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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 6 • Date Dec 1995

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Displaying Results 1 - 17 of 17
  • Cavity feed technique for slot-coupled microstrip patch array antenna

    Page(s): 452 - 456
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    Slot-coupled microstrip patch arrays fed by rectangular overmoded cavities are described and their radiation characteristics analysed using simplified cavity models both for the illuminating and patch resonant cavities. In particular, 4×4 single cavity-fed and 8×8 stepped cavity-fed patch arrays were built and studied. With regard to the radiation patterns and directivity the measurements indicated a satisfactory agreement with the theory. The measured relative gain bandwidth ranges from 1.2% to 3.1% depending on the antenna configuration. Compared with a similar size microstripline network-fed patch array the 8×8 stepped cavity-fed patch array antenna has better efficiency and much lower side lobes View full abstract»

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  • Backscattering study on non-orthogonal trihedral corner reflectors

    Page(s): 441 - 446
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Synthetic aperture radar external calibration requires the use of trihedral corner reflectors deployed on test sites. Construction defects and mechanical stresses can affect the orthogonality of the corner reflector faces, with an effect on their radar cross-section. A model for evaluating backscattering properties of perfectly conductive trihedral corner reflectors, with internal angles deviating from orthogonality, has been developed. The combination of geometrical optics and physical optics methods has been used to calculate single, double and triple reflections. Moreover, the analysis takes into account single diffraction contributions which are described by means of the physical theory of diffraction. The radar cross-section of a set of trihedral corner reflectors with right, acute and obtuse angles has been then measured in an anechoic chamber. The numerical results and the experimental data are in excellent agreement, thus validating the model which foresees a decrease in the radar cross-section as a consequence of the orthogonality loss View full abstract»

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  • Calculation of dielectric resonators with complicated constitutive parameters

    Page(s): 477 - 480
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    A novel approach for calculation of resonant frequencies of dielectric resonators in waveguides or cavities is presented. The resonant sample may be made from different materials: high-permittivity dielectrics, magnetic materials, chirals or general bi-anisotropic materials. The resonant frequencies of high-permittivity dielectric resonators in a cylindrical cavity are calculated and compared with the literature to validate the proposed method. Numerical results of chiral and Faraday chiral resonators are also given View full abstract»

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  • Vector complex eigenmode analysis of microwave cavities

    Page(s): 457 - 461
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    A vector complex eigenmode analysis procedure of microwave cavities is presented. The resonance problem of arbitrary shaped microwave cavities loaded with lossy dielectric material is formulated with the finite-element method in either E or H fields through a Galerkin-weighted residual procedure. Discretisation of the problem results in a very large, highly sparse, complex symmetric generalised eigenvalue problem. Inverse iteration with shifting in combination with a preconditioned conjugate gradient procedure is employed for the efficient solution of the complex eigenvalue problem. The method, being very efficient in terms of time and memory, is applied in the determination of the resonance of a cylindrical cavity loaded with lossy dielectric material. The obtained results are in very good agreement with experimental ones. A duality in the resonant frequencies is observed between the E and H formulations. Furthermore, the method can be used in the solution of the inverse problem of determining the dielectric properties of the loaded material View full abstract»

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  • Power synthesis of conformal arrays by a generalised projection method

    Page(s): 467 - 471
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    A new technique for the synthesis of conformal arrays in the full three-dimensional and vectorial case is presented. The technique exploits a generalised projection algorithm, and can easily be extended to deal with possible constraints on the excitation coefficients. To alleviate the most fundamental difficulty of the power synthesis problem, i.e. the possibility for the synthesis algorithm of being trapped by spurious solutions, a non-conventional choice for the variables occurring in the synthesis problem is made, following recent results in reflector antennas power synthesis. This choice makes the geometry of the sets involved in the projection algorithm more favourable from the point of view of the trapping problem. Numerical examples demonstrating the performances of the method are presented View full abstract»

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  • Spherical shell and volume arrays

    Page(s): 498 - 500
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    By applying appropriate phase weights, an array of omnidirectional elements on a spherical shell can be made to scan the main beam over 4π steradians. Although the general analytic solution for the radiation pattern appears to be intractable, the result when the elements are uniformly weighted in amplitude is a sinc function. This result is applied to derive the radiation pattern from a fully or partially filled spherical array with uniform amplitude weighting throughout. The established optimal aperture distributions used with linear arrays are adapted to obtain volume distributions to apply to the elementary shells in a fully filled sphere to obtain the corresponding radiation pattern characteristics View full abstract»

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  • Mobile radio propagation prediction in irregular cellular topographies using ray methods

    Page(s): 447 - 451
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The performance of a UTD-based technique for cellular mobile radio propagation modelling is investigated in situations of irregular topography and nonuniform building heights. The comparison between theoretical simulation (with limited topographic and ground cover data) and experimental measurements at 851 MHz is encouraging. The UTD-based technique is seen to exhibit a flexibility which is unlikely to be replicated by alternative physical optics based techniques View full abstract»

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  • Power handling capability of a HTS stripline structure using an efficient interior-exterior Green's function method

