Random Initial Phase Research Articles

Phaseless Characterization of Compact Antenna Test Range via Improved Alternating Projection Algorithm

A practical compact antenna test range (CATR) requires good quiet zone quality for antenna characterization. This paper addresses the phase profile of the CATR quiet zone from the known intensity pattern of spatial domain and Fourier domain based on a combined alternating projection algorithm. The proposed algorithm is composed of Gerchberg–Saxton (GS) and Hybrid Input–Output (HIO) algorithms and the two algorithms with spatial phase perturbation (SPP) work collaboratively or independently under predesigned conditions. It is observed that the algorithm with random initial phase guess can always converge to an optimal solution by performing a series of hierarchical optimizations of the problem. The numerical results are in good agreement with simulated results in different frequency bands, overcoming the phase retrieval limitation of local convergence in the iterative process. Furthermore, to validate the effectiveness and robustness of the proposed procedure, the related discussions corresponding to different sampling areas in Fourier domain and different signal to noise ratios (SNRs) are given.

Large field‐of‐view holographic display method with speckle noise suppression based on time multiplexing

AbstractIn this paper, we propose a method to enlarge the field of view (FOV) in holographic display with speckle noise suppression. Different from the traditional method, several subcomputer‐generated holograms (sub‐CGHs) with large size are generated in the proposed method. Through pixel separation, the recorded object is separated into multiple object point groups. The information of each object point group is recorded on different sub‐CGHs with independent initial random phases. In the holographic reconstruction, three spatial light modulators (SLMs) in a planar configuration are used to load the sub‐CGHs. The image is reconstructed through time multiplexing. The FOV is enlarged because the light distribution size of each image point is increased. Meanwhile, the speckle noise of the image is suppressed through the average effect and the separation of the adjacent image points. Experimental results prove the feasibility of the proposed method.

Flicker noise or fluctuation drift of the working point

An original scheme is proposed for generator of chaos oscillations of the microwave wavelength range. Generator contains nonlinear positive feedback amplifieran and inertial converter of the output signal of a nonlinear amplifier, the signal of which modulates the supply voltage of the active element (transistor). In the case when the value of the inertia parameter of the inertial converter becomes less than 0,06, the generator demonstrated chaotic behavior. An experimental model of a chaotic signal generator based on a powerful transistor 2T982A-2 was created. The generator was created using hybrid microstrip technology on the material FLAN-10 with a thickness of 1 mm. The inertial converter circuit contained a diode performing half-wave conversion of a part of the generator output signal and an RC circuit with a time constant equal to 0,05 of the time one oscillation at the central frequency of the generator. The signal from the output of the inertial converter was applied to the emitter power supply circuit of the transistor. Modulation of the supply voltage led to the fact that the output signal of the generator was a sequence of non-repeating oscillation trains with a random duration and a random initial phase. The frequency band of the generated chaos with an uneven power spectrum of 4 dB occupied a frequency range from 3,1 to 3,3 GHz with an integrated power of 1,2 W. The averaged spectral density of noise oscillations was 6 10-3 W/MHz. Generator efficiency 15%.

Фазовая кластеризация в иерархическом ансамбле связанных осцилляторов ван дер Поля

We demonstrate phase clusterization in a hierarchical network of mutually coupled van der Pole oscillators. We find that in the system with random initial phases there is a coupling parameter, which corresponds to intermittent transition from non-synchronous state to synchronous. Clusterization does not decay if oscillators have non-identical natural frequencies or randomly distributed initial phases. In this structure, those elements that are placed on the same hierarchical level have equal phases.

