Time-modulated Linear Antenna Arrays Research Articles

Time‐modulated multi‐tone antenna array for wireless information and power transfer

SummaryThis paper aims to design a multi‐tone radiator exploiting harmonic radiation characteristic of time‐modulated antenna array for wireless information and power transmission (WIPT) and multi‐operational WIPT receiver. The time‐modulated linear antenna array (TMLAA) radiating simultaneously at modulating and harmonic frequencies separated in multiple switching periods is utilized as a multi‐tone radiating system. TMLAA with suitable power in harmonic bands generates multi‐tone radiation by employing an optimized switching sequence. The ON and OFF time instants of the TMLAA are optimized to suppress sidelobe level and enhance sideband level. A population‐based optimization algorithm, teaching learning based optimization (TLBO), is employed to optimize the ON and OFF instants of the TMLAA to suppress sidelobe level and enhance sideband level. TLBO is utilized for a 16‐element TMLAA with minimizing cost function to achieve the above objectives. The 16‐element TMLAA with optimized switching radiates multi‐tone beams with a minimum of 5 dB peak power difference exploited as WIPT. The purpose of multi‐operation is accomplished by utilizing the Wilkinson power divider in the receiver system; its power dividing capability is analyzed using applied wave research (AWR). A voltage doubler type rectifier is modeled for DC generation and is tested using AWR. The DC generating capability is tested for fixed power available at various frequencies, and the fixed desired frequency with various available power levels is tested. The results show that the designed circuitry provides a maximum of 80% power conversion efficiency (PCE).

Power leakage minimization in time‐modulated linear antenna array with optimized switching strategies employing modified harmony search algorithm

Time-modulated linear antenna array (TMLAA) with periodic time modulation of antenna elements radiates infinite inevitable harmonic beams. The infinite harmonic sideband radiation is a wastage of power unless the power is exploited. This paper aims to minimize inevitable power wastage in the harmonic beams radiated from TMLAA by employing an optimized periodic timing sequence. The optimization of the timing sequence is conducted employing harmony search (HS) to suppress the power wastage, However, conventional HS achieves an acceptable sidelobe level (SLL) below – 30 dB. Nevertheless, a modified harmony search algorithm (MHSA) is proposed to attain more power in the desired fundamental beam. The algorithm is validated using an array of 4-, 10-, and 16-element uniform half-wavelength spacing TMLAA. The optimization is conducted on the ON and OFF time instants and the real current of the elements. The simulation results exhibit that HS and MHSA perform potentially alike to suppress the SLL of fundamental below –30 dB. However, the further suppression of the sideband levels employing MHSA justifies the modification proposed in this work. The MHSA performance in terms of radiation parameters is compared with the HS and also with previous works to show the potentiality of the modification.

Elements Failure Detection and Radiation Pattern Correction for Time-Modulated Linear Antenna Arrays Using Particle Swarm Optimization

Elements Failure Detection and Radiation Pattern Correction for Time-Modulated Linear Antenna Arrays Using Particle Swarm Optimization

Multi‐beam steered harmonic pattern synthesis in timed antenna array with optimized and pre‐defined RF switching

AbstractOptimal harmonic beam steering of the time‐modulated linear antenna array (TMLAA) with optimized and pre‐defined ON and OFF switching schemes are proposed in this work. Three different approaches are considered to obtain various beam steering behaviors of TMLAA. The first approach is considered for the optimization of ON–OFF switching sequence for the steering of the harmonic beams toward approximately ±30° along with the simultaneous reduction of side lobe level (SLL) and side band level (SBL). Second approach is considered for the optimization of ON–OFF switching sequence for the steering of the harmonic beams toward approximately ±30° and ±60° simultaneously. Third approach is considered for the optimal reduction of SLL and SBL of harmonically steered beams for a pre‐defined ON–OFF switching scheme. Two unique cost function is proposed in this work to achieve the optimal parameter for above mentioned three different approaches. The first cost function is used for the optimization of Ton and Toff switching sequence and antenna element spacing of the array. These optimal values will lead to steer the main beam of first positive and negative harmonic radiation from the main beam of the fundamental radiation pattern and reduce SLL and SBL simultaneously. Second cost function deals with the optimization of excitation amplitude and distance between any two consecutive antennas of the array. These optimal values lead to reducing the SLL and SBL simultaneously harmonically steered beam obtained by pre‐defined Ton and Toff switching sequence. Optimization algorithm applied to get the optimal value of the variable parameters is Novel Particle Swarm Optimization. Further to explain the stated proposed approach, four different sets of 10‐, 16‐, 20‐, 32‐element TMLAA are taken as an example. Some of the simulation results are validated through electromagnetic simulator to validate the result obtained by MATLAB.

