摘要:

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.

DOI:10.1049/ip-h-2.1985.0051

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0052

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0053

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0054

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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 apriori, and which is able to operate with less data samples than least-squares methods.

DOI:10.1049/ip-h-2.1985.0055

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0056

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0057

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0058

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0059

出版商:IEE    

年代:1985

数据来源: IET

摘要:

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.

DOI:10.1049/ip-h-2.1985.0060

出版商:IEE    

年代:1985

数据来源: IET