Dictionary Learning and Waveform Design for Dense False Target Jamming Suppression

For linear frequency modulation (LFM) pulse radars, dense false targets generated by new system jamming seriously damage the performance of such radar systems. In order to avoid the influence of dense false target jamming, an anti-jamming strategy combining waveform design and sparse decomposition are proposed. Specifically, the radar system transmits a random pulse initial phase (RPIP) signal, and uses peak detection method to detect the deception jamming. The phase distribution of the RPIP signal is partially randomly perturbed for a jamming, and we use optimization algorithm to design a phase perturbed LFM (PPLFM) signal with good autocorrelation characteristics. Using the correlation function of the designed signal, the target sample set and the jamming sample set are constructed, and the target echo and the jamming signal are separated using designed dictionary learning method to achieve suppression of dense false target jamming and range side-lobes. The effectiveness of the proposed method is verified by numerical simulation, and the results proved that this proposed method maintains good anti-jamming performance under low signal-tonoise ratio (SNR).

Super rogue wave generation in the linear regime.

Extreme or rogue waves are large and unexpected waves appearing with higher probability than predicted by Gaussian statistics. Although their formation is explained by both linear and nonlinear wave propagation, nonlinearity has been considered a necessary ingredient to generate super rogue waves, i.e., an enhanced wave amplification, where the wave amplitudes exceed by far those of ordinary rogue waves. Here we show, experimentally and theoretically, that optical super rogue waves emerge in the simple case of linear light diffraction in one transverse dimension. The underlying physics is a long-range correlation on the random initial phases of the light waves. When subgroups of random phases appear recurrently along the spatial phase distribution, a more ordered phase structure greatly increases the probability of constructive interference to generate super rogue events (non-Gaussian statistics with superlong tails). Our results consist in a significant advance in the understanding of extreme waves formation by linear superposition of random waves, with applications in a large variety of wave systems.

A straightforward derivation of the four-wave kinetic equation in action-angle variables

Starting from action-angle variables and using a standard asymptotic expansion, we present an original and coincise derivation of the Wave Kinetic equation for a resonant process of the type . Despite not being more rigorous than others, our procedure has the merit of being straightforward; it allows for a direct control of the random phases and random action of the initial wave field. We show that the Wave Kinetic equation can be derived assuming only initial random phases. The random action approximation has to be taken only after the weak nonlinearity and large box limits are taken. The reason is that the oscillating terms in the evolution equation for the action contain, as an argument, the action-dependent nonlinear corrections which is dropped, using the large box limit. We also show that a discrete version of the Wave Kinetic Equation can be obtained for the Nonlinear Schrödinger equation; this is because the nonlinear frequency correction terms give a zero contribution and the large box limit is not needed. In our calculation we do not make an explicitly use of the Wick selection rule.

Secret image sharing based on multiphase retrieval algorithm

This paper proposes a multiphase retrieval algorithm and then presents a secret image sharing scheme. The proposed algorithm can divide a secret image into multiple phase-only encodings (shadows) and then overcome the shadow expansion problem. When the shadows are arranged in a certain order, the light intensity detector can directly acquire the secret image using parallel light, and the recovery process is simple and easy to operate. Furthermore, Fresnel transform parameters are used for authentication, which can avoid deceit. The differences in the initial random phase encodings make the same secret image produce different shadows, which can effectively resist statistical analysis attacks. Finally, theoretical analysis and a simulation are used to verify the validity and feasibility of the proposed scheme.

Double resonance in star networks of bistable units with disordered signals**Supported by the NNSF of China under Grants No. 11305078 and No. 61877030.

It has been found that a hub node is better able to amplify weak external signals than leaf nodes in star networks. But hub-enhanced amplification is only attained by a single hub node and is limited to weak coupling strength. We show here that random initial phases in external weak signals do not affect the hub-enhanced amplification at weak coupling strength. Instead, they can improve the responses of all the leaf nodes to external signals at large coupling strength, resulting in a double resonance-like signal amplification. We use a reduced model to analyze the influence of the star structure and random initial phases on the emergence of double resonance.

Phase Calibration of On-Chip Optical Phased Arrays via Interference Technique

Optical phased arrays (OPAs) are promising in various applications owing to their excellent beam steering performance but suffer from the random initial phases ruining the beam patterns. In this work, an interference-based calibration method to align the random phases for OPA operations is proposed. Briefly, the phase differences are directly extracted from the interference fringes and used to build up the phase map. The feasibility and effectiveness of the proposed method were verified from an 8 × 8 OPA chip, in which the side-lobe suppression ratio of 10.1 dB was achieved. The proposed method can be utilized as a supplement of conventional calibration algorithms to reduce requirements for the sensitivity of the feedback system and avoid local optima, thus providing practical assistance for many OPA applications.

