Christos N. Capsalis

ELECTRONIC BEAM STEERING USING SWITCHED PARASITIC SMART ANTENNA ARRAYS

A method of designing smart antennas based on switched parasitic antenna arrays is presented in this paper. The direction of maximum gain can be controlled by a digital word, while the selection of element spacing and weighting is optimized using the method of genetic algorithms. Various results are presented to show how antennas of this type perform, outlining the advantages and limitations of their design.

THEORETICAL APPROACH OF THE INTERACTION BETWEEN A HUMAN HEAD MODEL AND A MOBILE HANDSET HELICAL ANTENNA USING NUMERICAL METHODS

The interaction of a helical antenna,mounted on a mobile handset,with a human head phantom is investigated in this paper. Using the Genetic Algorithms (GA) technique combined with the Method of Moments (MoM),an optimization of the antenna structure is achieved regarding the input impedance at the operating frequency. The Finite Difference Time Domain (FDTD) method is then applied to simulate the handsets function in the close region of a spherical homogeneous and heterogeneous head phantom. A formula,based on an application of an existing model proposed by Kuster and Balzano for dipole antennas,provides a rather accurate prediction of the induced Specific Absorption Rate (SAR) values in the human head due to the radiating helical antenna. The concept of relating the SAR to the current on the antenna is used in this study to formulate the final expression. Moreover,using the theory of regression,the results of the calculated peak or average SAR are correlated with the distance between the antenna and phantom and with the standing wave ratio (SWR) at the antenna feed point. Thus,the conception that the SAR is indeed related to the antenna operational parameters is reinforced by the outcome of the current study.

Design of primary and composite routing metrics for RPL-compliant Wireless Sensor Networks

The diversity of applications that current and emerging Wireless Sensor Networks (WSNs) are called to support imposes different requirements on the underlying network with respect to delay and loss, while at the same time the WSN imposes its own intricacies. The satisfaction of these requirements highly depends on the metric upon which the forwarding routes are decided. In this view, the IETF ROLL group has proposed the RPL routing protocol, which can flexibly work on various routing metrics, as long as they hold specific properties. The system implementer/user is free to decide whether to use one or multiple routing metrics, as well as the way these metrics can be combined. In this paper, we provide ways to quantify the routing metrics so that they can be combined in an additive or lexical manner. We use extensive simulation results to evaluate the impact of several routing metrics on the achieved performance.

Acute mobile phone effects on pre-attentive operation

There is a debate whether electromagnetic field (EMF) emitted by mobile phones (MP) have an effect on cognitive functions. Since the auditory P50 component of event-related potentials (ERPs) reflects pre-attentive processing and working memory (WM) operation, the present study was designed to investigate whether the exposure to MP-EMF affects the patterns of the P50 component of ERPs elicited during a WM test. The P50 elicited during a WM task and evoked by two warning stimuli low and high frequency (500 and 3000 Hz) has been assessed in 19 normal subjects (10 women and 9 men) both without and with exposure to a 900 MHz signal, emitted by a dipole antenna placed near the subjects. Results showed that the presence of MP-EMFs induced statistically significant increase in the amplitude of P50 evoked by the low frequency stimuli, at Fp1 and O1 electrode leads as compared to themselves without MP-EMF exposure. In contrast the exposure to MP-EMFs revealed statistically significant decrease of the amplitude of P50 evoked by the high frequency stimuli, at Fp1 electrode lead as compared to themselves without MP-EMF exposure. These findings provide evidence that the MP-EMF emitted by mobile phone affect pre-attentive information processing as it is reflected in P50 evoked potential. The basis of such an effect is unclear, although several possibilities exist and call for potential directions of future research.

DESIGN OF SWITCHED BEAM PLANAR ARRAYS USING THE METHOD OF GENETIC ALGORITHMS

Abstract—A system consisting of a smart antenna and a processor can perform filtering in both the time and space domain, thus reducing the sensitivity of the receiver to interfering directional noise sources. Smart antennas can be used for further increase in the capacity of a communication system and for variable speed of transmission for multimedia information. Switched beam antenna arrays are a subset of smart antennas that cover either the x-y plane or a portion of it with multiple radiation patterns. A processor can decide which pattern to use for reception or transmission. In this paper the use of genetic algorithms (GAs) is examined in the design of switched beam antenna arrays. The antenna consists of five or six elements and the radiation patterns vary from 4 to 8, covering the x-y plane with the main beams of the radiation patterns pointing at 0◦, 90◦, 180◦, 270◦ and 0◦, 45◦, 90◦, 135◦, 180◦, 225◦, 270◦, 315◦ respectively. The positions of the antenna elements are either chosen exclusively by the GA or are assumed to form a circular array with one central element and the GA decides for the radius and the offset angle of the circle. Furthermore, the GA is asked to design an array covering the first 120◦ of the x-y plane with 4 radiation patterns pointing at 15◦, 45◦, 75◦ and 105◦. Such a configuration can be used in sector antennas, which are widely used in 2G mobile communication systems.

