonal Polarization Isolation

Abstract: A wideband folded reflectarray antenna (FRA) operating in a frequency band of 11–15 GHz is proposed in this communication. It consists of novel dual-polarization elements with high orthogonal polarization isolation. A two-layer element structure is used to control the reflection phase of two orthogonally polarized waves independently and the element presents a large phase variation of about 700° and approximately linear phase curves. Meanwhile, the multifrequency phase matching method is applied in the FRA design. A 30% bandwidth for a 1-dB gain drop, a peak aperture efficiency of 49.1%, and sidelobe levels below −14 dB are achieved. Factors with strong influences on the aperture efficiency are discussed. The simulated results are experimentally verified by an FRA prototype fed by an open-ended waveguide.

Submillimeter-Wave 3.3-bit RF MEMS Phase Shifter Integrated in Micromachined Waveguide

Abstract: This paper presents a submillimeter-wave 500–550-GHz MEMS-reconfigurable phase shifter, which is based on loading a micromachined rectangular waveguide with 9 E-plane stubs. The phase shifter uses MEMS-reconfigurable surfaces to individually block/unblock the E-plane stubs from the micromachined waveguide. Each MEMS-reconfigurable surface is designed so that in the nonblocking state, it allows the electromagnetic wave to pass freely through it into the stub, while in the blocking state, it serves as the roof of the main waveguide and blocks the wave propagation into the stub. The phase-shifter design comprises three micromachined chips that are mounted in the H-plane cuts of the rectangular waveguide. Experimental results of the first device prototypes show that the microelectromechanical system (MEMS)-reconfigurable phase shifter has a linear phase shift of 20 $\mathbf {^{\circ }}$ in ten discrete steps (3.3 bits). The measured insertion loss is better than 3 dB, of which only 0.5–1.5 dB is attributed to the MEMS surfaces and switched stubs, and the measured return loss is better than 15 dB in the design frequency band of 500–550 GHz. It is also shown that the major part of the insertion loss is attributed to misalignment and assembly uncertainties of the micromachined chips and the waveguide flanges, shown by simulations and reproducibility measurements. The MEMS-reconfigurable phase shifter is also operated in an analog tuning mode for high phase resolution. Furthermore, a detailed study has been carried out identifying the reason for the discrepancy between the simulated (90 $\mathbf {^{\circ }}$ ) and the measured (20 $\mathbf {^{\circ }}$ ) phase shift. Comb-drive actuators with spring constant variations between 2.13 and 8.71 N/m are used in the phase shifter design. An actuation voltage of 21.94 V with a reproducibility better than $\mathbf {\sigma }=$ 0.0503 V is measured for the actuator design with a spring constant of 2.13 N/m. Reliability measurement on this actuator was performed in an uncontrolled laboratory environment and showed no deterioration in the functioning of the actuator observed over one hundred million cycles.

A Dual Layer Frequency Selective Surface Reflector for Wideband Applications

Abstract: A dual-layer, bandstop frequency selective sur- face (FSS) is presented in this paper for wideband applica- tions. Each layer uses patch type FSS with slots for minia- turization and are cascaded with an air gap in between. The low-profile FSS with unit cell dimension on the order of 0.2λ0 × 0.2λ0 provides transmission coefficient below -10 dB in the frequency range of 4-7 GHz with 56% bandwidth. The FSS exhibits a nearly linear phase varia- tion with frequency in the operating band and can be used as a substrate below planar wide band antennas with bi- directional radiation for enhancing its gain, directivity in the broadside direction as well as shielding it against nearby conductive surfaces such as metal cases, other printed antennas. Detailed design method, equivalent cir- cuit analysis and measurement results of the FSS are pre- sented in this paper.

A Tunable Si3N4 Integrated True Time Delay Circuit for Optically-Controlled K-Band Radio Beamformer in Satellite Communication

Abstract: In this paper we present the design, realization, and experimental characterization of a photonic integrated true time delay circuit on a CMOS-compatible Si3N4 platform. The true time delay circuit consists of an optical side band filter for single side band modulation and an optical ring resonator for broadband time delay. Two methods of optical delay tuning are investigated: 1) optical wavelength and 2) thermo-optic delay tuning. The wavelength controlled tuning enables a large delay tuning range and can be done remotely from a distant location. The close to a linear phase measurements can be used for full beam-scanning of radio signals with frequencies in the 20 GHz band. The thermal control results in a 5 GHz RF delay bandwidth. A proof-of-concept 2 × 1 beamforming is demonstrated in the 20 GHz band. The design presented here can be employed to realize multi-beams for multi-users serviced by multiple satellites.