ANALYSIS OF POSSIBILITIES OF PROVIDING OF NECESSARY EXACTNESS OF MEASURING OF SPATIAL COORDINATES OF AIR OBJECTS IN THE RADIO-LOCATION STATION OF ACCOMPANIMENT WITH PHASE AERIAL BY A GRATE

Modern Phased-Array Antenna (PAA) radars are an effective mean of aerial reconnaissance and provide radar information on aerial objects in a complex environment. The subject of the article is the influence of the inhomogeneities of the troposphere and the earth’s surface on the decrease in the accuracy of measurement of angular coordinates and altitude of air objects in radars with PAA. The purpose of the article is to numerically estimate the possible values of the root mean square error of measuring the angular coordinates and the height of air objects due to the influence of fluctuations of the phase edge of the radar wave. Task : analysis of possible mechanisms of origin and statistical characteristics of correlated phase fluctuations of a radio signal for a model of a signal with random amplitude and initial phase. Methods used : methods of probability theory and mathematical statistics. The following results were obtained . The estimation technique is developed and possible values of the mean-square errors of measurement of angular coordinates and altitude of air objects are obtained, which are caused by the influence of radar signal phase wave front fluctuations for the three-coordinate PAA radar of centimeter range. The above calculation method allows to carry out the numerical estimation of errors of measurement of angular coordinates and object height. Conclusions . This technique can be practically used in assessing the effect of real conditions of propagation and reflection of radar signal on the reduction of the capabilities of modern radars with PAA to perform tasks on purpose.

Characteristics of Radio-Signal Detection for the Nonlinear Decision Function of a Threshold Device

We consider the characteristics of radio-signal detection using the nonlinear decision function of a threshold device. This work is aimed at estimating the influence of the difference between the nonlinear decision function of the receiver threshold device and the step function on the characteristics of detecting radio signals with a random initial phase and random initial phase and amplitude. New analytical expressions for the probabilities of correct detection of radio signals and false alarm are obtained.

Data-driven simulation of multivariate nonstationary winds: A hybrid multivariate empirical mode decomposition and spectral representation method

Extreme winds such as thunderstorms and tornados typically exhibit nonstationary characteristics. Correspondingly, the structural response under these extreme winds tends to be nonstationary. To obtain more accurate nonstationary structural response, the time-domain analysis method is commonly used, which makes the simulation of multivariate nonstationary winds an essential prerequisite. Recently, some single sample-based simulation methods have received much attention due to their straightforwardness. In these schemes, the implied assumption of the random initial phase shift to represent the spatial correlation may not be always appropriate. In this study, a single sample-based simulation method which is a hybrid of the multivariate empirical mode decomposition (MEMD) and spectral representation method (SRM) is proposed. Central to this method is the MEMD-based IF spectral matrix used to naturally consider the spatial correlation of the simulated random process without any assumption and adopting SRM to generate the sample. This makes the proposed method more straightforward and realistic. Statistical characteristics of the simulated random process are presented in detail. Numerical examples are provided to demonstrate the effectiveness of the proposed method. Results show that the characteristic of the measured single sample can be effectively preserved in the simulated sample. The estimated covariance and cross-covariance also provide a good agreement with their target values. In addition, the proposed method is more convenient and realistic in maintaining the spatial correlation of the measured single sample as compared to the methods that invoke the assumption concerning the random initial phase shift. Accordingly, the proposed hybrid method offers an effective simulation of nonstationary random processes.

