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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 3 • Date June 2000

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Displaying Results 1 - 16 of 16
  • Methods for optimal focusing of microstrip array antennas including mutual coupling

    Page(s): 199 - 202
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1109 KB)  

    In several array synthesis problems the lack of a common element pattern among different antennas makes the use of classical synthesis methods based on the array factor questionable. A recently introduced approach to array synthesis is exploited to take account in an exact fashion of the mutual coupling between patches for the synthesis of pencil beams by microstrip arrays. Optimality of the approach allows quantifying the advantages of the method with respect to common approaches, which largely compensates in several cases for its additional computational burden. View full abstract»

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  • Surface electric fields of multi-layered medium Green's functions and the calculation of impedance matrix elements of microstrip structures

    Page(s): 179 - 186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The electric fields of the spatial Green's functions at the interfaces of a multi-layered medium are calculated by integrating along the Sommerfeld integration path. For the case when both sources and field points are on the same interface of two different dielectrics, convergence of the Sommerfeld integrals can be facilitated by higher-order asymptotic extractions. The results are illustrated for distance ranges from 0.02 free-space wavelengths to 1.5 free-space wavelengths. The tabulated electric field Green's functions are then used to compute the impedance matrix elements of multi-layered microstrip structures in the spatial domain View full abstract»

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  • Analysis of the rectangular patch antenna printed on elliptic-cylindrical substrates

    Page(s): 187 - 194
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    Cavity model analysis is presented of a rectangular patch antenna printed on a thin elliptic-cylindrical substrate. The field under the patch is expanded in terms of Mathieu functions of real and complex order. The radiated field is computed by considering equivalent current distributions on the surface of the elliptic cylinder and is expressed in terms of elliptical harmonics. The electrical parameters of the antenna are analysed as functions of the eccentricity of the elliptic support View full abstract»

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  • Time-domain analysis of thin-wire loaded antennas using integral equations

    Page(s): 203 - 206
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    A simple and efficient way of analysing the transient response of thin-wire antennas with connected passive linear elements is described. The method can easily be implemented in any existing code based on the solution, using a marching-on-in-time procedure, of the time-domain electric-field integral equation for thin wires. Two examples of antennas designed using reactive loads are analysed and the results are compared with those obtained using the NEC code View full abstract»

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  • TLM analysis of the mutual coupling of microstrip patch antenna arrays

    Page(s): 207 - 210
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    The transmission-line matrix (TLM) method is used to simulate the mutual coupling effect between two rectangular microstrip patch antennas, which are covered with a dielectric layer. A novel graded Heaviside absorbing layer (HAL) is used as the absorbing boundary condition to truncate the computational space. The numerical results obtained are compared with those of the finite-difference time-domain (FDTD) method as well as the published theoretical and experimental results of other authors, and good agreements are obtained View full abstract»

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  • Closed-form spatial electric field Green's functions of microstrip structures using the fast Hankel transform and the matrix pencil method

    Page(s): 161 - 166
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Closed-form expressions of spatial electric field Green's functions of microstrip structures are presented. These expressions are accurate for a radial distance from one hundredth to five wavelengths. Numerical spatial Green's functions are efficiently calculated by applying fast Hankel transforms (FHT). These numerical functions are then used to obtain the closed-form expressions in terms of a sum of complex exponentials using the matrix pencil method. Numerical results from this method compare well with those obtained by direct numerical integration. Owing to the utilisation of an FHT algorithm to calculate the Sommerfeld-type integral, the present method is very efficient in obtaining the spatial electric field Green's functions View full abstract»

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  • Dielectric-loaded cavity-backed slot radiator analysis

    Page(s): 195 - 198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    A dielectric-loaded cavity-backed slot antenna is analysed by the method of moments. Owing to the geometry, the dielectric material can contact the metal walls hence the problem is formulated to include polarisation currents on the dielectric body. In this way an analysis of the structure can be obtained in a single pass computation. The paper shows the far-field radiation pattern, theoretical predictions and experimental results for various dielectric material positions within the cavity View full abstract»

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  • Ultra-wideband transmit/receive antenna pair for ground penetrating radar

    Page(s): 231 - 235
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Experimental results from a novel compact transmit/receive antenna pair consisting of two loss-loaded bow-tie monopole antennas are described. Instead of using a distributed resistive loading of the antenna, a broadband microwave absorber is applied as a lossy dielectric loading of the bow-tie elements. The antenna pair has a number of remarkable features. It is characterised by a high bandwidth (400-6000 MHz), a low cross-coupling, and a sharp impulse response with low reverberation. The radiation pattern maintains the same shape and orientation across the whole bandwidth, with an E-plane beamwidth ranging from 100° to 40° and a maximum antenna gain of 3.0 dBi. The input impedance is resistive, and has a value of 75 Ω over a wide frequency range. Furthermore, the input impedance is not affected by the presence of the soil when the antenna is placed on the ground surface View full abstract»

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  • Extension of the forward-backward method using spectral acceleration for the fast analysis of large array problems

    Page(s): 167 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The analysis of large array problems has been a very difficult task because of the limitations of available numerical methods such as the method of moments (MoM), especially in the situation where nonperiodic structures are present. The approach of the forward backward method using the novel spectral acceleration (FBM/NSA) algorithm, previously developed for the modelling of scattering problems from large rough surfaces, has tremendous potential to overcome the current limitations in exact numerical studies. The extension of this FBM/NSA approach with O(N) in computational complexity is presented for treating large array problems. Similarly to its applications in rough surface problems, the efficiency and accuracy of this approach are validated and demonstrated by numerical results in comparison with rigorous MoM solutions View full abstract»

