Coplanar waveguide-fed slot antennas on cylindrical substrates

This paper describes cylindrical coplanar waveguide (CCPW)-fed slot and folded slot antennas encompassing cylindrical substrates. Using a 1.27 cm diameter Teflon substrate, antennas that operate around 7 GHz have been realized with gains of 1.5 dB (slot) and 2.8 dB (folded slot). The antennas have a well-defined pattern null of 8 dB along the side of the CCPW feedline. A 1.6 GHz slot antenna on a 1.27 cm diameter alumina substrate was also fabricated using a novel direct-write technique, and shown to have comparable performance characteristics.The results include measured data and simulated data using a 3D cylindrical finite difference time domain (FDTD) code.     

Linear quadratic regulators with eigenvalue placement in a specified region

A linear optimal quadratic regulator is developed for optimally placing the closed-loop poles of multivariable continuous-time systems within the common region of an open sector, bounded by lines inclined at ±π/2k (k = 2 or 3) from the negative real axis with a sector angle ≤π/2, and the left-hand side of a line parallel to the imaginary axis in the complex s-plane. Also, a shifted sector method is presented to optimally place the closed-loop poles of a system in any general sector having a sector angle between π/2 and π. The optimal pole placement is achieved without explicitly utilizing the eigenvalues of the open-loop system. The design method is mainly based on the solution of a linear matrix Lyapunov equation and the resultant closed-loop system with its eigenvalues in the desired region is optimal with respect to a quadratic performance index.     

Characterization of asymmetric coplanar waveguide discontinuities

A general technique to characterize asymmetric coplanar waveguide (CPW) discontinuities with airbridges where both the fundamental coplanar and slotline modes may be excited together is presented. First, the CPW discontinuity without airbridges is analyzed using the space-domain integral equation (SDIE) approach. Second, the parameters (phase, amplitude, and wavelength) of the coplanar and slotline modes are extracted from an amplitude modulated-like standing wave existing in the CPW feeding lines. Then a 2n×2n generalized scattering matrix of the n-port discontinuity without airbridges is derived which includes the occurring mode conversion. Finally, this generalized scattering matrix is reduced to an n×n matrix by enforcing suitable conditions at the ports which correspond to the excited slotline mode. For the purpose of illustration, the method is applied to a shielded asymmetric short-end CPW shunt stub, the scattering parameters of which are compared with those of a symmetric one. Experiments are performed on both discontinuities and the results are in good agreement with theoretical data. The advantages of using airbridges in CPW circuits as opposed to bond wires are also discussed     

Post-buckling behaviour of structures using a finite element–nonlinear eigenvalue technique

A series of finite element algorithms for the calculation of the post-buckling behaviour of structures are proposed. The algorithms represent a finite element implementation of a variational principle for nonlinear eigenvalue problems. Incremental amplitude solution schemes are defined. Numerical results are presented for the post-buckling behaviour of specific structures with linear and nonlinear pre-buckling states.     

Design and analysis of multifrequency Wilkinson power dividers using nonuniform transmission lines

In this article, based on nonuniform transmission lines, the design of compact multifrequency Wilkinson power dividers (WPDs) is presented. This is accomplished by replacing the quarter‐wave uniform transmission lines in the conventional WPD by multiband nonuniform transmission line transformers (NTLTs). The design of these NTLTs is performed under the even mode analysis of the WPD. A single isolation resistor is used between the two output ports whose value is determined using the simple odd mode analysis of the WPD. For verification purposes, a triple‐frequency WPD and a quad‐frequency WPD are designed, simulated, fabricated, and measured. The results of the full‐wave simulations and the measurements verify the validity of the design procedure. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

A second-order sliding mode and fuzzy logic control to optimal energy management in wind turbine with battery storage

