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Microwaves, Antennas & Propagation, IET

Issue 5 • Date August 2008

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Displaying Results 1 - 15 of 15
  • Editorial

    Page(s): 409
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (65 KB)  

    First Page of the Article
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  • Convergence acceleration of the doubly periodic Green's function for the analysis of thin wire arrays

    Page(s): 410 - 417
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    A method is proposed to accelerate the evaluation of the Green's function of an infinite double periodic array of thin wire antennas. The method is based on the expansion of the Green's function into series corresponding to the propagating and evanescent waves and the use of Poisson and Kummer transformations enhanced with the analytic summation of the slowly convergent asymptotic terms. Unlike existing techniques the procedure reported here provides uniform convergence regardless of the geometrical parameters of the problem or plane wave excitation wavelength. In addition, it is numerically stable and does not require numerical integration or internal tuning parameters, since all necessary series are directly calculated in terms of analytical functions. This means that for nonlinear problem scenarios that the algorithm can be deployed without run time intervention or recursive adjustment within a harmonic balance engine. Numerical examples are provided to illustrate the efficiency and accuracy of the developed approach as compared with the Ewald method for which these classes of problems requires run time splitting parameter adaptation. View full abstract»

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  • Bandwidth performance limits for finite antennas

    Page(s): 418 - 426
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (474 KB)  

    Bounded bandwidth performance measures are defined for any finite antenna, either in free space or above a perfectly conducting ground plane. The measures are valid for any class of antenna, for example, for patch antennas, dielectric resonator antennas and so on, the radiating currents of which can be confined to the Chu sphere or hemisphere of radius a. The performance bounds are believed to be nearly achievable for electrically small antennas. Examples are given for a loop antenna and a patch dipole antenna, where the former is electrically small and the latter has dimensions comparable to a wavelength. View full abstract»

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  • Reducing computational costs using a multi-region finite element method for electromagnetic scattering

    Page(s): 427 - 433
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (225 KB)  

    Electromagnetic scattering problems involving multiple scatterers can be solved by the finite element method using a single domain truncated with an absorbing boundary condition, but often it is more efficient to separate the single domain into several subdomains, separated by free-space, and to solve the set of subdomains iteratively. This multi-region method has been reported in the literature. Its relative computational cost is investigated and formulas for determining are provided when it is advantageous to use a multi-region against a single-region method. View full abstract»

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  • Analysis of scattering from arbitrary configuration of elliptical obstacles using T-matrix representation

    Page(s): 434 - 441
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (493 KB)  

    A new method of analysis of an arbitrary configuration of elliptical cylinders is presented. The treatment of such a problem is based on a combination of the cylindrical and elliptical coordinates systems. This approach is applied to the formulation of the scattered field at the surface of equivalent cylinder surrounding dielectric or metal elliptical object. To analyse the arbitrary set of elliptical cylinders, the iterative scattering procedure is used. A good agreement of the proposed method with the commercial FD simulator is achieved. View full abstract»

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  • Frequency-invariant pattern synthesis of conformal array antenna with low cross-polarisation

    Page(s): 442 - 450
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    Despite their potential and promising advantages over classical planar arrays, conformal arrays also present many challenges to the antenna designer, including varying element normal due to curvature, serious cross-polarisation effect, limited operational bandwidth and so on. A uniform method for the element polarised pattern transformation of arbitrary 3D conformal arrays is presented based on Euler rotation. A space-time-polarisation filter structure is proposed for the pattern synthesis of conformal array, in which the finite impulse response (FIR) filters assigned to every element are used to acquire the frequency-invariant array pattern and the element polarisation diversity in array global coordinates is used to depress the cross-polarisation level. The optimal weight vector is obtained by alternating projection method. The alternating projection method is a powerful and attractive method for the pattern synthesis in that it requires relatively smaller amount of computation burden and a wide variety of desirable constraints can be freely implemented in a -visible- way, which is usually impossible for other optimisation method. The pattern synthesis method proposed has established a unified frame for the frequency-invariant and low cross-polarisation pattern synthesis of conformal array. Simulation results are provided to demonstrate the effectiveness and behaviour of the proposed method. View full abstract»