Gender related differences on the EEG during a simulated mobile phone signal.

The present study investigated the gender-related influence of electromagnetic fields (EMF), similar to that emitted by mobile phones, on brain activity. Ten women and nine men performed a short memory task (Wechsler test), both without (baseline) and with exposure to a 900 MHz signal. The EEG energy of the total waveform and the &agr;, &bgr;, &dgr; and &thgr; rhythms were calculated from the recordings of 15 scalp electrodes. Baseline EEG energy of males was greater than that of females, while exposure to EMF decreased EEG energy of males and increased that of females. Memory performance was invariant to EMF exposure and gender influences. These findings indicate that EMF may exert a gender-related nfluence on brain activity.

Rain attenuation problems affecting the performance of microwave communication systems

Rain attenuation is considered to be a dominant factor affecting the reliability of both terrestrial and earth-to-satellite paths operating at frequencies above 10 GHz. The subject of the present paper is the development of some efficient models for the prediction of the operational characteristics (such as the path enlargement factor, accumulation thermal noise, site diversity improvement) of microwave systems operating at these frequencies. The numerical results taken from the present models have been compared with available experimental data from operated links in USA, Europe, Japan and the agreement has been found to be quite encouraging.RésuméL’affaiblissement dû à la pluie est considéré comme un facteur déterminant de la fiabilité des liaisons radio électriques terrestres et par satellite pour des fréquences supérieures à 10 GHz. Cet article traite des modèles efficaces dans la prévision des caractéristiques de fonctionnement des systèmes de radiocommunication hyperfréquences. La comparaison des résultats théoriques obtenus à partir de ces modèles avec les données expérimentales obtenues à partir des liaisons fonctionnant aux Etats-Unis d’Amérique, en Europe et au Japon montre une assez bonne concordance.

Theoretical investigation of the field conditions in a vibrating reverberation chamber with an unstirred component

In this paper, we examine the use of a vibrating reverberation chamber in which an equipment under test (EUT) is directly illuminated by a source antenna. A three-dimensional theoretical model, based on a simplified ray tracing method has been applied on a reverberation chamber whose dimensions were varied. The field distribution together with the field homogeneity was investigated, introducing the Rice distribution due to the presence of the line-of-sight component between the antenna and the EUT.

Genetic design of dual-band, switched-beam dipole arrays, with elements failure correction, retaining constant excitation coefficients

Switched-beam dipole arrays (SBAs) are widely used in order to increase system performance in wireless communications. They represent an attractive alternative to fully adaptive arrays, due to lower deployment and maintenance costs. Dual-band operation and elements failure correction are dealt with in this paper, since they are considered to be key characteristics in modern systems, like WiFi/WiMAX, and remote base stations maintenance respectively. The focus of the presented work is on the preservation of constant excitation coefficients during dual-band operation (coefficients will change after a possible elements failure), but the possibility of retaining universal, constant excitations, even after element failures, is also examined (the term universal means that excitations are kept constant, regardless of element failure or frequency of operation). This is accomplished using a genetic algorithm (GA), and numerical results are presented which demonstrate the eligibility of the proposed technique.

PREDICTION OF THE SAR LEVEL INDUCED IN A DIELECTRIC SPHERE BY A THIN WIRE DIPOLE ANTENNA

The interaction between a dipole antenna,representing a simplified model of a mobile terminal,and a homogeneous spherical model of the human head is examined. The Finite Difference Time Domain (FDTD) method is utilized,to calculate the either peak or average value of the Specific Absorption Rate (SAR),corresponding to different distances between antenna and phantom. The variation of the SAR with the distance between the mobile antenna and the human phantom has gained significant attention in the recent literature and is investigated here. An attempt to correlate the computed SAR values with the basic antenna characteristics,such as the standing wave ratio (SWR),reveals that a precise estimation of the level of the SAR can be achieved regarding data acquired from the mobile terminal.