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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 4 • Date 8 Aug. 2003

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Displaying Results 1 - 21 of 21
  • Bistatic multiple scattering from randomly rough surfaces

    Page(s): 214 - 218
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (273 KB)  

    The contribution of bistatic multiple scattering from randomly rough surfaces is studied. A model with consideration of multiple surface scattering for bistatic surface scattering from a randomly very rough surface is developed on an approximation of a pair of integral equations. Without the consideration of multiple surface scattering, a considerable difference between the measured data and theoretical estimation exists, especially from very rough surfaces. Comparisons of model prediction with and without the contributions of multiple scattering from rough surfaces, are shown together with comparisons of model prediction with measured data. View full abstract»

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  • Electronically steerable parasitic array radiator antenna for omni- and sector pattern forming applications to wireless ad hoc networks

    Page(s): 203 - 208
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    An electronically steerable parasitic array radiator antenna is presented. The antenna has only a single element connected to a receiver or a transmitter. This active element is surrounded by parasitic elements loaded with variable reactors (varactors). The loaded reactance and the length of the parasitic radiators are designed so that each of the parasitic elements plays its role of director or reflector depending on its bias voltage on the loaded reactance. This design guarantees that the radiation pattern can be controlled by changing the bias voltages on the varactors. For omnipattern forming, a voltage vector is obtained such that the received power is maximised under the assumption that each component of the voltage vector is equal. An experiment yields an omnipattern with an average -0.83 dBi gain over the angles [0°, 360°]. For sector pattern forming, a single-source power maximisation technique is proposed to optimise the voltage vector such that the received signal power is as large as possible in the direction of the source. Experiments yield twelve sector patterns at every 30°. The average gain is 5.5 dBi in the patterns' beam directions. The average 3 dB beamwidth is 72.4° for the sector patterns in the directions 0°, 60°, 120°, 180°, 240° and 300°, while the average value is 90.1° for the remaining patterns. View full abstract»

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  • Experimental characterisation of on-chip octagonal double-helix inductors on silicon substrates

    Page(s): 265 - 268
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (314 KB)  

    Experimental characterisation of on-chip octagonal double-helix inductors on silicon substrates is performed. These symmetrical inductors are fabricated with different turn numbers, inner first turn lengths and total strip lengths, but with the same strip width and spacing. Measurement and simulation for the two-port S-parameters are performed, and, in order to eliminate the pad-probe effects, the de-embedding technique is used. Further, the inductance, parasitic capacitances, self-resonance frequency and frequency corresponding to the maximum Q-factor are extracted and analysed. View full abstract»

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  • Tunable isolator using a coupled microstrip line with an obliquely magnetised YIG substrate

    Page(s): 219 - 222
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (303 KB)  

    A tunable isolator using a symmetrically coupled microstrip line is proposed. The even and odd mode dispersion characteristics of the symmetrically coupled microstrip line printed on a YIG substrate are obtained using a full wave spectral domain approach. The nonreciprocal coupling between the two-microstrip lines on a ferrite substrate can be exploited to achieve an isolation behaviour. The tunability is obtained by varying the applied angle of the DC bias magnetic field at the YIG substrate. Hence, a frequency tunable isolator is designed for use at the microwave frequency band. View full abstract»

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  • Mutual coupling in conformal microstrip patch antenna arrays

    Page(s): 191 - 196
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    A finite element-boundary integral method has been developed to investigate the impedance properties of patch elements in an array environment, when the array is embedded in a conformal surface. The effect of mutual coupling between elements in such an array is included in the analysis. The method is tested on patch antennas mounted on planar and cylindrical surfaces. For the examples considered, it is shown that the simulated results are in good agreement with measurement. View full abstract»

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  • Full-wave analysis of shielded planar circuits using different models of sources

    Page(s): 258 - 264
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A source method is developed for analysing N-port planar microwave circuits. It is proposed to model the circuit by a rigorous method including different definitions of sources. Two models of excitation terms are proposed: the source placed on the circuit plane (located source) and a vertical source (extended source). The advantages and limits of the method according to each definition are presented. Supportive numerical results for the characterisation of planar discontinuities are provided. View full abstract»

