Hasil untuk "Cellular telephone services industry. Wireless telephone industry"

Biao Wang, Yongwei Sun, Shuai Zhou et al.

The electromagnetic radiation sensitivity of the electric explosive device (EED) and its installed use state is closely related to the size of the equipment and radiation field strength constraints. The use of the traditional all-level electromagnetic radiation method for the effect of the actual installed EED test in the electromagnetic environment simulation encountered a technical bottleneck. The microwave band is difficult to effectively assess through the current standing wave distribution and skin effect. The temperature rise of the EED bridge wire has no relationship with the frequency of the electromagnetic wave. In this paper, through the analysis of the electromagnetic effect mechanism of the EED, the coupled power model of electromagnetic irradiation of the EED is obtained, and the relationship between the temperature rise of the bridge wire of the EED and the electric field strength model is established. Under the action of high-frequency continuous waves, the electromagnetic effect of the device is tested to verify the correctness of the mechanism analysis of the electromagnetic effect of the device under the action of continuous waves. The results provide crucial technical support for the electromagnetic protection of the device under the harsh electromagnetic environment of the battlefield.

Xianggang Hu, Jiancang Su, Mingtao Zhang et al.

High-power microwave (HPM) antenna, one of the key subsystems in the HPM system, is used for HPM radiation. Its performance is partly determined by the impulse responses of reflector materials under HPM. Therefore, it is essential to investigate the impulse response characteristics of reflector materials under HPM. Instead of the traditional waveguide cavity, this study was based on the double elliptical reflector system with an open boundary. By using this system, the impulse response of reflector materials was measured, and the response of reflector materials of multiple types under various environments with different electric field strengths and pulse widths was tested. In terms of breakdown, reflection efficiency, and pulse waveform, aluminum and carbon fiber test plates were affected by HPM and compared. Finally, the impulse response characteristics of carbon fiber test plates were summarized. The proposed method applied in this research is universal, matches the practical application environment, and can be extensively employed in the impulse response research and test of reflector materials.

A. Gokula Chandar, S. Kannadhasan, R. Nagarajan et al.

The wide-band circularly polarised (CP) monopole antenna structure described in this article combines a defective ground plane with an f-shaped radiating monopole that is intended for impedance bandwidth and high axial ratio bandwidth (IBW). The faulty ground structure is etched as twin rectangular slots, an F-shaped slot, and a square slot with a corner cut off. The proposed antenna is 25 × 25 × 1.6 mm3 in total. The prototype of the optimised antenna’s far-field characteristics has been constructed, modelled, and experimentally confirmed. The simulated and measured return loss values are 3.19 to 7.4 GHz, with −32.48 dB and −38.42 dB, respectively. Axial ratio values are 4.37 to 7.22 GHz and 4.52 to 7.15 GHz, with an efficiency of 49.18% and 45.07%, respectively, for the simulated and observed bands. Gain levels in the whole CP band range from 2.8 to 3.3 dB. A continuous radiation efficiency of more than 90% is realised in the CP band. The suggested CP antenna has constant radiation qualities and is suitable for WLAN and WiMAX applications.

Xin Zhang, Lipeng Wang, Xiaofei Ma et al.

Large deployable mesh reflectors typically require high surface accuracy and have large apertures. The accumulation of machining errors in a large number of cables can lead to significant deviations between the final manufactured surface and the theoretical surface, particularly due to the large number of cables involved. Adjusting the mesh reflector is often necessary to meet the surface accuracy requirements. However, traditional surface adjustment methods can be challenging to converge and time-consuming. To address this issue, our paper proposes an engineering surface based on measured manufacturing errors as a substitute for the theoretical surface. This method can save time on the coarse adjustment of surface accuracy for large deployable mesh reflectors, reducing the overall surface accuracy adjustment time by 30%.

Mama Djaouga, Ousséni Arouna, Soufouyane Zakari et al.

