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Microwaves, Antennas & Propagation, IET

Issue 15 • Date December 11 2012

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Displaying Results 1 - 14 of 14
  • Generic dipole-based antenna-featuring dual-band and wideband modes of operation

    Page(s): 1623 - 1628
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (547 KB)  

    A simple yet practical antenna structure composed of a regular half-wavelength dipole with coupling arms is presented. Adjustment of the amount of coupling to the main dipole through physical dimensions enables operation in either dual-band or wideband mode. Omni-directional radiation patterns can be achieved for both operation modes. The proposed antenna has been implemented for mid- and upper-bands of a WiMAX system. Good agreement between the simulation and measurement results has been observed. View full abstract»

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  • Design and analysis of a compact wideband pattern-reconfigurable antenna with alternate reflector and radiator

    Page(s): 1629 - 1635
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (697 KB)  

    The authors present a novel compact wideband pattern-reconfigurable antenna with alternate reflector and radiator. The proposed antenna consists of a pair of step-shape patches, four switches and a coplanar waveguide feeding line. By setting the switches ON or OFF, the two step-shape patches can alternately switch between the radiator and the reflector. As a result, the proposed antenna is able to provide two-directional radiation patterns whose main beams are roughly directed in opposing directions from 3.7 to 6 GHz. Compared with other current pattern-reconfigurable antennas, the proposed antenna exhibits advantages of better back-to-front radiation ratio, more compact antenna size and wider operating band. In this investigation, the optimised size of the proposed antenna is 20 20 mm2, which equates to 0.25×0.25×020 is the wavelength at the low edge of the operating frequency band). In addition, the time-domain characteristics of the proposed antenna are presented and analysed. The antenna shows a good time-domain performance. Measured results are presented. View full abstract»

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  • Efficiency of arrays composed of high-gain reflector antennas

    Page(s): 1636 - 1642
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (193 KB)  

    Arrays composed of high-gain reflector antennas are used for radio-astronomical purposes and, more recently, are proposed as ground station for deep space communications. This latter application requires a precise knowledge of the degradation that phase, amplitude and pointing fluctuations impose on the capability of the array to combine coherently the signal received or transmitted from each antenna. In this study, an analytical model for the fluctuation of each parameter (phase, amplitude and pointing) is derived and it is used to predict the efficiency of an array composed of an arbitrary number of high-gain reflector antennas. The analytical models are verified by numerical simulations and applied to an array layout currently proposed as possible future ground stations for the European Space Agency. View full abstract»

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  • Model management for cost-efficient surrogate-based optimisation of antennas using variable-fidelity electromagnetic simulations

    Page(s): 1643 - 1650
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    Electromagnetic (EM) simulation has become an important tool in the design of contemporary antenna structures. However, accurate simulations of realistic antenna models are expensive and therefore design automation by employing EM solver within an optimisation loop may be prohibitive because of its high computational cost. Efficient EM-driven antenna design can be performed using surrogate-based optimisation (SBO). A generic approach to construct surrogate models of antennas involves the use of coarse-discretisation EM simulations (low-fidelity models). A proper selection of the surrogate model fidelity is a key factor that influences both the performance of the design optimisation process and its computational cost. Despite its importance, this issue has not yet been investigated in the literature. Here, the authors focus on a problem of proper surrogate model management. More specifically, the authors carry out a numerical study that aims at finding a trade-off between the design cost and reliability of the SBO algorithms. Our considerations are illustrated using several antenna design cases. Furthermore, the authors demonstrate that the use of multiple models of different fidelity may be beneficial to reduce the design cost while maintaining the robustness of the optimisation process. Recommendations regarding the selection of the surrogate model coarseness are also given. View full abstract»

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  • Cramer-Rao bounds of angle-of-arrival and polarisation estimation for various triads

    Page(s): 1651 - 1664
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (971 KB)  

    This work derives the closed-form CraméŕRao bounds (CRBs) for the estimation of an incident far-field point-sourcés azimuth-elevation arriving angles and polarisation parameters. The receiving antennas are a triad of spatially collocated but orthogonally oriented dipole(s) and/or loop(s). The CRBs for all 20 possible compositions of such a triad are derived. The derived CRBs are verified by Monte Carlo simulations of maximum-likelihood estimation. Furthermore, the CRBs of triads with two antennas (one dipole and one loop) oriented along the z-axis plus another dipole/loop oriented along the x/y-axis have been simplified in the following three commonly encountered polarisation states: (i) horizontally linear polarisation, (ii) vertically linear polarisation and (iii) right-circular polarisation. Observations are obtained from the derived CRBs to help engineers select antennas among the 20 different triad-compositions for direction finding and polarisation estimation. View full abstract»