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  • Oblique ionogram features associated with off-great circle HF propagation at high and sub-auroral latitudes

    Page(s): 295 - 300
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    Oblique ionograms received over northerly paths are often difficult to interpret, with many features not being of the form observed on the more familiar mid-latitude soundings. In particular, the ionograms contain unusual traces at frequencies close to and above the conventional or basic maximum usable frequency, i.e. above the junction frequency of the high and low angle modes. A series of experiments have been undertaken over a period of several years to investigate off-great-circle propagation mechanisms over high latitude and sub-auroral oval paths. In addition to measurements of the signal direction of arrival, oblique ionograms were also recorded over several of the paths. By these means, the characteristic ionogram signatures associated with off-great-circle propagation effects arising due to the presence of convecting patches of enhanced ionisation or sun-aligned arcs within the polar cap ionosphere, or to the presence of steep gradients to the side of the path within the mid-latitude trough region, have been identified. View full abstract»

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  • Fast high-order FEM solutions of dielectric wave guiding structures

    Page(s): 230 - 236
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (389 KB)  

    Dielectric wave guiding structures are solved in terms of high-order hierarchal vector bases that provide maximum mutual orthogonality in both the approximation space and in the range space of the curl operator. This new finite element formulation results in well-conditioned matrices and makes the iterative solution of the system equation robust. Numerical examples show that p-refinement yields much higher rates of convergence than h-refinement when the resultant matrix is solved using the multilevel preconditioned conjugate gradient (MPCG) algorithm. View full abstract»

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  • Analysis of circular microstrip patch antenna as an equivalent rectangular microstrip patch antenna on iso/anisotropic thick substrate

    Page(s): 223 - 229
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    The input and radiation characteristics of a circular microstrip antenna on thick and lossy iso/anisotropic substrate are computed with the help of its equivalent rectangular microstrip antenna. The computed results show good agreement with the results of mode matching methods and experimental results. Results using three commercial software products are also compared against the same set of the experimental results. The performance of the present method (MWM) is better than the performance of commercial software. View full abstract»

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  • GPS signal fading model for urban centres

    Page(s): 245 - 252
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    The use of GPS receivers in wireless telephones has been proposed as a means of automatically identifying the position of wireless 911 callers. GPS simulators are an efficient means of testing the accuracy of such technology but require a channel model for GPS satellite signals. The paper presents a methodology for measuring and modelling the fading distribution of GPS satellite signals received in outdoor urban centres. GPS fading data, as collected in the downtown areas of Calgary and Vancouver, Canada, are used to generate fade histograms as a function of satellite elevation angle. These histograms are found to be sufficiently similar between the two cities and, therefore, lead to the conclusion that a generic fade distribution for urban centres is reasonable. Parameters for the urban three-state fade model (Akturan, R., and Vogel, W.J., IEEE Trans. Antennas Propag., vol.45, no.7, p.1107-16, 1997) are estimated from the empirical fading data collected in each city. Correlation between the model parameters derived for each city is significant and this also suggests that a generic model may be derived. The parameters from the two cites are averaged to produce a generic urban three-state fade model, which adequately represents the fade histograms of each city. These averaged parameters generally agree with parameters derived from data collected in Tokyo, Japan. View full abstract»

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  • Circular annular planar monopoles with EM coupling

    Page(s): 269 - 273
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A circular annular planar monopole with electromagnetic coupling shows broadband properties. The planar radiator is electromagnetically coupled with a probe-fed strip, and separated from it by a thin dielectric sheet. The parametric effects on the bandwidth are examined experimentally. The measurements demonstrate that the proposed monopoles have the merit of broad impedance bandwidths in the order of 100% for VSWR=2:1 and of 4:1 for VSWR=3:1 and acceptable radiation patterns across the bandwidths. View full abstract»

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  • Ground plane effects on planar inverted-F antenna (PIFA) performance

