Longitudinal slot with changing width cut in rectangular waveguide

The problem of excitation and radiation of the array of narrow circumferential or arc transverse slots cut in the infinitely thin and perfectly conducting coaxial line screen has been solved by the magnetomotive forces method (MMF) in this paper. The frequency-energy and spatial characteristics of these systems are calculated taking into account the internal and external space interconnections between the radiators on conditions of arbitrary location of the slot elements when internal and external spaces have been filled by the dielectric for any values of permittivity. The results of calculation and analysis of the amplitude and phase distributions in the slot arrays, directional and energy antenna characteristics depending on the working wavelength in cases of the slot element location on the infinite or semi-infinite coaxial lines have been proposed.

Distributions of amplitude and phase for bivariate distributions

For of applications of waveguide-slot antennas, it is important to know the radiation characteristics of the slot in a rectangular waveguide wall radiating into a parallel-plate waveguide (PPW). In this work the properties of a longitudinal slot in the narrow wall of a rectangular waveguide radiating into a PPW are investigated. A model of a waveguide-slot radiator is presented and an accurate mathematical analysis provided. It is shown how to improve and optimize the matching of the considered radiators.

Rectangular waveguide slot arrays are commonly used in several microwave antenna systems. The slots are most often located in the broad wall of the rectangular waveguide, arranged longitudinally parallel with the waveguide axis, because this provides good control of the excitation of each slot over a large dynamic range by adjusting the offset of the slot from the center line of the waveguide. However, longitudinal slots can only radiate electrical fields that are transversely polarized with respect to the waveguide axis. If longitudinal (or dual) polarization is required, the slots (or half of them) must be located transverse to the waveguide axis. Transverse resonant slots in the broad wall are too strongly excited for use in large arrays, so transverse narrow slots in the narrow wall are preferred. In the latter case the slots are not excited unless they are tilted or coupled to tilted parasitic elements like wires or posts inside the waveguide. The purpose of the present paper is to analyse an untilted narrow wall slot excited by two tilted wires. An improved and extended analysis in which the slot extensions into the neighboring two broad walls are included, is described. The virtual cylinder method is applied to the calculation of the external admittances of the slot using wedge dyadic Green's functions and entire-domain basis functions in order to get good convergence of the integrals of the spectral domain formulations.

The problem of electromagnetic waves radiation by a longitudinal slot in the broad wall of a rectangular waveguide is solved. The slot is radiating into half space above a perfectly conducting plane in the presence of two passive vibrators (monopoles) having variable distributed surface impedance in the space above the plane.

We inv estigate the problem in which a volume hologram is produced by two waves of arbitrary amplitude and phase distribution (the only restriction being that they must obey the rules of geometrical optics), and the developed hologram is illuminated by one of the waves having the same phase distribution but not necessarily the same amplitude distribution. Coupled partial differential equations are derived and solved in the form of an infinite series valid for both transmission and reflection holograms. For transmission holograms a simple approximate solution is given for the amplitude of the reconstructed wave in the immediate vicinity of the input surface.

Diffractive optical elements able to generate on-axis (zero-order) phase as well as amplitude distributions are described. The proposed elements are surface-relief plates, that is phase-only elements, that are based on concepts of computer-generated masks followed by lithographic and etching processes. The proposed encoding method assumes variable spatial partitioning of the cell and a fixed phase value allocated to each subcell. This method requires the minimal number of etching levels needed for full representation of the wave front, that is three, but can be applied with improved efficiency using more etching levels. The reconstructed amplitude and phase distributions contain some noise owing to the encoding process. Discussion of the error sources is given.

The feasibility of using a Kerr magneto-optic-effect display as the input to a coherent optical computer is discussed and experimentally verified. Simple amplitude and phase distributions were generated on a continuous ferromagnetic thin film and their Fourier transforms were displayed with a lens. An experiment was performed demonstrating spatial filtering of a magneto-optically generated amplitude distribution. Magneto-optic generation of more complicated amplitude distributions requires a matrix-type thin-film structure and this input must be treated as sampled data.

A compact quadriwave lateral shearing interferometer (QWLSI) with strong adaptability and high precision is proposed based on a novel randomly encoded hybrid grating (REHG). By performing the inverse Fourier transform of the desired ±1 Fraunhofer diffraction orders, the amplitude and phase distributions of the ideally calculated quadriwave grating can be obtained. Then a phase chessboard is introduced to generate the same phase distribution, while the amplitude distribution can be achieved using the randomly encoding method by quantizing the radiant flux on the ideal quadriwave grating. As the Faunhofer diffraction of the REHG only contains the ±1 orders, no order selection mask is ever needed for the REHG-LSI. The simulations and the experiments show that the REHG-LSI exhibits strong adaptability, nice repeatability, and high precision.

