Erkan Afacan

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.

The effect of frequency, multi resonator and relay resonator conditions on wireless power transmission

Wireless power transmission has begun to enter our daily life recently. In this paper, the effect of various frequencies on wireless power transmission is investigated. Energy transfer efficiency for multi transmitter and receiver condition is also presented. When there is a relay resonator between transmitter and receiver, it is shown that the efficiency increases. Also the alignment of resonators in vertical and horizontal axes is discussed.

Some experiments related to wireless power transmission

In recent years wireless power transmission has become very popular. We investigated how the efficiency changes when the characteristic impedance changes for single frequency and for several wave types. We have also emphasized single transmitter and double receiver conditions.

Beam steering antenna design for low altitude radar systems

A beam steering offset parabolic antenna with array feed is proposed for low altitude radar systems in order to minimize the undesired effect of irregular terrain obstacles between the radar and the target. This study provides information for the low altitude target located behind an obstacle. Focal region fields of the offset parabolic reflector are calculated in order to determine the array element location. Main beam of the reflector antenna with array feed is steered in order to compensate the low level field strength due to irregular terrain effects by adjusting excitation conditions of the array elements. The excitation conditions of the array elements are determined using Conjugate Gradient Method.

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.

Irregular terrain modeling for the low altitude radar applications

In this study obstacle models for wave propagation over irregular terrain for low altitude radar and TX-RX network planning are investigated. Obstacles between the radar and target can be modeled as wedges or convex surfaces depending on the terrain structure. The effect of these different models over field strength are calculated using the uniform geometrical theory of diffraction. The results are compared with each other.<<ETX>>

Modeling obstacles as cascaded ellipses

Obstacles over propagation paths are generally modeled as wedges and cylinders. For some terrain geometries it is more advantageous to use an ellipse model. In this study an ellipse is cascaded with a wedge or an ellipse. The results (for an operating frequency of 10 GHz) are compared with the results of the double wedge model of Luebbers (1984), and Afacan et. al. (1991).

Location Optimization for Square Array Antennas Using Differential Evolution Algorithm

In recent works thinned arrays giving minimum peak sidelobe levels for planar square antenna arrays are obtained using Hadamard difference sets. In the current work thinned array configurations giving lower peak sidelobe levels than those given in the literature are obtained for square arrays of , , , and elements. Differential evolution algorithm is used in the determination of the antenna locations.