ECG denoising and fiducial point extraction using an extended Kalman filtering framework with linear and nonlinear phase observations

Abstract: In this paper we propose an efficient method for denoising and extracting fiducial point (FP) of ECG signals. The method is based on a nonlinear dynamic model which uses Gaussian functions to model ECG waveforms. For estimating the model parameters, we use an extended Kalman filter (EKF). In this framework called EKF25, all the parameters of Gaussian functions as well as the ECG waveforms (P-wave, QRS complex and T-wave) in the ECG dynamical model, are considered as state variables. In this paper, the dynamic time warping method is used to estimate the nonlinear ECG phase observation. We compare this new approach with linear phase observation models. Using linear and nonlinear EKF25 for ECG denoising and nonlinear EKF25 for fiducial point extraction and ECG interval analysis are the main contributions of this paper. Performance comparison with other EKF-based techniques shows that the proposed method results in higher output SNR with an average SNR improvement of 12 dB for an input SNR of -8 dB. To evaluate the FP extraction performance, we compare the proposed method with a method based on partially collapsed Gibbs sampler and an established EKF-based method. The mean absolute error and the root mean square error of all FPs, across all databases are 14 ms and 22 ms, respectively, for our proposed method, with an advantage when using a nonlinear phase observation. These errors are significantly smaller than errors obtained with other methods. For ECG interval analysis, with an absolute mean error and a root mean square error of about 22 ms and 29 ms, the proposed method achieves better accuracy and smaller variability with respect to other methods.

Fault detection for singular switched linear systems with multiple time-varying delay in finite frequency domain

Abstract: This paper deals with the problem of the fault detection FD for continuous-time singular switched linear systems with multiple time-varying delay. In this paper, the actuator fault is considered. Besides, the systems faults and unknown disturbances are assumed in known frequency domains. Some finite frequency performance indices are initially introduced to design the switched FD filters which ensure that the filtering augmented systems under switching signal with average dwell time are exponentially admissible and guarantee the fault input sensitivity and disturbance robustness. By developing generalised Kalman–Yakubovic–Popov lemma and using Parseval's theorem and Fourier transform, finite frequency delay-dependent sufficient conditions for the existence of such a filter which can guarantee the finite-frequency H− and H∞ performance are derived and formulated in terms of linear matrix inequalities. Four examples are provided to illustrate the effectiveness of the proposed finite frequency method.

Nonlinear light behaviors near phase transition in non-parity-time-symmetric complex waveguides

Abstract: Many classes of non-parity-time (PT)-symmetric waveguides with arbitrary gain and loss distributions still possess all-real linear spectrum or exhibit phase transition. In this Letter, nonlinear light behaviors in these complex waveguides are probed analytically near a phase transition. Using multi-scale perturbation methods, a nonlinear ordinary differential equation (ODE) is derived for the light's amplitude evolution. This ODE predicts that a single class of these non-PT-symmetric waveguides supports soliton families and amplitude-oscillating solutions both above and below linear phase transition, in close analogy with PT-symmetric systems. For the other classes of waveguides, the light's intensity always amplifies under the effect of nonlinearity, even if the waveguide is below the linear phase transition. These analytical predictions are confirmed by direct computations of the full system.

Iterative Reweighted Minimax Phase Error Designs of IIR Digital Filters With Nearly Linear Phases

Abstract: Linear phase is an important characteristic of digital filters in many signal processing applications. In this paper, two iterative reweighted minimax phase error algorithms are proposed to design nearly linear-phase infinite impulse response (IIR) digital filters with prescribed or simultaneously minimized magnitude errors and preset transition-band gain. In each iteration of the algorithms, a weighted minimax phase error problem with a fixed weight function is firstly solved using a modified Gauss-Newton method with a variable step length, and the weight function of the phase error is then updated using the square root of a modified envelope of the group-delay error of the filter. With the proposed methods, both very small phase error and group-delay error have been obtained while meeting the requirements on the passband and stopband magnitude errors and the transition-band gain. Design examples demonstrate the effectiveness of the proposed methods and the excellent performance of the designed filters.

Linear phase encoding for holographic data storage with a single phase-only spatial light modulator.