La déforestation et la dégradation de l’environnement ont évolué au gré des conditions naturelles et de l’action anthropique. Dans le Département de l’Alibori, la production cotonnière, l’élevage bovin essentiellement extensif et transhumant, l’exploitation forestière,  les influences climatiques sahéliennes et l’urbanisation sont autant de facteurs qui accélèrent la déforestation. L’objectif de la présente recherche est d’évaluer la déforestation dans le Département de l’Alibori à base de l’imagerie satellitaire. Les données planimétriques issues des images SPOT 5 et 7 de 2005 et de 2015 fournies par le Projet OSFACO ont été interprétées et analysées. La classification supervisée couplée à l’interprétation visuelle des images SPOT dans le logiciel QGIS 2.18 ont été utilisées. Le contrôle-terrain a été effectué à travers 852 points GPS. La précision moyenne des cartes d’occupation des terres est d’environ 96 %. Les résultats révèlent une régression des formations végétales naturelles au profit des mosaïques de champs et jachères. Les forêts galeries, les forêts denses sèches, les forêts claires et savanes boisées et les savanes arborées et arbustives ont été converties en mosaïques de champs et jachères et en agglomérations. Les terroirs villageois sont plus touchés par la déforestation que les aires protégées qui occupent près de 45 % de la superficie du Département. Le taux de déforestation sur l’ensemble du Département est de 2,84 %. Ce taux est de 3,71 % dans les terroirs villageois et de 0,72 % dans les aires protégées. Ainsi, 37,56 % de la superficie du Département est touchée par la déforestation dont plus de 51,27 % des terroirs villageois et 15,05 % des aires protégées. Par ailleurs, 2,66 % du département est touché par la dégradation, 1,40 % a été reconstitué naturellement et seulement 0,35 % a connu une amélioration. La restauration de ces zones dégradées s’avère nécessaire dans le Département de l’Alibori considéré comme le bassin cotonnier du Bénin.

Yanqi Zhang, Zhaoming Zhang

The aerodynamic characteristics of radar antennas should be considered in computing their wind resistance and designing pedestal servo systems. In this paper, the aerodynamic characteristics of a flat plate antenna with azimuthal rotation are explored using a wind tunnel, and the effects of the antenna elevation angle and reduced frequency on the aerodynamic coefficients are analyzed. The corresponding results of numerical simulation are given to compare with the experimental results. The variation of aerodynamic coefficients with respect to the azimuth angle is found to depend on the reduced frequency and the antenna elevation angle. When the increase in antenna elevation angle is slight, the mean and root mean square values of the aerodynamic coefficients are not monotonic with respect to increases in elevation angle and may increase at individual elevation angles. When the elevation angle increases significantly, the mean, maximum, and root mean square values of the aerodynamic coefficients all significantly decrease. The simulation results are in good agreement with the experimental results, which verify the feasibility of using unsteady numerical simulations to obtain the flow field structure when the antenna is rotating. This approach allows the influence mechanism of the elevation angle change on the aerodynamic characteristics of the rotating antenna to be identified.

Ming Li, Haiping Wei, Jiahao Zhao et al.

This paper proposes a trifrequency reconfigurable antenna (FRA), which can work in the X-band, Ku-band, and Ka-band, by controlling only two RF MEMS switches. The antenna element has a frequency ratio beyond 3 : 1 and provides a good candidate for the frequency reconfigurable antenna array, since the size of the antenna is reduced by loading multiple metal shorting holes between the antenna radiating surface and the ground plate, and the overall size is only 0.14λX × 0.35λX (λX is the free-space wavelength at 8.6 GHz). Based on the proposed FRA element, a 1 × 16 linear irregular frequency reconfigurable antenna array (FRAA) with beam deflection ability is designed, which effectively addresses the element spacing problem in the optimization of the array. In addition, the close-coupling in X-band and the grating lobe caused by the long distance of array element spacing in Ka-band are comprehensively considered. With uniform amplitude feeding network, the sidelobe level is below −15 dB under beam deflection. Moreover, both FRA elements and FRAA prototypes have been fabricated and measured to verify their superiority. Good agreements are obtained between simulated and measured results, which indicates that the antenna has potential application in the future multifrequency wireless communication and intelligent radar anti-interference fields.

Ju Ge, Liping Gao, Rengang Shi

This paper presents a well-designed termination wall for the perfectly matched layers (PML). This termination wall is derived from Mur’s absorbing boundary condition (ABC) with special difference schemes. Numerical experiments illustrate that PML and the termination wall works well with ATS-FDTD(Shi et al. 2015). With the help of termination wall, perfectly matched layers can be decreased to two layers only; meanwhile, the reflection error still reaches -60[dB] when complex waveguide is simulated by ATS-FDTD.

Iury S. Batalha, Andréia V. R. Lopes, Jasmine P. L. Araújo et al.