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  • Dual band-notched tapered slot antenna using λ/4 band-stop filters

    Page(s): 1665 - 1673
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (846 KB)  

    This study proposed a novel quarter-wavelength band-rejected element for band-notched antennas. It consists of a metal via and a rectangular strip connected to the radiating patch. In order to validate the design, a dual band-notched elliptically tapered slot antenna for ultra-wideband (UWB) applications is designed using the loaded strips. This antenna is capable of filtering the coexistent WLAN802.11a frequency bands 5.15-5.35 and 5.725-5.825-GHz. Compared with other band-notched UWB antennas, this antenna features the merit of easy tuning of each rejected frequency band because of the low mutual coupling between loaded strips at rejected frequencies. Both simulated and measured results confirm that the proposed antenna is able to achieve a wide bandwidth from 3 to over 11-GHz with two unwanted frequency bands notched. Stable radiation patterns are observed across the operational frequency range, with cross-polarisation levels below -20-dB. View full abstract»

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  • Radio frequency IDentification miniature interrogator antenna sprayed over an in-vehicle chassis

    Page(s): 1674 - 1680
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (627 KB)  

    Among the different assets tracking solutions radiofrequency IDentification (RFID) is a promising technology for in-car communications because of its relatively low-cost deployment and real-time monitoring and processes. In this study, a hidden, miniature, narrow-band antenna of dimensions 0.18λ × 0.20λ × 0.005λ is presented, which is easy to manufacture using conductive paint sprayed over a car body. The design relies on a resonator, a negative image of the radiator for improved efficiency when in close proximity to ground planes and is suited for use in RFID networks using the unlicensed RFID band (865.6-867.6 MHz) described. The term miniature comes from the fact that the antenna is physically small given low proximity and insensitivity to the ground plane, which facilitates a possible coating layer over the antenna for hidden applications. View full abstract»

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  • Experimental investigation of a circularly polarised flexible polymer/composite microstrip antenna for wearable applications

    Page(s): 1681 - 1686
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    A novel highly flexible, lightweight square ring circularly polarised microstrip antenna composed of SrTiO3/polyolefin elastomer (POE) composite as substrate material and polypyrrole conductive polymer as radiating patch and ground plane is proposed, designed and fabricated for the first time. Circular polarisation is achieved by truncating the corners of square ring patch. The effect of composite substrate thickness is experimentally studied and antenna parameters are compared with a reference copper antenna. The antenna performance is experimentally studied when it is flexed under different curvature radii. Also its actual performance is investigated when mounted on human body. High frequency structure simulator (HFSS) simulation and measurement results show good performance of the proposed antennas. The polymer/composite antenna is very flexible and lightweight and can be used for flexible/wearable antenna applications. View full abstract»

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  • Design, analysis and implementation of novel metamaterial transmission line with dual composite right/left-handed and conventional composite right/ left-handed properties

    Page(s): 1687 - 1695
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (626 KB)  

    The design, analysis and implementation of new metamaterial transmission line (TL) are presented. The proposed metamaterial TL exhibits dual composite right/left-handed characteristics at low/middle-frequency bands and conventional composite right/left-handed characteristics at middle/high-frequency bands. Therefore it should be left-handed property at middle-frequency band and right-handed property at low/high-frequency bands to achieve the proposed characteristics. Circuit models that meet the requirements are discussed. The operating principles and characteristics of the representative circuit model are investigated by means of its balanced conditions, typical dispersion/attenuation and Bloch impedance curves. Furthermore, handedness characteristics of the metamaterial TL, including double positive (right handed), double negative (left hed), epsilon-negative and mu-negative bands, are discussed. An implementation of the proposed metamaterial TL is constructed based on microstrip line and defected ground structure technologies. View full abstract»

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  • On-body performance of dual-band textile antennas