    Page(s): 472 - 476
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    An accurate and efficient technique is developed to calculate the current distribution over the cross-section and close to the corners of a high-temperature superconducting (HTS) strip in a stripline structure. The problem is formulated in terms of a set of coupled integral equations for the axial electric field inside and outside of the strip. An accurate and fast converging complex images Green's function is derived for the exterior region. Numerical results are presented for a typical HTS stripline. Non-singular behaviour of the current density distribution close to the corners is demonstrated View full abstract»

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  • Optimisation approach to the time-domain electromagnetic inverse problem for a bi-isotropic slab

    Page(s): 429 - 434
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A one-dimensional time-domain electromagnetic inverse problem for a bi-isotropic slab is solved using an optimisation approach. The bi-isotropy and dispersion result in time convolutions of four susceptibility kernels in the time-domain constitutive relations. To make the computation simpler, dual functions are introduced to derive an explicit expression for the gradient. A matrix formalism is introduced to derive the system of equations for the dual functions. After the gradient has been computed, a conjugate gradient method is used to reconstruct all the four susceptibility kernels simultaneously. Numerical results for the reconstruction are presented, and the algorithm is tested with both the clean and noisy data View full abstract»

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  • Analysis of a coupled patch antenna with application in personal communications

    Page(s): 495 - 497
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    The behaviour of the printed monopole when used with a finite ground plane differs considerably from the expected behaviour in an infinite ground plane. When the ground plane is small, this influences the resonant frequency, acting like a reflecting plane. The polarisation is not linear, and the dependence of the operating frequency with the dimensions of the monopole is not linear. For that reason this monopole with a finite ground size is called a coupled patch antenna. This antenna has very good features for personal communications, i.e. very small size, good gain and high directivity. The antenna is designed for use with a wireless modem but can be used in any personal communications system. The analysis of the performance is achieved by using the non-uniform FDTD in combination with the recently developed perfect matching layer superabsorbing boundary condition View full abstract»

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  • Improved frequency domain analysis of microstrip circuits by the method of moments

    Page(s): 421 - 428
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    A popular full-wave analysis method for microstrip circuits is based on integral equation techniques solved by the method of moments. A novel formulation in the space domain of the pertaining Green's functions is investigated. The latter show a series form where the space dependence is in the analytic form of Legendre polynomials and the coefficients, determined by numerical integration, are discovered to be smooth functions of frequency. From these properties, the matrix of moments is rapidly filled, allowing saving of computation time, while maintaining accuracy in a wideband analysis View full abstract»

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  • New closed-form expression for coupling matrix elements related to scattering from planar periodic single-strip grating

    Page(s): 492 - 494
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    A new closed-form expression for the coupling matrix elements in the multimode equivalent network that describes plane wave scattering from a planar periodic single-strip grating at a dielectric interface is presented. After solving a Fredholm integral equation of the first kind whose kernel has a logarithmic singularity, the coupling matrix elements are obtained in the form of certain ordinary integrals involving the Legendre polynomials, which can be evaluated analytically View full abstract»

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  • Boundary-element approach to calculation of wire antenna parameters in the presence of dissipative halfspace

    Page(s): 435 - 440
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    The corresponding electric field integral equation for an antenna horizontally placed over an imperfectly conducting halfspace is solved by a boundary-element method developed for such operators. Sommerfeld integrals, appearing in the kernel of the integral equation, are evaluated by means of exponential approximations. This approach shows numerous advantages over the usual techniques of solving such an equation, particularly in calculating the input impedance View full abstract»

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  • High-gain microwave amplifier tuneable over a decade bandwidth

    Page(s): 489 - 491
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    A novel microwave single-stage MESFET distributed amplifier configuration based on the dual-fed distributed-amplification technique is described. In this configuration the input and output line idle ports are reactively terminated. This results in a significant improvement in gain and power added efficiency over conventional distributed and dual-fed distributed amplifiers. The amplifier band of operation can be tuned by varying the terminating reactances. This novel configuration also has the potential to be used as a tuneable oscillator with a decade tuning range View full abstract»

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  • A more rigorous UTD-based expression for multiple diffractions by buildings

    Page(s): 481 - 484
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    The paper derives and analyses a more rigorous UTD-based expression for multiple diffractions caused by buildings. The previous expression was addressed in the open literature. This new expression is more appropriate for numerical calculation as well as for theoretical analysis. The previous expression applied to the vertically polarised electric field. As a theoretical extension, the new expression applies to the horizontally polarised electric field as well. These suggest that the new expression be utilised in the propagation prediction for cellular mobile radio communications View full abstract»

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  • Improving efficiencies of superdirective arrays of monopoles over lossy groundplanes by using superconducting disc overlays

    Page(s): 462 - 466
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    Electrically small perfectly conducting superdirective monopole arrays above lossy metal groundplanes are analysed at 500 MHz using a moment method incorporating Sommerfeld terms. It is shown that significant improvements in efficiency are obtained when small perfectly conducting discs, which can be realised using high-temperature superconductors, are attached to the monopole bases, compared with monopoles being directly connected to groundplanes View full abstract»

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