The optimal control of large-scale wind turbine has become a critical issue for the development of renewable energy systems and their integration into the power grid to provide reliable, secure and efficient electricity, despite any possible constraints such as sudden changes in wind speed. This paper deals with the modeling and control of a hybrid system integrating a permanent magnet synchronous generator (PMSG) in variable speed wind turbine (VSWT) and batteries as energy storage system (BESS). Moreover a new supervisory control system for the optimal management and robust operation of a VSWT and a BESS is described and evaluated by simulation under wind speed variation and grid demand changes. In this way, the proposed coordinated controller has three subsystems (generator side, BESS side and grid side converters). The main function of the first one is to extract the maximum wind power through controlling the rotational speed of the PMSG, for this a maximum power point tracking algorithm based on fuzzy logic control and a second-order sliding mode control (SOSMC) theory is designed. The task of the second one is to maintain the required direct current (DC) link voltage level of the PMSG through a bidirectional DC/DC converter, whereas in the last, a (SOSMC) is investigated to achieve smooth regulation of grid active and reactive powers quantities, which provides better results in terms of attenuation of the harmonics present in the grid courant compared with the conventional first-order sliding controller. Extensive simulation studies under different conditions are carried out in MATLAB/Simulink, and the results confirm the effectiveness of the new supervisory control system.

     

iHOME: Index-Based JOIN Query Optimization for Limited Big Data Storage

Query optimization in Big Data becomes a promising research direction due to the popularity of massive data analytical systems such as Hadoop system. The query optimization is getting hard to efficiently execute JOIN queries on top of Hadoop query language, Hive, over limited Big Data storages. According to our previous work, HiveQL Optimization for JOIN query over Multi-session Environment (HOME) system has been introduced over Hadoop system to improve its performance by storing the intermediate results to avoid repeated computations. Time overheads and Big Data storages limitation are considered the main drawback of the HOME system, especially in the case of using additional physical storages or renting extra virtualized storages. In this paper, an index-based system for reusing data called indexing HiveQL Optimization for JOIN over Multi-session Big Data Environment (iHOME) is proposed to overcome HOME overheads by storing only the indexes of the joined rows instead of storing the full intermediate results directly. Moreover, the proposed iHOME system addresses eight cases of JOIN queries which classified into three groups; Similar-to-iHOME, Compute-on-iHOME, and Filter-of-iHOME. According to the experimental results of the iHOME system using TPC-H benchmark, it is found that the execution time of eight JOIN queries using iHOME on Hive has been reduced. Also, the stored data size in the iHOME system is reduced relative to the HOME system, as well as, the Big Data storage is saved. So, by increasing stored data size, the iHOME system guarantees the space scalability and overcomes the storage limitation.     

Circular antenna array synthesis using firefly algorithm

In this article, the design of circular antenna arrays (CAAs) and concentric circular antenna arrays (CCAAs) of isotropic radiators with optimum side lobe level (SLL) reduction is studied. The newly proposed global evolutionary optimization method; namely, the firefly algorithm (FA) is used to determine an optimum set of weights and positions for CAAs, and an optimum set of weights for CCAAs, that provides a radiation pattern with optimum SLL reduction with the constraint of a fixed major lobe beamwidth. The FA represents a new algorithm for optimization problems in electromagnetics. It is shown that the FA results provide a SLL reduction that is better than that obtained using well‐known algorithms, like the particle swarm optimization, genetic algorithm (GA), and evolutionary programming. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:139–146, 2014.     

CAD modeling of coplanar waveguide interdigital capacitor

A lumped‐element circuit is proposed to model a coplanar waveguide (CPW) interdigital capacitor (IDC). Closed‐form expressions suitable for CAD purposes are given for each element in the circuit. The obtained results for the series capacitance are in good agreement with those available in the literature. In addition, the scattering parameters obtained from the circuit model are compared with those obtained using the full‐wave method of moments (MoM) and good agreement is obtained. Moreover, a multilayer feed‐forward artificial neural network (ANN) is developed to model the capacitance of the CPW IDC. It is shown that the developed ANN has successfully learned the required task of evaluating the capacitance of the IDC. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.