With the advent of 5G mobile communication and researches into the propagation of large-scale channel modeling for frequencies above 6 GHz, measurement investigation was performed at 10 GHz with horn-type directional antennas in a corridor and a computer room within the Electrical and Computer Engineering Laboratories’ first floor, at Federal University of Pará (UFPA), Brazil. This paper presents data obtained through experimental work, channel modeling with co-polarization V-V and H-H and cross-polarization V-H in line-of-sight (LOS) or non-line-of-sight (NLOS) conditions. The large-scale close-in reference is sustained by a comprehensive analysis, considering propagation mechanisms such as reflection and diffraction. Results demonstrate that the established model had inferior standard deviation in relation to measured data, proving itself more significant to propagation in indoor environments.

Muhammad Irshad Khan, Muhammad Irfan Khattak, Gunawan Witjaksono et al.

The Federal Communication Commission (FCC) has authorized the use of unlicensed ultra-wide band (UWB) spectrum in the frequency range from 3.1 to 10.6 GHz for a variety of short-range applications, including wireless monitors and printers, camcorders, radar imaging, and personal area networks (PANS). However, the interference between coexisting narrowband channels and UWB signals that share the same spectrum should be avoided by designing UWB antennas with band notch characteristics. This work presents a printed monopole antenna (PMA) with slots of different shapes etched in the radiating element to obtain band rejection in the three coexisting communication bands, i.e., Worldwide Interoperability for Microwave Access (WiMAX), Wireless Local Area Network (WLAN), and International Telecommunication Union (ITU). A rectangular slot is etched to reject the WiMAX band (3.01-3.68 GHz), an upturned C slot stops the WLAN band (5.18-5.73 GHz) while an inverted-U slot halts the ITU frequency band (7.7-8.5 GHz). The proposed antenna occupies a volume of 32 x 30 x 1.6 mm3 and it radiates efficiently (>90%) with a satisfactory gain (>1.95 dBi) in the unnotched UWB frequency range. The simulations are performed in High Frequency System Simulator (HFSS), while the measurements are conducted in antenna measurement facility and found in close agreement with the former.

Youngje Sung

This paper proposes a dual-band reconfigurable square-ring antenna with a polarization diversity property. The proposed antenna consists of a square-ring resonator, two stubs with a shorting via, and two PIN diodes. The stub is positioned symmetrically to the left and right of the square-ring resonator, and the square-ring antenna connected to one of two stubs has a dual-band resonance. In this case, both resonant frequencies exhibit linear polarization (LP), and the two polarized waves are perpendicular to each other. The PIN diode selectively connects only one of the two stubs to the square-ring resonator. Thus, the polarization of the proposed antenna changes electrically at the two resonant frequencies. In addition, the frequency ratio (f2/f1) can be easily controlled by changing the length or width of the stub.

Mohammed LAYELMAM

Le criquet pèlerin, Schistocerca gregaria, est l'une des espèces acridiennes les plus redoutées en raison de l'ampleur des dégâts qu'il occasionne sur les cultures. Les pays touchés par cet insecte mobilisent des équipes de prospecteurs pour surveiller les habitats favorables à leur développement. Pour faciliter les interventions de ces prospecteurs et prédire la présence ou l'absence de criquets pèlerins, nous proposons pour le cas du Maroc une méthode basée sur l'historique des prospections et les variables explicatives calculées à la base des données de télédétection. Les données de télédétection utilisées sont issues du capteur MODIS et la technique CMORPH (NOAA CPC MORPHING Technique), ces données sont l'indice de végétation par différence normalisée (NDVI), la température de surface (LST) et la pluviométrie (P). Durant cette étude, nous avons testé deux modèles statistiques (Régression logistique et Forêts aléatoires) dans le but de trouver la meilleure approche à utiliser pour la production des cartes de prédiction. La comparaison des indicateurs extraits à partir de la matrice de confusion de chaque modèle nous a permis de conclure que la prévision par l'approche de forêts aléatoires semble meilleure que la régression logistique. Avec la modélisation statistique nous avons montré qu'il est possible de produire des cartes de prédiction de la présence/absence des criquets pèlerins en se basant sur les données de télédétection. Cette étude est une étape supplémentaire dans l'élaboration de cartes qui vont aider les prospecteurs à mieux orienter les missions de terrain et faciliter la localisation des zones favorables au développement des criquets pèlerins.

