Performance of hemielliptic dielectric lens antennas with optimal edge illumination

The role of edge illumination in the performance of compact-size dielectric lens antennas (DLAs) is studied in accurate manner using a highly efficient algorithm based on the combination of the Muller boundary integral equations and the method of analytical regularization. The analysis accounts for the finite size of the lens and directive nature of the primary feed placed close to the center of the lens base. The problem is solved in a two-dimensional formulation for both E- and H-polarizations. It is found that away from internal resonances that spoil the radiation characteristics of DLAs made of dense materials, the edge illumination has primary importance. The proper choice of this parameter helps maximize DLA directivity, and its optimal value depends on the lens material and feed polarization. Index Terms: Beam collimation, dielectric lens antenna, directivity improvement, edge illumination, edge taper, hemielliptic lens.Comment: 5 pages, 9 figure

Design considerations for the beam-waveguide retrofit of a ground antenna station

Retrofitting an antenna that was originally designed without a beam waveguide introduces special difficulties because it is desirable to minimize alteration of the original mechanical truss work and to image the actual feed without distortion at the focal point of the dual-shaped reflector. To obtain an acceptable image, certain Geometrical Optics (GO) design criteria are followed as closely as possible. The problems associated with applying these design criteria to a 34-meter dual-shaped DSN (Deep Space Network) antenna are discussed. The use of various diffraction analysis techniques in the design process is also discussed. GTD and FFT algorithms are particularly necessary at the higher frequencies, while Physical Optics and Spherical Wave Expansions proved necessary at the lower frequencies

Radar cross section studies

The ultimate goal is to generate experimental techniques and computer codes of rather general capability that would enable the aerospace industry to evaluate the scattering properties of aerodynamic shapes. Another goal involves developing an understanding of scattering mechanisms so that modification of the vehicular structure could be introduced within constraints set by aerodynamics. The development of indoor scattering measurement systems with special attention given to the compact range is another goal. There has been considerable progress in advancing state-of-the-art scattering measurements and control and analysis of the electromagnetic scattering from general targets

Numerical analysis and synthesis of 2D quasi-optical reflectors and beam waveguides based on an integral-equation approach with Nystrom's discretication

Cataloged from PDF version of article.Considered is the beam wave guidance and scattering by 2D quasi-optical reflectors modeling the components of beam waveguides. The incident field is taken as the complex-source-point field to simulate a finite-width beam generated by a small-aperture source. A numerical solution is obtained from the coupled singular integral equations (SIEs) for the surface currents on reflectors, discretized by using the recently introduced Nystrom-type quadrature formulas. This analysis is applied to study what effect the edge illumination has on the performance of a chain of confocal elliptic reflectors. We also develop a semianalytical approach for shaped reflector synthesis after a prescribed near-field pattern. Here a new point is the use of auxiliary SIEs of the same type as in the scattering analysis problem, however, for the gradient of the objective function. Sample results are presented for the synthesis of a reflector-type beam splitter. © 2007 Optical Society of Americ

Interactive raytraced caustics

technical reportIn computer graphics, bright patterns of light focused onto matte surfaces are called ?caustics?. We present a method for rendering dynamic scenes with moving caustics at interactive rates. This technique requires some simplifying assumptions about caustic behavior allowing us to consider it a local spatial property which we sample in a pre-processing stage. Storing the caustic locally limits caustic rendering to a simple lookup. We examine a number of ways to represent this data, allowing us to trade between accuracy, storage, run time, and precomputation time

Photoacoustic Microscopy and Photoacoustic Computed Tomography Using High-frequency Linear Array Ultrasonic Transducers

