Dynamic Range Ratio Research Articles

Linearly Polarized Shaped Power Pattern Synthesis With Dynamic Range Ratio Control for Arbitrary Antenna Arrays

This paper extends the semidefinite relaxation (SDR) method to be capable of synthesizing linearly polarized shaped patterns with accurate control of sidelobe level (SLL), cross-polarization level (XPL), and dynamic range ratio (DRR) of the excitation distribution for arbitrary antenna arrays. In addition, by using the vectorial active element patterns, mutual coupling and platform effect can be also incorporated into the proposed vectorial shaped pattern synthesis. Three examples for synthesizing linearly polarized patterns with different pattern shape requirements and different antenna array geometries have been conducted to check the effectiveness and robustness of the proposed method. Compared to the original vectorial shaped pattern synthesis without DRR control, the proposed method with the DRR control can significantly reduce the obtained DRR which is very useful in many antenna array applications.

Superposition Synthesis Method for 2-D Shaped-Beam Array Antenna

In this paper, a synthesis method for a shaped-beam pattern of the 2-D array antenna is proposed. The method is based on the array scanning principle and the superposition principle. The method can limit the ripple of the main beam by adjusting the sampling point interval and can easily achieve low sidelobe level (SLL). Compared to the stochastic optimization methods, this method has obvious time advantage when it is used to synthesize a large array antenna. The factors that affect the SLL, ripple, and dynamic range ratio (DRR) are discussed. Sparse array is used to reduce DRR.

Study of radial flow mode magnetorheological energy absorber with center drain hole

Magnetorheological energy absorbers (MREAs) have manifested their superiority as a controllable damper. An ideal feature for MREA is to remain a constant damping force within a certain impact displacement (referred to as plateau behavior) in the transient impact process. Realizing this plateau behavior by introducing the structure of drain hole is able to effectively reduce harmfulness from the overshoot to the buffered object. In this study, a radial flow mode MREA with a center drain hole configuration is proposed, in order to achieve an approximate plateau as well as to expand the dynamic range. The Power-Law model is employed to analyze the impact behaviors of the MREA due to its smooth shear stress-shear rate curve and simple mathematical form. Five parameters (i.e., plateau angle, radial flow velocity ratio, minor losses ratio, dynamic range ratio, and peak force ratio) are defined to characterize the effects of the drain hole quantitatively and comprehensively. The diameter of center drain hole is specially focused on because of its significant influences on the parameters. Two types of MREAs with/without drain holes are fabricated and tested using a drop tower facility with a 600 kg mass. The experimental results show that the plateau angle of MREA with drain hole is reduced by 56.1% compared to that without hole, and also demonstrate that the Power-Law based model is capable of well predicting the dynamic behavior of the MREA.

Evaluation of large-scale turbulent/non-turbulent interface detection methods for wall-bounded flows

The experimental analysis of the spatial organization of turbulent/non-turbulent interfaces (TNTI) is an important task in many fields of fluid dynamics, especially to characterize mixing processes. Mixing processes are often associated with the macroscopic motion of coherent flow structures. A classical example for illustration is the turbulent mixing layer visualization by Brown and Roshko (J Fluid Mech 64:775–816, 1974). Today, a question of actual research is if coherent large-scale motions observed in turbulent boundary layer flows have an impact on the structure of the TNTI. As the length of these motions extends over many boundary layer thicknesses and their turbulent energy, and thus significance or impact, raises with Reynolds number, the TNTI detection technique must be accurate at large Reynolds numbers. Furthermore, the technique must be able to resolve the TNTI locally with microscopic spatial resolution and, at the same time, globally over a large macroscopic spatial domain. As the last two points require techniques with a large dynamic spatial range (ratio between largest and smallest scales that can be resolved), only tracer particle-based imaging techniques are suited, as the spatial resolution and field of view (FOV) can both be tuned by adjusting the magnification of the lens and the size and number of camera sensors. In this work, three suited techniques are compared to assess the sensitivity of the TNTI measurement of the method applied. The techniques considered are based on the turbulent kinetic energy, the homogeneity of the non-turbulent flow region, and the particle image density. The effect of bias errors on the TNTI measurement is particularly considered, but the implication of the results for the working range of the various techniques is also outlined. The analysis illustrates exemplary the sensitivity of the intermittency factor and the length of the TNTI with respect to the method applied.

