Conventional Reflector Research Articles

Reflector antenna analysis by simple photography

The performance of a conventional microwave parabolic dish reflector can be estimated from a 35 mm photo, which is taken when the dish is illuminated by a small light bulb mounted at its feed point. Both random surface errors, structural deformations and feed positioning problems can be analyzed. If only go/no go-information is needed, no optical interferometry is necessary.

Polarimetry in the Presence of Various External Reflection and Retrodirection Mirroring Mechanisms, for Chiral and Gyrotropic Media

It is well known that in bi-anisotropic media, e.g., chiral media, gyrotropic media, the polarization vector of linearly polarized waves undergoes rotation. Upon reflection, the returning waves show different effects: In gyrotropic media the rotation is enhanced, while in chiral media it is unraveled and annulled. In general, these properties are not necessarily intrinsic to the media involved but depend on the reflection mechanism, as shown below. It must be emphasized at the outset that in the present study external mirroring mechanisms only are considered, so that the reflection at the interface separating the active medium (chiral or gyrotropic) from the external domain does not enter the discussion. Strictly speaking, the effect of these interfaces cannot be ignored, except in special cases. However, where our approach is valid, it leads to a simple consistent and non-trivial picture of the effects involving returned waves in the presence of external mirror mechanisms. Inasmuch as this analysis is of importance for practical applications, e.g., in ocular glucose polarimetry measurements, and because the mathematics involved here is minimal, the subject appears to be timely and worthwhile. Two different mirror mechanisms are shown to exist: The simple, conventional mirror mechanism, henceforth referred to as "reflection", and a different mechanism referred to as "retrodirection". The simplest example for retrodirection is a wave turned around by an optical fiber. A similar retrodirection effect occurs when the wave is turned around by a set of two conventional reflectors. In non-chiral non-gyrotropic media the two categories lead to identical effects, and the distinction is superfluous. Presently we consider the effect of such reflection and retrodirection mirroring mechanisms on the total rotation of the polarization vector of a wave undergoing a round trip in chiral, and in gyrotropic media. It is shown that for the case of reflection and chiral media, the rotation is canceled, while in the presence of a retrodirecting mirror, the rotation is enhanced. For gyrotropic media we have the opposite situation: A reflector will induce enhanced rotation, while a retrodirector will cause the total rotation to vanish. Various situations are considered below, involving mirroring mechanisms. Provided we stay within the limitations of the present model, simple well-known considerations relevant to the Fresnel theory of reflection of plane waves by plane interfaces, as well as simple geometrical observations, suffice for analyzing the problems and drawing the conclusions.

Iridescent anthophyllite-gedrite from Simiuttat, Nuuk district, southern West Greenland composition, exsolution, age

AbstractGolden iridescent, <1–100 mm crystals of alternating lamellae of anthophyllite and gedrite constitute the bulk of orthoamphibolite pods within quartz-cordierite gneisses of the Akulleq terrane at Simiuttat, SW Greenland. X-ray powder diffraction powder gavea= 18.526(7),b= 17.979(15),c= 5.285(23) Å; a single crystal hasa= 18.546(7),b= 17.950(16),c= 5.280(1) Å, space groupPnmawith some reflections being notably broader than others. Spot EMPA yielded composite analyses: AlIV= 0.89–1.3, Mg/(Mg+Fe2+) = 0.57–0.61, Na/AlIV= 0.22–0.26. AFM imaging of {210} cleavage surfaces, showed a uniform corrugated morphology parallel to [001]; wavelength was 190–350 nm, mean 250 nm, amplitude 3 nm. A plan view resembles TEM images of (010)-parallel exsolution textures of orthoamphiboles. A second set of corrugations may crosscut the [001]-parallel ridges at 20–25°, akin to reported lamellar intergrowths developed parallel to both (010) and (120). Unequivocal evidence linking topography with lamellae is absent. In contrast to the conventional multi-layer reflector model, the ridged surface provides an additional origin for iridescence, acting as a diffraction grating. Included zircons, 50–10 μm, have Hf/Zr = 0.008–0.012, Hf+FeIIc. 0.16.207Pb/206Pb ages are from 2690 to 2770 Ma, averaging 2732±10 Ma. Coexisting, included Th-, La-, Ce-, Pr-, Nd-, Gd-, Y-monazites have207Pb/206Pb ages from 2680 to 2720 Ma, averaging 2707±12 Ma. The included crystals grew during a late Archaean metamorphism that produced overgrowths on zircons within gneisses to the north, but with Simiuttat grains showing a more complex history. The lamellae may have developed at the same time, or during a reheatingc. 2550 Ma, or in a subsequent Proterozoic metamorphism.

