Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

Equivalent field of paraxial diffraction of a zone plate

Abstract: A simplified way is proposed to compute the paraxial diffraction of a zone plate. The complicated diffraction field is approximated by an equivalent field, which is the diffraction field of a hole weighted by the area. Based on this equivalent expression of the diffraction field, a graphic method is applied to calculate the resolving power of a zone plate. The result is consistent with those reported in earlier publications [Am. J. Phys. 19, 359 (1951); J. Opt. Soc. Am. 57, 610 (1967)].

Optical Analysis Of Segmented Aperture Averager

Abstract: High energy lasers with a non-uniform beam distribution are used to study materials properties. When it is required that the beam intensity distribution be uniform, beam averaging schemes have to be used, such as a segmented aperture averager. It consists of a set of small mirrors located on the surface described by an equation of second order. In order to determine the optical performance of the segmented aperture averager, a unit amplitude wave is assumed in the analysis. The averaging is accomplished because the beam is spatially multiplexed, resulting in the superposition of beam segments originally at different locations. Two phenomena con-tribute to the final intensity distribution: diffraction and interference. The uniform plane is located in the Fresnel zone, producing a Fresnel diffraction pattern with the intensity distribution dependent primarily on the Fresnel number. Due to the spatial superposition of beam segments, multiple beam interference pattern results because of the interference of light directed from each segment. Multiple beam interference pattern is characterized by high spikes separated by areas of low intensity with many points of zero intensity. The intensity pattern due to the segmented aperture averager is a multiplication of these two effects. The envelope of the intensity distribution is provided by the Fresnel diffraction pattern, while the spike distribution is specified by the interference parameters. The beam uniformity is achieved as an average over the area of several intensity spikes. This beam averaging procedure can only be used if a finite resolution area for intensity uniformity is required.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design of high efficiency broadband fresnel zone lens antenna at K band

Abstract: In this paper, a novel 24 GHz flat Fresnel zone plate lens antenna has been presented. It consists of three dielectric layers separated by the air gaps and six identical metallic patterns printed on the top and bottom surfaces of each layer. According to the design principle of the quarter-wave Fresnel zone lens, three required phase correction schemes are chosen, −270 degree, −180 degree, and −90 degree, which are realized by tuning the width of the conducting shapes. Simulations show that the presented lens antenna has an aperture efficiency of more than 44.5% in the band of 21.7GHz∼24 GHz, a directivity of 27.7 dBi, and a 1 dB bandwidth of about 10.18%.