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  • Errors analysis of transponder-based radiometric calibration for high-resolution imaging radars

    Page(s): 451 - 458
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (393 KB)  

    Calibration is often required for precision measurement instruments like synthetic aperture radar (SAR) such that an image pixel intensity is directly expressed in terms of the surface backscatter coefficient. An active reflector named as transponder is an effective SAR calibration device which yields a larger radar cross-section than a corner reflector. Likewise, encoding the retransmitted signal can decouple the transponder from the background scatterers, hence, it can be used to calibrate SAR for radiometry, polarimetry and interferometry. However, as this transponder acts as an amplitude modulator, any signal errors in the transponder will result in degraded performance of radiation calibration. Literature search reveals that little work has been reported. As such, various kinds of signal errors and their effects on radiometric calibration are investigated. The system configuration and corresponding signal processing algorithms are detailed. Starting with an investigation of different errors, closed analytic expressions for calibration performance are derived. Furthermore, the most essential element of this transponder, one X-band wideband voltage-controlled attenuator, is developed. Experimental results show that, because of its low cost and wideband modulation technique, this transponder has extensive applications, not just for radiometric calibration. View full abstract»

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  • Increasing capacity of blind mobile system using pre-filtering technique

    Page(s): 459 - 465
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (695 KB)  

    Increasing mobile system capacity is a hot topic in communication research. A new beamforming technique using a pre-filtering process that decreases noise and interference effects to improve capacity of cellular systems is proposed. Simulation results show significant improvement over the conventional beamforming techniques. The simulation is based on the constant modulus algorithm as a typical blind beamforming technique. This capacity enhancement is achieved with slight increase in computational cost. View full abstract»

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  • New CPW-fed monopole antennas with both linear and circular polarisations

    Page(s): 466 - 472
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (495 KB)  

    A low-profile, planar, circularly polarised monopole antenna with a shorting sleeve strip fed using a coplanar-waveguide transmission line for wireless communication in the digital communication system and the global positioning system bands is studied. By utilising the coupling effect between the monopole antenna and sleeve, two excited resonant modes, including the monopole and travelling-wave modes, cover the 1.57- and 1.8-GHz bands. Through modification with antennas of various geometrical parameters, the proposed antenna exhibits the wide bandwidth in the desired frequency bands, which has a bandwidth of 45% at 1.6%GHz for an input reflection coefficient of less than %10%dB. Meanwhile, the antenna has a 3-dB axial ratio bandwidth of 5%. Details of the design considerations for the proposed antennas are described, and the results of the antenna performances obtained are presented and discussed. View full abstract»

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  • Compact multiband planar monopole antennas for smart phone applications

    Page(s): 473 - 481
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (794 KB)  

    A compact multiband planar monopole antenna is discussed. Tuning techniques, including offset feed, etching meandered slot and cutting tuning inset, are applied to the radiator in order to maximise the operating frequency range of the antenna. Experimental results demonstrate that the proposed design covers the operating bands of seven wireless services including the DCS/PCS/W-CDMA/2.4-/5-GHz WLANs/Bluetooth and the WiMAX in United States. The design concept, step-by-step guidelines, radiation mechanism and the simulated and experimental results are carefully investigated. The finite-size ground plane effect is taken into account as well. This antenna features multiband operations, almost omnidirectional radiation patterns in one of the principal cuts, and a compact size of 22.75 times 20 mm2. It is especially suitable for smart phone applications which are involving in integrating multiple wireless services into a single hand-held unit. View full abstract»

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  • Scattering from a cylindrical resistive sheet using a modified physical optics current

