Array Errors Research Articles

Rectification of Images Distorted by Microlens Array Errors in Plenoptic Cameras.

A plenoptic cameras is a sensor that records the 4D light-field distribution of target scenes. The surface errors of a microlens array (MLA) can cause the degradation and distortion of the raw image captured by a plenoptic camera, resulting in the confusion or loss of light-field information. To address this issue, we propose a method for the local rectification of distorted images using white light-field images. The method consists of microlens center calibration, geometric rectification, and grayscale rectification. The scope of its application to different sized errors and the rectification accuracy of three basic surface errors, including the overall accuracy and the local accuracy, are analyzed through simulation of imaging experiments. The rectified images have a significant improvement in quality, demonstrating the provision of precise light-field data for reconstruction of real objects.

Detection and correction of errors in linear antenna arrays

AbstractDetection and correction of errors is a hot topic of research in the field of antenna arrays. The errors in the excitation amplitude result in the adulteration of the radiation pattern, and hence, the dynamic detection and correction of these errors are very important for proper maintenance of the radiation pattern. In this paper, a novel technique for detection and correction of errors in linear antenna arrays is presented. The analytical nature of the proposed approach makes it a viable alternative to the optimization techniques available in the literature. The error in the radiation pattern measured at an angle is expressed as a function of the individual excitation errors, and subsequently, several useful theorems and techniques are presented in the framework of error detection and correction. An exhaustive mathematical explanation followed by numerical simulations is presented to clearly illustrate the advantage of this method in the detection and correction of errors in antenna arrays.

A CMOS Timer-Injector Integrated Circuit for Self-Powered Sensing of Time-of-Occurrence

Self-powered sensing of the time-of-occurrence of an event is challenging, because it requires access to a reliable time reference or a synchronized clock. In this paper, we propose for the first time a self-powered integrated circuit that is capable of time-stamping asynchronous mechanical events of interest. The core of the proposed design is the integration of two self-powered modules: 1) a chip-scale Fowler–Nordheim tunneling-based timer array, for generating a precision, relative time reference; and 2) a linear piezoelectricity-driven hot-electron injector acting as a floating-gate memory to record the onset of mechanical events. This paper presents measured results from a $4 \times 4$ fully programmable timer array system-on-chip (SoC) and a linear injector array SoC, both of which have been prototyped in a standard double-poly CMOS process. The synchronization error of the timer array with respect to an external software clock was measured to be less than 1% over a duration of 100 h, and the average accuracy in sensing the time-of-occurrence of the event was measured to be 6.9%. The minimum activation energy of the self-powered system was measured to be 840 nJ (measured for event durations of 1 s), which is significantly lower than the energy that can be harvested from typical mechanical impacts.

Experimental Investigation of Measurement Error in Networked Resistors Arrays Based on Zero Potential Method

This paper provides a comprehensive study on the zero potential method for restriction of the crosstalk-based measurement error in network resistor arrays. We introduce four circuits with different architectures based on the zero potential method to comparatively study the effect of the switches on-resistance on the measurement error. Moreover, the effect of the operational amplifiers with different specifications on the measurement error will be investigated. The results show that the measurement error introduced by the onresistance of the switches can be effectively suppressed by inserting a buffer between the sensing elements and the switches on each driven electrode, and utilizing the virtual ground of the trans-impedance amplifier on each scanned electrode. We will show that, the efficiency of the circuits on elimination of the measurement error may be improved by employing high precision operational amplifiers.

Off‐grid effects mitigation exploiting knowledge of the clutter ridge for sparse recovery STAP

In this study, a novel method for overcomplete dictionary construction for sparse recovery (SR) space–time adaptive processing (STAP) is proposed, which can effectively mitigate the off-grid effect. The proposed method utilises the clutter ridge, calculated via some prior knowledge such as radar system parameters and modern inertial navigation system information, to discretise the grids in the angle–Doppler plane. The authors also investigate the accuracy of clutter ridge in the presence of several typical non-ideal factors such as array errors, intrinsic clutter motion and aircraft crab. In particular, a parameter is introduced to adaptively adjust the grid interval to avoid the strong column coherence of the dictionary. The simulation results show that the signal-to-clutter-plus-noise ratio for the SR STAP with the proposed dictionary is significantly improved, compared with the one utilising conventional dictionary. Moreover, it is shown that the novel method not only works more robustly for the side-looking array, but also has better performance for other array orientations.

