Alp Kustepeli

On the splitting parameter in the Ewald method

An investigation of the Ewald method is presented. The method involves a splitting parameter that is theoretically an arbitrary number. An analysis is presented to show why the splitting parameter cannot always be treated as arbitrary in calculations and how this parameter should be chosen for all periodic spacing of a structure.

Novel Square Spiral Antennas for Broadband Applications

An investigation of novel square spiral antennas is presented. The antennas are designed by considering the special arrangements of spiral arms. The new designs perform much better in terms of the frequency independency of the fundamental antenna parameters, when compared with the well known and widely used Archimedean spiral antenna, which makes the antennas very suitable for broadband wireless applications. Experimental results are also presented and there is a good agreement between themeasured and numerical data. Index Terms – Frequency independent antennas; square spiral geometries; wire, strip and slot antennas.

Subsectional Tapered Fed Printed LPDA Antenna With a Feeding Point Patch

In this letter, a log-periodic dipole array (LPDA) antenna operating between 1.1 and 13.8 GHz with and an average peak realized gain of 5.2 dB is presented. It is suitable for GPS (L1-L5), PCS, IMT-2000, Bluetooth, WLAN, WiMAX, UWB, and X-band applications. The antenna is designed by introducing a subsectional tapered feedline instead of standard microstrip feeding, which leads to a remarkable lower-frequency performance. The upper-frequency performance of the antenna is improved by adding a feeding point patch. The group delay is also examined for the final design, and maximum 1.5 ns deviation is observed in UWB. By using ordinary and simple dipoles with this modified feedline approach, a superior antenna performance is obtained over a very wide frequency band, and it is validated by the comparison of three fabricated antennas. Additionally, the antenna size is also reduced without using complicated and/or top-loaded dipole structures.

Wideband Printed Planar Monopole Antenna for PCS, UWB and X-Band Applications

In this paper, a printed planar monopole antenna (PPMA) is presented for PCS, UWB and X-band. The antenna is designed in two stages. In the design of the preliminary PPMA used to obtain the proposed PPMA, the structure is divided into sections, and they are optimized in the sense of bottom to up strategy. The bandwidth is enhanced by employing tapered transitions and inset feed. The resulting antenna operates between 2.37GHz and 12GHz with VSWR < 2 and an average peak realized gain of 4.95 dB. Therefore, the preliminary antenna can be considered to be suitable for Bluetooth, WLAN, WiMAX, UWB and X-band. The proposed PPMA is designed by implementing slots on the preliminary PPMA to include PCS, and to suppress Bluetooth and commonly used WLAN and WiMAX bands, the ones allocated out of UWB. The proposed antenna operates in the 1.67GHz– 1.91GHz and 3GHz–15GHz bands with VSWR < 2. The peak realized gain (Gpr) in PCS is 1.32 dB at 1.8GHz, and the average Gpr is 5 dB for the 3GHz–15GHz band. The group delay performances are also examined, and the maximum group delay deviations of preliminary and proposed PPMAs are observed as 1 ns and 1.25 ns, respectively.

Revised Distributional Forms of the Laplacian and Poisson’s Equation, Their Implications, and All Related Generalizations

Abstract The theory of distributions of L. Schwartz is a very useful and convenient way for the analysis of physical problems since physical distributions, especially charge distributions yielding the discontinuity of the potential and boundary conditions, can be correctly described in terms of mathematical distributions. To obtain the charge distributions, the distributional form of the Laplacian is applied to the Poisson’s equation; therefore, for the correct representations and interpretations, the distributional forms and their proper applications are very important. In this article, it is shown that the distributional form of the Laplacian has been presented by Schwartz and also others with a missing term, leading to confusing and wrong results mathematically, and as a result electromagnetically; and the revised, correct, and complete distributional representations of the Laplace operator, the Poisson equation, and double layers, defined as the dipole layer and equidensity layer, are obtained and presented with detailed discussions and explanations including boundary conditions. By using the revised form of the Laplacian, Green’s theorem is obtained explicitly with special emphases about important points and differences with previous works. The generalized forms of the Laplacian, Poisson’s equation, charge densities, boundary conditions, and Green’s theorem are also presented when there is a multi-layer on the surface of discontinuity.

A Novel Square-Spiral Strip Antenna

A square-spiral strip antenna is designed considering the procedure used to obtain log-periodic antennas. Simulation results of the new design are compared with those of the well known and widely used Archimedean spiral antenna in terms of the frequency dependency. The effect of dielectric substrate used to support the antennas is also investigated.

High Frequency Diffraction of Cylindrical Waves by Perfectly Conducting Successive Step Discontinuities

The diffraction of high frequency cylindrical electromagnetic waves by step discontinuities is investigated rigorously by using the Fourier transform technique in conjunction with the mode matching method. The hybrid method of formulation gives rise to a scalar Wiener-Hopf equation of the third kind, the solution of which contains infinitely many constants satisfying infinite systems of linear algebraic equations

On the Helmholtz Theorem and Its Generalization for Multi-Layers

ABSTRACT The decomposition of a vector field to its curl-free and divergence-free components in terms of a scalar and a vector potential function, which is also considered as the fundamental theorem of vector analysis, is known as the Helmholtz theorem or decomposition. In the literature, it is mentioned that the theorem was previously presented by Stokes, but it is also mentioned that Stokes did not introduce any scalar and vector potentials in his expressions, which causes a contradiction. Therefore, in this article, Stokes’s and Helmholtz’s representations are examined in detail to reveal and emphasize their differences, similarities and important points. The Helmholtz theorem is obtained for all kinds of spaces by using the theory of distributions in a comprehensive and rigorous manner with detailed explanations, which also leads to a new surface version of the Helmholtz theorem or a new surface decomposition, resulting in the canonical form; hence, it is different than the one suggested previously in terms of two scalar functions. The generalized form of the Helmholtz theorem is also presented by employing the same approach when there is a multi-layer on the surface of discontinuity, which also corresponds to the extension of the theorem to fields with singularities of higher order.

Electromagnetic scattering from arbitrary flat plates: Analysis of the problem by using method of moments with different sinc type basis functions

In this paper, three dimensional electromagnetic scattering problem is solved by using pulse-sinc type basis functions in the Method of Moments (MoM) procedure. This method is applied to the scattering problems of a plane wave illuminated flat arbitrary geometries. Pulse-sinc based MoM formulation is developed, the current densities and radar cross section of different geometries are investigated. The radar cross section (RCS) for co-polarized and cross polarized cases of the flat plate geometries are compared with both of the results obtained from the sinc-sinc based formulation and SuperNEC. The results obtained by using pulse-sinc fornulation are in very good agreement with those of the SuperNEC.

Three-dimensional electromagnetic scattering from flat plates by using sinc-type basis functions in method of moments

Sinc functions are used in the basis and testing procedures in the conventional method of moments (MoM) formulation. But unlike conventional MoM, simple pointwise meshing is enough and no integral computation is required due to the mathematical properties of the sinc function. The simulation results of surface current densities and radar cross section for a few wavelength square flat plate are obtained by using our own codes. The results are compared with those of the rooftop basis functions. The CPU-time decreases by half of the time of the conventional method. The error that occurs from the approximated integral of the sinc function in the computation of main matrix elements is very small and decreases while the bandwidth of the sinc function increases.