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  • Application of the TLM method to the interaction of EM fields with dispersive dielectric bodies

    Page(s): 211 - 217
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The application of the symmetric condensed node transmission line matrix method (SCN TLM) to three-dimensional scattering from biological tissue is investigated. To simulate the dispersive nature of biological tissue, a second-order Debye equation of the permittivity in the frequency domain is used in a modified TLM technique. In this technique, the scattering matrix is independent of the dielectric properties of the medium, which are accounted for via lumped equivalent networks or sources connected to the nodes. These equivalent sources are calculated at each time step and included in the scattering procedure of the TLM. Assuming the nondispersive nature of biological tissue, the nondispersive or stub-loaded SCN TLM method is used to obtain the near field data and the specific absorption rate (SAR) distribution. The results of both cases are compared. The modified TLM technique is then applied to a nonhomogeneous and geometrically complex dispersive dielectric body, which is the human head. Two models of the head are used, a simplified model of 209 coarse cells and a refined model of 24552 cells View full abstract»

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  • Scanned microstrip arrays using simple integrated ferrite phase shifters

    Page(s): 237 - 241
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A phase-steered microstrip antenna array is presented, suitable for application as a mobile vehicle satellite terminal. Phase shifters are implemented on a hybrid dielectric-ferrite substrate, and use is made of the phase transition near the cut-off region of the biased ferrite. Small permanent magnets and carefully biased ferrites remove the need for large applied electromagnetic fields. 2-, 3- and 4-element demonstrator arrays have been constructed, and up to 30° beam squint has been achieved for applied magnetic biases of about 100 Oe View full abstract»

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  • Analysis procedure for arrays of waveguide slot doublets based on the full T-network equivalent circuit representation of radiators

    Page(s): 173 - 178
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    An array of longitudinal slot doublets in a rectangular waveguide may be modelled by an equivalent single-slot array in a half-height waveguide. The slot electric fields display an increasing degree of asymmetry with large slot offsets and a reduction in waveguide height. In such cases, the values of the series elements in the equivalent T-network representation of radiators become significant. Existing analysis techniques ignore their effects and use a simple shunt element equivalent circuit model. The paper presents an off-centre-frequency analysis procedure for slot arrays which is based on the full T-network model for individual radiating elements. Calculations display excellent agreement with measured and fullwave analysis results for the scattering parameters of a slot doublet array View full abstract»

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  • Procedure for the spatial resolution of multipath signals in urban radio links

    Page(s): 224 - 230
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    The growing use and demand for microwave communication systems has led to an increase in system density, especially in urban areas where the abundant presence of potential obstacles increases the risk of propagation. For efficient frequency planning, knowledge of the multipath geometries involved is required. This can be obtained by resolving the multipath field into its constituent components, yielding their amplitudes and angles of arrivals at a receiver terminal. Investigations into the resolution of multipath height gain curves are documented in the literature. These generally concentrate on resolving the two predominant signal components. In an urban environment, the number of distinct signal paths generally exceeds two. Resolution of more than two components is more complex and requires considerably more effort. The paper presents a component resolution procedure which determines the individual amplitudes and angles of arrival of the constituent signal paths. The procedure is applied to the spatial amplitude envelope observed when displacing a receiver incrementally over a distance of a few wavelengths through a multipath field. The presented solution has the advantages of relatively simple measurements and post-processing of measured data. In stationary measurement environments and discrete ray distributions, the solution requires only the recording of envelope amplitude values and no phase information. The performance of the resolution procedure was evaluated using a receiver with a standard antenna. Examples including simulated and experimental radio paths supported by measurements are presented View full abstract»

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  • Intelligent quadrifilar helix antenna

    Page(s): 219 - 223
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The concept of the intelligent quadrifilar helix antenna (I-QHA) as an antenna for handheld mobile terminals is detailed. The potential advantages of using the I-QHA in both terrestrial and satellite mobile communications are presented. The I-QHA may be used as a multiband or multimode antenna, allowing a handset to operate in different frequency bands and in both terrestrial and satellite communications environments. The adaptive matching component of the I-QHA not only matches the antenna for different frequency bands, but counters the detuning effects caused by the user. Finally, diversity gain improvements of up to 14 dB in heavily shadowed environments, achieved by implementing diversity techniques on the elements of the I-QHA, are demonstrated View full abstract»

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  • Modelling lossy surfaces using a wire method-of-moments code

    Page(s): 247 - 248
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    A simple technique is presented for modelling a lossy surface using a wire method-of-moments code, where the surface grid model is loaded with lumped resistive loads. Good comparison is achieved between measured and computed input impedance against distance of a dipole in front of lossy sheets, over a wide range of surface conductivity View full abstract»

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  • Method-of-moments analysis of the narrow-wall slot array in a rectangular waveguide

    Page(s): 242 - 246
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    The method-of-moments has been used for the analysis of the nonresonant narrow-wall slot array in a rectangular waveguide. As this approach works with the fundamental integral equations that describe the entire array. No assumptions about the aperture electric fields are required. Also, the equivalent circuit representation for the individual radiating slots used in earlier designs is not required in the present method, as it deals directly with slot aperture voltages. The effects of internal higher-order and external mutual couplings, and finite wall thickness are rigorously incorporated in the design. Expressions are presented for the input reflection coefficient, transmission coefficient, and the far-field radiation pattern of the array. Numerical results are compared with the experimental results of a 78 element narrow-wall slot array. Good agreement has been observed between theory and experiment View full abstract»

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