Pattern synthesis of a practical conformal hydrophone array via second-order cone programming

Due to the production and installation error of the antenna array, there is mismatch between the actual array manifold and the ideal. Considering a practical conformal hydrophone array and the shielding of the sonar platform, the isotropy directivity of each sensor may be destroyed seriously, which is a big challenge to beam pattern synthesis. The method of measuring the actual array manifold was proposed, and second-order cone programming (SOCP) was applied to optimize the weights vector of the array sensors. The experiment result shows the irregular directivity of the array sensors. The weights vector was obtained from the measured array manifold and SOCP, and the synthesized beam pattern met the engineering requirements.

Study on Installation Error Analysis and Calibration of Acoustic Transceiver Array Based on SINS/USBL Integrated System

The installation error of USBL acoustic transceiver array is one of the important error sources for the SINS/USBL integrated navigation system. The installation error of USBL transceiver array can be divided into coordinate shift error and angle rotation error. The angle rotation error (i.e., installation error angle) has a great influence on the positioning accuracy of USBL. In this paper, the traditional surround sailing method is used to study the relationship between the installation error angle and the USBL positioning accuracy. The influence on USBL positioning is analyzed from the component of heading, pitch, and roll of installation error angle, and the simulation results show that the horizontal positioning errors of USBL are mainly affected by the heading and rolling installation errors. The horizontal positioning error of USBL caused by heading or rolling installation error of 1° will result in 17.45 m, under the circumstance that the depth of transponder is 100 m and the radius of surround sailing is 1000 m, without considering the influence of other positioning errors. 1.75 m horizontal positioning error of USBL caused by pitching positioning error of 1° pitching positioning error and the horizontal positioning error of USBL caused by heading and pitching positioning error is also related to the horizontal distance between the transmitter and transponder. A dynamic calibration algorithm of installation error angle based on incremental iteration is proposed in this paper, which could realize the dynamic on-line estimation of installation error angle of USBL transceiver array. The installation error angle increment module can accurately estimate the installation angle error by iterating more than 10 times. In the case of ignoring the other error terms, the horizontal positioning error caused by the installation error angle can be reduced from 8 to 2 m in the positioning range of 1000 m.

DOA error estimation in 3D cylindrical dipole array geometries including the mutual coupling effect

The direction of arrival (DOA) error in dipole 3D arrays is estimated through Monte-Carlo simulations using the standard MUSIC algorithm. Novel 3D geometries are implemented which demonstrate better precision given the same lateral area. The mutual coupling effect is included by changing the search vector in the MUSIC DOA algorithm for the novel 3D geometries. A simple straight forward method is used which does not need complex electromagnetic computations. Simulations show that the proposed method can successfully account for the mutual coupling effects in two dimensional direction finding (both azimuth and elevation angle) with novel 3D array geometries. Reduced DOA estimation error is observed in the novel geometries which can be used as a method of mitigation for the mutual coupling effect.

Alignment error analysis of detector array for spatial heterodyne spectrometer.

Spatial heterodyne spectroscopy (SHS) is a new spatial interference spectroscopy which can achieve high spectral resolution. The alignment error of the detector array can lead to a significant influence with the spectral resolution of a SHS system. Theoretical models for analyzing the alignment errors which are divided into three kinds are presented in this paper. Based on these models, the tolerance angle of these errors has been given, respectively. The result of simulation experiments shows that when the angle of slope error, tilt error, and rotation error are less than 1.21°, 1.21°, 0.066° respectively, the alignment reaches an acceptable level.

Proposal and analysis of three closed double magnetic circuits to obtain a very long stroke for electrodynamic force generators

Electrodynamic force generators with a stroke of up to several hundred millimeters are in high demand in fields such as voice coil actuators and low frequency vibration metrology. The key is to extend the effective length of the long air gap (LAG) with required uniform magnetic flux density (MFD) and low magnetic flux leakage. This paper focuses on a proposal and comparative analysis of three closed double magnetic circuits (CDMCs) to obtain long/ultra-long strokes. Analyses are performed from the viewpoint of the magnetic line distribution, fringing effect, distribution of the MFD, and magnetic flux leakage in order to evaluate the stroke potential of three proposed CDMCs, while taking into account the vacuum annealing, material differences in permanent magnet pairs (PMs), and assembling errors in PM arrays. Analyses show that the CDMC with PMs assembled at the ends of the center yoke exhibits advantages over the other two schemes. An electrodynamic force generator with an air gap length of 200mm is constructed with this structure. Experimental results reveal an MFD of up to 233.5 mT, MFD non-uniformity of 0.2% in the LAG, and magnetic flux leakage of 3 mT, which meet the strict requirements in low frequency vibration metrology.

