Ertugrul Aksoy

Thinned Nonuniform Amplitude Time-Modulated Linear Arrays

In this work, an array thinning procedure is introduced for nonuniform amplitude time-modulated linear arrays (TMLAs). Differential evolution algorithm (DE) is used for both thinning and time modulation (TM) of the given array to suppress the sidelobes and sidebands with fewer elements so as to achieve desired far-field radiation pattern. The array is thinned by using continuous weighting optimization. Several simulations are realized to evaluate the effectiveness and drawbacks of the proposed approach.

Calculation of Sideband Power Radiation in Time-Modulated Arrays With Asymmetrically Positioned Pulses

In this letter, the effect of shifting pulses of a time-modulated array (TMA) on sideband radiations is examined, and the total power formulation is generalized to asymmetric cases. Also, it is shown theoretically that shifting pulses changes the total power radiated in harmonics.

An Inequality for the Calculation of Relative Maximum Sideband Level in Time-Modulated Linear and Planar Arrays

In this work, the maximum point of relative sideband level (SBL) with respect to maximum level of main radiation (the radiation in carrier frequency) in time-modulated linear and planar arrays is examined. An inequality is derived which may be used for the determination and suppression of maximum relative sideband level. Performance analysis in terms of sideband level, harmonic power loss, directivity and feed network efficiency are conducted with state of the art methods to compare and to demonstrate the potential of the presented formulation for linear and planar cases.

Calculation of Sideband Radiations in Time-Modulated Volumetric Arrays and Generalization of the Power Equation

In this study, sideband radiation (SR) power calculation for time-modulated volumetric (conformal) arrays (TMVAs) is investigated and a closed form formulation is derived. The obtained formulation is combined with previous related works and a grid independent general representation of harmonic power radiation formulation is presented.

Estimating the parameters of 3-p Weibull distribution using particle swarm optimization

The Weibull distribution is used lifetime distributions in reliability engineering.The estimation of the parameters of this distribution is essential.Maximum likelihood (ML) estimation is a common method for parameter estimation.The working principle of ML estimation based on maximizing the likelihood function.We used particle swarm optimization as parameter estimation tool in 3-p Weibull. Weibull distribution plays an important role in failure distribution modeling in reliability studies and the estimation of its parameters is essential in the most real applications. Maximum likelihood (ML) estimation is a common method, which is usually used to elaborate on the parameter estimation. The maximizing likelihood function formed for the parameter estimation of a three-parameter (3-p) Weibull distribution is a quite difficult problem. Hence, the heuristic approaches must be used to discover good solutions. Particle swarm optimization (PSO) is a population based heuristic optimization technique developed from swarm intelligence. The performance of PSO greatly depends on its control parameters such as inertia weight and acceleration coefficients. Slightly different parameter settings may direct to very different performance. This paper gives a comprehensive investigation of different PSO variants (according to inertia weight procedures, acceleration coefficients, particle size, and search space) in the parameter estimation problem of 3-p Weibull distribution. Three explanatory numerical examples are given to show that PSO approach variants exhibit a rapid convergence to the maximum value of the likelihood function in less iteration, provides accurate estimates and PSO method is satisfactory for the parameter estimation of the 3-p Weibull distribution.

Estimating the parameters of 3-p Weibull distribution through differential evolution

The Weibull distribution is used lifetime distributions in reliability engineering.The estimation of the parameters of this distribution is essential.Maximum likelihood (ML) estimation is a common method for parameter estimation.The working principle of ML estimation based on maximizing the likelihood function.We used differential evolution algorithm as parameter estimation tool in 3-p Weibull. The Weibull distribution is one of the most widely used lifetime distributions in reliability engineering and the estimation of the parameters of this distribution is essential in the most real applications. Maximum likelihood (ML) estimation is a common method, which is usually used to elaborate on the parameter estimation. The working principle of ML estimation method based on maximizing the established likelihood function and maximizing this function formed for the parameter estimation of a three-parameter (3-p) Weibull distribution is a quite challenging problem. In this paper, this problem have been briefly discussed and an effective approach based on the differential evolution (DE) algorithm operators is proposed in order to enhance the estimation accuracy with less system resources. Three explanatory numerical examples are given to show that DE approach which requires significantly less CPU time and exhibits a rapid convergence to the maximum value of the likelihood function in less iterations, provides accurate estimates and is satisfactory for the parameter estimation of the 3-p Weibull distribution.

A dual channel AM receiver structure in 4D arrays

In this study, demodulation of two AM signals modulated using different frequencies and received by one time-modulated linear array is presented. In addition to sidelobe level control, fundamental harmonic beam is steered to desired direction to achieve the reception of both message signals, using pulse difference technique and variable pulse amplitude approach as excitation strategy for time modulation. It is asserted that two messages from different directions with different frequencies may be received simultaneously via a time-modulated array.

Harmonic beam steering in 4D linear arrays through pulse difference

In this study, a methodological beam steering approach in Time-modulated linear arrays is presented. The idea is simply based on the dynamic amplitude difference in order to provide a necessary phase shift to steer the main beam in harmonic frequencies. To illustrate the proposed approach a simple 10 element linear array with zero phase is considered and the asserted idea is tested on this reference array. The results show that the idea is applicable to harmonic beam steering problems.

Design of wideband conformal antenna array at X-band for satellite applications

In this study, the design and simulation of a circularly-bended antenna array at X-band for satellite applications is presented. Antipodal Vivaldi Antenna (AVA) is selected as an array element due to its wideband and end-fire characteristics. The proposed antenna, operating in the 8-12 GHz frequency range, provides good VSWR and high gain without degradation of radiation pattern caused by conforming operation. The design is intended to be used to in both satellite and ground systems with beam scanning capability.

A Comparative Study on Sideband Optimization in Time-Modulated Arrays

A comparative analysis of the three different methods known as sideband level suppression (SBL), sideband radiation suppression (SR), and sideband bound suppression (SB) which are used in sideband calculations for time-modulated arrays (TMAs) is presented. The three methods are investigated in terms of sideband level, sideband power, time average directivity, and solution time for TMAs so as to show the performances and potentialities of these distinct techniques. The problems of interference suppression, sidelobe cancelling, and joint interference suppression and sidelobe cancelling are analyzed for a time-modulated linear array. In the linear array 30 elements are used and the interelement spacing is determined to be a half-wavelength. During the investigations, differential evolution (DE) algorithm is chosen as the optimization tool. The common variable aperture size (VAS) time schemes are optimized to synthesize the desired goals in order to compare the techniques. The results show that the SB method is more convenient than the other two compared methods.