R. Rudduck

A doubly periodic moment method solution for the analysis and design of an absorber covered wall

A periodic moment-method solution for scattering from a doubly periodic array of lossy dielectric bodies is developed. The purpose is to design electromagnetic wedge and pyramidal absorbers for low reflectivity so that one can improve the performance of anechoic chamber measurements. The spectral-domain formulation and the moment-method volume polarization current approach are used to obtain the expressions for determining the scattering from a doubly periodic array of lossy dielectric bodies. Some wedge and pyramidal absorber configurations that have been designed, fabricated, and tested in the OSU/ESL compact range measurement facility are presented. By taking into account the complexity of real-world material structures, good agreement between calculations and measurements has been obtained. >

Comprehensive analysis for E-plane of horn antennas by edge diffraction theory

Edge diffraction theory is used in analyzing the radiation characteristics of typical horn antennas. The far-sidelobe and backlobe radiation has been solved without employing field equivalence principles which are impractical in the problem. A corner reflector with a magnetic line source located at the vertex is proposed as a model for the principal E -plane radiation of horn antennas. A complete pattern, including multiple interactions and images of induced line sources, is obtained in infinite series form. Diffraction mechanisms are used for appropriate approximations in the computations. The computed patterns are in excellent agreement with measured patterns of typical horn antennas. Radiation intensity of the backlobe relative to mainlobe intensity is obtained as a back-to-front ratio and plotted as a function of antenna dimensions.

A periodic moment method solution for TM scattering from lossy dielectric bodies with application to wedge absorber

The periodic moment method (PMM) solution for the scattering from two-dimensional lossy dielectric bodies is developed. The purpose is to design a microwave wedge absorber for low reflectivity so that one can improve the performance of anechoic chamber measurements. With PMM, the reflection and transmission coefficients of periodically distributed bodies illuminated by a plane wave have been accurately calculated using a Cray Y-MP supercomputer. Through these studies, some wedge absorber configurations have been designed, fabricated, and then tested in the OSU/ESL compact range measurement facility. Two 8-in commercial wedges, a curved wedge, and a four-layer wedge, were studied. In all cases, good agreement between calculations and measurements was obtained. >

Aperture reflection coefficient of TEM and TE 01 mode parallel-plate waveguides

The reflection coefficient of parallel-plate waveguide apertures is analyzed by wedge diffraction theory for the TEM and TE 01 modes. Results are compared with those obtained by other analyses for the special case of the normally truncated guide mounted in a ground plane and for that with thin walls. Measured values of reflection coefficient are used as verification of results for other guide geometries. The method gives accurate results for guide widths as narrow as \lambda/4 .

On higher-order diffraction concepts applied to a conducting strip

The derivation emphasizing cylindrical-wave diffraction is given for a high-frequency approximation to the diffraction of a plane wave by a conducting strip. The resulting formulation is basically the same as the formulations of Karp and Russek. The range of usefulness of this formulation has apparently been unrecognized. The validity of the approximation presented here is checked by comparison with the exact solution for strip diffraction; the backscattered field for normal incidence is in good agreement for strip widths larger than 0.55\lambda and in fair agreement for widths as narrow as 0.125\lambda . This approximation and Kellers geometrical theory of diffraction, which uses plane-wave diffraction coefficients, are compared with measurements made by Ross. Diffraction patterns and echo widths for various incidence angles are calculated for various strip widths.

A new method for obtaining antenna gain from backscatter measurements

A method is presented for determining the gain of an antenna from analysis of backscatter data of the antenna. This approach is different from those which have been presented in the past because it accounts for the presence of resonances which can occur in the antenna during a backscatter measurement. In particular, this type of resonance appears in the backscatter measurement of symmetric reflector antennas. This technique is applied to determine the gain of a Ka-band Cassegrain antenna and an X-band prime focus-fed antenna. >

New plane wave spectrum formulations for the near-fields of circular and strip apertures

The plane wave spectrum (PWS) method has previously been applied to analyze the near-field of planar apertures. The main goal of this paper is to present new PWS formulations for the near-fields of strip and circular apertures. Only special cases are developed in detail. For example, the uniform and parabolic aperture distributions are developed for the circular aperture. These new formulations are expressed in terms of either elementary functions or Fresnel integrals. Consequently, they permit considerably more rapid and efficient calculations than previous near-field formulations, by either the PWS or the aperture integration approach. The new formulations are especially advantageous for large circularly symmetric apertures (on the order of 100\lambda and larger) in that computational efficiencies are improved by an order of magnitude or two over the original PWS formulation. The improvement over aperture integration techniques is more than a factor of 1000 for the 100\lambda aperture.

Near-field analysis by the plane-wave spectrum approach

Historically, most near-field analyses have relied upon aperture-integration techniques. The purpose of this paper is to point out the advantage of the plane-wave spectrum (PWS) approach for analysis of antenna near fields. The advantage of the PWS approach over aperture-integration techniques is quite substantial throughout the entire near-field region for circular apertures. Furthermore, the advantage increases in proportion to closeness to the aperture. The PWS approach also appears to offer advantage for noncircular apertures, e.g., rectangular, at least for large aperture sizes.

Pattern measurements of reflector antennas in the compact range and validation with computer code simulation

The measurements were performed at the Universitys compact range facility. They demonstrated: (1) the excellent dynamic range that can be achieved with antenna pattern measurements in a compact range facility; and (2) the excellent validation achieved for the calculated patterns of two 8-ft diameter reflector antennas. The compact range has a rolled edge modification to its reflector and uses a pulsed radar system to eliminate the clutter interference such that a dynamic range of more than 80 dB can be obtained. The measured far field patterns of two 8-ft reflector antennas, a prime focus fed antenna and a Cassegrain antenna, at 11 GHz were compared with those calculated by Ohio State Universitys Reflector Antenna Code. The computer code simulations approach is also briefly described. >

Slope diffraction analysis of TEM parallel-plate guide radiation patterns

The radiation pattern of the transverse electromagnetic- (TEM) mode parallel-plate waveguide is analyzed by the wedge-diffraction theory in conjunction with a slope-correction term. This term takes into account the nonuniform wave in the analysis of second-order diffractions for an open-ended guide. This slope-correction term provides improved accuracy of the pattern in the region near the plane of the aperture when compared to the usual wedge-diffraction method.