    Page(s): 209 - 213
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (354 KB)  

    The planar inverted-F antenna (PIFA) is popular for portable wireless devices because of its compact size and low profile. The PIFA is designed to operate with a ground plane and the ground plane is an integral part of the antenna assembly. In fact, the ground plane size is the limiting factor for the PIFA in many applications. Some work has been reported on the performance of PIFAs mounted on a conducting box of fixed size; however, what is lacking is a parametric study on the antenna behaviour as a function of geometry or antenna position and orientation on a finite ground plane. The paper presents results from a comprehensive investigation on the performance of a conventional PIFA mounted on ground planes of various sizes and shapes. The orientation and position of the antenna on a fixed-size ground plane is analysed. The influence of ground plane geometry on resonant frequency, bandwidth, gain, and radiation patterns are presented. These results are very useful in the design of a PIFA for applications requiring a small ground plane. Specifically, the results show the trade-offs between PIFA geometry and ground plane size with electrical performance. Both numerical simulation and experimental data are presented. View full abstract»

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  • Novel RF front end antenna package

    Page(s): 290 - 294
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (655 KB)  

    Two methods for achieving a complete RF front end equipped with its radiator within a single chip package are presented. This packaging technique, which uses a parasitic radiator, provides an alternative solution to problems associated with reduced size electrically small antennas, such as restoration of the antenna gain to 6 dBi and increasing its bandwidth to over 4%. Several parasite configurations have been described and sensitivity of the overall antenna performance to coupling height, parasite dimension, and position with respect to the feed antenna have been assessed. Circular polarisation of such a configuration using a truncated square parasite has also been demonstrated. View full abstract»

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  • Wideband 0.9 GHz to 5 GHz six-port and its application as digital modulation receiver

    Page(s): 301 - 307
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    A six-port reflectometer which operates from 0.9 GHz to 5 GHz is proposed, constructed and characterised using MIC techniques. Results from the new structure, when compared to those obtained from a commercial network analyser, show a maximum error of about 2° in phase and about 0.6 dB in reflection coefficient over the entire operating band. In addition, the reflectometer exhibits less than 3 dB noise figure below 3 GHz. The use of the six-port reflectometer as a digital receiver is presented, along with modifications to the demodulation, diode linearisation and calibration algorithms normally associated with this class of receiver. Bit error rate measurements and simulation results are given for QPSK signals under a variety of operating conditions. It is shown that the resulting receiver can give bit error rates of as low as 8×10-7 for input power levels of -37 dBm. Such a receiver should find application across all of the available frequency bands currently used for personal wireless communications. View full abstract»

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  • Radiation efficiency and impedance bandwidth of conductor-backed CPW-fed broadside twin slot antennas on two-layer dielectric substrate

    Page(s): 185 - 190
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (310 KB)  

    The radiation efficiency and impedance bandwidth of matched broadside twin slot dipoles, fed by a coplanar waveguide on a conductor-backed two-layer substrate, are investigated as a function of distance between the slots and height of the bottom substrate layer. It is confirmed that the low radiation efficiency associated with a single slot due to the excitation of parallel-plate modes may be greatly increased by using two slots spaced half a wavelength of the dominant two-layer parallel-plate mode apart. It is also demonstrated that the radiation efficiency of optimally spaced twin slots may be further improved by increasing the height of the bottom substrate layer, in general at the cost of decreased bandwidth. The effect of bottom substrate height on gain and directivity is investigated, and radiation patterns are provided for the case of optimally spaced twin slots. Twin slots on a conductor-backed two-layer substrate can yield high radiation efficiencies similar to those of previously reported twin slot antennas with a back plane, with the advantage of reduced overall height. View full abstract»

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  • Analysis of coupled Hermite transmission lines

    Page(s): 279 - 284
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    A new method for frequency domain and transient analysis of the multiple coupled non-uniform lossless Hermite transmission lines is presented. First, the system of coupled differential equations is decomposed into a set of uncoupled differential equations. Then the analytical solution in the frequency domain is obtained as an ABCD matrix. Finally, the time domain response is derived using a simple FFT algorithm. View full abstract»

