S. K. Chowdhury

Study of impedance and radiation properties of a concentric microstrip triangular-ring antenna and its modeling techniques using FDTD method

A concentric microstrip triangular-ring antenna structure using the log-periodic principle for increasing the impedance bandwidth of the microstrip patch antenna is described. The finite-difference time-domain (FDTD) method is applied to analyze the proposed structure. A special technique to model the slanted metallic boundaries of the triangular ring has been used in the general FDTD algorithm to avoid the staircase approximation. The method improves the accuracy of the original FDTD algorithm without increasing the complexity. The radiation patterns at different frequencies over a wide bandwidth are obtained experimentally.

Equivalence of radiation properties of square and circular microstrip patch antennas

The radiation properties of a circular microstrip antenna are compared with those of an equivalent square microstrip antenna. On the basis of this comparison, a simple method of computing the far field of a circular microstrip antenna is suggested. >

Game-Theoretic Modeling and Optimization of Contention-Prone Medium Access Phase in IEEE 802.16/WiMAX Networks

IEEE 802.16/WiMAX is an emerging standard for broadband wireless networks. It operates in both point-to-multipoint (PMP) and mesh modes. In the former, a number of subscriber stations communicate directly with a central base station. Although it supports different traffic classes characterized by distinct QoS requirements, the simplest is the best effort traffic. In this class, the subscriber stations first send bandwidth requests to the base station in a contention prone manner. Once the desired bandwidth is granted, scheduled transmissions take place. With increasing number of subscriber stations, due to media contention, collisions increase causing high loss to request packets and hence fall in data throughput. In this paper we address the issue by designing a new medium access control protocol GTMA for this random access phase, using ideas from non-cooperative game theory. We show that the resulting game converges to a unique non-trivial Nash equilibrium. NS-2 simulations confirm the reduction in packet collisions and consequent increase in system-wide data throughput and improvement in short-term fairness. To the best of our knowledge, this is one of the first applications of game-theoretic ideas in the explicit setting of contention control in IEEE 802.16/WiMAX networks.

Design and analysis of a compact monitor-shaped multifrequency microstrip patch antenna

This article proposes a monitor-shaped single layer, single feed compact rectangular microstrip patch antenna for multifrequency operation. Two unequal rectangular slots are introduced at the left- and right-side radiating edges of the patch to reduce the size of the antenna by reducing the resonant frequency. Multiple resonant frequencies are also obtained by cutting unequal rectangular slots. The measured result shows that the size of the antenna has been reduced by 66% with an increased frequency ratio (the ratio of second or higher resonant frequency to the first resonant frequency). The characteristics of the proposed antenna are investigated using method of moment-based electromagnetic solver, IE3D.

Concentric microstrip ring antenna : theory and experiment

The impedance and radiation properties of an electromagnetically fed concentric microstrip ring antenna using log-periodic principle is investigated experimentally and compared with those of two single ring resonators. The experimental result is verified numerically by Finite Difference Time Domain (FDTD) method. The variation of voltage standing wave ratio with frequency is also measured and computed numerically for both the single rings and concentric structure. The comparison between numerical and experimental results shows good agreement over a wide frequency range. The results indicate a considerable improvement of 1:2 VSWR bandwidth for the concentric structure.

A throughput-efficient cooperative sensing and allocation model for cognitive radio networks

In this paper, we propose a modified cooperative sensing scheme as documented by IEEE 802.22 standard to develop a spectrum agile simpler implementable cognitive radio network (CRN) by minimizing the probability of false alarm and maximizing the probability of detection to optimize the maximum achievable system throughput through the optimal decision fusion rule. In addition, we develop a dynamic channel allocation algorithm on the basis of a defined parameter called performance index of SUs.

Accurate Formula to Determine Resonant Frequency of Double Sided Printed Dipole Antenna

ABSTRACT Two arms of double-sided printed dipole antenna (DSPDA) are printed on opposite faces of a dielectric material. The antenna is fed by the printed version of two-wire parallel transmission line. This configuration has the advantages of high impedance bandwidth and low cross polarization. The width of each dipole arm is generally kept below 0.05λ0 to achieve high cross polar discrimination. However, it is observed that, in case of DSPDA the resonating length is different from that of the conventional half-wave dipole antenna. In this paper, we have proposed a semi-empirical but accurate formula to predict the resonant frequency for a given length of DSPDA. A prototype antenna is fabricated using the proposed formula which is validated against experimental results. Measured resonant frequency of the fabricated DSPDA matches closely with the theoretical one.

Analysis of an open-ended inverted L-shaped slot-loaded microstrip patch antenna for size reduction and multifrequency operation

This paper proposes a detail analysis of a single layer, single-feed microstrip patch antenna for size reduction and multifrequency operation. An open-ended inverted L-shaped slot is introduced at the left-hand side radiating edge of the patch to reduce the size of the antenna by reducing the resonant frequency. Multiple resonant frequencies are also obtained by introducing the open-ended inverted L-shaped slot. The measured result shows that the size of the proposed antenna has been reduced by 74.3% when compared with conventional rectangular microstrip antenna with same patch area. The proposed antenna also provides increased frequency ratio (the ratio of second or higher resonant frequency to the first resonant frequency). The conventional and proposed antennas are designed and simulated by method of moment-based IE3D software. An extensive analysis of the antenna parameters (reflection coefficient, radiation pattern, gain, etc.) including surface current distribution is given in this paper.

ON A SELF-COMPLEMENTARY MICROSTRIP ANTENNA

A configuration for increasing the impedance bandwidth of a microstrip patch antenna is described. The FDTD method is applied to analyze the proposed structure. The experimental results are in reasonable agreement with the computed data. The radiation patterns at different frequencies over a wide bandwidth are obtained experimentally.

Some Investigations on the Effect of Aspect Ratio on the Impedance of a Microstrip Antenna AT TM11 Mode

Previous experimental investigations revealed that by properly locating the feed along one of the radiating edges of rectangular microstrip antenna, 1:2 VSWR bandwidth can be improved considerably at TM11 mode. In this paper, keeping the location of the feed at a suitable point the effect of the variation of aspect ratio of the patch has been investigated. Further improvement in 1: 2 VSWR bandwidth with the change of aspect ratio has been observed and the measured data has been presented. These experimental results have been verified by FDTD method. Measured radiation patterns have also been presented alongwith theoretical computation by cavity model.