HIGH POWER CHAOTIC OSCILLATOR

The article presents a novel design of a microwave chaotic oscillator. The oscillator contains an inertial converter for the nonlinear amplifier output signal that modulates the supply voltage of the transistor. When the inertia of the converter becomes less than 0.06, the oscillator demonstrates chaotic behavior. We present an experimental model of a chaotic oscillator based on a high power transistor 2T982A-2. The inertial converter circuit contains a diode that perform half-wave conversion of a part of the output signal and a RC circuit with a time constant equal to 0.05 of the duration of an oscillation at the central frequency of the oscillator. The output signal of the inertial converter has been applied to the emitter power supply circuit of the transistor. Modulation of the supply voltage caused the output signal of the oscillator to become a sequence of non-repeating oscillation trains with a random duration and initial phase. The frequency band of the generated chaos with an uneven power spectrum of 4 dB was in a range from 3.1 to 3.3 GHz with an integrated power of 1.2 W. The averaged spectral density of noise oscillations was 6 10-3 W / MHz. Efficiency of the oscillator was 15%.

Truly Distributed and Ultra-Fast Microwave Photonic Fiber-Optic Sensor

Brillouin-based optical fiber sensing has gained considerable attention for the past few years thanks to its ability to offer distributed sensing. The major limitation of a Brillouin-based optical fiber sensor is its complexity because a time-consuming frequency-sweeping process is needed to obtain a local Brillouin gain spectrum (BGS) and to calculate the local Brillouin frequency shift (BFS). Thus, it is only suitable for static or slow-varying measurements. In this article, we propose an approach to achieve truly distributed and ultra-fast fiber-optic sensing based on an active and distributed bandpass microwave photonic filter (MPF) through stimulated Brillouin scattering (SBS). To obtain a truly distributed BFS, a counter-propagating single-shot pump pulse is launched into the fiber link and a microwave multi-tone (MMT) signal with a random initial phase distribution which is phase modulated on an optical carrier is launched into the fiber link from the other end. Due to the SBS effect, the −1st order sideband of the phase-modulated signal will experience Brillouin amplification while the +1st order sideband will experience Brillouin attenuation, and the phase-modulated signal is converted to an intensity-modulated signal. The entire operation is equivalent to a bandpass MPF. By detecting the optical signal at a photodetector (PD), a regenerated MMT signal with its magnitude and phase that are shaped by the MPF is obtained. By evaluating the regenerated MMT signal, the Brillouin information corresponding to the temperature or strain change at a specific location is revealed. The major advantage of the approach is that time-consuming frequency-sweeping process is avoided. Truly distributed strain, temperature, and vibration sensing with a 2 m spatial resolution over 49.5 m distance at a speed up to 83.3 kHz is experimentally demonstrated.

Method to suppress speckle noise using time multiplexing in phase‐only holographic display

AbstractIn holographic display, the reconstructed image suffers from speckle noise severely. In this paper, we propose a method to suppress speckle noise using time multiplexing in phase‐only holographic display. Adjacent pixels of the recorded object are separated into object point groups firstly. Particularly, the pixel interval of each object point group is larger compared with the conventional pixel separation method. And then, sub‐computer–generated holograms (sub‐CGHs) are calculated by the modified Gerchberg–Saxton (GS) algorithm with different initial random phases. Finally, the final integrated image is reconstructed with low speckle noise using time multiplexing technique. Both numerical and optical experimental results are presented to demonstrate the effectiveness and feasibility with our proposed method.

A PVT-Robust Super-Regenerative Receiver with Background Frequency Calibration and Concurrent Quenching Waveform

A process-voltage-temperature (PVT)-robust, low power, low noise, and high sensitivity, super-regenerative (SR) receiver is proposed in this paper. To enable high sensitivity and robust-PVT operation, a fast locking phase-locked-loop (PLL) with initial random phase error reduction is proposed to continuously adjust the center frequency deviations of the SR oscillator (SRO) without interrupting the input data stream. Additionally, a concurrent quenching waveform (CQW) technique is devised to improve the SRO sensitivity and its noise performance. The proposed SRO architecture is controlled by two separate biasing branches to extend the sensitivity accumulation (SA) phase and reduce its noise during the SR phase, compared to the conventional optimal quenching waveform (OQW). The proposed SR receiver is implemented at 2.46 GHz center frequency in 180 nm SMIC CMOS technology and achieves better sensitivity, power consumption, noise performance, and PVT immunity compared with existent SR receiver architectures.

