The uniform geometrical theory of diffraction (GTD) is employed for calculating the edge diffracted fields from the finite ground plane of a microstrip antenna. The source field from the radiating patch is calculated by two different methods: the slot theory and the modal expansion theory. Many numerical and measured results are presented to demonstrate the accuracy of the calculations and the finite ground plane edge effect.

The finite ground plane effect on the microstrip antenna radiation patterns

New expressions are derived for the fringe current components of the equivalent edge currents. They are obtained by asymptotic endpoint evaluation of the fringe current radiation integral over the "ray coordinate" measured along the diffracted ray grazing the surface of the local wedge. The resulting expressions, unlike the previous ones, are finite for all aspects of illumination and observation, except for the special case where the direction of observation is the continuation of a glancing incident ray propagating "inwards" with respect to the wedge surface (the Ufimtsev singularity).

Elimination of infinities in equivalent edge currents, part I: Fringe current components

A summary of various high-frequency techniques is presented for analyzing the electromagnetic radiation from antennas in the presence of their host environment. These techniques provide physical insight into antenna radiation mechanisms and are found to be highly efficient and accurate for treating a variety of practical antenna configurations. Examples to which these techniques have been applied include open-ended waveguide antennas, horn and reflector antennas, and antennas on aircraft and spacecraft. The accuracy of these techniques is established via numerical results which are compared with those based on other independent methods or with measurements. These high frequency methods can be combined with other techniques, through a hybrid scheme, to solve an even greater class of problems than those which can be solved in an efficient and tractable manner by any one technique alone. >

High frequency techniques for antenna analysis

The equivalent current concept is used to compute the scattering patterns of flat plate structures. It is also used to obtain the broadside scattering lobe for any incidence plane. The essential feature introduced in this paper is that only the components of the equivalent current perpendicular to the incidence plane are used. No special treatment of the singularity in the plane wave diffraction coefficient (which is the basis of the equivalent current concept) is required. Instead, this choice of equivalent current components is such that the singularity at one edge segment is canceled by the singularity at the opposite edge segment. For modern day computers there is sufficient accuracy that the main scattering lobe can be obtained in the limit as one approaches broadside. The same results can be obtained for plate structures made of straight edges by using a new corner diffraction analysis. For certain cases where the observation angle is sufficiently removed from normal incidence to an edge, the corner diffraction analysis appears to yield more accurate results.

First-order equivalent current and corner diffraction scattering from flat plate structures

This dissertation treats the potentials and limitations of wireless LANs intended for the support of services as envisioned for Broadband ISDN. The treatment is based on the assumption that the transmission takes place via millimetre"wave indoor radio channels. A method is discussed for the measurement of the wideband characteristics of millimetre-wave indoor radio channels. Measurements results obtained with this method are presented. These results are used for the development of a statistical model of the millimetre-wave indoor radio channel. In addition, a deterministic channel model is developed based on Geometrical Optics. A discussion concerning the applicability, limitations and accuracy of such a model is included. Results of simulations ba.~ed on the deterministic model developed are presented. These results give an indication of the influence of the environment and antenna radiation patterns on the channel characteristics. Using the measurement results, the maximum feasible bit rate is evaluated for millimetre-wave indoor radio transmission assuming QPSK modulation. In addition, the improvement by channel equalization is examined. The evaluation includes the influence of noise, number of equalizer taps, antenna diversity and antenna directivity pattern. It is shown in which way efficient, reliable and flexible information transfer can be achieved in broadband wireless LANs on the basis of the Asynchronous Transfer Mode. In this context a contention-free multi-access protocol is proposed.

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Broadband wireless LANs : a feasibility study

The first order geometrical theory of diffraction (GTD) predicts vanishing fields along the surface of a conducting wedge for the incident electric field polarized parallel to the diffracting edge The slope diffraction coefficient is a valid correction term for incidence angles removed from the shadow boundary A new slope diffraction function for the half plane is presented along with applications This new form of slope diffraction coefficient for the half plane is valid through the shadow region Reciprocity is invoked to find the far-fields for a source on the surface of the conducting wedge In addition to applying the two-dimensional slope diffraction analysis to practical problems, the equivalent current concepts have been extended to include equivalent slope currents for the analysis of either finite or curved edges This new form of the slope diffraction function has been successfully used to provide an H -plane horn pattern analysis that is considerably less tedious than previously possible with GTD Both pure GTD solutions and hybrid solutions using conventional aperture integration for the main beam region and GTD for the far-out side and back lobes are compared with experimental results

C. Mentzer

Papers

Slope diffraction and its application to horns