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Microwaves, Antennas & Propagation, IET

Issue 10 • Date July 15 2014

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Displaying Results 1 - 15 of 15
  • Specific absorption rate reduction based on outage probability analysis for wireless capsule endoscope with spatial receive diversity

    Publication Year: 2014 , Page(s): 695 - 700
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (333 KB)  

    This study investigates the effect of spatial receive diversity on specific absorption rate (SAR) reduction based on outage probability analysis for wireless capsule endoscope (WCE). The communication performance of WCE depends much on the transmit power, which is strictly regulated in order to satisfy a safety guideline in terms of SAR, whereas WCE requires high communication performance due to its real-time data transmission. For the purpose of SAR reduction for a WCE scenario, the authors pay attention to the expectation that applying spatial diversity reception to WCE systems can not only improve the wireless communication performance but also reduce SAR. To begin with, based on finite-difference time-domain simulations with a numerical human body model, the outage probability is calculated under this implant propagation channel and the required transmit power is derived to secure a permissible outage probability. Then, the local peak SAR is calculated under the required transmit power when the WCE moves through the digestive organs. Finally, the simulation results demonstrate that applying spatial diversity reception can significantly reduce SAR for WCE. View full abstract»

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  • Feed adjustment method of reflector antenna based on far field

    Publication Year: 2014 , Page(s): 701 - 707
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    To improve the electrical properties of a reflector antenna, the reflector surface distortion is compensated to some extent and the feed installation error is reduced by adjusting the feed position based on far field. Considering the fact that the traditional method of best-fit paraboloid needs to obtain the accurate reflector deformation beforehand, a novel method to determine feed adjustment amounts based on far field is proposed, with no need to know the deformation. Based on aperture field method, explicit expressions of the sensitivity of far field to fitting parameters of the distorted reflector are established. Then fitting parameters and far field are linked with over-determined linear equations, and by measuring far field, the reflector deformation is approximately calculated based on least square method thereby providing guidance for the feed adjustment of the deformed reflector. In addition, the proposed method is also employed to determine the feed installation error, which is adopted instead of fitting parameters to describe the aperture phase error. Simulation cases show the correctness of the proposed method and the validity of the compensation of reflector distortion and the accurate installation of the feed. View full abstract»

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  • Optimising capacity-coverage of a fixed WiMAX network

    Publication Year: 2014 , Page(s): 708 - 713
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (383 KB)  

    The capacity and coverage area are the two most important design considerations for the planning and optimisation of cellular networks. In this paper, we report on the field measurements of received signal strength (RSS) and available data transfer rate (DTR) at user end in a fixed WiMAX network operating at 2.62 GHz. The coverage area of the network under study covers both rural and urban sectors. Comprehensive measurements of RSS and available DTR are recorded for different settings of the base station antenna tilt and the height of customer premise equipment (CPE) antenna installed at the user premise. It is a directional antenna oriented towards the base station facilitating line of sight communication. It is interesting to observe that base station antenna down-tilt of 2° results in almost 100% fulfilment of the coverage and capacity requirements in rural sector of the network. Up-tilt of 1°, yields 97% fulfilment of the requirements in the entire cell area. These settings of the base station antenna tilt offers encouraging results for the optimisation of both capacity and coverage area and establishes that antenna tilt is an effective optimisation tool to achieve better utilisation of the network resources with enhanced quality of service. View full abstract»

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  • Design of a leaky-wave long slot antenna using ridge waveguide

    Publication Year: 2014 , Page(s): 714 - 718
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    A new design of the leaky-wave long slot waveguide antenna with low cross-polarisation is proposed. The proposed antenna consists of a straight long slot located at the centre of the broad wall of the ridge waveguide. By properly designing the ridge, the amount of leakage power along the slot is controlled, which results in the desired aperture distribution. The aperture has a Taylor distribution with a sidelobe level of -35 dB. Such a design has a low cross-polarisation level as well as a desired beam pointing angle, which is defined at the beginning of the design procedure. The simulation results confirm the high accuracy of the design procedure. The proposed antenna is also fabricated and measured. According to the measurement results, the structure has a cross-polarisation of -41.9 dB and a sidelobe level of -26.3 dB. The measured reflection coefficient of the proposed antenna is -22.8 dB at the design frequency. View full abstract»

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  • Comment on 'compensate for the coupled radiation patterns of compact transmitting antenna arrays'

    Publication Year: 2014 , Page(s): 719 - 723
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (517 KB)  

    In a recent study by Niow et al., it has been shown that an effective method for mutual coupling compensation in antenna arrays can be based on mutual impedances between antenna elements and the active element input impedance. Consequently, Niow et al. have derived an equation for compensated excitation voltages, which allows the radiation pattern of an antenna array to be predicted accurately using the principle of pattern multiplication. In the current comment, the authors show that the effectiveness of those equations depends on the level of mutual coupling between radiating elements, and becomes lower for strong mutual coupling. The authors explain the reason for this deficiency and a corrected form of the equations was proposed for the compensated excitation voltages. View full abstract»