A PSO-CVX Algorithm of Sum and Difference Beam Patterns for Time-Modulated Antenna Array

An integrated optimization of sum and difference beam for time-modulated linear antenna array is studied in this paper. The goal of sum and difference beam synthesis is to generate sum beam in the main band and difference beams in the first-order sideband with low side-lobe level through timing switches. The turn-on times of antenna array are achieved by solving a quadratic constraint linear programming; meanwhile, the opening times are optimized by particle swarm optimization algorithm. The results of linear array show that the sum and difference beam can be scanned within ± 40 degrees, with lower peak side-lobe level.

An optimal far‐field radiation pattern synthesis of time‐modulated linear and concentric circular antenna array

AbstractIn this paper, an optimal far‐field radiation pattern synthesis by using time modulation technique is carried out for linear antenna array (LAA), and concentric circular antenna array (CCAA) designs using a stochastic optimization method called grey wolf optimization (GWO). An improved far‐field radiation characteristic mainly depends on the synthesis of low side lobe level (SLL) and narrow first null beam width (FNBW). A low SLL is a requirement to reduce the interference by the other systems operating in the same frequency band. A narrow FNBW is necessary to obtain a high directivity. In time modulation technique, “time” has a most significant role. It is considered as the fourth‐dimensional parameter as it plays the role of an additional degree of freedom to achieve an improved radiation pattern. The time‐modulated antenna array (TMAA) radiates at various harmonic frequencies for the periodic switching time sequence. In this paper, the generation of radiation pattern only at the fundamental/central frequency and at its first two harmonic frequencies are considered. The GWO algorithm is a flexible and robust search algorithm and is applied here to find out the optimum sets of switching on‐time duration for each array element and to determine the optimum inter‐element separation between two array elements of the 16‐element time‐modulated linear antenna array (TMLAA) and the nine‐ring time‐modulated concentric circular antenna array (TMCCAA). The GWO algorithm‐based results show a substantial improvement in far‐field radiation pattern synthesis compared with the uniform radiation pattern and those of the methods reported in state‐of‐the‐art literature.

Null Placement in Time-Modulated Linear Antenna Arrays of Dipole Element

ABSTRACTThis paper describes the practical implementation of time-modulated linear dipole antenna arrays (TMLDAAs) using EM simulator. Cat swarm optimization (CSO) algorithm is applied to improve the null performance of TMLDAAs by radio frequency switch. The nulls at the particular positions of the direction of arrival of a TMLDAA can be reduced effectively by the proper optimization of current excitation weights and an effective design of switch-on time intervals of each element. CSO gives the optimized value of the current excitation weights of the radiation pattern. The optimized results obtained by CSO algorithm using MATLAB simulation are practically implemented and are designed through computer simulation technology–microwave studio simulation software for half-wave dipole antenna arrays. The dipole antenna is designed to operate at a resonant frequency of 2 GHz. The antenna exhibits a frequency band from 1.8331 to 2.1285 GHz, which is applicable for wireless applications.

