Scheduled System Maintenance:
On May 6th, single article purchases and IEEE account management will be unavailable from 8:00 AM - 5:00 PM ET (12:00 - 21:00 UTC). We apologize for the inconvenience.
By Topic

Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 5 • Date August 1985

Filter Results

Displaying Results 1 - 12 of 12
  • Coaxially fed hollow probe in a rectangular waveguide

    Publication Year: 1985 , Page(s): 273 - 285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1457 KB)  

    The problem of a coaxially excited hollow probe in a rectangular waveguide has been analysed by an approach in which the electric field off the end of the probe is the unknown that may be obtained by the solution of an integral equation. The electric field is represented as the static gap field multiplied by a Chebyshev series. The unknown coefficients may be found from a matrix equation in which the square matrix has dominant diagonal terms. It is shown that this permits accurate results to be obtained by retaining only a few terms of the series. Expressions are derived for the exterior and interior current distributions, and for the admittance presented to the coaxial line from which the probe is driven. Comparison of theoretical and experimental results shows the theory to be very accurate. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Tomographic image reconstitution of objects from multi-incidence microwave exploration

    Publication Year: 1985 , Page(s): 286 - 290
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (485 KB)  

    To compete with other methods of diagnosis, microwave imagery has to be given in three dimensions with good accuracy in all directions. Experiments carried out with a single incident-beam illumination gave a good transverse accuracy, but the longitudinal one was not as good. To obtain a good image reconstitution, new computational simulations were carried out using many different incident angles to improve longitudinal accuracy. The results show that a choice must be adopted between the image quality and the required computing ability. Criteria given in the paper can help in this choice. Finally, we have shown that three-dimensional images can be obtained with good accuracy from a multi-incidence exploration. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New possibilities for phaseless microwave diagnostics. Part1: Error reduction techniques

    Publication Year: 1985 , Page(s): 291 - 298
    Cited by:  Papers (13)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1367 KB)  

    The relevance of the phase retrieval problem to microwave diagnostic imaging is considered. Existing iterative (error-reduction) techniques originally devised for problems in optics and electron microscopy are applied to a microwave-imaging situation. A new algorithm, which is superior for microwave diagnostics, is introduced. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New possibilities for phaseless microwave diagnostics. Part2: The uniqueness problem and half plane imaging

    Publication Year: 1985 , Page(s): 299 - 306
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1092 KB)  

    The ambiguity of the phase-retrieval problem has been investigated. Theoretical studies have concentrated on the asymptotic properties of the Fourier-transform integral to investigate the band-limiting function of the aperture in determining the zeros of the transform. For one-dimensional functions, the phase-ambiguity problem is identified as finite permutations of zero conjugation, which, although modifying the existing phase, leave the intensity unperturbed. Based on these studies a new practical algorithm for halfplane imaging is proposed for one-dimensional functions. The relevance of the proposed technique has been discussed, with a theoretical analysis which studies the distribution of transform zeros for two-dimensional functions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Antenna adaptivity by direction finding and null steering

    Publication Year: 1985 , Page(s): 307 - 311
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (750 KB)  

    A maximum-likelihood procedure, in conjunction with a point-source emitter assumption, is used to estimate the directions of arrival of multiple signals at an antenna; followed by direct calculation of beamweighting coefficients, which will receive one source while steering nulls to all other sources. Estimation of element-sensitivity error is also undertaken, and the beam coefficients are compensated to reduce sensitivity to such unknown variables. The result is a robust, adaptive algorithm, which behaves optimally in coherent or incoherent interference situations even when the desired signal direction is not known a priori, and which is able to operate with less data samples than least-squares methods. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the efficient evaluation of integral arising in the sommerfeld halfspace problem

    Publication Year: 1985 , Page(s): 312 - 318
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (654 KB)  

    An efficient approach is described for the numerical evaluation of the Sommerfeld integrals which arise in analyses of antennas radiating over a dielectric halfspace. The main features of this approach can be summarised as follows. The contour deformation principle is employed to express the original integral as a sum of the steepest descent-path (SDP) integral and the possible branch-cut-path (BCP) integral, which are then evaluated numerically. If the branch point is captured, the SDP is allowed to go to the bottom sheet of the Riemann surface, resulting in a continuous behaviour of the integrand. In the last case, the BCP is deformed to the SDP emanating from the branch point, on which the integrand decays rapidly. Also, the Zenneck pole is subtracted, resulting in a smooth behaviour of the integrand on the SDP. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis and design of double-layer frequency-selective surfaces

    Publication Year: 1985 , Page(s): 319 - 325
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (786 KB)  

    A dichroic structure consisting of two parallel arrays of crossed dipoles supported by various dielectric sheets is investigated. An efficient analysis method, based on a modal expansion that takes into account the interaction of the reactive field between the gratings, is outlined for this purpose. The method uses a Galerkin procedure combined with a generalised wave-matrix formulation. The analysis method is also implemented in a systematic design procedure, and the design of a double-layer grating structure intended for a dichroic subreflector operating at 10.7¿11.7 GHz and 18.1¿20.1 GHz is carried out. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vector potential of a vertical current element over a lossy ground

    Publication Year: 1985 , Page(s): 326 - 328
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    A comparison is made of the three numerical techniques for evaluating the vector potential arising in the problem of a vertical current element radiating over a lossy ground: (i) the exact Sommerfeld integration, (ii) the high-contrast approximation (HCA) and (iii) the reflection-coefficient method (RCM). Extensive calculations are carried out to determine the range of applicability of the approximate techniques. The comparison shows good accuracy of the results derived from HCA for a relatively wide range of parameters of practical interest and indicates that the RCM is of a questionable validity for the vertical-antenna problem. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dyadic green function for the electromagnetic field in multilayered isotropic media: an operator approach

    Publication Year: 1985 , Page(s): 329 - 334
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    The dyadic Green functions of electric and magnetic type for multilayered isotropic media are discussed, and a tractable form is obtained by an operator method, which does not involve infinite sums of Hansen functions. The formulation considers a TE-TM decomposition and the use of propagation matrices. Special attention is given to the application of these functions to the analysis of problems in the field of nondestructive measurement of materials. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of a horizontal two-element antenna array above a dielectric halfspace

    Publication Year: 1985 , Page(s): 335 - 338
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (433 KB)  

    The mixed-potential integral equation is employed to compute the current distribution on two parallel wire antennas placed horizontally above an air/water interface. The Sommerfeld integrals incorporated in the kernel of the integral equation are evaluated by numerical integration along the steepest-descent path in the complex plane. Sample results are presented for several cases of interest and are compared with measured data. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An efficient algorithm for antenna synthesis updating following null-constraint changes

    Publication Year: 1985 , Page(s): 339 - 341
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (305 KB)  

    The procedure to maximise the array signal to noise ratio with null constraints involves an optimisation problem that can be solved efficiently using a modified Cholesky decomposition (UD) technique. Following changes in the main lobe and/or null positions, the optimal element weight vector can be updated without the need for a new complete matrix inversion. Some properties of the UD technique can be utilised such that the updating algorithm reprocesses only a part of the unit triangular matrix U. Proper ordering of matrix entries can minimise the dimension of the updated part. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Characteristics of asymmetrical coupled shielded microstrip lines

    Publication Year: 1985 , Page(s): 342 - 343
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    Closed-form expressions are derived for the characteristics of the asymmetrical coupled shielded microstrip lines. Numerical results using these expressions approach those of the asymmetrical unshielded microstrip lines as the shieldheights ratio approaches the critical value. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.