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  • Improving the convergence of the iterative solution of matrix equations in the method of moments formulation using extrapolation techniques

    Page(s): 253 - 257
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    A strategy is presented for improving the convergence of iterative solvers when used for solving the matrix equations of the method of moments (MOM) formulation of EM scattering problems in a frequency sweep. Based on the use of an initial guess, which is derived via an extrapolation procedure involving the solution obtained at previous frequency steps, this procedure improves the convergence behaviour over the use of either a zero initial guess or the employment of the solution at the last frequency as the initial value for conjugate gradient (CG) iteration. View full abstract»

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  • Equivalent impedance boundary conditions for refined meshes applied to planar circuits

    Page(s): 237 - 243
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    The application of an iterative method based on the wave concept to model planar circuits using a multiscale grid is investigated. The novelty of this method consists in substituting selected coarse meshes by their equivalent surface impedances. This approach offers high spatial-resolution with low computing resources, and results are presented to demonstrate its efficiency. View full abstract»

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  • U-shaped planar inverted-F microstrip antenna with a U-shaped slot inset for dual-frequency mobile communications

    Page(s): 197 - 202
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    This paper presents a novel configuration of a U-shaped, dual-frequency, single-feed, planar inverted-F microstrip antenna with a U-shaped slot (UU-PIFA). The antenna is well suited to telephone handsets used in today's mobile communication systems operating in both GSM and DCS 1800 bands, namely 0.9 and 1.8 GHz, respectively. An initial design is derived from an empirical approximation and a transmission line model of a rectangular microstrip antenna. The paper analyses, examines, and fine-tunes the electrical performance of the antenna, including the return loss, operating frequencies, bandwidths, input impedance, and far-field radiation patterns, by using the generalised non-uniform finite difference time domain (NU-FDTD) Maxwell solver. In addition, to increase the efficiency of the FDTD solver, the concept of domain decomposition is utilised, which enables one to eliminate redundant computational space, and thereby reduce the memory and CPU time requirements. View full abstract»

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  • Suppression of spurious modes for performance enhancement of hybrid planar/NRD-guide integrated circuits

    Page(s): 285 - 289
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (373 KB)  

    A technique for suppressing spurious modes is presented with experimental and analysis results. It is simple and very effective in rejecting spurious modes for performance enhancement of hybrid planar/NRD-guide integrated circuits. As a practical example, a millimetre-wave planar/NRD-guide filter is designed to evaluate features of the proposed technique, which yields good results. It is found through preliminary analysis and experiments that the rejection of all spurious modes (including TE and LSE modes) can be better than -35 dB for a single microstrip-to-NRD-guide transition over the broadband frequency range of interest, and performance can be further enhanced using optimised design procedures. This new technique provides an alternative solution to the inherent problem of spurious modes occurring (especially TE modes) in the standard NRD-guide circuit design. View full abstract»

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  • Low-profile directive quasi-planar antennas based on millimetre wave Fabry-Perot cavities

    Page(s): 274 - 278
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    A new configuration of directive and quasi-planar antennas is presented at millimetre wave frequencies. It comprises a plano-convex Fabry-Perot (FP) resonator excited by an arbitrary printed primary source. The total thickness of these low-profile antennas does not exceed 4 mm (0.8×λ0) at 60 GHz for directivities usually varying between 15.5 dB and 23.5 dB. By analogy with dielectric loaded open resonators, their theoretical radiation patterns are perfectly Gaussian. Experimental results obtained with single- or multi-layer planar feeds and with FP cavities of various radii of curvature and grid mirror reflectivities, confirm theoretical predictions. As examples, the patterns of two structures illuminated by the same aperture-coupled microstrip antenna array are compared in the 60 GHz band. They are rotationally symmetric and have low sidelobes (<-27 dB). No significant depolarisation effect is observed. The efficiency of these new radiating structures varies between 20% and 65%, depending on the quality factor of the FP cavities. View full abstract»

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