Abstract: A linear phase encoding is presented for realizing a compact and simple holographic data storage system with a single spatial light modulator (SLM). This encoding method makes it possible to modulate a complex amplitude distribution with a single phase-only SLM in a holographic storage system. In addition, an undesired light due to the imperfection of an SLM can be removed by spatial frequency filtering with a Nyquist aperture. The linear phase encoding is introduced to coaxial holographic data storage. The generation of a signal beam using linear phase encoding is experimentally verified in an interferometer. In a coaxial holographic data storage system, single data recording, shift selectivity, and shift multiplexed recording are experimentally demonstrated.

Closed-Form FIR Filter Design Based on Convolution Window Spectrum Interpolation

Abstract: This paper proposes a closed-form linear phase FIR filter design concurrently possessing high efficiency and excellent transfer characteristic. This design is derived from conventional frequency sampling method through replacing its frequency-domain interpolation function with the Fourier spectrum of a convolution window. Meanwhile, this derivation inherently contains a mechanism of synthesizing all possible sub filters into one better FIR filter, which also plays the role of optimizing the transfer characteristic in nature. The above synthesizing process is equivalent to three simple steps, from which a closed-form formula of tap coefficients can be summarized. We further prove the proposed filter’s five properties, from which a modified closed-form design without any redundant parameters is also derived. Numerical results show that, the transfer performance of the proposed design is comparable to the mainstream designs (such as WLS method, Parks- McClellan method). Meanwhile, the proposed design can achieve an extremely high efficiency when designing high-order FIR filters.

Maximally Flat IIR Smoothers With Repeated Poles and a Prescribed Delay

Abstract: The problem of optimal high-frequency noise suppression and low-frequency signal transmission in sampled sensor systems is considered in this paper. Low-delay digital filters with linear phase and unity magnitude at the dc limit (i.e., maximally flat) are of particular interest. Savitzky–Golay smoothers with an infinite impulse response (IIR) are introduced and their properties are explored. The filter coefficients are derived via regression analysis using orthogonal Laguerre polynomials in the time domain. A generalized form with a shape parameter included in the error-weighting function is proposed. This extension may be used to further reduce the white noise gain of the filter. A design process that determines the optimal position of the repeated real poles, either to minimize the white noise gain, or to maximize the high-frequency attenuation, for a specified low-frequency group delay, is discussed. An alternative process for the design of a generic class of maximally flat repeated-pole filters is also presented. This allows colored noise to be handled and/or additional frequency-domain constraints, such as Nyquist flatness, to be applied.

Terahertz Wide-Angle Imaging and Analysis on Plane-wave Criteria Based on Inverse Synthetic Aperture Techniques

Abstract: This paper presents two parts of work around terahertz imaging applications. The first part aims at solving the problems occurred with the increasing of the rotation angle. To compensate for the nonlinearity of terahertz radar systems, a calibration signal acquired from a bright target is always used. Generally, this compensation inserts an extra linear phase term in the intermediate frequency (IF) echo signal which is not expected in large-rotation angle imaging applications. We carried out a detailed theoretical analysis on this problem, and a minimum entropy criterion was employed to estimate and compensate for the linear-phase errors. In the second part, the effects of spherical wave on terahertz inverse synthetic aperture imaging are analyzed. Analytic criteria of plane-wave approximation were derived in the cases of different rotation angles. Experimental results of corner reflectors and an aircraft model based on a 330-GHz linear frequency-modulated continuous wave (LFMCW) radar system validated the necessity and effectiveness of the proposed compensation. By comparing the experimental images obtained under plane-wave assumption and spherical-wave correction, it also showed to be highly consistent with the analytic criteria we derived.

Generation of singular optical beams from fundamental Gaussian beam using Sagnac interferometer

Abstract: We propose a simple free-space optics recipe for the controlled generation of optical vortex beams with a vortex dipole or a single charge vortex, using an inherently stable Sagnac interferometer. We investigate the role played by the amplitude and phase differences in generating higher-order Gaussian beams from the fundamental Gaussian mode. Our simulation results reveal how important the control of both the amplitude and the phase difference between superposing beams is to achieving optical vortex beams. The creation of a vortex dipole from null interference is unveiled through the introduction of a lateral shear and a radial phase difference between two out-of-phase Gaussian beams. A stable and high quality optical vortex beam, equivalent to the first-order Laguerre–Gaussian beam, is synthesized by coupling lateral shear with linear phase difference, introduced orthogonal to the shear between two out-of-phase Gaussian beams.

Subaperture translation estimation accuracy in transverse translation diversity phase retrieval.

