Fresnel zone

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

Numerical and experimental analysis of a novel aircraft landing antenna system

Abstract: A numerical and experimental analysis leading to the determination of the geometrical design parameters for an antenna array utilized in the Portable Air Traffic Control Approach and Landing System, developed by the Sierra Nevada Corporation, Sparks, Nevada, has been performed. Numerical modeling using the Method of Moments software package MININEC Professional for Windows was used to obtain the optimal heights above ground of the antennas of the array. The design goal was to obtain a glide slope of 3° for aircraft landing guidance. The two-ray model and Fresnel zones were used to calculate the longitudinal dimension of the region between the transmitting and receiving antennas, which is required to be flat and free of any scattering obstacles. Experimental measurements in an outdoor antenna range confirmed the theoretical and numerical predictions.

Diffraction on a hole in rotating screen

Abstract: A screen with a hole is considered. A diffraction image arises on the receiving plane located in the Fresnel zone in parallel to the screen. If the screen rotates in its plane, then the image does as well. The question is discussed what is distribution of the field energy on the receiving plane averaged over the period.

Spatial intensity correlations of Mathieu speckle fields

Abstract: Analytical expressions are derived for the spatial coherence function of a speckle field that is generated by the scattering of a Mathieu beam from a random phase mask by following the Fresnel diffraction theory. The general results in the free-space propagation show that the intensity correlation factor is a function of the order of the Mathieu beam, and it evolves spatially as the speckle field propagates. Also, we demonstrate that the intensity correlation factor is non-evolving with the propagation distance in the far-field regime when a lens is placed at the focal distance after the diffuser. The results of this analysis can be used in applications where random fields need to be engineered with structured light beams.

A Comparisonal Analysis of Computer Generated Holograms (CGHs) for the Application of Security in Communication System

Abstract: In this work, various images were used in place of textual information as a source to develop a secure communication system with the assist of Fraunhofer, Gerchberg-Saxton & Fresnel holographic algorithm. The communicative hologram was developed by means of adding the far-field amplitude of the main object image and reference or noise image in the Fraunhofer algorithm. The output image overlapping constraints occurred at the receiver side. This problem can be resolved by using an algorithm called the GS algorithm. GS algorithm provides an iterative approach to improve the probability of success of phase retrieval. Because of its iterative nature, this process is relatively slow. Finally, the Fresnel algorithm was used where the wave amplitude was obtained by the Fresnel diffraction formula and the hologram is calculated by the Fast Fourier Transform (FFT). Among these fast algorithms, the contrast level of the 256×256 reconstructed image in the Fresnel algorithm was 0.875, where Fraunhofer and GS algorithm returned only 0.6643 and 0.7314 respectively, and the entropy was 7.9895, which was higher than the other two. Owing to having these promising results, the proposed Fresnel algorithm can be used for security in the field of communication.