Hany F. Hammad

Graphical Representation and Evaluation of Attenuation and Coupling Parameters of Whispering-Gallery-Mode Resonators

A new graphical approach for extracting the attenuation and coupling coefficients of traveling-wave whispering-gallery-mode (WGM) resonators is proposed. This approach starts by representing the transmission coefficient circle on the complex plane at the resonance frequency. From the metrics of this circle (center position and radius), both the attenuation and coupling coefficients can be extracted. This technique simplifies the evaluation of the loaded and unloaded Q factors of WGM resonators directly from the extracted coefficients. It is applied to a K-band planar WGM resonator coupled to a dielectric image guide in a reaction-mode configuration. The extracted values from both simulations and measurements show a close agreement with the mathematical model of traveling-wave WGM resonators.

A preprocessing dependent image theory based ray tracing algorithm for indoor coverage solution

Hot spot coverage requirements of indoor environments necessitate adequate network platforms and optimal network planning. Optimal network planning imposes numerous iterative computations and evaluations of network coverage until the best antenna layout is achieved. Therefore, accurate and scalable indoor propagation models become of the ultimate essence. In this paper, image theory adopting a feasible reflection region concept is significantly enhanced using a pre-processing approach. The proposed method stores each mirrored image location, the corresponding feasible reflection region boundaries and the angles between walls of the indoor environment. Received power is calculated using stored data significantly reducing computational complexity in terms of the number of wall intersection tests that are necessary for coverage computations. The preprocessing approach is tested in different indoor configurations with multiple antennas. Simulation results confirm the superior accuracy of the proposed approach as well as the major complexity gain attained relative to other image theory based approaches.

Indoor Distributed Antenna System Planning with Optimized Antenna Power Using Genetic Algorithm

Distributed Antenna System (DAS) promises an attractive solution to cope with the increasing demand for high data rate services inside building. DAS divides the indoor Base Station power among a group of spatially separated antennas that are connected to the BS. The power sharing makes the planning of (DAS) more challenging compared to other wireless networks. The previous To simplify the problem DAS planning approaches divided power equally among the antennas and focused on finding the optimal number and locations of antennas. This paper optimizes the transmitted power of the DAS antennas along with their location and shows that this will enhance the performance compared to the equal power structure. The paper formulates the DAS planning problem as an optimization problem that considers the power division among antennas. The optimization aims to minimize the deployment cost and the power leakage outside the building while the maximizing the average data rate and the indoor coverage. To deal with these conflicting objectives and with the non-convexity of the formulated function, the paper develops meta-heuristic genetic algorithm with novel mutation and crossover methods that are customized to this problem.

A size-reduced wearable antenna for Zigbee indoor localization

In this paper, a size-reduced wearable microstrip patch antenna is presented. The antenna is developed for a Zigbee platform for Child Indoor Localization purposes. It is to operate at 2.4 GHz, with a linearly polarized radiation. For the wearable antenna, a conductive textile was used, namely Shieldit, and for the substrate layer, a 3.5 mm felt fabric was used. The multislots-loading technique was utilized, resulting in a 62% size reduction of the patch size compared to the size of a regular rectangular patch antenna. The reduced size design achieved a fractional bandwidth of 1.4%. Furthermore, investigations were conducted on different antenna bending and the antennas performance in proximity to human body.

Adaptable Reconfigurable Antenna Array System with Multi-Angle and Tri-Polarization Diversity [Education Column]

A reconfigurable antenna system is proposed here that aims to find the best communication link with respect to power. The system consists of two arrays: one on the transmitter side and one on the receiver side. Both arrays were developed using microstrip transmission-line technology. The frequency of operation was (as required) 2.4 GHz, and was supplied by ZigBee chips. Each ZigBee chip was connected to a personal computer to facilitate power measurement, and hence determine the best communication link possible.

