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Microwaves, Antennas & Propagation, IET

Issue 2 • Date Feb. 2010

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Displaying Results 1 - 15 of 15
  • Neural network method for direction of arrival estimation with uniform cylindrical microstrip patch array

    Page(s): 153 - 161
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (743 KB)  

    In this study, a new neural network algorithm is proposed for real-time multiple source tracking problem with cylindrical patch antenna array based on a previously reported modified neural multiple source tracking (MN-MUST) algorithm. The proposed algorithm, namely cylindrical microstrip patch array modified neural multiple source tracking (CMN-MUST) algorithm implements MN-MUST algorithm on a cylindrical microstrip patch array structure. CMN-MUST algorithm uses the advantage of directive pattern of microstrip patch elements by considering only a part of array elements for a chosen sector. This reduces neural network sizes and also improves the spatial filtering performance. The proposed algorithm improves MN-MUST algorithm in the sense of accuracy and speed while covering the full azimuth range. View full abstract»

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  • Design, simulation and experimental study of near-field beam forming techniques using conformal waveguide arrays

    Page(s): 162 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1406 KB)  

    Microwave hyperthermia is rapidly evolving as a fourth modality in the fight against cancer, along with surgery, radiation and chemotherapy. This form of cancer treatment utilises a narrow microwave beam to heat the tumour volume to a temperature of ~42??C; however, with minimal energy delivery to neighbouring healthy tissue, which is one of the main challenges in hyperthermia technology. Potentially, this application can be achieved by using a phased array of apertures or dipoles to generate and control the beam focus within the near-field treatment region. This paper describes another approach to near-field beam forming by using of a conformal waveguide array, operating in the K band (18-26 GHz). The array comprises a central movable element that acts as the focusing element, and surrounding fixed directing elements. The focusing element gives conformal property to the array and serves two purposes: firstly to obtain a sharp focus at a prescribed near-field location, and secondly the added flexibility to move the beam around the tumour. Several simulations and measurements have been performed on linear and planar configurations, which demonstrate the ability of the array to achieve beam widths as small as ~4 mm, with a maximum beam movement range of ~15 mm. View full abstract»

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  • Design of fractal patch antenna for size and radar cross-section reduction

    Page(s): 175 - 181
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    This research study presents a novel design of star-shaped fractal patch antenna for miniaturisation and backscattering radar cross-section (RCS) reduction. The proposed fractal antenna gives 50% size reduction compared with a conventional circular microstrip patch (CCMP) antenna. The antenna is studied experimentally for return loss behaviour using vector network analyser R&S ZVA40. It can be useful for wireless application in 0.85-4 GHz frequency band. Further, the study focuses on backscattering RCS (both monostatic and bistatic) reduction by the proposed antenna compared with the CCMP antenna. It is found that increase in number of fractal iterations included in the conventional patch to design fractal antenna geometry reduces backscattering RCS at multiband compared to the conventional patch antenna. This reduction in backscattering RCS by the antenna is observed at multiband. The antenna can be tuned for low backscattering by variation in the substrate dielectric constant and thickness and the superstrate dielectric constant and thickness. For maximum RCS reduction by the antenna, optimisation of substrate thickness becomes necessary. The study also deals with effect of frequency and aspect angle variation on backscattering RCS reduction. View full abstract»

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  • Dual-band wearable metallic button antennas and transmission in body area networks

    Page(s): 182 - 190
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (543 KB)  

    A dual-band metallic antenna with the appearance of a button on a pair of jeans for use with wearable computer networks, emergency rescue scenarios and future wireless medical applications is presented. The design operates at 2.4 GHz WLAN and the HiperLAN/2 bands and a parametric study is given to aid the design process together with measurement and simulation of the structure on a body. A study of transmission between pairs of on-body antennas is presented to give insight into on-body propagating line of sight and non-line of sight channels. A term body gain is defined to quantify how the body attenuates the channel. View full abstract»

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  • E-plane sectoral horn power divider

    Page(s): 191 - 199
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (757 KB)  

