Phase-only Control Research Articles

Synthesis Technique of Array-Fed Shaped-Reflector Antenna for DBF-SAR Application

This letter presents a new approach to synthesize patterns of a phased-array-fed shaped-reflector antenna for digital beamforming (DBF) synthetic aperture radar (SAR). This type of reflector antenna is capable of radiating different broad transmitting beams under phase-only control and can generate narrow receiving beams using DBF technique in the elevation direction, which is applicable to a high-resolution wide swath (HRWS) SAR system. The linear array feed locates at the defocused area of the reflector, which can enhance the beam reconfiguring ability. The elevation patterns are optimized mainly by adjusting the excitation coefficients of the array feed using improved Projection Matrix Algorithm (PMA). The azimuth patterns are optimized mainly by adjusting the reflector shape using Differential Evolution method with Global and Local neighborhood (DEGL). The patterns of the shaped reflector antenna fed by a defocused feed array are effectively synthesized, including scanning and reconfiguring beams. A numerical analysis is performed that validates the effectiveness of the approach. The beam direction, beamwidth, and sidelobe level requirements are all met.

Control of dephasing in rotationally hot molecules

We consider a rotationally hot diatomic molecule as an example of an open quantum system, where molecular vibrational wave packets are subject to dephasing due to rovibrational coupling. We report analytical and numerical results addressing whether the dephasing rate can be controlled by adjustment of the initial wave packet phases. It appears that over long time scales, phase-only control is not possible, but for earlier time scales the possibility of phase-only control of dephasing remains. In addition, we point out that the time dependence of the dephasing process depends significantly upon the degeneracy of the rotational environment states.

Mode selectivity with polarization shaping in the mid-IR

We report that polarization-shaped mid-infrared (IR) pulses can be used to enhance the vibrational population of one mode over another in a coupled molecular system. A genetic algorithm and a new mid-IR polarization shaper were used to alter the relative vibrational excitation of the two carbonyl stretching modes in Mn(CO)5Br. One mode could be selectively enhanced over the other by 2–3 times. Control over the polarization leads to better optimization than phase-only control. Several possible mechanisms that indicate how polarization shaping leads to selective vibrational excitation are discussed using a formalism that separates polarization shaping effects on the signal strength from amplitude or phase shaping. The techniques introduced herein will have broad applications in quantum gating schemes, controlling ground state chemistry and enhancing the sensitivity of multidimensional IR and visible spectroscopies.

Reconfigurability and Beam Scanning With Phase-Only Control for Antenna Arrays

A new method is presented on constrained power synthesis for reconfigurable arrays of arbitrary geometry. Given a number of suitable masks, the algorithm yields excitation vectors whose array patterns belong to such masks, and for each array element the excitation amplitude holds constant during the pattern reconfiguration, so as to ensure phase-only control. Each excitation amplitude is optimized, and the method allows to control the dynamic range ratio (DRR) of the excitations. The solution to the synthesis problem is found as a point of the intersection between two suitable sets, by using the method of successive projections. The proposed method can also be used to solve problems of constrained beam scanning. To this aim it is sufficient to select a high number of masks, close to each other in the angular sector of interest and shaped in such a way as to reproduce the desired scanning beam. The algorithm yields array patterns belonging to these masks, thus performing a discrete scanning by phase-only control, and allows to control the DRR. Several numerical examples show the effectiveness and the capabilities of the method.

General synthesis method for linear phased antenna array

An efficient phase-only control method is presented to synthesise directive lobe and multilobe patterns, and create adaptive nulls in interference direction. The proposed method is based on iterative minimisation of a function that incorporates constraints imposed in each direction with respect to excitation phases. To verify the performances of the proposed technique, an eight-element array has been realised and tested for various types of beam configurations.

Interference suppression of linear antenna arrays by phase-only control using a clonal selection algorithm

In this paper, an efficient technique based on clonal selection algorithm (CLONALG) for linear antenna array pattern synthesis with null steering by controlling only the element excitation phases is presented. The CLONALG is an evolutionary computation method inspired by the clonal selection principle of human immune system. To show the versatility and flexibility of the proposed CLONALG, some examples of Chebyshev array pattern with the imposed single, multiple and broad nulls are given. The sensitivity of the nulling patterns due to small variations of the element phases is also investigated.

