Microstrip antennas are in demand for many radar and satellite communication applications due to their attractive features such as low profile, low cost and ease of integration and fabrication. They have also been found suitable in high-speed space vehicles and other strategic defense equipments due to their compatibility with planer solid-state devices. In this journal, several articles on this subject have been published in the past. A method to enhance the impedance bandwidth of rectangular microstrip antenna, by suitably modifying its geometry, is described in the paper, “Effect of Slot on Ground Plane in Enhancing the Impedance Bandwidth of Modified Rectangular Microstrip Antenna and its Array”, by S L Mallikarjun, P M Hadalgi, S K Satnoor and P V Hunagund. By suitably modifying the geometry of a rectangular microstrip antenna in the form of plus shape, bandwidth enhancement is achieved. The proposed antennas are designed using low cost glass epoxy substrate material having dielectric constant of 4.2 and thickness of 0.16 cm. The antennas are fabricated using the photolithographic process.

Dielectric rod antennas provide significant performance advantages and are a low cost alternative to free space high-gain antennas at millimeter-wave frequencies and at the higher end of the microwave band. These can be used in applications where the excitation system has to be sealed. The dielectric rod antenna is mechanically strong and robust, though rain and moisture on the surface of the rod show an effect on antenna gain. In Space Division Multiple Access (SDMA) applications, dielectric rod antennas made of Polystyrene, Perspex and Teflon are used in adaptive phased arrays. The radiation patterns of dielectric rod antennas are studied by J Subramanyam and M V S Prasad in their paper, “Radiation from Tapered Nylon Rod Antennas: A Computational Study”, with the objective of finding the optimum dimensions of the antenna.

Wearable antenna is the one using a conductive fabric that can be attached to clothing and other items. It is a high-performance mobile antenna that can act as a supplementary antenna in areas with poor reception. Antennas are generally designed to operate in open space and, if used in close proximity to human bodies or other objects, the impedance deteriorates, causing a noticeable reduction in performance. In order to design an antenna for wearable devices deployed for commercial applications, accurate knowledge of dielectric properties of fabric materials is needed. An approach to the measurement of dielectric constant and loss tangent of fabric substrate materials, used for the development of wearable antennas, is presented in the paper, “Measurement of Dielectric Constant and Loss Tangent of Fabric Materials Suitable for Wearable Antennas”, by S Sankaralingam, Bhaskar Gupta and S Raghavan. The technique presented in this paper for dielectric material characterization is based on the parallel plate method and uses RF impedance/material analyzer. The measured results for Teflon are compared with the data supplied by the manufacturer. The technique is then applied to measure varieties of cotton fabric.

In their paper, “Space Vector PWM for a Six-Phase VSI Supplying a Six-Phase and a Three-Phase Series-Connected Machine”, Atif Iqbal, Mohd. Ayyub and M Arif Khan analyze the two-motor drive system, supplied from a single six-phase Voltage Source Inverter (VSI), and controlled using vector control scheme. A scheme is proposed to generate inverter output voltages using space vector Pulse Width Modulation (PWM) in such a way that independent control of two series-connected machines is achieved with minimum interaction between the two machines; the concept is verified by simulation.

In the paper, “Fuzzy Logic-Based Controller for Three Area Power System”, by H D Mathur, H V Manjunath and R C Bansal, a fuzzy logic controller is proposed for the problem of Load Frequency Control (LFC) of electrical power system. The study considers a three area interconnected power system with generation rate constraint. Simulation results of the proposed fuzzy controller show that the proposed controller has better dynamic response when compared to the conventional Proportional Integral (PI) controller. Robustness of the proposed controller is achieved by analyzing the system response with varying system parameters.

Power distribution systems are difficult to analyze as they are ill-conditioned, unlike normal transmission systems. Moreover, distribution systems are inherently unbalanced. Special three-phase load flow methods are needed to exploit the special topological properties as well as to overcome the difficulties arising out of the ill-conditioned nature of the distribution systems. In their paper, “Load Flow Analysis for Unbalanced Radial Distribution Systems: A Comparison of Different Practical Methods”, Sivkumar Mishra and Debapriya Das observe that the Forward-Backward Sweep (FBS)-based method is most suitable for Unbalanced Distribution System Load Flow (UDSLF) as this method exploits the radial nature of the distribution networks fully.

-- M S R Murty
Consulting Editor