Beampattern synthesis with minimal dynamic range ratio

Abstract The excitations with a small value of dynamic range ratio (DRR) are helpful to control the mutual coupling between array elements, reduce the output power loss, and simplify the feeding network design. Unlike the commonly specified DRR, this communication focuses on finding the minimal DRR of the excitations while synthesizing a desired beampattern. To address this issue, a nonconvex and nonlinear optimization problem is formulated to synthesize array pattern while minimizing the DRR of the excitations, which is solved by extending the penalty method. Firstly, violations of all the inequality constraints are augmented into the original objective function as penalty functions which are nonsmooth. Secondly, a new smooth function is introduced to replace the nonsmooth penalty functions. These operators convert the constrained optimization problem to a smooth unconstrained one which can be easily solved. Theoretical analysis on the approximation error between the constrained optimization problem and the transformed one is provided. Numerical results are also given to verify the proposed scheme in achieving the minimal DRR.

The preferred system gamma is primarily determined by the ratio of dynamic range of the original scene and the displayed image.

The dynamic range of real world scenes may vary from around 102 to greater than 107 , whilst the dynamic range of monitors may vary from 102 to 105 . In this paper, we investigate the impact of the dynamic range ratio (DRratio) between the captured scene and the displayed image, upon the value of system gamma preferred by subjects (a simple global power law transformation applied to the image). To do so, we present an image dataset with a broad distribution of dynamic ranges upon various subranges of a SIM2 monitor. The full dynamic range of the monitor is 105 and we present images using either the full range, 75% or 50% of this, while maintaining a fixed mid-luminance level. We find that the preferred system gamma is inversely correlated with the DRratio and importantly, is one (linear) when the DRratio is one. This strongly suggests that the visual system is optimized for processing images only when the dynamic range is presented correctly. The DRratio is not the only factor. By using 50% of the monitor dynamic range and using either the lower, middle or upper portion of the monitor, we show that increasing the overall luminance level also increases the preferred system gamma, although to a lesser extent than the DR ratio.

Gaussian approach versus Dolph‐Chebyshev synthesis of pencil beams for linear antenna arrays

A very simple and fast method for the synthesis of pencil beams with linear antenna arrays of equally spaced elements is presented. The proposed procedure starts selecting the desired pencil beam as a Gaussian function. This is very convenient for two reasons: first, the continuous line-source distribution that exactly produces the desired pencil beam (i.e. the Fourier transform of it) is in turn a Gaussian function and is immediately calculated. Second, a suitable weighted sampling of this distribution gives the excitations of the array elements in closed form. Two numerical examples reveal the good performances of the proposed approach, also in comparison with the classical method by Dolph-Chebyshev. It is shown that the synthesised array factors well approximate the desired pencil beams in real time, in particular ensuring a very good behaviour in the side lobe regions. Furthermore, the ‘dynamic range ratio’ of the excitations, defined as the ratio between the maximum and the minimum amplitude of the excitations, is very low and close to unity when the array length is sufficiently small.

Synthesis of a Scannable Pattern for 3D Cubic Antenna Arrays

ABSTRACTThe design of antenna arrays in a cubic geometry is presented in this paper. The decision variables considered for this synthesis problem are: the amplitude and phase excitations. The synthesis process is carried out by the technique of DEMO (Differential Evolution for Multi-objective Optimization) and NSGA-II (Non-Dominated Sorting Genetic Algorithm). Simulation results detailed by using an antenna array with isotropic elements and with circular patch antenna optimized by DEMO and NSGA- II are provided and compared. The disk patch antenna is formulated by the well-known cavity model. Furthermore, in order to discover which design case could provide a better performance in side lobe level, directivity, and the dynamic range ratio, a comparative analysis of the performance of the optimized design case with a conventional-phased cubic array is undertaken.

Pattern Synthesis of Unequally Spaced Linear Arrays Including Mutual Coupling Using Iterative FFT via Virtual Active Element Pattern Expansion

A virtual active element pattern (AEP) expansion method is presented in which each AEP in an unequally spaced array is considered to be the pattern radiated by a subarray of some equally spaced virtual elements. With the help of this method, the pattern of an unequally spaced array including mutual coupling can be efficiently evaluated by fast Fourier transform (FFT). By incorporating this idea into the iterative Fourier transform procedure, we develop a novel iterative synthesis method, which can apply the iterative FFT to efficiently synthesize unequally spaced arrays including mutual coupling. Different excitation constraints, such as phase-only control and amplitude-phase optimization with a prescribed dynamic range ratio, can be easily added into the proposed synthesis procedure. A set of synthesis examples for different antenna arrays with pencil and shaped beam patterns are provided to validate the effectiveness and advantages of the proposed method.

