Topic
Fresnel zone
About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, the authors investigated the power transfer between two ellipsoidal reflector antennas with common focal points and dual-mode feeds, assuming a circularly symmetric feed pattern, the H-plane pattern of an open-end circular waveguide excited by the TE 11 mode, the maximum transmission coefficient between reflector apertures was found to be within 0.5 percent of the value computed for transmission between two circular aperture with optimum illumination described by the generalized prolate spheroidal function.
Abstract: Power transfer between two ellipsoidal reflector antennas with common focal points and dual-mode feeds has been investigated. Assuming a circularly symmetric feed pattern, the H-plane pattern of an open-end circular waveguide excited by the TE 11 mode, the maximum transmission coefficient between reflector apertures is found to be within 0.5 percent of the value computed for transmission between two circular apertures with optimum illumination described by the generalized prolate spheroidal function. Transmission loss between two reflector antennas versus illumination taper is computed for various values of the parameter [p = (ka 1 a 2 )/R]. The minimum transmission loss is obtained as a compromise between feed spill-over and aperture transmission efficiency. In view of the inconvenience of building different ellipsoidal reflectors for different antenna spacings in order to achieve maximum power transfer, we examine the feasibility of using a defocused ellipsoid to simulate ellipsoids of different focal lengths. The deviation of the aperture phase distribution of a defocused ellipsoid from a required spherical phase front is approximately given by an explicit expression. A simple upper bound of the transmission loss due to small phase deviation is obtained for a given maximum phase deviation.
2 citations
Journal Article•
TL;DR: In this paper, the authors gave three theoretical expressions of characteristic parameters of Fresnel zone with different offsets and approximate expressions associated with zero-offset in spatially horizontal interface and proved the importance of (first) Fresnel Zone from the angle of energy.
Abstract: There is wide application for Fresnel zone of seismic prospecting in aspects of optimizing geometry design,studying lateral resolution,determining optimum migration aperture and seismic interpretation. The paper gave three theoretical expressions of characteristic parameters of Fresnel zone with different offsets and approximate expressions associated with zero-offset in spatially horizontal interface and proved the importance of (first) Fresnel zone from the angle of energy. The theoretical analysis and numeric simulation showed that there exists critical offset only relative to dominant wavelength:along with the increase of the depth of reflecting interface,the radius (area) of Fresnel zone increases when the real offsets are less than critical offset and decrease first and then increase when the real offsets greater than critical offset,existing the issue of min Fresnel zone relative to large offsets.
2 citations
01 Jan 1989
TL;DR: In this paper, the focusing performance of different types of Fresnel-zone plate (FZP) transducers has been analyzed and it has been shown that the positive and negative patterns exhibit significantly different focusing characteristics when the number of zones is less than ten.
Abstract: Theoretical study of the focusing performance of different types of Fresnel-zone plate (FZP) transducers shows that the positive and negative patterns exhibit significantly different focusing characteristics when the number of zones is less than ten. The study also shows that for B-scan imaging, high resolution and effective sidelobe reduction can be obtained by using a single-ring annular transducer for transmitting in combination with a two-phase FZP transducer for receiving.
2 citations
TL;DR: Diffraction of a Gaussian beam passing through a circular aperture subsequently focused by a lens is investigated and an expression is derived for the amplitude distribution beyond the lens for the effect of the aperture-lens separation on the focal shift.
Abstract: Diffraction of a Gaussian beam passing through a circular aperture subsequently focused by a lens is investigated. An expression is derived for the amplitude distribution beyond the lens. With the aid of the axial intensity and encircled energy, the effect of the aperture-lens separation on the focal shift is obtained, and the quantitative influence of the truncation parameter and Fresnel number on the focal shift is also presented.
2 citations
01 Apr 1992
TL;DR: In this article, the authors formulate an aiming problem pertaining to an RKA-driven launcher of microwave pulses, and draw on a study of quantum measurements to develop an approach to aiming.
Abstract: Antenna arrays are potentially useful for both the transmission and the reception of trains of electromagnetic pulses. In this paper, we formulate an aiming problem pertaining to an RKA- driven launcher of microwave pulses, and draw on a study of quantum measurements to develop an approach to aiming. Appendix A reviews the behavior of microwave radiation focused at a target in the Fresnel zone. Appendix B derives the antenna current for optimal angular sensitivity of a monopulse radar for a target in the Fresnel zone, very close to the axis.
2 citations