The paper presents investigations on the mutual impedance between two slots placed in close proximity. An analytical expression for the mutual impedance between two parallel longitudinal resonant slots in the broad wall of a rectangular waveguide is derived from the reaction of the magnetic field due to one of the slots, with the magnetic current exciting the other slot and with discontinuities in modal currents due to the two slots. The method of analysis is of general applicability. In the case under investigation, both slots are active, and a method for the experimental determination of mutual impedance between two active slots is presented. The values of mutual impedance computed from the theoretical formula are in good agreement with those obtained experimentally.

The problem of scattering of electromagnetic waves from cavity-backed apertures (CBAs) has received considerable attention. Single elements with resonant cavities have been investigated by a number of authors. A thin, cylindrical conducting screen with a longitudinal slot is a simple case of a two-dimensional CBA. An efficient solution to the problem of scattering from the slotted cylinder with a circular cross-section has obtained by using a rigorous approach based on the solution to the Riemann-Hilbert problem in the theory of functions of complex variables. The paper shows that the occurrence of the superdirectivity can be attributed to the excitation of modes that induce a phase reversal in the adjacent scatterers, and that the amplitude distribution also plays an important role. It demonstrates that a moderately high superdirective antenna can be achieved by using passive scatterers formed by resonant elements. It shows how the mutual coupling between the elements can be exploited to generate and control the desired phase and amplitude behavior of the near field that lead, in turn, to the superdirectivity in the radiated field. Since all the elements of the scattering array are entirely passive, it is somewhat remarkable that such a structure would generate a superdirective behavior. Representative numerical results are presented to illustrate the performance of superdirective arrays.

Crystalline materials are not perfectly ordered periodic structures but present obvious disordered characteristics, which determine their intrinsic properties. Halide perovskites typically consist of ordered and disordered phases due to continuous octahedral rotations among the α, β, and γ phases. However, unraveling the spatial phase distribution requires a real-space imaging method with sufficient resolution. Here, we apply low-dose electron microscopy to study the rotation angle phase distribution in perovskites and reveal the factors affecting the phase structure and spatial distribution. Phase structures can be quantified by measuring the rotational angles of octahedra atomically. Then, we investigate how crystal size, temperature, surface, and interface structures affect the spatial phase distribution. These results provide local structural information about the phase distribution in halide perovskites for further applications and provide crucial insights into the ordered and disordered nature of crystalline materials in real space.

Continuous-wave off-axis and in-line terahertz digital holography with phase unwrapping and phase autofocusing

This paper proposes a novel hybrid antenna configuration, which combines two kinds of high-performance antennas, i.e., reflectarray and transmitarray, creating a low-profile low-cost low-mass design with both amplitude and phase distribution controls. In this hybrid arrangement, a flat Cassegrain reflectarray, with compact ring focus, is implemented as the feed to illuminate the upper transmitarray. In the process of reflectarray design, the particle swarm optimization technique is utilized to synthesize the phase distribution on the reflectarray aperture to generate a desired amplitude distribution on the upper transmitarray aperture. During the transmitarray design process, the dimensions of the double-loop elements of the upper transmitarray are adjusted to compensate for the phase delay of the wave from the lower reflectarray and form a desired phase distribution on the transmitarray aperture. A detailed design procedure for a Cassegrain-reflectarray-fed transmitarray antenna with a small focus-to-diameter ratio of 0.3 is presented. The simulated and measured results demonstrate that the hybrid-configuration antenna can achieve an aperture efficiency of around 40%.

The theoretical resonant length and experimental normalized conductance of inclined slots are applied in the design of an X-band edge slot waveguide array antenna over the frequency range of 9.5 to 10.5 GHz. The array consists of eight radiating slots machined in the narrow wall of a WR90 waveguide. The array has a non-uniform amplitude distribution with all of the elements fed in-phase. Since the array consists of only eight elements, each element contributes significantly to the overall antenna's characteristics. Experimental results of the measured slot conductances and a formula for the slot depth, including the waveguide wall thickness, for any slot orientation less than 46.6/spl deg/ is presented. This data was used to determine the amplitude distribution and configuration for each element of the array. Measured radiation patterns are presented and characteristics of the antenna examined.