Synthesis of Conformal Phased Antenna Arrays With A Novel Multiobjective Invasive Weed Optimization Algorithm

AbstractBy virtue of the excellent aerodynamic performances, conformal phased arrays have been attracting considerable attention. However, for the synthesis of patterns with low/ultra-low sidelobes of the conventional conformal arrays, the obtained dynamic range ratios of amplitude excitations could be quite high, which results in stringent requirements on various error tolerances for practical implementation. Time-modulated array (TMA) has the advantages of low sidelobe and reduced dynamic range ratio requirement of amplitude excitations. This paper takes full advantages of conformal antenna arrays and time-modulated arrays. The active-element-pattern, including element mutual coupling and platform effects, is employed in the whole design process. To optimize the pulse durations and the switch-on instants of the time-modulated elements, multiobjective invasive weed optimization (MOIWO) algorithm based on the nondominated sorting of the solutions is proposed. A S-band 8-element cylindrical conformal array is designed and a S-band 16-element cylindrical-parabolic conformal array is constructed and tested at two different steering angles.

55‐3: Invited Paper: Delivering Content for HDR

In 2016, every major manufacturer revealed High Dynamic Range (HDR)‐compatible TVs. The technology promises a major improvement of the quality of images delivered to consumers. The goal of HDR technology is not to simply increase the contrast of existing images but to display more tonal details in the shadows and highlights. In combination with higher brightness levels and a larger color gamut, more realistic and captivating images are created.Current industry standards demand a contrast of 20000:1 or better for HDR displays opposed to about 1000:1 for traditional displays. This raises the requirements for the dynamic range of cameras used to produce HDR content. The ARRI ALEXA camera, released in 2010, is based on a sensor that has a dynamic range (ratio of full‐well capacity to read‐out noise) of approx. 30000:1. This very high range is achieved by a combination of a dual‐gain pixel architecture and an elaborate sensor calibration procedure. Without effective correction of nonuniformities, the usable dynamic range of the complete sensor may be less than the dynamic range of its single pixels. While existing workflows in motion‐picture and digital video are suitable to produce HDR content there are no well‐established procedures for the evaluation of the performance of digital cameras. An outline of such a procedure is proposed.

Reconfigurable Antenna Arrays with Multiple Requirements: A Versatile 3D Approach

This paper proposes a deterministic method for the 3D synthesis of antenna arrays that jointly accounts for far-field pattern reconfigurability, polarization setting, dynamic range ratio reduction, and near-field control. The conceived algorithm, which generalizes some existing solutions, relies on a weighted cost function, whose iterative minimization is accomplished by properly derived closed-form expressions. This feature, combined with the possibility of selecting the weighting parameters, provides a fast and versatile approach, whose capabilities are numerically checked by considering different synthesis problems and array structures in the presence of mutual coupling.

Multiple-ring Circular Array for Ground-Penetrating Radar Applications: Basic Ideas and Preliminary Results

In this paper, the possibility of using a multiple-ring circular array as an antenna array for Ground-Pene-trating Radar systems is investigated. The theory behind theproposed idea is presented. The preliminary numerical re-sults that are obtained suggest that the proposed congura-tion is promising. It allows achieving a wide frequency bandand low dynamic range ratio of excitations, thus simplifyingthe feeding network. Further interesting requirements maybe satised by exploiting a combination of deterministic andstochastic synthesis techniques to design the array.

Synthesis of Steered Flat-top Beam Pattern Using Evolutionary Algorithm

In this paper a pattern synthesis method based on Evolutionary Algorithm is presented. A Flat-top beam pattern has been generated from a concentric ring array of isotropic elements by finding out the optimum set of elements amplitudes and phases using Differential Evolution algorithm. The said pattern is generated in three predefined azimuth planes instate of a single phi plane and also verified for a range of azimuth plane for the same optimum excitations. The main beam is steered to an elevation angle of 30 degree with lower peak SLL and ripple. Dynamic range ratio (DRR) is also being improved by eliminating the weakly excited array elements, which simplify the design complexity of feed networks.

