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IET Microwaves, Antennas & Propagation
Volume 4, issue 5, May 2010
Volumes & issues:
Volume 4, issue 5
May 2010
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- Author(s): M.M. Banat
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p.
563
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(3)
- Author(s): O. Ramadan
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p.
566
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Unconditionally stable finite difference time domain (FDTD) formulation is presented for modelling electromagnetic wave propagation in open region double-negative meta-material domains. The formulation is based on incorporating the bilinear transformation technique and the stretched coordinate perfectly matched layer into the split-step FDTD algorithm. Numerical examples carried out in one- and two-dimensional domains show that the proposed formulation not only maintains the accuracy level of the conventional alternating direction implicit FDTD scheme but also reduces the required computational time by 21%. - Author(s): A. Hrovat; G. Kandus; T. Javornik
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p.
571
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The present study analyses radio propagation at the 400 MHz frequency band inside road and railway tunnels. It proposes, on the basis of field measurements, a path loss model consisting of four segments, namely: the free space segment, the high path loss segment, the waveguide segment and, in the furthest region, the free space propagation segment. Free space propagation is characteristic in a region close to an antenna. In the next region, the near region, only a few reflected rays reach the receiver resulting in high path loss. Further away, in the far region, the waveguide effect occurs because of a set of waves reflected from the tunnel walls resulting in low path loss. In the extreme far region, the waveguide effect vanishes because of attenuation of reflected rays. The points separating the individual segments are analytically defined. Model applicability and accuracy are checked by calculating the mean error and standard deviation. The results indicate reasonable agreement between measurements and the model. This four-slope path loss channel model can be applied for rapid and simple coverage prediction of direct mode operation in TETRA systems. - Author(s): G.M. Qubati; R.A. Formato; N.I. Dib
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p.
583
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Central force optimisation (CFO) is a new deterministic multi-dimensional search evolutionary algorithm (EA) inspired by gravitational kinematics. CFO is a simple technique that is still in its infancy. This study evaluates CFO's performance and provides further examples of its effectiveness by applying it to a set of ‘real-world’ antenna benchmarks and to pattern synthesis for linear and circular array antennas. A new selection scheme is introduced that enhances CFO's global search ability while maintaining its simplicity. The improved CFO algorithm is applied to the design of a circular array with very good results. CFO's performance on the antenna benchmarks and the synthesis problems is compared to that of other EAs. - Author(s): S. Dikmese; A. Kavak; K. Kucuk; S. Sahin; A. Tangel; H. Dincer
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p.
593
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Software radio implementations of beamformers on programmable processors such as digital signal processor (DSP) and field programmable gate array (FPGA) still remain as a challenge for the integration of smart antennas into existing wireless base stations for 3G systems. This study presents the comparison of DSP- and FPGA-based implementations of space–code correlator (SCC) beamformer, which is practical to use in CDMA2000 systems. Implementation methodology is demonstrated and results regarding beamforming accuracy, weight vector computation time (execution time) and resource utilisation are presented. The SCC algorithm is implemented on Texas Instruments (TI) TMS320C6713 floating-point digital signal processors (DSPs) and Xilinx's VirtexIV family FPGA. In signal modelling, CDMA2000 reverse link format is employed. The results show that beamformer weights can be obtained within less than 10 ms via implementation on c6713 DSP with direction-of-arrival (DOA) search resolution of Δthetas=2°, whereas it can be achieved within less than 25 µs on VirtexIV FPGA for five-element uniform linear array (ULA). These results demonstrate that FPGA implementation achieves weight vector computation in much smaller time (nearly 500 times) as compared to DSP implementation in this study. - Author(s): D. Zhou; R.A. Abd-Alhameed; C.H. See; A.G. Alhaddad; P.S. Excell
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600
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A novel miniature balanced mobile handset antenna is presented in this study, which covers digital communication system (DCS) (1710–1880 MHz), personal communication system (PCS) (1850–1990 MHz), universal mobile telecommunications system (UMTS) (1920–2170 MHz) and wireless local area network (WLAN) (2400–2484 MHz) frequency bands. The antenna is a built-in planar dipole with folded structure and with the addition of a dual arm on each half of the dipole. The performance of the antenna is analysed and optimised under certain design constraints. The stability performance of the proposed antenna against proximity effects is evaluated. The effects of the phone user's hand on the return loss and radiation patterns have been characterised by simulation with a simple hand model. A prototype of the proposed antenna is fabricated and tested. A wide bandwidth planar balun is used to feed the wideband balanced antenna from an unbalanced source. The calculated and measured results show good agreement and confirm good wideband characteristics with multiband operation. The specific absorption rate (SAR) performance of the antenna is also studied experimentally by measuring near field exposure. The measured results have shown low induced current in the ground plane and thus confirm minimisation of performance variations and SAR. - Author(s): C.G. Kakoyiannis; A. Kyrligkitsi; P. Constantinou
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609
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The design of low-cost, wideband, printed inverted-F antennas (PIFAs) that are suitable for portable devices operating at the 2–3 GHz band is described. The design specifications were extracted according to the constraints of high data rate wireless sensor devices. Reactive tuning through slot loading was applied to enforce degeneration of a higher resonance, and thus double the bandwidth in the band of interest. Three slotted antenna configurations are reported plus a baseline configuration; a thorough numerical characterisation of performance is provided. Fractional bandwidth (FBW) in the range 22–34% was achieved, which is almost quadruple that of existing implementations. The antennas exhibit total efficiencies around 80% and are elliptically polarised. A suitable figure-of-merit is suggested for performance comparisons; it attempts to capture overall antenna performance in a single quantity. Antenna performance depends heavily on electrical size, which depends on the size of the ground plane, since the RF ground is an integral part of the total radiator. The ground-effect study showed that wrong choice of size can force resonant modes to vanish. Best performance for a slotted PIFA was obtained with a ground plane measuring 0.20λ×0.28λ, significantly smaller than predicted in prior studies. Bandwidth augmentation through slot loading is supported by measurements. Fabricated antennas with sub-optimal ground plane sizes exhibit FBWs in the range 20–23%. - Author(s): C.G. Kakoyiannis; P. Constantinou
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p.