Optimized transmitted antenna power indoor planning using distributed antenna systems

This paper aims to optimize the indoor planning of distributed antenna systems (DAS). The objective of the optimization is to find the number of deployed antennas, their optimal locations and the power transmitted from each antenna. The optimal configuration should minimize the deployment cost, maximize wireless coverage while minimizing power leakage outside a building. One of the main challenges in this problem is that in DAS all antennas are fed from the same base station. This means that the total power transmitted is constant and hence increasing the power assigned to one antenna would require decreasing the power on all other antennas. Similarly adding an antenna would require decreasing the power assigned to existing antennas. Previous approaches simplified the problem by assuming equal transmitted power from all antennas in the DAS, and they ignored the fact that the sum of these powers should remain constant. This paper provides a new multi-objective formulation for indoor DAS planning that considers a fixed total transmitted power constraint. The paper proposes a solution method that uses simulated annealing with smart neighborhood search steps to reach a near optimal solution. Results showed that the proposed formulation obtained better indoor DAS configuration and that including antenna power in the optimization provided a solution that contain less antennas and better average power compared to the equal power configuration.

A novel microstrip rotating cell for CP-reflectarray applications

This paper presents a new low-profile rotating element for circularly polarized microstrip reflectarray antennas. The proposed cell was first designed to operate in the X-band frequency range at 9.4 GHz, then the cell dimensions were reduced to shift the operating frequency up to 30 GHz. The element is printed on a thin substrate with εr = 2.2 and 0.254 mm thickness. Unlike most of the cp-reflectarray elements the ground sheet is directly attached to the down layer of the substrate and no foam is needed which in turn reduces the fabrication costs and facilitates the mounting of the cp-reflectarray antenna. A full wave simulation using CST-MWS was applied on the proposed element and farfield monitors were assigned to the simulation setup. The proposed element proved to maintain the sense of polarization of the incident circularly polarized plane wave upon reflection, having a cross-polarization component of -30 dB at 9.4 GHz and -20 dB at 30 GHz. Also, it showed an axial ratio of 0 dB at the line of sight θ=0o at both frequencies and provides a 10.6% fractional bandwidth.

BROADBAND MATERIAL CHARACTERIZATION USING TRAVELING-WAVE WHISPERING-GALLERY -MODE DIELECTRIC RESONATORS

A new technique for broadband material characterization, using a whispering-gallery-mode (WGM) resonator, is proposed. The resonant perturbation method is applied for the measurement of both the dielectric constant and loss tangent of various types of materials and over a wide frequency band. A comprehensive study on the reliability of using such technique, via simulations and measurements, is conducted as well. The feasibility of this device in sensing small variations of the dielectric properties of the material is investigated. Furthermore, the geometry of the resonator is slightly modifled to flt liquid materials as well. This can be a promising solution for sensing human-body tissues or liquids such as blood or urine due to the sensitive nature of these resonators. The experimental setup is successfully utilized to measure the dielectric constant of a water droplet as a liquid sample as well as difierent material samples of arbitrary shapes and dielectric properties. The measurements are performed over the whole X- and K-bands where the obtained results are with a maximum deviation of only 3.3% for solids and 4.5% for liquids.

Non-destructive broadband material characterization over the K-band using whispering-gallery-mode resonators

A precise technique for broadband material characterization, using a whispering-gallery-mode (WGM) resonator, is proposed. The resonant perturbation method is successfully applied for extracting both the dielectric constant and loss tangent of materials over a wide frequency band. Two experimental prototypes are fabricated and employed over the K-band where consistent results are obtained with a maximum error of ±3.3%.

An enhanced preprocessing dependent image theory algorithm for indoor coverage solutions

Hot spot coverage requirements of indoor environments necessitate adequate network platforms and optimal network planning. Optimal network planning imposes successive iterative computations and evaluations of network coverage until the best antenna layout is attained. Accordingly, accurate and scalable indoor propagation models become of the ultimate essence. In this paper, an efficient methodology for feasible reflection region assessment is developed to enhance a recently proposed preprocessing dependent image theory based ray tracing algorithm. The feasible reflection region depicts reception point grids of the indoor layout under study that fall within the foot print of a given transmitter image. The methodology proposed in this paper utilizes the intersection points between the stored preprocessing bounds of the feasible reflection region with lines that are drawn parallel to the walls of the indoor layout to achieve significant computational enhancements in the feasible reflection region assessment phase of the indoor coverage computations. The proposed enhanced ray tracing algorithm is tested in different indoor configurations. Simulation results confirm the major computational gain attained through the proposed enhancements while maintaining computational accuracy.