Array Pattern Synthesis With Excitation Control via Norm Minimization

Simple and efficient procedures are presented to synthesize antenna array patterns (focused or shaped beams) while controlling the excitations. This synthesis problem is of great practical interest as it makes active arrays more attractive by reducing their complexity, cost, and weight. With a proper regularization of the array pattern synthesis solution, the excitations can be optimized in order to design uniform amplitude sparse arrays, arrays whose excitations have a low dynamic range ratio or a smooth amplitude variation. More specifically, the synthesis procedures are composed of the minimization of a norm (mixed $\ell _{1}/\ell _{\infty }$ norm, total variation norm, or a combination of the $\ell _{1}$ - and $\ell _{\infty }$ -norms) associated with radiation pattern constraints. Various representative array synthesis problems are considered. Examples including the coupling between antennas and a comparison with a deterministic approach confirm both the usefulness and effectiveness of the proposed procedures.

Reduction of Dynamic Range Ratio through Competition Over Resources to synthesize planar array antennas

To synthesize planar arrays, a new optimization algorithm namely Competition Over Resources (COR) is presented. This method imposes deeper nulls with the constraint of Side Lobe Level (SLL). COR is a new meta-heuristic algorithm based on competitive behavior of animal groups over food resources. The algorithm restricts Dynamic Range Ratio (DRR) in order to achieve a better control of the mutual coupling and feed network. Simulation results for optimal patterns, possessing multiple and broad nulls, are presented. The approach is implemented based on the position-only and the space/amplitude optimization. Furthermore, in order to find the better performance in imposing deeper nulls and reducing SLL, a comparative evaluation between Particle Swarm Optimization (PSO) and COR is presented. Numerical results show that COR has better performance compared with PSO.

Focus on lasers and imaging

Focus on lasers and imaging

Full‐polarisation three‐dimensional pattern synthesis for conformal conical arrays with dynamic range ratio constraint by using the initialisations based on equivalence theorem

To design three-dimensional (3D) conformal conical arrays with desired 3D co-polarisation and cross-polarisation radiation patterns, a pattern synthesis method based on equivalent principle and trust region method is presented. Dynamic range ratio (DRR) of element excitations is taken into consideration. An analytical function is utilised to constrain DRR and avoid discontinuity of objective function. Owing to the optimisation is based on very good initial currents distribution, the optimisation procedure is very fast. The analytical gradient and Hessian matrix expressions of the objective function are derived. This also improves the optimisation efficiency compared with using the finite difference methods to solve gradient and Hessian matrix. To demonstrate the effectiveness of this proposed method, a conformal conical array with 454 elements has been designed. The amplitude and phase excitations were optimised by using the proposed method.

Pattern synthesis approach for circularly polarised four‐dimensional antenna arrays

A novel pattern synthesis approach for circularly polarised (CP) four-dimensional (4D) antenna arrays with microstrip patch elements is presented. Sequential rotation method is used to reduce the cross-polarisation component of the CP antenna array and good circular polarisation purity is achieved. Moreover, the time modulation technique of 4D antenna arrays is adopted for the realisation of low sidelobe levels (SLLs), thus forming a CP 4D antenna array. The differential evolution (DE) algorithm is used to optimise the time sequences, and hence low SLLs and sideband levels (SBLs) are obtained. To achieve low SLLs and low SBLs simultaneously, both of the static amplitude excitations and time sequences are optimised by the DE algorithm. Simulation results show that the CP 4D patch arrays can be used to achieve lower SLLs, while the dynamic-range ratios of the amplitude excitations can be very small or even uniform.

Shaped beam synthesis of concentric ring array antenna using Differential Evolution Algorithm

A shaped beam synthesis from a concentric ring array has been presented. Two different cases are considered. In the first case, a flat-top beam with desired specification has been generated and in the second case, a cosec2 beam pattern from the same array configuration is generated. The desired beam pattern in each of the individual case is obtained by finding optimum excitations of the array elements using Differential Evolution (DE) algorithm. Dynamic range ratio (DRR) of the excitation amplitudes are improved by eliminating the weakly excited array elements from the optimized array without distorting the obtained pattern. To illustrate the effectiveness of DE, the two beam-patterns are computed from the same array using Genetic Algorithm (GA) by finding out optimum excitations among the elements. Results clearly show the superiority of DE over GA to handle the proposed problem.