Monopulse time‐modulated antenna array using iterative Fourier technique

SummaryThe iterative Fourier technique (IFT) is applied to design monopulse radar tracking system using time‐modulated linear antenna array (TMLA). IFT is used to modify the time sequences of the radio‐frequency switches connected to the antennas to generate sum and difference patterns with suppressed interference‐plus‐noise signal while constraining the power losses associated with side‐band radiation (SBR). The time modulation allows quick and precise control of the excitation distribution, which increases the tracking accuracy. To obtain best angle sensitivity, the article computes the tradeoff among side‐lobe level (SLL), half power beam width, directivity, and dynamic efficiency. The approach is proved successful to handle several design constraints through adaption in radiation domain as well as in aperture domain. Authors illustrate additional representative TMLA examples where the time sequences of the selected elements are prefixed to enhance the dynamic efficiency and directivity for different SLL and side‐band level (SBL). Application of IFT saves the computational cost significantly with respect to existing state‐of‐the‐art optimization techniques. Introduction of the symmetric switching sequences simplifies the feed network greatly. The proposed design solution is validated with a fabricated TMLA prototype consisting of two time‐switched printed dipoles with microstrip via‐hole balun at 2.45 GHz. Copyright © 2016 John Wiley & Sons, Ltd.

Design of digitally controlled multiple-pattern time-modulated antenna arrays with phase-only difference

An optimization approach based on differential evolution (DE) is proposed to design multiple-pattern time-modulated linear antenna arrays (TMLAAs) with phase-only control by using 5-bit digital phase shifters. The synthesized multiple patterns include a pencil beam (PB), a flat-topped beam (FTB), and a cosec squared pattern (CSP). The function of the DE is to find, simultaneously, a common, i.e., fixed, set of continuous values of switch-on time durations and discrete static excitation amplitudes for 5-bit digital attenuators, and different sets of discrete excitation phase distributions for 5-bit digital phase shifters; to generate different power patterns in the far field of the TMLAA. By perturbing the static amplitude distribution of a 20-element TMLAA in the discrete search range of “(0.2–1),” the patterns are obtained by reducing side lobe levels (SLLs) to almost −20 dB and sideband levels (SBLs) to less than −25 dB. Towards the end, the same on-time and amplitude distribution is used to produce a symmetric side lobe (S-SL) and asymmetric side lobe (A-SL) CSP, and their usefulness under a noisy signal environment is discussed.

SYNTHESIS OF SIMULTANEOUS MULTIPLE-HARMONIC-PATTERNS IN TIME-MODULATED LINEAR ANTENNA ARRAYS

In time-modulated antenna arrays (TMAAs), as a result of periodical switch-on and switch- ofi of the antenna elements, including operating frequency (termed as center frequency) signal, sideband signals are appeared at either sides of the center frequency in integer multiples of the modulation frequency. In this paper, it is shown that without using phase shifters, just by suitably controlling the on-time instants (OTIs) and on-time durations (OTDs) of a time-modulated linear antenna array (TMLAA) elements, simultaneously, along with a pencil beam pattern at the operating frequency, a shaped beam pattern can be obtained at both the flrst positive and negative harmonics of the time- modulation frequency. The important advantage of such a technique is that realization of multi-beam pattern in conventional antenna array (CAA) system generally requires complex feed network, whereas by using simple radio frequency (RF) switching circuit in the feed network of TMLAA, by virtue of the properties of harmonic radiations, synthesis of a shaped pattern at either (positive or negative) harmonic results in generating the same pattern in its opposite harmonic, and the synthesized patterns at difierent harmonics can be simultaneously used as independent communication channels. By employing a difierential evolution (DE) based optimization method, numerical results for a 16-element TMLAA with uniform excitation show that in conjunction with a pencil beam pattern at the center frequency, a ∞at-top or a cosec square pattern at flrst positive and negative sidebands of side-lobe levels (SLL) i20dB can be synthesized by suppressing the higher sideband level (SBL) to below i10dB.

Nulls and side lobe levels control in a time modulated linear antenna array by optimizing excitations and element locations using RGA

In this paper a novel approach based on the Real coded Genetic Algorithm (RGA) is proposed to improve nulling performance as well as suppression of Side Lobe Level (SLL) of a Time Modulated Linear Antenna Arrays (TMLA). RGA adjusts the static excitation amplitudes as well as the location of each element from the origin to place deeper nulls in the desired direction. Three design examples are presented that illustrate the use of the RGA, and the optimization goal in each example is easily achieved.

