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Microwaves, Antennas & Propagation, IET

Issue 12 • Date Sept. 17 2013

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Displaying Results 1 - 12 of 12
  • Generation of arbitrary polarisation in any direction by cross dipole

    Page(s): 949 - 953
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (382 KB)  

    The authors show that a wave with any desired polarisation state can generally be generated in any direction with respect to two crossed dipoles, and a closed-form expression is provided for the complex ratio of the required drive voltages. The authors also provide a simple projection method for the polarisation ellipse in the case where the dipole centres coincide. For achieving the authors' aim of exploiting closed-form equations to generate circularly polarised (CP)/elliptically polarised (EP)/linearly polarised in any direction, two orthogonally placed dipoles resonating at 1 GHz each are designed. By selecting complex feed solutions, which are provided from the proposed closed-form equations, it is realised precise polarisation states in a number of directions. Four separate such cases to generated CP and EP were investigated, and in all of them the numerical simulations and experiments validated the proposed theoretical predictions. View full abstract»

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  • Stability and dispersion analysis of higher order unconditionally stable three-step locally onedimensional finite-difference time-domain method

    Page(s): 954 - 960
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (443 KB)  

    Stability and dispersion analysis of higher-order three-step locally one-dimensional (LOD) finite-difference time-domain (FDTD) method is presented here. This method uses higher order cell-centred finite-difference approximation for the spatial differential operator and second-order finite difference approximation for the time differential operator. Unconditional stability of the higher-order three-step LOD-FDTD method is analytically proven and numerically verified. Numerical results show improvement in the overall performance of higher-order three-step LOD-FDTD method compared with that of second order. Also, the effects of the order of approximation, the time step and the mesh size on numerical dispersion are explained through analytical results and verified by simulation results. View full abstract»

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  • Compact ultra-wideband bandpass filters with narrow notched bands based on a ring resonator

    Page(s): 961 - 969
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (769 KB)  

    In this study, compact ultra-wideband (UWB) bandpass filters with single/dual-notched bands are proposed based on a ring resonator and transversal signal-interference concept. Broad passband and narrow notched bands with controlled even/odd-mode resonator frequencies can be adjusted conveniently by changing the characteristic impedance of the ring resonator. Transmission zeros are introduced to improve selectivity and harmonic suppression of the proposed UWB bandpass filters with notched bands. To verify the presented strategies, three prototypes (εr = 2.65, h = 0.5 mm) with 3 dB fractional bandwidth >120% are designed and fabricated. Simple structure and good in/out-of-band performances can be achieved in the proposed UWB bandpass filters. View full abstract»

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  • New physical-mathematical model for predicting slant-path rain attenuation statistics based on inverse Gaussian distribution

    Page(s): 970 - 975
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (455 KB)  

    A new physical-mathematical model for predicting first-order rain attenuation statistics for slant-path links is presented in this study. It is assumed that point rain rate and slant-path rain attenuation follow the inverse Gaussian (IG) distribution. The statistical parameters of the IG distribution of the induced rain attenuation on a slant path are calculated in terms of the rain rate statistical parameters by adopting a spatial inhomogeneity model for specific rain attenuation. The method is validated using experimental data taken from Database of Study Group 3 (radiowave propagation) of International Telecommunication Union-Radio (ITU-R), hereafter named DBSG3 and with simulated rain attenuation data using the Synthetic Storm Technique on recent rain rate measurements in Athens, Greece. Its performance is also compared to the ITU-R P. 618-10 model. The proposed model shows better performance comparing to the ITU-R model and the results are very encouraging. View full abstract»

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  • Robust mask-constrained linear array synthesis through aninterval-based particle SWARM optimisation

    Page(s): 976 - 984
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (654 KB)  

    An innovative strategy for the robust design of linear antenna arrays is presented. Being the array elements characterised by tolerance errors, the synthesis is aimed at determining the intervals of values fitting the user-defined mask constraints on the radiated power pattern. With reference to the upper and lower bounds of the power pattern analytically determined for given tolerances through interval analysis, the nominal excitations of the array elements are then optimised by means of a global stochastic optimiser suitably customised to deal with interval numbers. A set of numerical examples is reported to show the behaviour of the proposed method as well as to assess its potentials in dealing with the robust synthesis of pencil and shaped beams. View full abstract»

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  • Wideband planar Goubau line (PGL) couplers and six-port circuits compatible with short range (60 GHz) radio

    Page(s): 985 - 990
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    In this study, wideband planar Goubau line (PGL) couplers were simulated, designed, fabricated and measured. The designed PGL edge coupler is simple, compact and with broad bandwidth. Based on the results of these couplers, six-port circuits and their application to the digital communication wave radio were studied. Simulated and measurement results show that PGL couplers and PGL six ports work well over a wide frequency range (more than one octave) as six-port demodulators for digital communications systems, including short range (60 GHz) wave radio. View full abstract»

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  • Linearly polarised planar inverted F-antenna for global positioning system and worldwide interoperability for microwave access applications

    Page(s): 991 - 998
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (975 KB)  

    A compact dual-band planar inverted-F antenna in conjunction with an inverted L-shaped parasitic and reduced ground-plane structure working in the GPS (Global Positioning System) band (1565-1585 MHz) and Worldwide Interoperability for Microwave Access band (3300-3800 MHz) is presented. The antenna meets the strict space requirements of the portable devices and the final design fits a volume of 100 × 24 × 9.7 mm3 (L × W × H). It is composed of a series of branches, properly dimensioned and separated to generate the resonances at the desired frequencies. The antenna is fabricated using a 0.2 mm thick copper foil. The linearly polarised antenna exhibits good impedance matching performance, wide beam radiation pattern and high gain. Also, carrier-to-noise ratios for three different satellite locations, that is, 5°, 50° and 90° elevation are 47.58, 50.49 and 45.86 dB/Hz, respectively, at the centre frequency (1575 MHz) of GPS L1 band, which is well within the maximum allowable limit (50.5 dB/Hz) at room temperature. View full abstract»