629
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Printed sinusoidal monopoles are enhanced meander-line antennas (MLAs). The antennas were designed in the 2.0–3.5 GHz band according to the size and bandwidth constraints of high data-rate wireless sensor nodes. Their performance was characterised in terms of electrical size, bandwidth and broadband radiation efficiency. A suitable scalar quantity was used to capture the overall performance. Numerical results show that sinusoidal monopoles can achieve 50% fractional bandwidth (FBW), which is a 60% improvement compared to an MLA of similar size and efficiency. Antenna performance depends heavily on electrical size, which depends on the size of the ground plane; its effect on radiation was also included. Compact printed arrays built with sinusoidal monopoles were also studied. Their performance was characterised in terms of active impedance bandwidth, broadband radiation efficiency, active element pattern, mutual coupling and broadband correlation coefficient. The results showed that densely packed compact arrays feature controllable element detuning, whereas correlation coefficient stayed below 0.5 even for λ/10 spacing. The computational results were supported by measurements on actual hardware. Antennas mirrored against the nominal 20 mm×30 mm ground plane achieved FBWs in the range 23–28%. Those that used the adapted ground plane (GNDP) size scored 24–34% FBWs. In the case of arrays, the active impedance FBW degraded gracefully with decreasing inter-element distance from 33% to 27%. - Author(s): I.H. Naqvi; G. El Zein; G. Lerosey; J. de Rosny; P. Besnier; A. Tourin; M. Fink
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643
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An experimental validation of high data rate communication for a time reversal (TR) ultra wide-band (UWB) communication system is performed using binary pulse amplitude modulation (BPAM) in two different dense multipath propagation channels for different data rates (15.62 Mbps≤Rb≤1 Gbps). From the measured received signals, signal, interference and noise contributions are separated. At very high data rates, interference has the most dominant contribution of all. Furthermore, without any processing and equalisation at the receiver, bit error rate (BER) performance is compared for different Rb. It is shown that for Rb≤125 Mbps, TR system gives a good BER performance. Finally, the authors introduce a modified TR scheme in which total bandwidth of the TR system is divided into N sub-bands contributing equal power in the power spectral density (PSD). This technique enables a flat PSD of the TR transmitted signal, reduces inter symbol interference (ISI) and therefore improves the BER performance of the system. - Author(s): M.A. Jarajreh; Z. Ghassemlooy; W.P. Ng
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p.
651
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Numerical simulations of the coherent optical orthogonal frequency division multiplexing modems are undertaken to investigate the effect of the adaptive modulation, the number of sub-carriers, the cyclic prefix (CP) length, the clipping ratio, quantisation bit resolution and the sampling speed of analogue-to-digital converters (ADCs) on the chromatic dispersion (CD) of a single mode fibre (SMF) at data rates up to 80 Gbps. The use of a large number of sub-carriers is more effective in combating fibre dispersion than employing a long CP; moreover, the optimum number of sub-carriers in the presence of both SMF non-linearities and CD has been identified. The authors show that using a high bit resolution ADC with a high clipping ratio, the transmission distance can be increased at specific data rates. Furthermore, it is shown that ADCs with a low sampling speed also improve the system tolerance to the fibre CD. In addition, simulation results show that the use of adaptive modulation schemes improves spectrum usage efficiency, thus resulting in higher tolerance to the CD when compared with the case in which identical modulation formats are adopted across all sub-carriers.
Editorial: Selected papers from Mosharaka International Conference on Communications, Propagation and Electronics (MIC-CPE2009)
Split-step finite difference time domain algorithm for double negative meta-materials
Four-slope channel model for path loss prediction in tunnels at 400 MHz
Antenna benchmark performance and array synthesis using central force optimisation
Digital signal processor against field programmable gate array implementations of space–code correlator beamformer for smart antennas
Compact wideband balanced antenna for mobile handsets
Bandwidth enhancement, radiation properties and ground-dependent response of slotted antennas integrated into wireless sensors
Radiation properties and ground-dependent response of compact printed sinusoidal antennas and arrays
Experimental validation of time reversal ultra wide-band communication system for high data rates
Improving the chromatic dispersion tolerance in long-haul fibre links using the coherent optical orthogonal frequency division multiplexing
