Browsing by Subject "Antenna arrays"
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Item Open Access Analysis of cylindrically conformal antennas using closed-form Green's function representations(IEEE, 2015-04) Kalfa, Mert; Karan, S.; Ertürk, Vakur B.Probe-fed microstrip patch antennas and slotted sectoral waveguide array antennas embedded in cylindrically stratified media are analyzed with a hybrid Method of Moments/Green's function technique, where closed-form Green's function representations for electric and magnetic current sources are used as the kernel of the associated integral equations. Various patch and slot antennas are analyzed using the proposed method. Numerical results in the form of input impedance, S-parameters, and radiation patterns are presented and compared to the results obtained from CST Microwave Studio™ and HFSS™.Item Open Access Analysis of finite arrays of axially directed printed dipoles on electrically large circular cylinders(IEEE, 2004) Ertürk, V. B.; Rojas, R. G.; Lee, K. W.Various arrays consisting of finite number of printed dipoles on electrically large dielectric coated circular cylinders are investigated using a hybrid method of moments/Green's function technique in the spatial domain. This is basically an "element by element" approach in which the mutual coupling between dipoles through space as well as surface waves is incorporated. The efficiency of the method comes from the computation of the Green's function, where three types of spatial domain Green's function representations are used interchangeably, based on their computational efficiency and regions where they remain accurate. Numerical results are presented in the form of array current distributions, active reflection coefficient and far-field pattern to indicate the efficiency and accuracy of the method. Furthermore, these results are compared with similar results obtained from finite arrays of printed dipoles on grounded planar dielectric slabs. It is shown that planar approximations, except for small separations, can not be used due to the mutual coupling between the array elements. Consequently, basic performance metrics of printed dipole arrays on coated cylinders show significant discrepancies when compared to their planar counterparts. © 2004 IEEE.Item Open Access Analysis of finite arrays of circumferentially oriented printed dipoles on electrically large cylinders(Wiley, 2004) Ertürk, V. B.; Güner, B.An efficient and accurate hybrid method of moments (MoM)/Green's function technique in the spatial domain is developed for the rigorous analysis of large, finite phased arrays of circumferentially oriented printed dipoles on electrically large, dielectric-coated, circular cylinders. Basic performance metrics (in the form of array current distribution, active reflection coefficient, far-field patterns, and so forth) of several arrays have been obtained and compared with similar printed arrays on grounded planar substrates. Certain discrepancies have been observed and discussed. © 2004 Wiley Periodicals, Inc.Item Open Access Applications of hybrid discrete Fourier transform moment method to the fast analysis of large rectangular dipole arrays printed on a thin grounded dielectric substrate(Wiley, 2002) Chou, H.-T.; Ho, H.-K.; Civi, O. A.; Erturk, V. B.Recently a discrete Fourier transform-method of moments (DFT-MoM) scheme was developed for fast analysis of electrically large rectangular planar dipole arrays, which has been shown to be very efficient in terms of number reduction of unknown variables and computational complexity. The applications of this DFT-MoM to treat dipole arrays printed on a grounded dielectric substrate are examined in this Letter. Numerical results are presented to validate its efficiency and accuracy.Item Open Access Capacity of printed dipole arrays in the MIMO channel(Institute of Electrical and Electronics Engineers, 2008-10) Tunc, C. A.; Aktas, D.; Ertürk, V. B.; Altintas, A.Moments performance of printed dipole arrays in the MIMO channel is investigated using a channel model based on the Method of solution of the electric-field integral equation. Comparisons with freestanding dipoles are given in terms of channel capacity. Effects of the electrical properties (such as the dielectric thickness and permittivity) on the MIMO capacity are explored. Various dielectric-substrate configurations yielding high-capacity MIMO arrays are presented.Item Open Access Comparison of the CAF-DF and sage algorithms in multipath channel parameter estimation(IEEE, 2008-07) Güldoğan, M. Burak; Arıkan, OrhanIn this paper, performance of the recently proposed Cross Ambiguity Function - Direction Finding (CAF-DF) technique is compared with the Space Alternating Generalized Expectation Maximization (SAGE) technique. The CAF-DF, iteratively estimates direction of arrival (DOA), time-delay, Doppler shift and amplitude corresponding to each impinging signal onto an antenna array by utilizing the cross ambiguity function. On synthetic signals, based on Monte Carlo trials, performances of the algoritms are tested in terms of