Hung‐Tai Tsou, Hsuan-Yu Hsu

Xingxing Li, Dangwei Wang, Xiaoyan Ma

Target localization using a frequency diversity multiple-input multiple-output (MIMO) system is one of the hottest research directions in the radar society. In this paper, three-dimensional (3D) target localization is considered for two-dimensional MIMO radar with orthogonal frequency division multiplexing linear frequency modulated (OFDM-LFM) waveforms. To realize joint estimation for range and angle in azimuth and elevation, the range-angle-dependent beam pattern with high range resolution is produced by the OFDM-LFM waveform. Then, the 3D target localization proposal is presented and the corresponding closed-form expressions of Cramér-Rao bound (CRB) are derived. Furthermore, for mitigating the coupling of angle and range and further improving the estimation precision, a CRB optimization method is proposed. Different from the existing methods of FDA-based radar, the proposed method can provide higher range estimation because of multiple transmitted frequency bands. Numerical simulation results are provided to demonstrate the effectiveness of the proposed approach and its improved performance of target localization.

Kun Wei, Jian-ying Li, Ling Wang et al.

A horizontally polarized omnidirectional microstrip antenna is proposed in this paper. The structure of designed antenna is with two back-to-back horizontally polarized microstrip antenna elements. Gain variation on main radiation plane of this new antenna is analyzed and radiation theory is deduced; formula of directivity on main radiation plane is given. Better omnidirectional characteristic of this antenna can be obtained by decreasing patch physical length. Both simulated and measured results verify the omnidirectional radiation patterns and input impedance characteristics. Good omnidirectional radiation patterns (gain variation in E-plane less than ±0.4 dBi) and input impedance characteristics are obtained; moreover, cross polarization less than −20 dBi is achieved.

Zhangjing Wang, Xing Fan, Haijuan Cui et al.

A novel thinned array with symmetric distribution along the array center is proposed in this paper. The proposed symmetric thinned array is based on the theory of unequally spaced array and the amplitude of each element in the array can be changed by introducing the weighted function. The pattern of the proposed array can be properly adjusted by changing the weighted function and the amplitude of the weighted factor, which obviously releases new degrees of freedom in array design. It has advantages such as low side lobe level (SLL) in the visible region, no grating lobes, and low nearby side lobe level (NSL), which has good potential for wide-angle scanning. Both simulation and experiment have been done; the experiment results show that, by applying this novel symmetric thinned array with pattern reconfigurable quasi-Yagi antenna, the scanning range of the array is −70°~70° in H-plane with SLL almost −10 dB below the maximum of the main beam. The 3 dB beam-width coverage is −86°~86°, which means that the proposed array can realize the entire upper-space beam coverage and restrain the SLL at the same time.

Ananta Heri Pramono

Céline Puig

La référence altimétrique nationale, nommée RGE Alti, est actuellement composée de données issues de traitements Radar sur les zones de montagne qui ne satisfont pas pleinement les spécifications. Dans le même temps, les caractéristiques d'acquisitions des satellites imageurs se sont considérablement améliorées permettant aux satellites comme Pléiades de devenir une alternative intéressante à l'aérien dans les zones où les prises de vues sont coûteuses et complexes à organiser tels que les massifs montagneux. Quatre acquisitions Pléiades réparties sur deux zones d'études, le col de Bavella en Corse et le massif du Mont-Blanc, ont servi à réaliser des Modèles Numériques de Surface (MNS) par corrélation. Des Modèles Numériques de Terrain (MNT) ont ensuite été calculés à l'aide d'une méthode développée à l'Institut National de l'Information Géographique et Forestière (IGN) qui se base sur une interpolation de points sols extraits des MNS. Ces MNT obtenus avec les acquisitions Pléiades possèdent une précision altimétrique de 3m à 4m et des résultats homogènes quel que soit le type de terrain ce qui est indispensable pour la réalisation d'une référence nationale. L'étude montre aussi une forte corrélation entre la qualité du MNT final et les caractéristiques de prise de vue, ce qui entraîne des contraintes d'acquisition particulières et la mise en place d'étapes supplémentaires dans le calcul du MNT. Moyennant ces adaptations, l'utilisation d'images Pléiades pour compléter le RGE Alti dans les zones de montagne est envisageable et les utilisateurs du RGE Alti ont d'ores et déjà montré leur intérêt pour ces MNT Pléiades.

Shang-Te Yang, Hao Ling

An efficient approach to compute the near-field distribution around and within a wind farm under plane wave excitation is proposed. To make the problem computationally tractable, several simplifying assumptions are made based on the geometry problem. By comparing the approximations against full-wave simulations at 500 MHz, it is shown that the assumptions do not introduce significant errors into the resulting near-field distribution. The near fields around a 3×3 wind farm are computed using the developed methodology at 150 MHz, 500 MHz, and 3 GHz. Both the multipath interference patterns and the forward shadows are predicted by the proposed method.

D. Castro, R. Atkinson, Stephen J. Ezell