Array error estimation method for multichannel synthetic aperture radar systems in azimuth

Multichannel synthetic aperture radar systems are usually employed to suppress azimuth ambiguity and realize high-resolution wide-swath imaging. However, unavoidable array errors will significantly degrade the performance of ambiguity suppression and imaging quality. This paper presents an array error estimation method based on cross correlation. First, unambiguous Doppler spectra are obtained by selecting a short length of range profiles from strong targets. Then, array errors are estimated by a proposed cross-correlation method. Finally, a preprocessing method to improve the estimation accuracy is proposed. The proposed method takes full advantage of the training samples from strong targets and estimates array errors by the coherent integration technique, which improves the estimation accuracy and robustness. Theoretical analysis and experiments based on simulations and measurements showed the validity of the proposed method, especially in low signal-to-noise ratios.

DOA and phase error estimation using one calibrated sensor in ULA

A new method is presented to effectively estimate the direction-of-arrival of a source signal and the phase error of a uniform linear array. Assuming that one sensor (except the reference one) has been calibrated, the proposed method appropriately reconstructs the data matrix and establishes a series of linear equations with respect to the unknown parameters through eigenvalue decomposition. The unknown parameters can be determined directly by the least squares method. Unlike the conventional methods, the proposed method only requires one calibrated sensor, which may not be consecutively spaced to the reference one. The computational complexity analysis is given and the effectiveness of the proposed method is validated by simulation results.

Design of robust high-order superdirectivity for circular arrays with sensor gain and phase errors

Though the high-order superdirectivity theory proposed in recent years is attractive, it is hard to implement in practice due to its poor robustness to small random array errors. Hence, in this paper, we present two robust designs of high-order superdirectivity for circular arrays with gain and phase errors. Firstly, we study on the sensitivity function of the high-order superdirectivity and give an alternative solution for a robust superdirective beamformer based on sensitivity function constraint. This method could achieve an arbitrary compromise between directivity and robustness, so it is more flexible and applicable than the existing higher-order truncation method. Although it does not improve on computational complexity or performance with respect to the second-order cone programming obviously, it could lay the foundation for the following robust design method. Then, considering the fact that different eigenbeams correspond to different eigenvalues, we study the method of diagonal loading with variable factors in detail, and further improve the performance of the former sensitivity function constrained method by loading variable factors to different eigenbeams, which results in better performance and greater flexibility in making a compromise. We also show that this proposed loading variable factors method can achieve an equivalent result to the higher-order truncation method by setting proper factors. Simulation results demonstrate the robustness and effectiveness of the above two methods, especially the performance improvement of the loading variable factors method.

List Decoding of Crisscross Errors

In this paper, list decoding of crisscross errors in arrays over finite fields is considered. For this purpose, the so-called cover metric is used, where the cover of a matrix is a set of rows and columns which contains all non-zero elements of the matrix. A Johnson-like upper bound on the maximum list size in the cover metric is derived, showing that the list of codewords has polynomial size up to a certain radius. Furthermore, a simple list decoding algorithm for a known optimal code construction is presented, which decodes errors in the cover metric up to our upper bound. These results reveal significant differences between the cover metric and the rank metric and show that the cover metric is more suitable for correcting crisscross errors.

Tolerance Analysis of Antenna Array Pattern and Array Synthesis in the Presence of Excitation Errors

This paper analyzes array pattern tolerance against excitation errors. The nonprobabilistic interval analysis algorithm is used for tolerance analysis of the nonideal uniform linear array in this work. Toward this purpose, corresponding interval models of the power pattern functions are established, respectively, with the consideration of the amplitude errors, phase errors, or both simultaneously, in antenna arrays. The tolerance for the amplitude-phase error of the main function parameters including the beamwidth, sidelobe level, and the directivity is simulated by computer according to the indicators and the actual requirements. Accordingly, the worst admissible performance of an array can be evaluated, which may provide theoretical reference for optimal antenna array design. As for the problem of array synthesis in the presence of various array errors, interval analysis-convex programming (IA-CP) is presented. Simulation results show that the proposed IA-CP based synthesis technique is robust for the amplitude and phase errors.