Arbitrary reconfiguration of universal silicon photonic circuits by bacteria foraging algorithm to achieve reconfigurable photonic digital-to-analog conversion

Reconfigurable/reprogrammable universal silicon photonic circuits represent a paradigm shift in designing photonic devices. However, it is very challenging to perform adaptive arbitrary reconfiguration when the high-dimensional solution of phase distribution cannot be explicitly determined, especially when there are random initial phase errors, which hinder the implementation of novel potential functions in universal circuits. This work presents an arbitrary black-box reconfiguration for universal circuits with random phase errors by a bacteria-foraging algorithm and unlocks a novel function of arbitrary-port-and-arbitrary-bit-resolution reconfigurable 6-bit photonic digital-to-analog conversion. This work offers a general and efficient method to ease multipurpose reconfiguration for universal silicon photonic circuits.

Simulation method of ground motion matching for multiple targets and effects of fitting parameter variation on the distribution of PGD

When generating spectrum-compatible artificial ground motion in engineering practices, the effect of the variation in fitting parameters on the distribution of the peak ground displacement (PGD) has not yet drawn enough attention. In this study, a method for simulating ground motion matching for multiple targets is developed. In this method, a frequency-dependent amplitude envelope function with statistical parameters is introduced to simulate the nonstationarity of the frequency in earthquake ground motion. Then, several groups of time-history acceleration with different temporal and spectral nonstationarities were generated to analyze the effect of nonstationary parameter variations on the distribution of PGD. The following conclusions are drawn from the results: (1) In the simulation of spectrum-compatible artificial ground motion, if the acceleration time-history is generated with random initial phases, the corresponding PGD distribution is quite discrete and an uncertain number of PGD values lower than the limit value are observed. Nevertheless, the mean values of PGD always meet the requirement in every group. (2) If the nonstationary frequencies of the ground motion are taken into account when fitting the target spectrum, the corresponding PGD values will increase. A correlation analysis shows that the change in the mean and the dispersion values, from before the frequencies are controlled to after, correlates with the modal parameters of the predominant frequencies. (3) Extending the maximum period of the target spectrum will increase the corresponding PGD value and, simultaneously, decrease the PGD dispersion. Finally, in order to control the PGD effectively, the ground motion simulation method suggested in this study was revised to target a specified PGD. This novel method can generate ground motion that satisfies not only the required precision of the target spectrum, peak ground acceleration (PGA), and nonstationarity characteristics of the ground motion but also meets the required limit of the PGD, improving engineering practices.

Dynamic visual simulation of marine vector field based on LIC—a case study of surface wave field in typhoon condition

Line integral convolution (LIC) is a useful visualization technique for a vector field. However, the output image produced by LIC has many problems in a marine vector field. We focus on the visual quality improvement when LIC is applied in the ocean steady and unsteady flow field in the following aspects. When a white noise is used as the input in a steady flow field, interpolation is used to turn the discrete white noise into continuous white noise to solve the problem of discontinuity. The “cross” high-pass filtering is used to enhance the textures of streamlines to be more concentrated and continuity strengthened for each streamline. When a sparse noise is used as the input in a steady flow field, we change the directions of background sparse noise according to the directions of vector field to make the streamlines clearer and brighter. In addition, we provide a random initial phase for every streamline to avoid the pulsation effect during animation. The velocities of vector field are encoded in the speed of the same length streamlines so that the running speed of streamlines can express flow rate. Meanwhile, to solve the problem of obvious boundaries when stitching image, we change the streamline tracking constraints. When a white noise is used as an input in an unsteady flow field, double value scattering is used to enhance the contrast of streamlines; moreover, the “cross” high-pass filtering is also adopt instead of two-dimensional high-pass filtering. Finally, we apply the above methods to a case of the surface wave field in typhoon condition. Our experimental results show that applying the methods can generate high-quality wave images and animations. Therefore, it is helpful to understand and study waves in typhoon condition to avoid the potential harm of the waves to people’s lives and property.