S. Moseley

Bio: S. Moseley is an academic researcher from United States Department of the Army. The author has contributed to research in topics: Main lobe & Beamwidth. The author has an hindex of 1, co-authored 1 publications receiving 23 citations.

On-axis defocus characteristics of the paraboloidal reflector

Abstract: Lack of an adequate test site often requires the use of on-axis defocusing to obtain simulated Fraunhofer radiation patterns in the optical-Fresnel region from microwave reflector-type antennas. This note presents a way of determining the required amount of defocus from the viewpoint of aperture phase correction. It is shown that the important part of the main lobe of the radiation pattern can be approximately reproduced in the optical-Fresnel region with proper amount of defocus. For a given amplitude illumination function, the change in beamwidth with the position of the primary source can also be predicted.

Determination of far-field antenna patterns from near-field measurements

Abstract: In many cases, it is impractical or impossible to make antenna pattern measurements on a conventional far-field range; the distance to the radiating far field may be too long, it may be impractical to move the antenna from its operating environment to an antenna range, or the desired amount of pattern data may require too much time on a far-field range. For these and other reasons, it is often desirable or necessary to determine far-field antenna patterns from measurements made in the radiating near-field region; three basic techniques for accomplishing this have proven to be successful. In the first technique, the aperture phase and amplitude distributions are sampled by a scanning field probe, and then the measured distributions are transformed to the far field. In the second technique, a plane wave that is approximately uniform in amplitude is created by a feed and large reflector in the immediate vicinity of the test antenna. And in the third technique, the test antenna is focused within the radiating near-field region, patterns are measured at the reduced range, and then the antenna is refocused to infinity. Each of these techniques is discussed, and the various advantages and limitations of each technique are presented.

Focal region characteristics of focused array antennas

Abstract: The effects of focused aperture amplitude tapering, both direct and inverse, on axial forelobes and aftlobes are investigated. Taylor tapers give low sidelobes but high forelobes and aftlobes, plus a modest gain degradation. Inverse tapers give low forelobes and aftlobes but high sidelobes and large gain degradation. Uniform excitation gives comparable axial and transverse subsidiary lobes, and is probably the best choice. Focal shift, where the peak axial power density occurs between the aperture and the phase (geometric) focus, due to the 1/R^{2} factor, is accurately calculated for a uniform square aperture. Since peak axial power density available from a focused aperture depends only on aperture size in wavelengths and on distance, these focal shift results allow system trade-offs to be made.

Measurement of near fields of antennas and scatterers

Abstract: A tutorial review of techniques used for the measurement of near-fields of antennas and scatterers, and an extensive bibliography of the readily available literature in this area, are presented.

Frequency Steerable Two Dimensional Focusing Using Rectilinear Leaky-Wave Lenses

Abstract: The concept of frequency steerable two-dimensional electromagnetic focusing by using a tapered leaky-wave line source embedded in a parallel-plate medium is presented. Accurate expressions for analyzing the focusing pattern of a rectilinear leaky-wave lens (LWL) from its constituent leaky-mode tapered propagation constant are described. The influence of the main LWL structural parameters on the synthesis of the focusing pattern is discussed. The ability to generate frequency steerable focusing patterns has been demonstrated by means of an example involving a LWL in hybrid waveguide printed-circuit technology and the results are validated by a commercial full-wave solver.

On the simulation of Fraunhofer radiation patterns in the Fresnel region

Abstract: Physical limitations on the size of obstacle-free test sites give rise to the need of making radiation-pattern measurements on high-gain antennas at a reduced distance. The general practice is to defocus the primary source along the principal axis of the antenna reflector by a small distance so that Fraunhofer patterns may be simulated in the Fresnel region. This note summarizes and compares three different approaches with which the proper amount of defocus may be determined.