Abstract: For optical metrology by transverse translation diversity phase retrieval (or ptychography), information theoretic limits on the ability to estimate subaperture translation, essential for accurate metrology, are assessed as a function of the optical aberrations of the system being measured. Special attention is given to the case that an unknown linear phase aberration, or equivalent detector or target motion, is present that varies with each point spread function in the measured data.

Greedy Algorithm for the Design of Linear-Phase FIR Filters with Sparse Coefficients

Abstract: In this work, a greedy algorithm for the design of sparse linear-phase finite impulse response filters wherein the coefficients are successively fixed to zero individually is proposed To meet the filter specifications, the coefficient for which the middle value of its feasible range is closest to zero is selected to be set to zero, whereas all the other unfixed coefficients are free to change Design examples show that the proposed technique can design FIR filters with higher sparsity than that obtained by existing nonexhaustive algorithms for given specifications To show the optimality of the algorithm, we design 100 filters, with results showing that the global optimal solution, ie, the sparsest solution found by exhaustive search, can be achieved in most cases, but with much less computation time

A 1.5 V 28 GHz Beam Steering SiGe PLL for an 81-86 GHz E-Band Transmitter

Abstract: This letter presents measurement results for a low supply voltage 28 GHz beam steering PLL, designed in a SiGe bipolar process with $f_{T}= 200$ GHz. The PLL, designed around a QVCO, is intended for a beam steering 81-86 GHz E-band transmitter. Linear phase control is implemented by variable current injection into a Gilbert type phase detector, with a measured nominal phase control sensitivity of 2.5 °/ $\mu \text {A}$ . The demonstrated LO generation method offers great advantages in the implementation of beam steering mm-wave transmitters, since only the low frequency PLL reference signal of 1.75 GHz needs to be routed across the chip to the different transmitters. Except for an active loop filter, used to extend the locking range of the PLL, the design uses a low supply voltage of 1.5 V. The PLL obtains a measured in band phase noise of −107 dBc/Hz at 1 MHz offset. The power consumption equals 54 mW from the 1.5 V supply plus 1.8 mW for the variable supply of the active low pass filter.

The application of artificial bee colony (ABC) algorithm in FIR filter design

Abstract: The FIR filter has been widely used in the digital signal processing and other engineering calculations for its strictly linear phase and stability performance. The artificial bee colony (ABC) algorithm is a new kind of swarm intelligence optimization algorithm which has a strong search mechanism. This paper applies ABC into the linear-phase FIR filter design based on frequency sampling method which can search the optimal frequency sampling points in order to obtain the top minimum stop-band attenuation. By comparing the maximum stop-band attenuation of the traditional frequency sampling method, common genetic algorithm (GA) and ABC algorithm, the experiment shows that the application of ABC algorithm used in FIR filter design is effective.

Minimax design of linear phase FIR filters using cuckoo search algorithm

Abstract: A method for minimax design of linear phase finite impulse response (FIR) digital filters using cuckoo search algorithm (CSA) is presented. Lowpass and bandpass digital filters are used as filter examples. Equiripple linear phase FIR digital filter design results indicate that the peak errors in passband and stopband(s) obtained using the cuckoo search algorithm are similar to those obtained by the Parks-McClellan optimal method but smaller than those obtained by the particle swarm optimization method.

A Novel Interference Rejection Method for GPS Receivers

Abstract: This paper proposes a new method for rejecting the Continuous Wave Interferences (CWI) in the Global Positioning System (GPS) receivers. The proposed filter is made by cascading an adaptive Finite Impulse Response (FIR) filter and a Wavelet Packet Transform (WPT) based filter. Although adaptive FIR filters are easy to implement and have a linear phase, they create self-noise in the rejection of strong interferences. Moreover, the WPT which provides detailed signal decomposition can be used for the excision of single-tone and multi-tone CWI and also for de-noising the retrieved GPS signal. By cascading these two filters, the self-noise imposed by FIR filter and the remaining jamming effects on GPS signal can be eliminated by the WPT based filter. The performance analysis of the proposed cascade filter is presented in this paper and it is compared with the FIR and the WPT based filters. Experimental results illustrate that the proposed method offers a better performance under the interference environments of interest in terms of the signal-to-noise ratio gain and mean square error factors compared to previous methods.

Generation of optical vortex dipole from superposition of two transversely scaled Gaussian beams.