Genetic Algorithms for Design of Discrete Phase-only Reconfigurable Array Antennas with Fixed Dynamic Range Ratio

In this paper, we present a new method based on real-coded Genetic Algorithm (GA) with elitist model for optimal design of a reconfigurable symmetrical dual-beam uniformly spaced linear isotropic antenna array with phase-only control of quantized phase shifters. The problem is to find a common amplitude distribution that will generate a pencil beam with zero phases and a flat-top beam with discrete phases of a six-bit discrete phase shifter, without or with pre-fixing the value of dynamic range ratio (|I max/I min|) of excitation current amplitude distribution equal to or less than five.

Beam Scanning with Null and Excitation Constraints for Linear Arrays of Antennas

We describe a synthesis technique that allows to scan the radiation pattern of a linear antenna array within a wide angular sector, in presence of null constraints and excitation constraints. In particular, the method allows the beam scanning with null constraints and phase-only control. The algorithm yields a number Q of array patterns approximating Q desired patterns close to each other in the scan sector, while satisfying the assigned constraints. The solution, that is, the sequence consisting of the Q synthesized patterns and of the corresponding excitation vectors, can be seen as the point of intersection between two sets of sequences, Y and Z. The points of Y satisfy a part of the design requirements, while the points of Z satisfy the remaining requirements. If the set Y ∩ Z is empty, the solution is found as a point of one of the two sets minimizing a suitable distance from the other. This point is determined by the method of projections.

Analytical array polynomial method for linear antenna arrays with phase-only control

A new analytical synthesis technique is developed for the phase-only control of linear antenna arrays and is based on the Schelkunoff's unit circle. The array factor is formulated as an array polynomial in the complex z-plane and as a product of corresponding subpolynomials such that their roots are located on the unit circle. A constraint is derived such that the expansion of the subpolynomials yields current excitations with unity magnitudes. In general, the constraint of phase-only control forces some element excitations to be zero for an arbitrary number of array elements. The subpolynomial with the largest degree is used to synthesize the main beam characteristics. The null steering for interference suppression is obtained by using only one subpolynomial to steer only one null. The results verify the developed analytical solution to synthesize the prescribed patterns using the phase shifters of the linear antenna arrays.

An Innovative Computational Approach Based on a Particle Swarm Strategy for Adaptive Phased-Arrays Control

In this paper a new approach to the control of phased arrays is presented and assessed. Starting from the adaptive array theory, a particle swarm strategy is used to tune the phase coefficients of the array in order to adaptively minimize/avoid the effects of interfering signals at the receiver. To show the effectiveness of the proposed approach, a selected set of numerical examples, concerned with linear as well as planar arrays, is presented. Furthermore, to evaluate the advantages of the particle swarm optimizer (PSO)-based strategy over state-of-art methods, a comparative study is carried out by analyzing the performance of the method in terms of both the signal-to-interference-plus-noise-ratio and resulting beam pattern. The achieved results, even though preliminary, seem to confirm that the PSO-based approach satisfactorily works and it generally outperforms previously proposed/state-of-art phase-only adaptive control strategies

PSO-Based Real-Time Control of Planar Uniform Circular Arrays

This letter is aimed at assessing the effectiveness of the phase-only control strategy based on a customized PSO when applied to planar uniform circular arrays (PUCA) and in the presence of interferences both in the near-field and far-field of the antenna. The employed geometry seems to be suitable for a reliable and effective implementation of adaptive arrays in mobile devices thanks to its symmetry and geometric simplicity. For validation purposes, the proposed architecture is evaluated in the presence of a complex time-varying scenario both in terms of synthesized beam patterns and signal-to-interference-plus-noise ratio

GENETICALLY EVOLVED PHASE-AGGREGATION TECHNIQUE FOR LINEAR ARRAYS CONTROL - Abstract

This paper presents a modified Genetic Algorithm (GA) technique in which the large phase perturbations are calculated by aggregating small phase increments. The proposed aggregation GA technique overcomes the major drawback of the large solution space required by the classical GA techniques. The proposed method adopts small ranges for increments of the parameters and the optimality is reached via aggregation of the best increments of phases. Consequently, the GA searches in a smaller solution space and finds the solution with reduced number of iterations. Simulation results show the achieved improvement of the proposed technique over the classical GA. The suppressed sectors using phase-only control are accomplished with and without element failures. Problems like imposing symmetrical nulls around the mainbeam and compensation for the failure of center element have been achieved.