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  • Quad band-notched ultrawideband antenna with a modified H-shaped resonator

    Page(s): 999 - 1004
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    In this study, a novel planar ultrawideband antenna, with a quad band-notched function, is investigated. The proposed antenna consists of a circular-shaped radiating element, a 50 Ω microstrip feed line, a modified H-shaped resonator, and a partially truncated ground plane. The proposed H-shaped resonator, with quadruple resonance characteristics, is realised without any change in its size but instead, by modifying the simplified composite right/left-handed resonator with dual resonance characteristics. By embedding the modified H-shaped resonator beside the microstrip feedline, band-rejected filtering properties in the wireless local area network /worldwide interoperability for microwave access bands are generated. By changing the modified H-shaped resonator's dimensions, the proposed antenna shows variable quadplex-filtering characteristics, such as band-notch frequency and its bandwidth. The measured results show that the proposed antenna design exhibits a 10 dB return loss bandwidth from 2.12 to 13.63 GHz, excluding the rejection bands. Very sharp notch and high band-rejection are achieved, and relatively stable omnidirectional radiation performance over the entire frequency range is also obtained. View full abstract»

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  • High-selectivity wideband balanced bandpass filters using symmetrical multi-mode resonators

    Page(s): 1005 - 1015
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1120 KB)  

    Two novel high-selectivity wideband balanced bandpass filters using symmetrical multi-mode resonators are presented. The proposed novel multi-mode resonator is used to realise a six-order wide passband in the differential mode. In addition, wide stopbands with insertion loss greater than 15 and 20 dB for the commode mode (0-18.5 GHz, 0-19 GHz) can also be achieved by the multi-mode resonators. The even/odd-modes of the symmetrical multi-mode resonators can be adjusted by changing the characteristic impedance of the shorted/open stubs. Two planar wideband balanced filters with 3 dB fractional bandwidths of 67.6 and 63.7% are designed and fabricated. The theoretical and measured results are in good agreement and show good in-band filtering performances and high selectivity. View full abstract»

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  • Resolving manifold ambiguities for direction-of-arrival estimation of sparse array using semi-circular substrates

    Page(s): 1016 - 1020
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (298 KB)  

    Sparse linear array has some advantages over uniform linear array in some applications. However, it is well known that sparse array always suffers from manifold ambiguity, which has significant influence on direction-of-arrival (DOA) estimation and resolution. In this study, a new method based on the multiple signal classification (MUSIC) for resolving manifold ambiguities of uncorrelated sources by using semi-circular substrate is proposed for DOA estimation of sparse array. Spurious MUSIC peak spectrums are generated because of a linear combination of the steering vectors of true DOAs. The main idea of the proposed method is to setup one or several semi-circular medium substrates at the front of some elements. The phases of these elements are changed through the refractive index and the radii of those semi-circular substrates. This treatment breaks down the previous linearity of the steering vectors for the array without adding the substrates. Thus, true DOA peaks can be discriminated according to this feature. Simulation results show good performance of the proposed method. Trivial and non-trivial ambiguities are efficiently resolved. View full abstract»

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  • Comparative study on pulse distortion and phase aberration of directive ultra-wideband antennas

    Page(s): 1021 - 1026
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (698 KB)  

    The authors study and compare the properties of two types of highly directive broadband antennas: linear tapered slot antenna (LTSA) and leaky lens antenna (LLA). The performance in terms of dispersion and phase centre stability is investigated for both antennas over a bandwidth exceeding 1:3, by means of experimental results. The pulse distortion is quantified by calculating the angular dependence of the fidelity factor directly from the measurements. The phase centre movement with frequency is also measured and the corresponding phase error loss is estimated when these antennas are to be used as wideband feeds of reflectors. As a consequence of its high phase centre stability, LLA achieves better efficiency than LTSA in terms of phase aberration for broadband reflector systems. However, the efficiency of LTSA can be considerably enhanced by proper positioning of the antenna along the reflector axis. View full abstract»

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  • Dual-mode dual-band bandpass filters design using open-loop slotline resonators

    Page(s): 1027 - 1034
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (693 KB)  

    A dual-mode open-loop slotline resonator with a centre-loaded stub is proposed. The loaded stub is used to excite non-degenerate modes, that is, the even and odd modes. Distinct characteristics of this dual-mode resonator are investigated by using even-odd mode analysis. Also, equivalent circuit models for non-degenerate modes are given to determine the resonance conditions and the location of transmission zero. Then, two novel approaches for designing dual-mode dual-band bandpass filters are presented. One approach consists of simple microstrip feedlines and two embedded open-loop slotline resonators for single substrate configuration. The other is composed by using dual-mode open-loop resonators in the form of microstrip and slotline structures on a single substrate. A microstrip invert L-shape feeding structure is employed to simultaneously feed the microstrip and slotline resonator on different layers for broadside coupling. Both of them provide sufficient degrees of freedom to control the centre frequencies and fractional bandwidths of both passbands independently. The two filters are designed, fabricated and measured. A good agreement between the simulation and measurement verifies the validity of this design methodology. View full abstract»

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