Triple corner reflector antenna and its performancein H-plane

An experimental investigation of a novel corner reflector antenna with improved performance is reported. The corner reflector antenna has been structurally modified by attaching two more reflector elements. The parameters such as the primary corner angle, position, width and angle of the secondary elements have significant effects on the H-plane radiation characteristics of the antenna. Certain symmetric configurations of this triple corner reflector (TCR) antenna provide sharp beams with a gain of the order of 3 dB over that of the conventional corner reflector (CR) antenna.

Depolarizing trihedral corner reflectors for radar navigation and remote sensing

A conventional trihedral corner reflector can be modified to present either a twist-polarizing or a circularly polarizing response by adding conducting fins of rectangular corrugations of prescribed dimensions and orientation to one of its interior surfaces. Since the modified reflector retains most of the mechanical ruggedness and ease of manufacture of the original, it is suitable for deployment in the field for extended periods as required in radar navigation and remote sensing applications. For most directions of incidence the response of the reflector is dominated by triple-bounce reflections from the interior and is a function of the size and shape of the reflecting panels, the dimensions of the corrugations, and the orientation of the reflector with respect to the radar. Experimental results show that prototype twist-polarizing and circularly polarizing reflectors respond as predicted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A curved field reflectron time-of-flight mass spectrometer for the simultaneous focusing of metastable product ions.

The ability to simultaneously focus a wide mass range of metastable fragment ions formed after the initial ionization event in a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer has been made possible by the development of a new type of ion reflector. This coaxially designed time-of-flight instrument employs a modified single stage reflector whose axial voltage gradient rises differentially in order to produce an alignment of energy focal points for product ions. In contrast, product-ion focusing in conventional constant field reflectors occurs over a broad range of distances from the reflectron exit. Approximately 90% of the product-ion mass spectrum can be collected without adjustment, thereby eliminating the need to scan the reflector voltage. Design considerations of the curved field reflectron, its calibration properties and representative metastable spectra of several peptides are discussed.

Characteristics of hydrogenated amorphous silicon alloy solar cells on a Lambertian back reflector

Hydrogenated amorphous silicon (a-Si) alloy n i p solar cells have been prepared on back reflectors exhibiting Lambertian light scattering characteristics. The Lambertian back reflector consists of highly textured Ag/ZnO films deposited on stainless-steel substrates. Contrary to expectation, the current voltage (I-V) characteristics under illumination are marginally poorer than the corresponding characteristics of cells grown on conventional back reflectors. The stabilized efficiency is similar for both cases. The dependence of the cell performance on the texture of the back reflector is discussed.

Design method for an offset dual-shaped reflector antenna with high efficiency and an elliptical beam

A newly developed method of design for a shaped reflector antenna is described. A conventional quadratic reflector configuration is assumed; the reflectors are then modified to yield the desired aperture shape and field distribution by introducing shaping functions. This method is useful for designing antennas with an arbitrary shaped beam, such as an elliptical-beam antenna, and has been verified through a 4.7 m * 2.3 m (equivalent to 3.3 m diameter) dual-band (30-20 GHz) earth-station antenna for the Japanese domestic satellite system CS. The measured aperture efficiency is more than 76%, and the ratio of the major and minor axes of the elliptical beam is 2:1. >

Bragg reflector of GaAlAs/AlAs layers with wide bandwidth applicable to light emitting diodes

Reflective spectra of the Bragg reflectors applied to GaAs infrared light emitting diodes were simulated. Bragg reflectors are composed of alternating Al0.2Ga0.8As/AlAs layers where the ratio of high- and low-refractive indices is as small as 1.16. The reflectance bandwidth can be broadened by employing chirped structures where the optical thicknesses of the respective layers are changed arithmetically. On the other hand, for chirped Bragg reflectors, resonant reflection drops appeared at some wavelengths. These drops can be corrected by inserting periodic alternating layers. The reflectance band of 80% reflectivity is 2.7 times as wide as that of the conventional reflector of the periodic sequence in the case of 66 layer stack.