root Mean Squared Error (rMSE) at different Signal-to-Noise Ratios (SNR). Cramer-Rao lower bound is included for statistical comparisons. Simulation results indicate the superior performance of the CAF-DF technique over SAGE technique for low and medium SNR values. © 2008 IEEE.Item Open Access Decoupling of multifrequency dipole antenna arrays for microwave imaging applications(Hindawi Publishing Corporation, 2010) Saenz, E.; Guven, K.; Özbay, Ekmel; Ederra, I.; Gonzalo, R.The mutual coupling between elements of a multifrequency dipole antenna array is experimentally investigated by S -parameter measurements and planar near-field scanning of the radiated field. A multifrequency array with six dipoles is analyzed. In order to reduce the coupling between dipoles, a planar metasurface is placed atop the array acting as superstrate. The mutual coupling of the antenna elements in the absence and presence of the superstrate is presented comparatively. Between 3 and 20dB mutual coupling reduction is achieved when the superstrate is used. By scanning the field radiated by the antennas and far-field measurements of the radiation pattern, it is observed that the superstrate confines the radiated power, increases the boresight radiation, and reduces the endfire radiation.Item Open Access Efficient computation of surface fields excited on a dielectric-coated circular cylinder(IEEE, 2000-10) Erturk, V. B.; Rojas, R. G.An efficient method to evaluate the surface fields excited on an electrically large dielectric-coated circular cylinder is presented. The efficiency of the method results from the circumferentially propagating representation of the Green’s function as well as its efficient numerical evaluation along a steepest descent path. The circumferentially propagating series representation of the appropriate Green’s function is obtained from its radially propagating counterpart via Watson’s transformation and then the path of integration is deformed to the steepest descent path on which the integrand decays most rapidly. Numerical results are presented that indicate that the representations obtained here are very efficient and valid even for arbitrary small separations of the source and field points. This work is especially useful in the moment-method analysis of conformal microstrip antennas where the mutual coupling effects are important.Item Open Access European collaboration in conformal antenna research(IEEE, 2007-09) Sipus, Z.; Persson P.; Lanne, M.; Heckler, M.; Maci, S.; Campos, J. L. M.; Knott, P.; Ertürk, Vakur; Vandenbosch, G.The work carried out within Work Package 2.4-3 of the EU network "Antenna Centre of Excellence" (ACE) is presented in this paper. This work package is concerned with structuring research on conformal antennas. In more details, the work is focused on the problems associated with full benchmarking of conformal antennas, on development of hybrid programs for analyzing different classes of conformal antennas, and on investigation of properties of algorithms for optimizing beam synthesis and beam-steering for conformal arrays.Item Open Access Extension of forward backward method with DFT based acceleration algorithm for the efficient analysis of large periodic arrays with arbitrary boundaries(IEEE, 2003) Çivi, Ö. A.; Chou, H. T.; Ertürk, Vakur B.An extension of Forward-Backward (FB) with Discrete Fourier Transform (DFT) based acceleration approach is presented. This is given to provide a relatively efficient analysis of EM radiation/scattering from an electrically large, planar, periodic, finite arrays with arbitrary boundaries, such as arrays with circular or elliptical boundaries. It is shown that only very few significant DFT terms are sufficient to provide accurate results.Item Open Access Fast algorithm for scattering from planar arrays of conducting patches(Institute of Electrical and Electronics Engineers, 1998-04) Gürel, Levent; Chew, W. C.A direct (noniterative) algorithm for the solution of the electromagnetic scattering from three-dimensional planar arrays of conducting patches is developed. For an N-unknown problem, the computational complexity of this new solution technique is shown to be O(N2 log2N), which is considerably lower than the O(N3) computational complexity of the conventional direct solution techniques. The advantages of the reduction in the computational complexity is pronounced in the solution of large electromagnetics problems, such as scattering from large and finite arrays of patches, synthesis and analysis of finite-sized frequency selective surfaces (FSS's), and radiation and scattering from large phased-array antennas, to name a few.Item Open Access Fast noniterative steepest descent path algorithm for planar and quasi-planar patch geometries(IEEE, 1998) Gürel, Levent; Chew, W. C.The fast noniterative steepest descent path (SDP) algorithm for planar and quasi-planar patch geometries are discussed. The comparison of scattered fields as computed by the method of moments (MOM) and fast direct algorithm (FDA)/SDP are described. The solution times of FDA/SDP, MOM, and recursive aggregate-T-matrix