Abstract: We propose a distinct concept on the generation of optical vortex through coupling between the amplitude and phase differences of the superposing beams. For the proof-of-concept demonstration, we propose a simple free-space optics recipe for the controlled synthesis of an optical beam with a vortex dipole by superposing two transversely scaled Gaussian beams. The experimental demonstration using a Sagnac interferometer introduces the desired amount of radial shear and linear phase difference between the two out-of-phase Gaussian beams to create a vortex pair of opposite topological charge in the superposed beam. Flexibility to tune their location and separation using the choice of direction of the linear phase difference and the amount of amplitude difference between the superposing beams has potential applications in optical tweezers and traps utilizing the local variation in angular momentum across the beam cross section.

Extraction of Building Features from Stand-Off Measured Through-Wall Radar Data

Abstract: Automated extraction of building features is a great aid in synthesizing building maps from radar data. In this paper, a model-based method is described to detect and classify canonical scatters, such as corners and planar walls, inside a building. Once corners and walls have been located, a building map can be synthesized. To detect and classify the canonical scatterers, sparse reconstruction with an overcomplete dictionary is used. The dictionary is tuned to phase models that are specific to the different canonical scatterers, i.e., a linear phase change for walls and a quadratic phase change for corners. This is a potentially robust method for detecting canonical scatterers because the polynomial degree of the measured phase is preserved, even after propagation through a wall. Building-feature extraction results obtained with actually stand-off measured through-wall radar data are discussed.

Minimax design of linear phase FIR Hilbert transformer using teaching-learning-based optimization

Abstract: In this paper, teaching-learning-based optimization (TLBO) is used for minimax design of linear phase finite impulse response (FIR) digital Hilbert transformers. TLBO is a population-based and heuristic search algorithm which is parameter-free and exhibits a strong convergence ability. The results obtained from using TLBO to design Type 4 linear phase FIR highpass digital Hilbert transformers indicate that it is an effective method to reach smaller equiripple peak errors as compared to those obtained by the least-squares error minimization method and the optimal Parks-McClellan algorithm.

A low-power calibration-free fractional-N digital PLL with high linear phase interpolator

Abstract: This paper presents a low-complexity calibration-free digital PLL architecture. The PLL adopts a fractional frequency divider with a harmonic rejection current steering phase interpolator which is free from pre- and background-calibration. The harmonic rejection technology could improve linearity of interpolator. A simplified glitch-free control logic for fractional operation is proposed to lower architecture complexity and minimal design effort. A high frequency resolution digitally-controlled oscillator with an equivalent variable inductor is also utilized. A 2.2-GHz digital PLL has been implemented in a 55-nm CMOS technology. The frequency resolution of DCO is 1.58 kHz, and in-band phase noise of PLL is −104.4 dBc/Hz. The PLL consumes 2.43 mA from a 1.2-V supply voltage and occupies an active area of 0.216 mm2.

A new method for higher-order linear phase FIR digital filter using shifted Chebyshev polynomials

Abstract: In this work, a new method for the design of linear phase finite impulse response (FIR) filters using shifted Chebyshev polynomial is proposed. In this method, magnitude response of FIR filter is approximated with the help of shifted Chebyshev polynomials. The number of polynomials used for approximation depends upon the order of filter. Design problem of filter is constructed as minimization of integral mean-square error between the ideal response and actual response through differentiating it with respect to its coefficients, which leads to a system of linear equations. The simulation results included in this paper show the efficiency of proposed method. It is also evident from the results that the proposed method is suitable for higher filter taps.

High-Resolution Group Quantization Phase Processing Method in Radio Frequency Measurement Range.

Abstract: Aiming at the more complex frequency translation, the longer response time and the limited measurement precision in the traditional phase processing, a high-resolution phase processing method by group quantization higher than 100 fs level is proposed in radio frequency measurement range. First, the phase quantization is used as a step value to quantize every phase difference in a group by using the fixed phase relationships between different frequencies signals. The group quantization is formed by the results of the quantized phase difference. In the light of frequency drift mainly caused by phase noise of measurement device, a regular phase shift of the group quantization is produced, which results in the phase coincidence of two comparing signals which obtain high-resolution measurement. Second, in order to achieve the best coincidences pulse, a subtle delay is initiatively used to reduce the width of the coincidences fuzzy area according to the transmission characteristics of the coincidences in the specific medium. Third, a series of feature coincidences pulses of fuzzy area can be captured by logic gate to achieve the best phase coincidences information for the improvement of the measurement precision. The method provides a novel way to precise time and frequency measurement.