    E-plane sectoral horn power divider design method for high-power antenna array applications is presented. In this method, power division is proportional to the cross section areas of the waveguide channels at the aperture of an E-plane sectoral horn antenna. Two different power dividers are designed and produced to be used with an X-band antenna array having 30 dB Taylor distribution. The first one employs a simple E-plane sectoral horn antenna. This straightforward application of the method might be limited with production tolerances. The second one incorporates a corrugated E-plane sectoral horn antenna, whose design is relatively complex but less sensitive to production tolerances. The produced dividers are compared based on simulations and measurements and good agreement with the theoretical expectations is observed for both types. View full abstract»

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  • Gradient-based shape optimisation of conformal array antennas

    Page(s): 200 - 209
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    We present and test a gradient-based shape optimisation method for the minimisation of the active reflection coefficient for conformal array antennas. The goal function is an average of the active reflection coefficient with respect to all antenna elements, a prespecified frequency interval, and a set of excitation modes. The sensitivity of the goal function with respect to changes of the antenna's shape is based on the continuum form of Maxwell's equations, which provides good flexibility for the choice of field solver. The sensitivity is formulated in terms of the field solution of the original antenna problem and a similar adjoint field problem, which gives the sensitivity for an arbitrary number of design parameters given the solution of Maxwell's equations. We test the optimisation method in two dimensions for array antennas that conform to a circular cylinder, where both uniform arrays and arrays that occupy a part of the cylinder's circumference are considered. For some cases, we find that it is feasible to reduce the active reflection coefficient for arrays that partially cover the circumference of the cylinder by means of end elements that differ from the bulk elements of the array. In general, substantial reductions in the active reflection coefficient can be achieved by relatively small shape changes of the antenna elements. For the test cases considered in this article, the optimisation method typically converges to an optimised design within 5-15 iterations. View full abstract»

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  • Sectorised WiMAX antenna for future vehicular communications systems

    Page(s): 210 - 218
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    A narrow band antenna of dimensions 0.54????0.28????0.09?? is presented. The design is suited for use in cellular radio-over-fibre networks. Associated mobile equipment using the international unlicensed WiMAX band (5.470-5.725 GHz) is also described. The antenna is well matched across the band and is suitable for a full-duplex bi-directional system with simultaneous transmission (Tx) and reception (Rx). It can be used with mobile handsets offering WiMAX connections, and in multi-sector configurations for vehicular communication systems. View full abstract»

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  • Dual-frequency characteristics of minkowski-square ring antennas

    Page(s): 219 - 224
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (642 KB)  

    Fractal Minkowski curves to design a compact dual-frequency microstrip ring antenna are proposed. Sides of a square ring have been selectively replaced with first and second iterations of the generalised fractal geometry to design a smaller antenna with dual-frequency operation. This behaviour has been explained based on current distributions on the antenna structure. Measured results compare well with electromagnetic simulations. View full abstract»

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  • Dual-band Ka/X reflectarray with broadband loop elements

    Page(s): 225 - 231
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (922 KB)  

    The objective of this paper is to carry out analysis and design for X/Ka dual-band, frequency selective surface (FSS)-backed reflectarrays. In this design, a novel ring structure has been developed as the cell element for both the X- and Ka-bands to achieve dual-band performance. A single loop was used for the construction of the FSS-backed reflectarray in the Ka-band and a reflectarray with a solid ground plane was designed for the other band. Prototypes of these reflectarrays were fabricated and tested. The measurements demonstrated that for an optimum design, the gain of the FSS-backed reflectarray is almost the same as its counterpart backed by a solid ground plane. Characterisation of the out-of-band performance of these antennas demonstrated a close to 0.6-dB insertion loss. View full abstract»

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  • Analysis of electromagnetic scattering from dielectric objects above a lossy half-space by multiresolution preconditioned multilevel fast multipole algorithm

    Page(s): 232 - 239
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (362 KB)  

    In this study, a synthesis of the multilevel fast multipole algorithm (MLFMA) and the multiresolution (MR) preconditioning technique is presented for the analysis of scattering from homogeneous dielectric targets above a lossy half-space. The Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) integral equation and the MLFMA are used for efficient analysis of scattering problems in half-space. The MR preconditioning technique is used to speed up the convergence rate of the iterative solver. The numerical results are presented to demonstrate that the proposed method is efficient for the scattering from homogeneous dielectric objects above a lossy half-space. View full abstract»