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  • Bandwidth enhancement in coplanar waveguide-fed slot antennas designed for wideband code division multiple access/wireless local area network/ worldwide interoperability for microwave access applications

    Publication Year: 2014 , Page(s): 724 - 729
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (603 KB)  

    A multiband coplanar waveguide-fed slot antenna design is proposed for use in wireless and mobile communication applications. This antenna was designed on a single-layer printed circuit board FR4 substrate featuring a permittivity εr = 4.4, a loss tangent tan δ = 0.0245 and a thickness of h = 1.6 mm. The antenna consists of a T-shaped signal strip and a U-shaped conducting strip placed on the upper side of the T-shaped signal strip. After simply tuning the slot parameters of the ground plane, the proposed antenna can be used in the following operations: wireless local area networks at 2.4/5.2/5.8 GHz, worldwide interoperability for microwave access at 2.5/3.5/5.5 GHz and wideband code division multiple access at 1.92-2.17 GHz. The -10 dB bandwidth measured for the proposed antennas was 109.2% (1.85-6.3 GHz). The bandwidth was enhanced by choosing suitable combinations of the upper and lower ground slots. The geometrical parameters were examined to optimise the performance of the proposed antenna. The results of the return loss, far-field H- and E-planes radiation patterns, gain and radiation efficiency of the proposed antenna are presented and discussed herein. The antenna size of the radiation area and the ground plane was 50 × 50 mm2. Detailed simulations and experiments were conducted to optimise broadband operations, and the measured results concurred with the simulated results. View full abstract»

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  • Non-conforming finite element tearing and interconnecting method with one Lagrange multiplier for solving large-scale electromagnetic problems

    Publication Year: 2014 , Page(s): 730 - 735
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (550 KB)  

    A non-conforming finite element tearing and interconnecting method is proposed for the numerical analysis of large-scale three-dimensional electromagnetic problems. The whole computational domain is partitioned into many smaller subdomains, and a Robin-type transmission condition is introduced at the shared interfaces to exchange data among subdomains. A set of orthogonal polynomials is introduced to approximate auxiliary unknowns between adjacent subdomains. Then, a one-Lagrange multiplier scheme is applied to deal with non-conforming meshes at the interfaces. With the help of the Schur complement approach, the method formulates a reduced-order interface problem, which can be solved using an iterative algorithm. Once the resulting interface problem is solved, the unknown electric field in each subdomain can be calculated in parallel. Numerical examples are given to demonstrate the efficiency of the method. View full abstract»

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  • Compressive sensing-based approach to the design of linear robust sparse antenna arrays with physical size constraint

    Publication Year: 2014 , Page(s): 736 - 746
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1041 KB)  

    In sparse arrays, the randomness of antenna locations avoids the introduction of grating lobes, while allowing adjacent antenna spacings to be greater than half a wavelength. This means a larger array size can be implemented using a relatively small number of antennas. However, careful consideration has to be given to antenna locations to ensure that an acceptable performance level is achieved. Model perturbations can also cause steering vector errors, which in turn cause discrepancies in the array's response, making robust arrays desirable. This study presents various compressive sensing-based methods that can solve this problem, while also imposing the antenna size as a constraint on the minimum adjacent antenna separations. Narrowband and multiband design examples are presented to verify the effectiveness of the proposed design methods, with comparisons being drawn with a previously proposed genetic algorithm-based approach. View full abstract»

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  • Compact ultra-wideband diversity antenna with a floating parasitic digitated decoupling structure

    Publication Year: 2014 , Page(s): 747 - 753
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    A compact planar ultra-wideband (UWB) multiple-input-multiple-output antenna array with two radiating elements is proposed in this work. Elements separation is kept at 5.5 mm and the isolation is achieved with a floating parasitic decoupling structure not known for UWB diversity antennas previously. The antenna system performs very well over the entire UWB frequency range of 3.1-10.6 GHz. The mutual coupling between the radiating elements is below -20 dB in most of the band. The decoupling structure is investigated in detail and the diversity analysis of the antenna in Rayleigh fading environment for indoor and outdoor propagations is also presented by computing envelope correlation coefficients. The proposed antenna array measures 33 × 45.5 mm2 only and it is suitable for handheld devices, personal digital assistant (PDA)s, next generation home entertainment systems and robots. View full abstract»

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  • Near field multifocusing on antenna arrays via non-convex optimisation

    Publication Year: 2014 , Page(s): 754 - 764
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (842 KB)  

