Fresnel zone

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

Fresnel zone plate telescopes for X-ray imaging I: experiments with a quasi-parallel beam

Abstract: Combination of Fresnel Zone Plates (FZP) can make an excellent telescope for imaging in X-rays. We present here the results of our experiments with several pairs of tungsten made Fresnel Zone plates in presence of an X-ray source kept at a distance of about 45 feet. The quasi-parallel beam allowed us to study sources placed on the axis as well as off the axis of the telescope. We present theoretical study of the fringe patterns produced by the zone plates in presence of a quasi-parallel source. We compare the patterns obtained from experiments with those obtained by our Monte-Carlo simulations. The images are also reconstructed by deconvolution from both the patterns. We compare the performance of such a telescope with other X-ray imaging devices used in space-astronomy.

Errors in Measuring the Angular Coordinate of Extended Targets by the Monopulse Method in the Fresnel Zone of the Linear Antenna Array

Abstract: 2020. Т. 20, No 2. С. 67–76 67 Introduction The operation of the direction finder as part of a radio-angle measuring system is usually accompanied by interfering influences caused by re-reflected signals. In this case, the direction-finding radio source and interfering reflectors may be in the Fresnel zone of the receiving antenna of the direction finder, that is, the condition 2 . , 2 / , i d z R R R L    where R, Ri – distance from the center of the opening of the receiving antenna to the radiation source and the i-th reflector, respectively; Rd.z – far zone receiving antenna;  – wavelength of the observed field; L – the length of the antenna. The results of the analysis of the accuracy characteristics of the monopulse method relate to the case when, within the opening of the receiving antenna, the wavefront of the signal of the direction-finding target can be considered almost flat [1–11, 13]. Known estimates of the mean square deviation (MSD) of errors in determining the angular position of the center of a small-sized radar target in the Fresnel zone of a receiving antenna, consisting of a large number of unresolvable “brilliant points” [12]. In this case, the estimation of the angular coordinates of the targets is formed to the maximum of the output effect of the spatial processing system, regardless of any particular algorithm. In this paper consider the problem of determining the measurement errors monopulse radio direction finder angular coordinates of a point radio source in the Fresnel zone of the receiving filled LAR under the combined influence of internal noise and angular noise generated by signals of statistically independent point reflectors. DOI: 10.14529/ctcr200207

Analysis of wavefront reconstruction in surface wave holography

Abstract: Holography is a well-known technique that has a wide range of applications in information processing and data storage. Recently, a methodology named surface wave holography (SWH) that merges the concepts of conventional holography and nanophotonics was proposed to implement plasmonic wavefront shaping and manipulation. By advoiding the complicated inverse-problem solution and directly designing grooves on a metallic surface, this method has been exploited to realize the deliberate scattering and interference of surface waves in the Fresnel zone. Here we address the mathematical foundation of this methodology in order to place it on a solid physical ground. We present a detailed scalar-field analysis of the image recording and reconstruction processes involved in SWH. The theory shows that the discrete curves of holographic pattern on a metallic surface can indeed reconstruct the predesignated image, albeit with undesired slight aberration and distortion due to loss of some information.

Metodología para el cálculo adecuado de las alturas de antenas en un radioenlace de microondas en Línea de Vista

Abstract: The methodology to properly calculate the heights of the antennas above the surface of the Earth in a line-of-sight (LOS) microwave link from its radio profile is presented. The effect of the Earth's atmosphere on RF signals, the effective Earth radius factor for Mexico and the analysis of the first Fresnel zone are described. With the proper position of the antennas ensuring clearance of the first Fresnel zone the proper reception of transmitted beams arriving from different paths to the antenna at the other end, all in phase with the direct beam in LOS is achieved.