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  • Wideband balanced folded dipole antenna with a dual-arm monopole structure for mobile handsets

    Page(s): 240 - 246
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    In this study, a balanced antenna for mobile handset applications with enhanced bandwidth performance, covering the bands from 1.8 to 2.45 GHz, is investigated. The antenna is a slot planar dipole with folded structure and a dual-arm on each half. The antenna impedance was investigated using a two-port S-parameter method. For the purpose of antenna power gain measurement, a wide bandwidth planar balun was employed to support a balanced feed from an unbalanced source. For validation, a prototype of the proposed antenna was fabricated and tested. The performance of the antenna was then verified in terms of return loss, radiation patterns and power gain. The calculated and measured results show good agreement and the results also confirm good wideband characteristics with low induced current in the ground plane, thus minimising performance variations and SAR. View full abstract»

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  • Coupled structural-electromagnetic-thermal modelling and analysis of active phased array antennas

    Page(s): 247 - 257
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    The electromagnetic performance of an active phased array antenna (APAA) is obviously degraded because of structural distortion caused by thermal power consumption and exterior load. The coupled structural-electromagnetic-thermal (SET) model of APAA is developed on the analysis of the phase difference of radiating elements in the aperture field caused by structural displacement including load-displacement and thermal distortion of structure. Based on the cascade coupled finite element analysis of antenna structure, thermal distortion and other structural distortions are obtained. The coupled SET model is verified by analysing the degradation of the electromagnetic performances of a planar hexagonal APAA operating under different temperature distributions and structural constraints. View full abstract»

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  • Direct use of discrete complex image method for evaluating electric field expressions in a lossy half space

    Page(s): 258 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (433 KB)  

    A modelling technique is proposed for direct use of the discrete complex image method (DCIM) to derive closed-form expressions for electric field components encountered in the electric field integral equation (EFIE) representing a lossy half space problem. The technique circumvents time consuming numerical computation of Sommerfeld integrals by approximating the kernel of the integrals with appropriate mathematical functions. This is done by appropriate use of either the least-square Prony (LS-Prony) method or the matrix pencil method (MPM) to represent electric field expressions in terms of spherical waves and their derivatives. A comparison is made between the two methods based on the computation time and accuracy and it is shown that the LS-Prony method performs two-three times faster than the MPM in approximating the integral kernels depending on the platform. The main feature of the proposed technique is its ability for direct inclusion in the kernel of computational tools based on the method of moments solution of the EFIE. This can be viewed as an advantage over the conventional DCIM approximation of spatial Green's functions for mixed potential integral equation for cases where the problem in hand can be more efficiently represented by the EFIE (e.g. the thin-wire EFIE). The accuracy of the proposed technique is validated against numerical integration of Sommerfeld integrals for an arbitrary electric dipole inside a lossy half space. View full abstract»

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  • Narrowband filters with tightly coupled resonators

    Page(s): 269 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1083 KB)  

    The design of narrowband combline filters implemented in double-layered microstrip is presented. The filters realise finite-frequency transmission zeros located within close proximity with respect to their passband edges. This is achieved by tightly coupling the resonators of the filters. Experimental evaluation of several fabricated filters demonstrates the principle. View full abstract»

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  • Reduced-size multilayer X-band filters with stacked resonators on a flexible organic substrate

    Page(s): 277 - 285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (766 KB)  

    This work presents the design of two four-pole, quasi-elliptic microwave bandpass filters with stacked open-loop resonators on an emerging low-loss organic dielectric material. Both filters are based on a multilayer microstrip structure that uses low-cost and flexible liquid crystal polymer substrates to produce a compact size. The first filter, which has a bandwidth of 17% at 9.3% GHz, was designed to control the high coupling strength between overlapped resonators without sacrificing its compact size. It has a measured 1.7%dB of insertion loss. The second filter uses the same topology, but its measured parameters include a bandwidth of 9% at 10.5 %GHz and an insertion loss of 4.5 %dB. To achieve the 9% bandwidth, two metallic patches were added between layers to limit the higher coupling between the overlapped resonators. Both bandpass filters have a footprint area reduction of at least 25% when compared to an equivalent single-layer, open-loop resonator filter. View full abstract»

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