This paper presents a novel implementation of an electromagnetically coupled patch antenna using air gap filled substrates to achieve the maximum bandwidth. We also propose an efficient modeling technique using the FDTD method which can substantially reduce the simulation cost for modeling the structure. The simulated results have been compared with measurement to show the broadband behavior of the antenna and the accuracy of the proposed modeling technique. The measured results show a 16% of VSWR<2 bandwidth which is considerable considering the inherent bandwidth limitations in microstrip antenna technology.

Top-hat monopole antennas loaded with radially layered dielectric are analyzed using the finite-difference time-domain (FDTD) method. Unlike the mode-matching method (MMM) (which was previously used for analyzing these antennas) the FDTD method enables us to study such structures accurately and easily. Using this method, results can be obtained in a wide frequency band by performing only one time-domain simulation. For the FDTD modeling, the type of medium at each grid point is specified by a code. Also an efficient non-uniform meshing scheme and a novel perfectly matched layer (PML) are presented and used. The excitation signal can be chosen in the form of Gaussian pulse (GP) or sine carrier modulated by Gaussian pulse (SCMGP). These enable us to increase the accuracy of simulation and decrease the required memory and CPU time. Simulation results are presented in the form of graphical figures, which display the spatial variations in amplitude and phase of radiated field. Also, the FDTD computed input impedances of several top-hat monopole antennas are compared with those obtained by measurement. The agreement between computed and measured results is quite well.

Anisotropic media appear regularly in electromagnetic wave engineering. The finite-difference time-domain (FDTD) method is a robust technique to model such media. However, the value of the time step in the FDTD algorithm is bounded by the Courant-Friedrichs-Lewy (CFL) condition. In this paper, a simple analytical approach is developed using the Gershgorin circle theorem to derive a point-wise closed-form relation for the CFL condition in bounded inhomogeneous anisotropic media. The proposed technique includes objects of arbitrary shapes with straight, tilted, or curved interfaces located in a computational space with uniform or adaptive gridding schemes. Both axial and non-axial anisotropies are considered in the analysis. The proposed method is able to investigate the effect of boundaries and interfaces on the stability of the algorithm. It is shown that in the presence of an interface between two anisotropic media, the von-Neumann criterion is not able to predict the stability bound for specific ranges of the permittivity tensor components and unit cell aspect ratios. Exploiting the proposed closed-form formulations, it is possible to tune the CFL time step and avoid the temporal instability by the wise selection of the gridding scheme especially in curved boundaries where subcell modelings such as Yu-Mittra formalism are applicable. Some illustrative examples are provided to verify the method by comparing the results with those of the eigenvalue analysis and time-domain simulations.

In this paper we describe the design and evaluation of Vivaldi elements optimization ‎for operation in the array environment over a wide range of frequency (12-18GHz). ‎The Finite Difference Time Domain (FD TD) is used in design and analysis of finite ‎Vivaldi array and genetic algorithm (GA) for optimization of its radiation pattern. The ‎hybrid method is used to find maximum side lobe level (SLL) over a range of ‎frequency (12-18GHz) by adjustment of the antenna and array parameters. An array ‎SLL improvement of MB was attained by optimization. Here a single Vivaldi antenna ‎and a four-element array are analyzed and compared with measurements. Theoretical ‎and experimental results show good agreement with each other.‎

All types of Light Emitting Diodes (LEDs) are desirable because of their widespread applications. The Quantum Dot-Based Light Emitting Diodes (QDLEDs) have a lot of unique properties attracting more attention. Predicting performance of QDLEDs can lead to a better and more efficient design of the device. In this paper, we have attempted to investigate the dependency of the device performance on the location of Quantum Dots (QDs) and determine the best location for the QDs in the QDLEDs. We use FDTD method to simulate and analysis the QDLEDs structure. The QDs are located in five different positions in TPBi layer then results are compared with each other. The results show that the closer the QDs to the hole transport layer (HTL), the better the luminescence. This improvement would be explained by two charge transport mechanisms including direct charge injection and exciton energy transfer. The results show that when the QDs are closer to the HTL, the device performance is better due to the greater balance of carriers. In this condition holes can transfer from the HTL to the valence band easier.