    Page(s): 482 - 491
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Applicability of a modified resistive physical optics (PO) current expression to electrically large cylindrical structures is validated by analytical and numerical computations and measurement. It is shown that the radar cross-section (RCS) computed using an exact series representation and the modified PO current approximation matches well in the backscatter direction, and the forward scatter RCSs differ in magnitude by a couple of decibels for a closed resistive sheet. The PO current is compared with the series solution to explain the discrepancy of the forward scatter RCS. It is also shown that an open resistive sheet segment shows excellent agreement with the PO result in both the forward and backscatter directions. Lastly, a simple modified PO shadow-zone current is given for penetrable cylindrical sheets. View full abstract»

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  • Design of low-temperature co-fired ceramic bandpass filter with transmission zeros in the stopband

    Page(s): 492 - 496
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (363 KB)  

    A multilayered bandpass filter with low-temperature co-fired ceramic technology is proposed. By integrating two types of filters as one filter, four transmission zeros can be generated. Each type of filter with a source-load coupling capacitor and a grounded coupling inductor, simultaneously, can generate two transmission zeros located on the opposite side of the passband skirt separately. Moreover, the fabricated filter provides good matching with the electromagnetic simulation and can prove the availability of the filter configuration. View full abstract»

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  • Wideband circularly polarised slot antenna

    Page(s): 497 - 502
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    A wideband circularly polarised slot antenna is presented. The slot antenna is fed by four microstrip line feeds orientated to have relative phases of 0deg, 90deg, 180deg and 270deg using a feed network comprising a pair of broadband 90deg hybrid. The proposed antenna delivers measured and simulated impedance bandwidths of 77.8% (1.02-2.32 GHz) and 89.1% (1.02-2.66 GHz), respectively, for standing wave ratio (SWR) < 2, measured and simulated axial-ratio bandwidths of 88.9% (1-2.6 GHz) and 81% (1.1-2.6 GHz), respectively, for axial ratio < 3 dB and measured and simulated gain bandwidths of 33% (1.5-2.1 GHz) and 27% (1.6-2.1 GHz), respectively, for gain >3 dB. A good agreement is observed between simulation and measurement. View full abstract»

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  • Fast and accurate modelling of frequencyselective surfaces using a new modular neural network configuration of multilayer perceptrons

    Page(s): 503 - 511
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (759 KB)  

    The authors consider the analysis and modelling of the scattering from frequency-selective surfaces (FSSs), in the 6-14-GHz band, as a function of its periodic array geometry of thin dipole elements on an anisotropic layer. The accurate full-wave electromagnetic (EM) analysis of each FSS was carried out using the method of moments. From the available EM data, the artificial neural network (ANN) models can be developed. The modelling problem was solved by using a new modular configuration of multilayer perceptrons (MLPs), which is an implementation of the proposal modified from the previous knowledge method of neuromodelling information. Each MLP in the modular configuration was trained separately from the others through the resilient backpropagation algorithm. Within the region of interest studied, the ANN model developed is able to estimate the resonance frequencies and the bandwidths of the FSS band-stop filters, with high accuracy and low computational cost. To verify the advantageous properties of the modular MLP/MLP model, a neural model using a simple MLP was developed in order to analyse the same learning task. A comparative study was done between these models in terms of training the convergence, the accuracy and the computational cost. View full abstract»

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  • Ultra-wideband antenna with improved gain characteristics

    Page(s): 512 - 517
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (531 KB)  

    A ultra-wideband (UWB) antenna with improved gain characteristics is proposed. With the improvements, it is discussed in terms of the band notch and enhanced radiation patterns. Shaping the return loss as an approach in order to achieve these characteristics is introduced and a multi-resonant dipole structure is designed and experimented in frequency and time domains. The proposed UWB antenna provides the band notch with a sharp slope and improved gain deviation on azimuth plane for the UWB communication. View full abstract»

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IET Microwaves, Antennas & Propagation covers all aspects of microwave and antenna engineering and propagation.

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