High solar performance selective surface using bi-sublayer cermet film structures

Numerical modelling calculations have been used to design solar selective absorbers with new cermet film structures, composed of two cermet sublayers, each having a different metal volume fraction, located between a conventional metal reflector and a dielectric anti-reflection layer. These selective surfaces may use a variety of practical cermet materials and all achieve better solar thermal performance than any published results. For example, our best predicted ratio of absorptance to normal emittance α/e at room temperature is 46 for a CuSiO2 cermet. The best experimental result of α/e at room temperature is also 46 for the same cermet. From a computer optimazation using published experimental dielectric functions of CoAl2O3 cermets, we clearly show improved performance is obtained by using two cermet layers rather than one. For example, an absorptance of 0.90 and normal emittance of 0.024 at 50°C (α/e = 37) could be obtained for a film composed a two cermet sublayers on a Mo reflector with an Al2O3 antireflection layer. For an optimized low emittance double cermet coating, hemispherical emittance at 350–400°C is very close to hemispherical emittance at room temperature.

チャープ状ブラッグ反射層の反射特性について

Reflective spectra of Bragg reflectors composed of alternating AlGaAs/AlAs layers were simulated. The band width of high reflectivity can be broadened by employing chirped structures where the optical thicknesses of the respective layers are changed continuously around a quarter wavelength. On the other hand, for chirped BRs, decreases in the reflective spectra appeared at some wavelength(s). These decreases are avoided by inserting conventional Bragg reflectors composed of several pairs of layers. The band width of more than 300nm was realized for reflectivity which exceeds 70%. This is three times wider compared with the non-chirped structure. The simulated results show good agreement with experiments.

Theory of phase-conjugate oscillators II

This paper is the second in a series describing propagation of electromagnetic radiation in phase-conjugate oscillators. We apply the formulation developed in the first paper to study the phase-conjugate resonator (PCR) and the Fabry–Perot cavity with an intracavity phase-conjugate mirror (PCM). Our results show that nondegenerate oscillation occurs in the PCR for large parametric gains and fixed separation between the conventional reflector and the PCM. The bandwidth is considerably reduced from that of a PCM alone. In the phase-conjugate oscillator, oscillation will occur at the pump frequency only if there is no separation between the conventional mirrors and the phase-conjugate element and if the nonlinear medium fills the entire Fabry–Perot cavity.

Computation and Optimization of Beam Efficiency for Reflector Antennas*

ABSTRACT This paper presents several topics on the beam efficiency of a reflector antenna. (i) A simple definition for the “main beam” is suggested for calculating beam efficiency. This definition is related to the reflector aperture diameter, but is independent of the feed edge taper. Use of this definition allows a fair comparison of beam efficiencies due to different feeds to be made. (ii) Physical optics theory does not conserve power. Therefore conventional reflector pattern computation methods based on PO can calculate beam efficiency only within 2% to 3% accuracy. A method for calibrating out this PO error is described. (iii) Beam efficiency curves are presented for typical parabolic reflectors fed by open-ended circular cylinder waveguide feeds. While directivity is optimized by a 10 dB edge taper, beam efficiency is optimized for a higher edge taper of over 20 dB. (iv) Beam efficiency curves for cases in which the beam is scanned off-axis are presented. (v) A cluster feed is utilized to improve b...

Uniform isotropic emission from an aperture of an involute reflector.

Directional emission characteristics of various reflectors are compared by ray tracing analysis taking into account the directional reflectivity of mirror surfaces. For the case of a perfect reflector surface, the aperture of an involute reflector has an isotropic uniform distribution of radiant intensity. The hemispherical emissive power and directional radiant intensity of the involute reflector for metallic surfaces are slightly lower than the values for the ideal case. The distributions of emissive power and directional radiant intensity of conventional reflectors are signgficantly nonuniform compared with those of the involute reflector.

Equivalent circuit model for positive/negative reflection—type SAW reflectors

AbstractAn analysis method is proposed herein which uses an equivalent circuit model as a means to evaluate positive/negative reflection‐type (PNR) SAW reflectors. The PNR reflector consists of reflecting elements which have 180° phase difference (positive and negative reflection coefficients). Each element is spaced with a period of one‐quarter wavelength. Compared with the conventional reflectors, these new reflectors have larger reflection‐efficiencies. In this paper, an equivalent circuit model for the PNR reflectors is presented. Circuit parameters can be determined theoretically by applying the finite‐element method to an infinite array. Examples are computed for two kinds of PNR reflectors on 128° Y‐X LiNbO3 or ST‐X quartz substrate. For each of them, we determined the circuit parameters and analyzed the reflection characteristics. We obtained good agreement between theoretical and experimental results.

