New Fundamental Approach To Antennas Near Field and Impact on Characterizing Antenna Systems and some other Electromagnetic Applications

There is a growing interest within the applied electromagnetic community in designing electromagnetic systems involving parts and subsystems interacting at close distances to meet emerging applications. Examples are compact antenna arrays, wireless devices working in dense and crowded electromagnetically changing environments such as MIMO(Multiple Input Multiple Output) and DoA(Directional of Arrival) applications, miniaturized circuits and radiators, near- field communication, and wireless energy transfer. A common denominator in all of these applications is the existence of the problem of illumination by and/or interactions of near fields. In theory, the near field is much more complex than the far field or waveguide modes. Until recently there was no comprehensive theory that explains the near field structure. This presentation will describe a new fundamental approach to the near field structures and energy around antenna systems and the possible implication on antenna design, and the electromagnetic environment. Applications to antenna synthesis, MIMO systems design, and other types of antennas for emerging applications will be discussed.

Türkiye’de Radar : Neredeyiz, neler yapmalıyız?

Radarlar, 100 yıla yaklaşan tarihlerinde askeri ve sivil alanlarda önemli aktörler olarak görev almışlardır. Radar sistemlerinden beklentiler her geçen gün artmakta, sistemler büyük bir hızla gelişmeye devam etmektedir. Konuşmada, Türkiye’de yapılan dünya ölçeğinde ileri teknoloji içeren radar çalışmaları sunulacak ve radar geliştirmede endüstriye ivme kazandıracağı öngörülen araştırma alanları ve çözülmesi gereken problemlere değinilecektir.

Lightning-driven Phenomena in Near-Earth Space

Radar Cross Section of a Finite Parallel-Plate Waveguide with Material Loading

The analysis of electromagnetic scattering by open-ended metallic waveguide cavities is an important subject in the prediction and reduction of the radar cross section (RCS) of a target. This problem serves as a simple model of duct structures such as jet engine intakes of aircrafts and cracks occurring on surfaces of general complicated bodies. Some of the diffraction problems involving two- and three-dimensional cavities have been analyzed thus far based on high-frequency techniques and numerical methods. It appears, however, that the solutions due to these approaches are not uniformly valid for arbitrary dimensions of the cavity. Therefore it is desirable to overcome the drawbacks of the previous works to obtain solutions which are uniformly valid in arbitrary cavity dimensions. The Wiener-Hopf technique is known as a powerful, rigorous approach for analyzing scattering and diffraction problems involving canonical geometries. In this paper, we shall consider a finite parallel-plate waveguide with four-layer material loading as a geometry that can form cavities, and analyze the plane wave diffraction rigorously using the Wiener-Hopf technique. Both E and H polarizations are considered. Introducing the Fourier transform of the scattered field and applying boundary conditions in the transform domain, the problem is formulated in terms of the simultaneous Wiener-Hopf equations. The Wiener-Hopf equations are solved via the factorization and decomposition procedure leading to the exact solution. However, this solution is formal since infinite series with unknown coefficients and infinite branch-cut integrals with unknown integrands are involved. For the infinite series with unknown coefficients, we shall derive approximate expressions by taking into account the edge condition. For the branch-cut integrals with unknown integrands, we assume that the waveguide length is large compared with the wavelength and apply a rigorous asymptotics. This procedure yields high-frequency asymptotic expressions of the branch-cut integrals. Based on these results, an approximate solution of the Wiener-Hopf equations, efficient for numerical computation, is explicitly derived, which involves a numerical solution of appropriate matrix equations. The scattered field in the real space is evaluated by taking the inverse Fourier transform and applying the saddle point method. Representative numerical examples of the RCS are shown for various physical parameters, and the far field scattering characteristics of the waveguide are discussed in detail. The results presented here are valid over a broad frequency range and can be used as a reference solution for validating other analysis methods such as high-frequency techniques and numerical methods.

Frequency and polarization selectivity of graphene strip gratings in the THz range: surface plasmon resonances and effect of substrate

We consider the scattering and absorption of THz waves by infinite flat gratings made of graphene strips, suspended in the free space and placed in a dielectric slab. Both the H and E-polarization regimes are analyzed. Accurate numerical treatment is based on the use of singular integral equations discretized using the advanced mathematical schemes. The resulting numerical algorithm possesses guaranteed convergence and controlled accuracy of computations including the natural resonances. Reflectance, transmittance, and absorbance by the graphene-strip gratings are studied; the resonances on the surface-plasmon modes, the grating modes, and the slab modes are identified and quantified. Note than the grating resonances appear only in the presence of dielectric slab and possess Q-factors far exceeding those of the plasmons and the slab modes. These results can be useful in the development of novel electrically tunable filters, sensors, absorbers, and polarizers designed using a periodically patterned graphene. Being efficient and economic, our advanced algorithm can serve as a core of a numerical optimization code.