algorithm (RATMA) are obtained by solving the scattering problems of increasingly larger planar arrays of patches without taking advantage of the periodicities and the symmetries of these arrays.Item Open Access A model with electric fields for the inclusion of mutual coupling effects in the MIMO channel(IEEE, 2007) Tunç, Celal Alp; Ircı, Erdinç; Bakır, Onur; Aktaş, Defne; Ertürk, Vakur B.; Altıntaş, AyhanMultiple input multiple output (MIMO) wireless communication systems have been a focus of interest, due to their ability to increase the capacity in rich scattering environments by using multi-element antenna arrays both at the transmitter and the receiver sides. However, when dealing with multi-element antenna arrays, effects of mutual coupling among the array elements become significant and should be included in the channel matrix properly. These effects were included in the MIMO channel matrix mainly for free standing linear arrays (FSLA) of uniform thin-wire dipole antennas using coupling matrices obtained from the mutual interaction matrix and terminations. These matrices reduce to the identity matrix when the interactions are ignored, because of the scaling factors related with termination impedances. Therefore, in this paper we propose a partially stochastic full-wave electromagnetic model with electric fields (MEF), to evaluate the MIMO channel matrix accurately with and/or without including effects of mutual coupling. Effects of mutual interactions among the array elements through space and surface waves (when printed arrays are considered) are included in the channel matrix using a full-wave hybrid method of moments (MoM)/Green's function technique. The stochastic part of the model comes from a local cluster of uniformly distributed scatterers. Consequently, the proposed method is exact except the scatterer scenario, thus, besides achieving the accuracy to be used as a benchmark solution for other approaches, comparisons can be made among any kind of arrays.Item Open Access On the capacity of printed planar rectangular patch antenna arrays in the MIMO channel: analysis and measurements(IEEE, 2010) Tunc, C. A.; Olgun, U.; Ertürk, V. B.; Altintas, A.Printed arrays of rectangular patch antennas are analyzed in terms of their MIMO performance using a full-wave channel model. These antennas are designed and manufactured in various array configurations, and their MIMO performance is measured in an indoor environment. Good agreement is achieved between the measurements and simulations performed using the full-wave channel model. Effects on the MIMO capacity of the mutual coupling and the electrical properties of the printed patches, such as the relative permittivity and thickness of the dielectric material, are explored.Item Open Access Reconfigurable nested ring-split ring transmitarray unit cell employing the element rotation method by microfluidics(Institute of Electrical and Electronics Engineers, 2015) Erdil, E.; Topalli, K.; Esmaeilzad, N. S.; Zorlu, O.; Kulah, H.; Aydin, C. O.A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360° linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.Item Open Access Robust direction-of-arrival estimation in non-Gaussian noise(Institute of Electrical and Electronics Engineers, 1998-05) Yardımcı, Y.; Çetin, A. Enis; Cadzow, J. A.In this correspondence, a nonlinearly weighted least-squares method is developed for robust modeling of sensor array data. Weighting functions for various observation noise scenarios are determined using maximum likelihood estimation theory. Computational complexity of the new method is comparable with the standard least-squares estimation procedures. Simulation examples of direction-of-arrival estimation are presented.Item Open Access Simulation of a digital communication system(IEEE, 2005-09) Güngör, A.; Arıkan, F.; Arıkan, OrhanIn this paper, basic components of a digital communication system are simulated by a computer program. The simulation program is modular and flexible to incorporate any future additions and updates. The simulation program allows the user to choose from various channel models, transmitter and receiver antenna systems, modulation and channel coding techniques. A communication system is defined by various parameters including the source, coding, modulation, antenna systems. In order to facilitate the input of these parameters and follow the flow of the simulation, the Graphical User Interface (GUI) is designed for convenience to the user. The input parameters can both be entered from the GUI or from prepared user files. The major contribution of this simulation system to the existing communication simulators is the addition of flexible antenna systems both at the transmitting and receiving ends. With this simulation program, the antenna arrays can be located anywhere on Earth, on any platform and array elements can be placed on the platform by any desired orientation. The simulation program results are compared with both theoretical computations and commercial simulator results and excellent agreement is observed in both cases.