Analysis of finite periodic waveguides for elastic waves using finite‐element method

AbstractA solution based on a finite‐element method is proposed for calculation of the reflection and transmission characteristics of a finite periodic waveguide for elastic waves. Although finite‐element methods have already been applied to the discontinuity problem in an acoustic waveguide, it has not been possible due to excessive computation time and memory requirement to apply directly the finite‐element method to many discontinuities such as a periodic acoustic waveguide. In this paper, formulations have been undertaken with the substructure which is a related technology of the finite‐element method. Hence, the finite‐element method can be applied directly to all the discontinuities. As a result, in the finite periodic waveguides for acoustic waves, the mutual interaction of the surface wave and the bulk wave can be taken into account over all the discontinuities. The present method has been applied to a groove‐type grating reflector and the validity and effectiveness of the method has been confirmed by comparison with experimental results. An analysis has also been carried out for the positive and negative reflection‐type reflector proposed recently in which the grooves and ridges are combined. It has been confirmed numerically that this reflector has a larger reflection coefficient and smaller bulk wave conversion loss than the conventional reflector.

Beam scanning characteristics of front fed offset cassegrain–type multibeam antenna

AbstractThis paper shows theoretically and experimentally that the front‐fed offset Cassegrain (FFOC) antenna is suited as a multi‐beam antenna to be borne on an international satellite. First, the problems are identified for conventional reflector configurations. Then the beam deflection characteristics are shown numerically in the case where an FFOC reflector surface is used as a multibeam antenna. The performance of the test antenna is confirmed experimentally. From the measured results of a test antenna of 120 wavelengths, it is found that the reduction of the gain in the beam deflection within a circle of the visible radius of 10° is less than 1.8 dB which agrees well with the computed results. The cross‐polarization level is less than‐34 dB. Because the cross‐polarization component generated by the primary radiator is −40 dB, the cross polarization generated by the reflector system is quite small.

Energy characteristics of a laser with a wavefront-reversing mirror utilizing a degenerate four-wave interaction in a medium with a local response

The output characteristics of a laser are calculated for the case of a frequency-degenerate four-wave interaction of light in media with a local nonlinearity. Nonmonotonic dependences of the output radiation intensity on the interaction constant are predicted, as well as the existence of regions of bistable and multistable solutions. The results are generalized to the case of a resonator formed by a four-wave mirror and a conventional reflector, and filled with an additional active medium.

A surface acoustic wave resonator on a LiTaO3 substrate and its application to video tape recorder oscillators

AbstractAn oscillator using a surface acoustic wave resonator is capable of directly generating fundamental frequencies in the region beyond VHF. In this paper, a surface acoustic wave resonator using a reflector consisting of aluminum ridges on a LiTaO3 substrate is studied. It is shown that this resonator exhibits a high Q with smaller chip size and has better frequency reproducibility than conventional reflectors on quartz and LiNbO3. A surface acoustic wave resonator having a suitable resonance circuit is designed, using experimental data and results of one analysis of the resonance conditions of the resonant circuit.Finally, a surface acoustic wave resonator suitable for an RF converter IC is designed for application to the oscillator of video tape recorder and is evaluated. the resultant video tape recorder resonator has good reproducibility, suitable for mass production.

Anti‐fading polygonal cylinder passive repeater

AbstractFor economical construction of general microwave communication channels passive repeaters are used. Effective improvement in avoiding momentary interruptions cannot be expected unless measures are adopted to prevent fading at passive repeaters and space diversity is employed at the antenna side.The radiation field of an aperture type antenna is represented by the product of the amplitude distribution and the phase distribution of the field at the aperture. Amplitude distribution has been the main area considered in analyses to date. This paper discusses a method for controlling the phase distribution and shows that this method is best suited to prevent fading. the method modifies the shape of a conventional flat reflector excited by plane waves into a polygonal cylinder which inscribes a shallow parabolic cylinder, so that a near‐axis directional beam is formed in even the direction of the first null point of the reflected waves. the level at the first null point of a polygonal cylindrical reflector designed to keep the gain reduction directly on the axis below about 1 dB agrees well with the predicted mean field intensity due to fading at a receiving point. the use of a polygonal cylinder reflector is economical and prevents momentary interruptions due to fading so that the communication channels remain stable and possess high quality with improved reliability.