This paper presents results of comparison of modern effective numerical techniques for the calculation of microwave devices. Nowadays finite difference time domain method and finite elements method are the most frequently used numerical techniques, which are applied for the simulation of electromagnetic fields in various antennas and bounded structures. Modern modifications of these numerical methods and their pro and contras are considered in the paper. Besides, we have compared finite difference time domain technique and finite elements method in the case of calculation of polarization and matching characteristics of microwave waveguide iris polarizers. Using this example we have found that the convergence of the calculated matching characteristics of microwave waveguide devices is fast for both considered numerical techniques. On the other hand, the accuracy of calculation of the phase and polarization characteristics is very sensitive to the number of mesh cells, at which the volume of device structure is divided. It has been found that more than 100 000 tetrahedral mesh cells per structure volume must be used, if calculation of the polarizer’s axial ratio and crosspolar discrimination is performed by finite elements method in the frequency domain with required accuracies of 0.5 dB. If axial ratio and crosspolar discrimination must be calculated with the accuracies of 0.5 dB by the finite difference time domain method, then the utilization of more than 800 000 hexahedral mesh cells per structure volume is required. In has been found that the computation time of the finite elements method in the frequency domain is more than 2 times less than the same time required by finite difference time domain method. Besides, the corresponding number of tetrahedral mesh cells in finite elements method is 10 times less, than the number of hexahedral mesh cells in finite difference time domain method.

FDTD and FEM Simulation of Microwave Waveguide Polarizers

The systematic and accurate design process of realistic nanocomposite applications and finite-sized graphene setups with arbitrary media uncertainties is presented in this paper by a 3-D covariant/contravariant stochastic finite-difference time-domain method. The new technique uses extra nodes pertinent to a convex combination of all obtainable spatial increments and introduces a robust domain-decomposition formulation combined with Lagrange multipliers to considerably decrease the system overhead. In this way, the mean value and the standard deviation of field components are evaluated in a single run. The performance of the proposed algorithm is validated by various statistically varying nanoscale applications.

A Generalized Domain-Decomposition Stochastic FDTD Technique for Complex Nanomaterial and Graphene Structures

Multi-carrier multiplexing systems, used in high bit rate communication applications, are more affected by the time- or frequency-dependent fading effects incurring in the channel than the single-carrier systems. When the fading effects at multi-carrier systems are not taken into consideration, inter-carrier interference or inter-symbol interferences that cause bit error rate increase at the receiver would occur. In order to eliminate these interference effects, the cyclic prefix is used in MC-CDMA systems, which are the kind of multi-carrier systems. However, determining how long the CP length is to be used will directly affect both the error and the capacity performance of the system. In this study, multi-objective bat algorithm is proposed for the adaptive arrangement of the CP lengths according to the channel conditions. Contrary to the standard CP determination methods, not only the bit errors are minimized, but also the maximization of the channel capacity is provided by the utilization of MOBA.

Adaptive arrangement of cyclic prefix length for MC-CDMA systems via multi-objective bat algorithm

Context. Today, there is a rapid expansion of the range of modern branches of science and technology, which actively use satellite telecommunication systems to receive, process and transmit various information. These radioelectronic systems quite often require an increase of the volumes of information, which they are processing and transmitting. Increase of the volumes of transmitted information in two times can be achieved by using dual-polarization antenna systems and devices. Nowadays, most part of the specialists, who are engaged in the development of various modern polarization-processing microwave devices, carry out their numerical modeling and optimization using variational techniques, methods of integral equations, method of fields matching in partial regions. The methods with division of the internal region of the device into elementary cells are applied most actively. Among them in the time domain the most often used approach is finite difference method with the decomposition at hexagonal mesh, while and in the frequency domain the finite elements method with the adaptive tetrahedral mesh is applied. Therefore, the estimation of the speed and accuracy of these methods with the purpose of determination of more effective among them is a relevant problem.
Objective. The goal of the research is comparison of speed and accuracy of the calculations of electromagnetic characteristics of waveguide polarizers using FEM and FDTD methods, as well as the comparison of the convergence of these methods for the analysis of polarization-processing microwave devices with diaphragms.
Method. For the calculations and analysis of electromagnetic characteristics in the article we used the method of finite differences in the time domain (FDTD) and the method of finite elements in the frequency domain (FEM). In FEM the volume is split into the tetrahedral mesh cells. In FDTD the computational domain is divided into hexagonal mesh cells.
Results. It was found that the convergence of voltage standing wave ratio for the waveguide polarizer is fast for both methods. It was obtained that the convergence of the characteristics of differential phase shift, axial ratio, and crosspolar discrimination of the developed microwave device turned out to be much more sensitive to the number of mesh cells used. Moreover, in the research it was obtained by calculations that the computation time by the finite elements method in the frequency domain is more than 2 times less than the corresponding time required for calculations by the finite difference time domain method. When using the finite elements method in the frequency domain the corresponding number of tetrahedral mesh cells is 10 times less than the number of hexagonal mesh cells, which are used in the finite difference time domain method.
Conclusions. Performed investigations have shown that FEM in the frequency domain, which applies an adaptive tetrahedral mesh, is more efficient than the FDTD method for the calculations of phase and polarization characteristics of modern waveguide polarizers and other microwave devices for various applications.

Estimation of fem and fdtd methods for simulation of electromagnetic characteristics of polarization transforming devices with diaphragms

We discuss a generalized strategy to model material interfaces in the finite integration technique (FIT) on Cartesian meshes. It originates from the exact formula for the ratio of grid fluxes and grid voltages, which requires a priori knowledge of the local fields. For axis-parallel material interfaces, this field information is canceled out, yielding the standard expressions of the FIT’s material operators. For nonconformal interfaces, two concepts are discussed to obtain feasible implementations. Applied to an exemplary quasistatic example, the generalized formula shows superior accuracy compared with staircase approximations.

Accurate Treatment of Nonconformal Material Interfaces in the Finite Integration Technique

Local Approximation Based Material Averaging Approach in the Finite Integration Technique

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Local Approximation Based Material Averaging Approach in the Finite Integration Technique