    Page(s): 1696 - 1703
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    For reliable on-body communications, the antennas involved need to meet certain requirements such as minimal frequency de-tuning and minimal efficiency degradation. The textile antenna has emerged as a promising candidate for the role in on-body communications but its performance characteristics have not yet been adequately treated in literature; particularly so in the on-body scenario. In a recent investigation into small-sized textile antennas, the authors remarkably determined that a lossier free-space antenna could outperform an antenna with higher free-space efficiency when placed on-body. The purpose of this study, therefore is to determine the practical on-body performance of two larger sized dual-band textile antennas using human subjects to see if this relation holds. The results show that a higher conductivity-based textile material in conjunction with a suitably large-sized ground plane performs more resiliently when placed on-body; about a 20% degradation in radiation efficiency is observed as compared with free-space levels, which is much less than the lower conductivity textile material in this study. The authors concur therefore that in addition to the conductivity of the textile material, the ground plane dimension is also of crucial importance in relation to how efficient the textile antenna performs on human subjects. The on-body frequency de-tuning of these antennas is also investigated, concluding that in the higher-frequency sub-band, both antennas remain well matched. However, detuning is apparent in the lower band, which should be taken into account when designing these antennas for on-body applications. Theoretical, simulated and experimental evidence is provided to verify the conclusions. View full abstract»

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  • Dual-layered substrate-integrated waveguide six-port with wideband double-stub phase shifter

    Page(s): 1704 - 1709
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1040 KB)  

    A dual-layered six-port front-end circuit on the basis of substrate-integrated waveguide (SIW) technology is presented and demonstrated. The use of SIW technology allows the development of a compact circuit with low radiation loss at millimetre-wave frequencies. The six-port architecture makes use of multilayer couplers that provide a wide coupling area through two slots; a new broadband SIW phase shifter composed of two H-plane stub lines and a reference line; and two SIW power dividers. The six-port design is free from loads as in the case of classic modified six-port architectures with eight ports. To validate the proposed concept, an integrated broadband six-port front-end circuit prototype was designed, fabricated and measured. Simulation and measurement results show that the proposed six-port circuit can easily operate at 60 GHz for V-band system applications. The two-layered structure presents interesting technological features including low profile, small volume and footprint and high-density integration. View full abstract»

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  • Time series prediction of rain rate during rain events at a tropical location

    Page(s): 1710 - 1716
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    A new model is proposed to predict rain rate series during a rain event at a tropical location. The model is based on Gaussian distribution of conditional occurrence of rain rate with a particular value of the rain occurring earlier. The mean and standard deviation of the distribution are modelled with the measured data. The rain rate at a particular time instant is predicted from the knowledge of previous samples. The predictor has tested well with a maximum mean error within 20%. This model produces predicted rain rate series whose first and second-order statistics fit very accurately with those of the experimental data. The method can also be applied with increased error, even if rain rate measurements are missing for certain periods of time. Comparisons with other models are also shown. View full abstract»

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  • Low-cost antenna array with wide scan angle property

    Page(s): 1717 - 1727
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1468 KB)  

    The scan range of an antenna array can be increased by providing a degree of curvature to its structure. However, achieving a wide scan range with an antenna array with limited number of elements is a challenging design issue. In this study, a novel 8-element linear array of polarisation reconfigurable antennas conformed to four different array structures; namely 2-faceted, 3-faceted, 4-faceted and 8-faceted are analysed and synthesised. Observations are made on the influence of the tilting angle of the faceted structures to the geometrical characteristics and the scan range of the array. It is shown that the 3-faceted array can achieve the widest scan range with the smallest dimension compared with the other faceted structures. Furthermore, the results show that the 3-faceted structure achieves ±69± scan range, compared to ±56± achieved with a linear array. View full abstract»

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  • Two-dimensional loaded wire grid for modelling dielectric objects and its application in the implementation of Luneburg lenses

    Page(s): 1728 - 1737
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (849 KB)  

    In this study, the performance of two-dimensional (2D) loaded wire grids for modelling the dielectric objects is investigated. In addition, the loaded wire grid is applied to realise a 2D Luneburg lens. First, the accuracy of the loaded wire grid for 2D problems is validated by calculating the fields scattered by an infinite dielectric cylinder illuminated by a line source, and comparing the results with the analytical solution. The effect of the permittivity of the objects on choosing the grid period and of applying the equal area rule to determine the radius of the wires on the accuracy of the far field radiation is investigated. Based on the results on the accuracy of the loaded wire grid, a 2D Luneburg lens is implemented. The issues such as the losses in the lens, the use of a coarse mesh to reduce the number of the wires, the performance of the lens across a frequency bandwidth, and the control of the side lobe level and back radiation are studied. View full abstract»

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