Synthesis and analysis of a frequency-scanned planar waveguide array focused in the Fresnel zone

A 2D array of radiators excited by the modes of a planar array of parallel waveguides and focused in the Fresnel zone is considered. The problem of determining the positions of array radiators for focusing the field at a finite distance from the array aperture is solved for the cases of plane and cylindrical fronts of the initial distribution of the phases of waveguide modes. A phenomenological model of the slotted-waveguide array is used to determine the position of the focal line, the aberration of the scattering spot, and the frequency scanning sector.     

Offset Fresnel zone plate antennas

The theory of offset Fresnel zone plate antennas is presented. Explicit formulae for the design of the zone boundaries for the offset Fresnel zone plate are given. Theorectical equations and numerical results for the far-field analysis are presented. It is found that when the offset angle increases, the zone boundaries become more elliptic and the plate becomes more asymmetric in the E-plane. With the number of full wave zones and the plate width in the W-plane fixed, the plate width in the E-plane increases with the offset angle, which keeps the projected aperture area constant. Within a limited range of offset angles, the offset configuration can be employed without degrading the radiation performance much. For large offset angles, however, the asymmetry of the configuration may lead to increased sidelobes and decreased antenna directivity. An experiment with one particular phase reversal zone plate antenna with 30° offset angle shows good agreement between the measured antenna pattern and the theoretical prediction.     

A cylindrical Fresnel zone antenna

A cylindrical Fresnel zone antenna as a candidate for a base station in wireless indoor LAN systems is described. An arbitrary angle-tilted fan beam in azimuth can be achieved by moving the position of the strip dipole feed at the cylinder center. A simple theory based on the diffraction integral is developed which predicts the antenna radiation characteristics. The antenna fabrication and measurement are carried out at 9 GHz with good agreement between calculated and measured results     

Signal delay characteristics of the measuring repeater unit operating in the Fresnel zone

A modification of the numerical technique for calculating the field and delay of the signal reflected by a flat reflector and based on the Fresnel-Kirchhoff equation of the diffraction scalar field has been proposed. The relationships taking into account the size of antennas and reflector as well as changes of the amplitude and phase characteristics of repeater channels were obtained. It was shown that the signal delay characteristics in the Fresnel zone depended on the size of reflector shifting with the signal delay variations.     

Focusing characteristics of curvilinear half-open Fresnel zone plate lenses: plane wave illumination

A diffraction field-focusing equation based on a specific conical-segment linearization procedure is derived for the Fresnel zone plate (FZP) lens of arbitrary curved profile and is applied for contrasting plane, spherical, parabolic and conical zone plate lenses, convex-side illuminated by a paraxial plane wave front. Two sets of 100-GHz curvilinear and plane FZP lenses are studied numerically with regards to their dimensions, axial focusing intensity and footprint, and frequency bandwidth. For the first set , where the curvilinear and plane lenses share a common lens base aperture and have equal focal lengths, the following new finding has resulted: regardless of their different in shape profiles the FZP lenses have equal zone numbers and produce similar axial focusing. The second set also consists of plane, spherical, parabolic and conical lenses. They share a common apex, and have equal in diameter base apertures and focal lengths but different thicknesses. For such disposition and proportions, the FZP lenses possess different zone numbers and focusing parameters (gain, efficiency, footprint and bandwidth). The belief that the curvilinear FZP have superior (or inferior) electromagnetic characteristics, compared to those of the plane FZP lens with equal number of zones is not in general true. Their relative focusing qualities can vary significantly depending on the lens positioning and dimensions.     

Synthesis and analysis of a planar waveguide array with two-dimensional frequency scanning focused in the Fresnel zone

A 2D array of radiators with raster frequency scanning focused in the Fresnel zone is presented. The problem of determining the radiator positions for field focusing at a finite distance from the array plane is solved. An approximate matrix model of the array antenna describing its properties as a microwave multiport and allowing determination of the distribution of radiation sources in the array aperture is proposed. The problem of improvement of the array matching in scanning ranges is considered. An approximate model describing radiation from the array is built. This model is used for determining the position and shape of the scanning surface and the field distribution inside the focal spot as well as for the analysis of the dynamics of the field maximum in the frequency scanning sector.     

Fresnel zone plate antennas at millimeter wavelengths

The performance characteristics of Fresnel zone plates are described with emphasis on applications at millimeter wavelengths. Recent results are included along with a summary from numerous earlier investigations. Parameters described include design information, efficiency, bandwidth, focal characteristics, off-axis performance, axial intensity dependence, aberrations, and far-field pattern. Both transmission and reflection configurations are discussed, mostly for cases where the focal length and diameter are comparable. This type of zone plate has advantages (compared to a lens or paraboloid) of reduced loss, weight, volume, and cost, as well as simple planar construction, with similar diffraction-limited beamwidth and major sidelobe performance, but lower efficiency.     

相位差异的三反光学系统波前传感技术

分析了基于相位差异（Phase Diversity,PD）的波前传感技术的基本原理,针对该技术的目标函数自变量多、非线性程度较高等特点,提出基于遗传算法（Genetic Algorithm,GA）的改进相位差异技术。在传统目标函数的基础上增加了Tikhonov 正则项,提高了算法的稳定性和收敛效率;对光学系统利用PD 技术波前检测的噪声适应性进行了仿真分析;模拟了不同波前离焦量对检测精度的影响,获得最优的波前离焦相位值并应用于检测实验;利用PD 技术分别对离轴三反光学系统的中心视场和边缘视场进行波前检测,并将解算得到的Zernike 系数和波前图分别与干涉检验的结果进行对比。实验结果表明:相位差异技术与干涉检验的偏差小于0.013（RMS）,其检测精度满足工程需求。     

Array of hexagonal Fresnel zone plate lens antennas

An array of overlapping single-zone hexagonal Fresnel zone plate lens antennas was designed and tested at 30 GHz. By arraying smaller-diameter lenses, a significantly lower overall profile can be achieved compared to a single lens of equivalent diameter. These arrays can also find use in spatial power combining or in imaging applications.