مجله مهندسی برق و الکترونیک ایران
سال دهم شماره 1 (بهار و تابستان 1392)

In this paper، a simple dual-band dual-polarized aperture stacked patch antenna with double sided notch is presented. This antenna is suitable for operation in telecommunication base stations. One of the bands covers the GSM band، while the other covers both DCS and UMTS bands. The proposed antenna shows good port decoupling of less than -30dB for dual linear polarization over its operating bands. The antenna is based upon an aperture stacked patch layout and incorporates a simple dual-layered feeding technique to achieve dual polarization radiation. A peak antenna gain of about 11. 8dBi and 7dBi has been obtained for lower & upper band respectively. The effort was directed towards the design of a single stand alone antenna; however، the performance would be better when it is incorporated as an array element.

This theoretical study examines the characteristics of a surface wave driven plasma monopole antenna using finite difference time domain method (FDTD) as well as commercial full wave simulator. The results show that the full wave simulator can be considered as an acceptable tool in simulation of a plasma antenna. Input impedance، radiation pattern، gain، efficiency and radar cross section of plasma antenna at plasma and collision frequency values are presented here using FDTD numerical method. Comparison between the achieved results with a conventional metallic antenna shows that the plasma antenna is an acceptable radiation tool in the first resonant region and can provide a dynamically reconfigurable antenna.

The accuracy of improved two dimensional finite difference time domain method (2D FDTD) is verified by comparing with 3D FDTD method and experimental data. The optimized 60° photonic crystal waveguide bend، used in this study as a test case، is composed of InPGaAs/InP material and air holes and TE polarization is considered. The photonic crystal waveguide bend transmission data was measured by End-Fire technique. This computational method can be applied to investigate photonic crystals with irregularly shaped and different materials. Comparison of experimental data with two and three dimensional simulations، it is evident that the improved 2D FDTD simulation shows a very good agreement with 3D FDTD simulation and also with the experimental data of the transmission properties. The efficiency and simplicity of 2D FDTD makes this algorithm promising for simulation of photonic crystals on personal computers of reasonable speed. Since the improved 2D FDTD simulation has a high performance compared to its 3D counterpart and also could easily be run on PCs، the improved 2D FDTD simulation can be considered as a useful tool in studying، designing and improving photonic crystal devices.

This paper proposed a new voltage control strategy for an islanded Microgrid (MG). A MG is consists of several Distributed Generation (DG) and local loads and controllers which it should be capable to operates in both connected and disconnected mode from main grid. Often there are some uncertainties in load and system parameters in isolated mode hence، robust control of electrical quantities is necessary for the system. The control structure proposed utilizes an internal oscillator to frequency control and a PI controller to voltage control which it is tuned based on Kharitonov’s theorem. D-stability approach has been used to fine tuning of PI controller. The simulation results show that the proposed control strategy based on Kharitonov’s theorem has a very effective performance in robust control of voltage.

A method for concurrent clearing of energy and reserve market is presented in this paper. The proposed method considers two important objectives in an optimization problem; the first one is including the stochastic nature of power generation variations by applying a probabilistic clearing model and Monte-Carlo simulation; the second one is assignment of energy and reserve capacities to generating units with consideration of economic and reliability criterions. In the objective function of the considered problem، in addition to the offered costs for energy and reserve، the costs of non-delivered energy and non-delivered reserve are included. Solution results of the optimization problem can be applied as a guidance to provide incentives for generating companies to improve their reliability and have higher share in the market. The proposed method is validated through its application to a test system

Accurate locating of fault in power distribution system (PDS) can significantly improve the reliability indices. In this paper، a new simple and practical method is proposed for estimating the section and distance of fault in PDS. In the proposed method، at first the protective devises are allocated and then specially set in such a way that they are coordinated and the unique current pattern is generated at the beginning of feeder for fault in each section. For approving and analyzing the accuracy of the proposed method، the method is tested on two test feeders and one real feeder of Bushehr Distribution Company under different fault conditions. Also، in the real test system two actual faults are applied and the section of fault is correctly determined by the proposed method.