Jalil Rashed-Mohassel
Center of Excellence on Applied Electromagnetic Systems, School of ECE, College of Engineering, Univ. of Tehran, P. O. Box 14395-515, Tehran, Iran.
[ 1 ] - Coupling Effects and Performance of Loran Transmitter Antennas
It is known that if a conductor resides in the neighboring of an antenna with a small distance relative to the wavelength, it induces a reverse current on the conductor. This paper involves the unavoidable coupling effects on some common types of LF antennas, due to the large wavelength in this frequency band. In particular, after some discussions about top-loaded antennas, the coupling effect ...
[ 2 ] - A Planar, Layered Ultra-wideband Metamaterial Absorber for Microwave Frequencies
In this paper, an ultra-wideband metamaterial absorber is designed and simulated. The proposed absorber is planar and low profile. It is made of a copper sheet coated with two dielectric layers. Each unit cell of the metamaterial structure is composed of multiple metallic split rings, which are patterned on the top and middle boundaries of the dielectrics. The designed absorber utilizes differe...
[ 3 ] - Complementary Periodic Structures for Miniaturization of Planar Antennas
In this paper various layered planar periodic structures which provide miniaturization of planar antennas are proposed and discussed. The proposed designs are based on two concepts, reactive impedance surfaces and complementary periodic structures. In the proposed structures, complementary periodic rings and slots are patterned on the intermediate boundaries of the dielectric layers. A patch an...
[ 4 ] - Auxiliary Potentials In Chiral Media
In the present paper, the expressions for scalar and vector potentials in lossless isotropic chiral media are analyzed. Propagating eigenvalues of these potentials are then obtained. Furthermore by decomposition of sources and fields in a chiral medium, we introduce the auxiliary right-and left-handed potentials and find the associated fields. These potentials are used to solve the problem of a...
[ 5 ] - Optimization of Array Factor in Linear Arrays Using Modified Genetic Algorithm
The array factor (sidelobe level, SLL) of a linear array is optimized using modified continuous genetic algorithms in this work. The amplitudes and phases of the currents as well as the separation of the antennas are all taken as variables to be controlled. The results of the design using modified GA versions are compared with other methods. Two design problems were studied using several contin...
[ 6 ] - Significant Error Propagation in the Finite Difference Solution of Non-Linear Magnetostatic Problems Utilizing Boundary Condition of the Third Kind
This paper poses two magnetostatic problems in cylindrical coordinates with different permeabilities for each region. In the first problem the boundary condition of the second kind is used while in the second one, the boundary condition of the third kind is utilized. These problems are solved using the finite element and finite difference methods. In second problem, the results of the finite di...
[ 7 ] - Quasi-Static Theory for Uniaxial Chiral Omega Media
The problem of unbounded uniaxial chiral omega media in the presence of both static electric and magnetic point charges is investigated. For this purpose scalar electric and magnetic potentials in these media are introduced. Using these potentials, the corresponding electric and magnetic fields are determined. The similar problem of static electric and magnetic current sources with the goal of ...
[ 8 ] - On the Optimum Directivity of Uniformly Spaced Broadside Arrays of Parallel Half-Wave Dipoles (RESEARCH NOTES)
The nominal directivity for uniformly spaced broadside parallel half-wave dipoles associated with a uniform excitation is evaluated. The amplitude distribution for an optimized directivity is then obtained for different numbers of elements with the separations between the dipoles as a variable. The optimum and nominal directivities are compared for different spacings of the elements. While thes...
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