A Uniform Linear Array Self-Calibration Method for UHF River Flow Detection Radar

This letter proposes a uniform linear array (ULA) self-calibration method for ultrahigh-frequency (UHF) river flow detection radar (URFDR). URFDR usually uses ULA with less array elements, thus traditional self-calibration methods are all ineffective. This method using river echo signals with single direction of arrival as calibration sources mainly includes two steps: 1) A cost function is constructed based on eigenstructure decomposition, and the array error with Vandermonde fuzziness is estimated by minimizing the cost function using the gradient descent method. 2) The fuzzy array error estimation is corrected by nonlinear least square method based on the characteristics of river echo signals. A field experiment was conducted in the Yangtze River in October 2016, the processing results of which verify the effectiveness of the proposed method.

Direction-of-Arrival Estimation and Sensor Array Error Calibration Based on Blind Signal Separation

We consider estimating the direction-of-arrival (DOA) in the presence of sensor array error. In the proposed method, a blind signal separation method, the joint approximation and diagonalization of eigenmatrices algorithm, is implemented to separate the signal vector and the mixing matrix consisting of the array manifold matrix and the sensor array error matrix. Based on a new mixing matrix and the reconstruction of the array output vector of each individual signal, we propose a novel DOA estimation and sensor array error calibration procedure. This method is independent of array phase errors and performs well against difference of SNR of signals. Numerical simulations verify the effectiveness of the proposed method.

Generation of OAM Beams Using Phased Array in the Microwave Band

A system is proposed to generate vortex electromagnetic (EM) beams in the microwave band, which generates high-order vortex beams at the X-frequency band for the first time. First, the orbital angular momentum (OAM)-generating system is designed and the signal model based on the uniform circular array is presented. Subsequently, the mathematical model with array error contributions is established and, comprehensively, numerical simulations are conducted to analyze how amplitude and phase errors affect the radiation field and the EM vortex imaging. The experimental results validate that the proposed system can readily generate vortex beams of high quality, which are in agreement with the simulated results. The work paves the way to applications of OAM-carrying beams as well as a novel information-rich radar paradigm.

Array-error estimation method for multi-channel SAR systems in azimuth

For multi-channel synthetic aperture radar (SAR) systems, since the minimum antenna area constraint is eliminated, wide swath and high resolution SAR image can be achieved. However, the unavoidable array errors, consisting of channel gain-phase mismatch and position uncertainty, significantly degrade the performance of such systems. An iteration-free method is proposed to simultaneously estimate position and gain-phase errors. In our research, the steering vectors corresponding to a pair of Doppler bins within the same range bin are studied in terms of their rotational relationships. The method is based on the fact that the rotational matrix only depends on the position errors and the frequency spacing between the paired Doppler bins but is independent of gain-phase error. Upon combining the projection matrices corresponding to the paired Doppler bins, the position errors are directly obtained in terms of extracting the rotational matrix in a least squares framework. The proposed method, when used in conjunction with the self-calibration algorithm, performs stably as well as has less computational load, compared with the conventional methods. Simulations reveal that the proposed method behaves better than the conventional methods even when the signal-to-noise ratio (SNR) is low.

Angle Estimation and Self-calibration Method for Bistatic MIMO Radar with Transmit and Receive Array Errors

The mutual coupling, gain-phase error and sensor position error of the transmit and receive arrays would significantly degrade the performance of high-resolution direction of departure and direction of arrival estimation algorithms. By applying two well-calibrated instrumental sensors in both transmit and receive arrays, a novel angle estimation and self-calibration method, which considers the combined influences of the above three array errors, is proposed for bistatic MIMO radar. We show that the integrated array errors can be translated to angularly dependent gain-phase error. Then, a reduced dimensional method is used to estimate the angles and the angularly dependent gain-phase error coefficients. Based on the estimated angularly dependent gain-phase error coefficients, the nonlinear least squares optimization model for the three array errors are established and a quasi-Newton optimization method is applied to estimate the mutual coupling matrix, gain-phase error and sensors position errors of the transmit and receive arrays, respectively. Our simulation results corroborate our analysis.