    An optimisation framework for near field multifocusing on antenna arrays is proposed. Its aim is to obtain the feeding weights that must be applied to the elements of the array so that the antenna focuses on two or more targets simultaneously. The method is based on the definition of a proper cost function, which is minimised using an optimisation algorithm over an equivalent least squares problem. The success of the technique is noted in the fact that different array parameters can be obtained: magnitude and phase of the array elements or only phase synthesis. In order to show the efficiency of the method, several tests are carried out using different arrays and optimisation parameters. The simulation, manufacture and measurement of an 8 × 8 planar array able to focus on two different targets is also performed. Results show how the framework can be applied to general arrays and demanding requirements, so it may be easily extended to different synthesis problems besides multifocusing. View full abstract»

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  • Differential grid array antenna to radiate pencil beam at 24 GHz for radar and sensor applications

    Publication Year: 2014 , Page(s): 765 - 769
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (514 KB)  

    A new differential grid array antenna that radiates a pencil beam is reported. The difference between the half-power beam widths of the E- and H-planes is used to assess the pencil beam quality. Also, a novel differential feeding scheme that eases the testing and improves the pencil beam quality, impedance matching and gain bandwidth is proposed. The prototype was designed and fabricated on RT/duroid 5880 substrate with the size of 40 × 50 × 0.787 mm3 and the number of 16 radiating elements. Measured results show that the differential grid array antenna achieved 4.37% impedance bandwidth and 17 dBi gain at 24.25 GHz. View full abstract»

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  • Waveguide-based combining S-band high power microwaves

    Publication Year: 2014 , Page(s): 770 - 774
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (634 KB)  

    Incoherent power combining system is a promising technique for enhancing the output power level of narrow-band high-power microwave devices, and waveguide-based combiner usually has the virtues of high transmission efficiency, proper bandwidth and high power-handling capacity within a compact structure. A specific cross-junction combiner is proposed for combining the S/S band microwave beams, and the detailed simulation and experimental results are presented. The investigations show that the combiner realises integration of GW level power combination and mode conversion from two microwave sources simultaneously. View full abstract»

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  • Rapid electromagnetic-based microwave design optimisation exploiting shape-preserving response prediction and adjoint sensitivities

    Publication Year: 2014 , Page(s): 775 - 781
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    A new development of the shape-preserving response prediction (SPRP) technique for microwave design optimisation is presented here. The original SPRP method is enhanced by employing low-cost derivative information obtained through adjoint sensitivities. The authors propose using operator notation to simplify the SPRP surrogate description. The enhancement through sensitivity data is twofold: to ensure first-order consistency between the SPRP surrogate and the high-fidelity electromagnetic (EM) model under optimisation and to speed up the surrogate optimisation process. Fast surrogate optimisation allows us to use coarse-discretisation EM simulations as an underlying low-fidelity model and, therefore, efficiently apply SPRP to cases where reliable circuit models are not available (e.g. design of antenna structures). The proposed approach is demonstrated using a dielectric resonator filter and an ultra-wideband monopole antenna. Comparison with three benchmark techniques, including the original SPRP methods, space mapping with sensitivity and direct optimisation of the high-fidelity model, is also provided. View full abstract»

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  • A detailed experimental study on the benefits of electrically grounding glass mounted global positioning system antennas to the vehicle roof

    Publication Year: 2014 , Page(s): 782 - 793
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2072 KB)  

    The placement of global positioning system (GPS) patch antennas on vehicles is important as its location directly affects navigation system performance. GPS antennas mounted on the front glass window has been adopted by several vehicle manufacturers around the world. In this work, we present a detailed experimental study on the effect of antenna mounting parameters as well as shorting it to the roof of the vehicle on its performance characteristics. Specifically, we investigate the effect of the glass tilt angle, the distance of the antenna from the rooftop of the vehicle in addition to grounding it to the rooftop versus not-grounding to the rooftop of a vehicular platform. View full abstract»

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  • Synthesis of linear multi-beam arrays through hierarchical almost difference set-based interleaving

    Publication Year: 2014 , Page(s): 794 - 808
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1508 KB)  

    The study presents an innovative `almost difference set (ADS)'-based analytical approach for the design of fully interleaved arrays supporting Q > 2 independent functions on a shared aperture. Such a hierarchical subarraying methodology allows one to interweave, on the same lattice, Q = 2P non-overlapped arrangements with beam properties a-priori predictable from the descriptive parameters of the chosen ADSs. A general formulation for the pattern analysis of subarray layouts is derived and successively employed to assess features and potentialities of the multi-level `ADS' interleaved scheme. A set of representative numerical results, concerned with different apertures, balancing factors and number of interleaved functions, is presented to give some indications on the effectiveness, the efficiency and the reliability of the proposed approach. View full abstract»

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