The phase-only shaping and adaptive nulling of an amplitude pattern

An efficient phase-only control method is reported for shaping a given antenna array amplitude pattern and simultaneously placing adaptive nulls in unknown interference directions. The method iteratively minimizes a functional (that incorporates constraints imposed on the desired pattern shape and power measured at the array output) with respect to phases of the array element excitations and to the phase of the given amplitude pattern by a coordinate-by-coordinate (single-coordinate) method that finds the minimum along each coordinate by a closed-form formula using three power measurements per one iteration. The method shows fast convergence, is stable to phase shifter errors, and complies with the digital phase control. Results of computer modeling are provided.

Genetically Evolved Phase-Aggregation Technique for Linear Arrays Control

This paper presents a modified Genetic Algorithm (GA) technique in which the large phase perturbations are calculated by aggregating small phase increments. The proposed aggregation GA technique overcomes the major drawback of the large solution space required by the classical GA techniques. The proposed method adopts small ranges for increments of the parameters and the optimality is reached via aggregation of the best increments of phases. Consequently, the GA searches in a smaller solution space and finds the solution with reduced number of iterations. Simulation results show the achieved improvement of the proposed technique over the classical GA. The suppressed sectors using phase-only control are accomplished with and without element failures. Problems like imposing symmetrical nulls around the mainbeam and compensation for the failure of center element have been achieved.

Low-sidelobe patterns from linear and planar arrayswith uniformexcitations except for phases of a small number of elements

The use of genetic algorithms allows synthesis of linear and planar arrays with excitations of uniform amplitude that generate radiation patterns with sidelobe levels closely approaching the recognised minima for phase-only control, in spite of only a small number of elements having non-zero phase.

Ultrafast unidirectional beam deflection using an electrooptic traveling phase grating with periodic domain inversion

We report a new electrooptic traveling-phase grating with periodic domain inversion and its application to ultrafast unidirectional beam deflection. The electrooptic traveling phase grating utilizes Raman-Nath diffraction to spatially separate input light to many diffracted beams on the far-field plane. Then, unidirectional optical beam deflection can be achieved by adjusting amplitudes and phases of the diffracted beams. In the experiment, ultrafast unidirectional deflection by the traveling phase grating is demonstrated at 16.25 GHz using a simple phase-only control.

Phase-only control of antenna sum and shaped patterns through null perturbation

Satisfactory sum or shaped antenna radiation patterns can often be synthesized by modifying just the phase distribution of an initial excitation by an arbitrary amplitude distribution. As examples, we calculate linear and circular apertures with uniform, Taylor, or cosine-section amplitude distributions, affording symmetric sum patterns with low sidelobe levels or symmetric shaped patterns with low ripple and sidelobe levels; linear aperture distributions, affording patterns with low sidelobe levels on one side of the beam; and planar arrays, with uniform or cosine-section amplitude distributions affording /spl phi/-symmetric or elongated-oval footprints.

Null synthesis by phase control for antenna arrays

The author presents a method for forming nulls in prescribed directions in the radiation pattern P0 of an antenna array by phase-only control. The method modifies the excitation phases of P0, allowing the construction of a sequence of patterns {Pn} having increasingly deeper nulls. A solution is provided by terminating the sequence at a suitable step.

Synthesis of spectrum of packet of radio pulsesby phase-only control

An iterative fast-convergent phase-only method for shaping the amplitude spectrum of a packet of radio pulses is developed. Its efficiency is verified by a numerical experiment.

Pattern Nulling By Iterative Phase Perturbation

This paper presents a method for linear array pattern synthesis with multiple suppressed sectors using phase-only control of the antenna elements. Large phase perturbations are obtained by solving the nonlinear problem using an iterative procedure with linear programming. This technique can impose symmetrical and non-symmetrical suppressed sectors in the perturbed pattern. The full phase-only control is accomplished as well as the partial control of the edge elements. The partial control leads to a significant reduction in the number of phase shifters used for sector suppression as compared to the full control implementation.