DIFFERENTIAL EVOLUTION ALGORITHM FOR OPTIMIZING THE CONFLICTING PARAMETERS IN TIME-MODULATED LINEAR ARRAY ANTENNAS

In this paper, a new technique is proposed to optimize the con∞icting parameters like low value of maximum side lobe level (SLL), narrow beam-width of the main beam and low value of maximum sideband radiation level (SRL) of time-modulated linear antenna arrays (TMLAAs). The method is based on minimizing a multi-objective fltness function by using single-objective difierential evolution algorithm (DEA) technique. The method is applied to both uniformly excited TMLAA (UE-TMLAA) and non-uniformly excited TMLAA (NUE-TMLAA) to synthesize low side lobe optimum pattern at operating frequency by suppressing the sideband radiation level to a su-ciently low value. For UE-TMLAA only the switch- on time durations of the array elements and for NUE-TMLAA the switch-on time durations and the static amplitudes with predetermined dynamic range ratio (DRR) of static amplitudes are taken as the optimization parameters for the DEA. To show efiectiveness of the proposed approach, the single-objective DEA optimized results are compared with those obtained by other single objective and multi- objective techniques that has been reported previously. Also, flrst null beam width (FNBW) and half power beam width (HPBW) of the DEA optimized patterns at fundamental radiation are compared with those of the Dolph-Chebyshev (D-C) pattern of same SLL.

Adaptive Nulling with Time-Modulated Antenna Arrays Using a Hybrid Differential Evolution Strategy

A flexible approach based on a hybrid differential evolution strategy was developed for adaptive pattern nulling with time-modulated linear antenna arrays. The hybrid differential evolution strategy adjusts only the least significant bits of the digital phase shifters and the on—off time sequence to minimize the total output power; deep nulls can then be placed in the direction of the interferences without much compromise of the shape of the main beam. Thanks to the new design freedom introduced in time-modulated antenna arrays, this adaptive nulling approach exhibits better performance over the traditional phase-only, amplitude-only, and phase-amplitude adaptive nulling methods, in terms of the practical implementation, nulling depth, and pattern deterioration. Numerical examples are presented to demonstrate the effectiveness and robustness of the proposed approach.

DESIGN OF TIME-MODULATED LINEAR ARRAYS WITH A MULTI-OBJECTIVE OPTIMIZATION APPROACH

This article proposes a Multi-objective Optimization (MO) framework for the design of time-modulated linear antenna arrays with ultra low maximum Side Lobe Level (SLL), maximum Side Band Level (SBL) and main lobe Beam Width between the First Nulls (BWFN). In contrast to the existing optimization-based methods that attempt to minimize a weighted sum of SLL, SBL, and BWFN, we treat these as three distinct objectives that are to be achieved simultaneously and use one of the best known Multi- Objective Evolutionary Algorithms (MOEAs) of current interest called MOEA/D-DE (Decomposition based MOEA with Difierential Evolution operator) to determine the best compromise among these three objectives. Unlike the single-objective approaches, the MO approach provides greater ∞exibility in the design by yielding a set of equivalent flnal solutions from which the user can choose one that attains a suitable trade-ofi margin as per requirements. We compared time-modulated antenna structures with other methods for linear array synthesis such as the excitation method and the phase-position synthesis method on the basis of the approximated Pareto Fronts (PFs) yielded by MOEA/D-DE and the best compromise solutions determined from the Pareto optimal set with a fuzzy membership- function based method. The flnal results obtained with MOEA/D-DE were compared with the results achieved by two state-of-the-art single objective optimization algorithms and flve other MO algorithms. Our simulation studies on three instantiations of the design problem re∞ect the superiority of the MOEA/D-DE based design of time-modulated linear arrays.

Multiple Patterns from Time-Modulated Linear Antenna Arrays

In this article, the design of multiple radiation patterns from time-modulated linear antenna arrays is presented. As compared to conventional linear arrays in generating multiple patterns by switching among different phase distributions, the time-modulated linear arrays are capable of realizing more stringent requirements such as lower sidelobes for the multiple patterns. Moreover, the time-modulated linear arrays with pre-assigned amplitude distributions can be used to synthesize a greater number of desired patterns due to their additional degree of design freedom. Different excitations for multiple patterns are obtained through the differential evolution algorithm while keeping the sidebands minimized. Numerical examples of synthesizing several typical radiation patterns from time-modulated linear arrays are presented.