Photoacoustic tomography (PAT) is a highly promising imaging technology which forms images by detecting the induced pressure waves resulting from pulsed light absorption in biological tissues. Because the excitation source is light, PAT is a very safe, non-ionizing, and non-carcinogenic imaging technology. In biomedicine, PAT has the unique advantage of probing endogenous optical absorbers at different length scales with 100% relative sensitivity. With such scalability, PAT can image anatomical, functional, metabolic, molecular, and genetic contrasts of vasculature, hemodynamics, oxygen metabolism, biomarkers, and gene expression. Among several implementations of PAT, optical-resolution photoacoustic microscopy (OR-PAM) and photoacoustic computed tomography (PACT) are two of the most widely used. OR-PAM can achieve optical diffraction limited spatial resolution with maximum imaging depths up to one transport mean free path (~1 mm in biological tissue). PACT can achieve several centimeters imaging depth in tissue by employing ultrasonic array detectors and inverse algorithms. This dissertation aims to improve the functionality of OR-PAM using a high-frequency linear ultrasonic array, and to advance the performance of linear-array PACT to full view angle capability and higher resolution. The first part of this dissertation describes the technological advancement of multifocal optical-resolution photoacoustic microscopy (MFOR-PAM). Compared with single-focus OR-PAM, 1D multifocal OR-PAM utilizes both multifocal optical illumination and an ultrasonic transducer array, significantly increasing the imaging speed. We present a reflection-mode 1D multifocal OR-PAM system based on a 1D microlens array that provides multiple foci as well as an ultrasonic transducer array that receives the excited photoacoustic waves from all foci simultaneously. Using a customized microprism to reflect the incident laser beam to the microlens array, the multiple optical foci are aligned confocally with the focal zone of the ultrasonic transducer array. Experiments show the reflection-mode 1D multifocal OR-PAM is capable of imaging microvessels in vivo, and it can image a 6 × 5 × 2.5 mm3 volume at 16 μm lateral resolution in ∼2.5 min, limited by the signal multiplexing ratio and laser pulse repetition rate. While 1D-MFOR-PAM accelerates the scan in only one direction, a two-dimensional MFOR-PAM (2D-MFOR-PAM) fully explores the advantage of a 2D microlens array. By scanning a small range of 250 mm × 250 mm, we eventually obtained a large field of view of 10 mm × 10 mm in ~50 seconds, with a spatial resolution of 15.2 mm. The second part of this dissertation describes methods of increasing the view angle of linear-array PACT, which suffers from a limited view. While rotating either the transducer array or the imaging objects circularly enables full-view linear-array PACT, this process is time consuming. Here we propose two innovative methods to increase the view angle. The first method is to triple the detection view angle by using two planar acoustic reflectors placed at 120 degrees to each other. Without sacrificing the imaging speed, we form two virtual linear transducer arrays, adding two vantage points. Experimental results show the detection view angle of the linear-array PACT was increased from 80 to 240 degrees. The second method is an ultrasonic thermal encoding approach that is universally applicable to achieve full-view imaging with linear-array PACT. We demonstrate full-view in vivo vascular imaging and compare it to the original linear-array PACT images, showing dramatically enhanced imaging of arbitrarily oriented blood vessels. The last part of the dissertation describes the development of algorithms for linear-array PACT. The first proposed algorithm is a multi-view Hilbert transformation, which provides accurate optical absorption for full-view linear-array PACT. A multi-view high-frequency PACT imaging system was implemented with a commercial 40-MHz central frequency linear transducer array. By rotating the object through multiple angles with respect to the linear transducer array, we acquired full-view photoacoustic pressure measurements. The in-plane spatial resolution of this full-view linear-array PACT was quantified to be isotropically 60 mm within a 10×10 mm2 field of view. The system was demonstrated by imaging both a leaf skeleton and a zebrafish in vivo. The second algorithm is an inverse linear Radon transformation (ILRT), which allows linear-PACT to achieve isotropic resolution at all depth planes. Images of microspheres acquired by inverse linear Radon transformation PACT (ILRT-PACT) demonstrate that our technique improves the elevational resolution by up to 9.4 times over that of a single linear scan. The technique is further demonstrated through in vivo imaging of the mouse brain through an intact scalp

Holography Measurement for Crossed-Dragone Type Telescope & its Application to the Fred Young Submm Telescope

Microwave Holography is an accurate and efficient method for measuring the surface shape of large reflector antennas. The method is based on the Fourier transform relationship between the antenna's far-field diffraction beam pattern and its aperture field. Measuring the antenna's far-field beam both in amplitude and phase can deduce the aperture field distribution. The phase deviations of the aperture field are directly related to the antenna's surface shape. This technique has become a well-established method for surface metrology of large radio telescopes because of its high efficiency and measurement accuracy. However, employing the traditional holography cannot identify the surface deformity in a 'two-reflector' antenna system. This thesis investigates a new multi-map holography metrology to overcome this limitation. The new method is developed to align the Fred Young Sub-millimeter telescope (FYST), a coma-corrected Crossed-Dragone antenna with two 6-m off-axis reflectors. The surfaces of the two reflectors must be aligned to be better than 10.7um. The multi-map holography identifies the surface errors between the two reflectors by taking five holographic beam measurements by placing the receiver at well-separated points in the focal plane. The parallactic shift of the surface errors allows assigning them to either one of the two mirrors. A new data processing technique is developed using an inference technique to simultaneously analyze the five beams and convert them to two surface error maps. Extensive numerical simulations have been carried out to check the feasibility, measurement accuracy, and optimum set-up of the new holographic system by modeling the systematic errors in the system, such as random instrument noise and fluctuation of performance of the instruments. These indicate that a measurement accuracy of ~2um is achievable. The critical part of the data processing technique of the 'Multi-map' holography is to develop a fast and accurate beam simulation algorithm. The conventional physical optics method is very time-consuming for analyzing the FYST antenna. A new 'two-step' Kirchhoff-Fresnel diffraction method is developed, which, compared to the conventional physical optics analysis, can reduce the computational time by four orders of magnitude without noticeable accuracy degradation. The new multi-map holography and its data processing technique are implemented to measure the reflector errors for a 0.4-m diameter Crossed-Dragone antenna in the laboratory. The experiments prove that the errors on the two reflectors can be discriminated and accurately measured with a statistic error lower than 1um. The holographic measurements and reflector corrections also indicate that the large spatial errors existing on the two reflectors also can be measured

A Discrete Radiosity Method

International audienceWe present a completely new principle of computation of radiosity values in a 3D scene. The method is based on a voxel approximation of the objects, and all occlusion calculations involve only integer arithmetics operation. The method is proved to converge. Some experimental results are presented

Transformers for Lunar Extreme Environments: Ensuring Long-Term Operations in Regions of Darkness and Low Temperatures

This report shows how solar power could enable robotic operations in permanently shaded regions at lunar poles, to extract water ice and further produce liquid hydrogen and oxygen (LH2/LO2) propellant. The power needs are derived from an Architecture for Human Exploration of Mars based entirely on lunar propellant. The extraction of 10 metric tons of water per day (at 10% water in regolith) requires approx. 0.6 MW thermal power. Additional approx. 2 MW electric power are required to produce 7.5 metric tons of LH2/LO2 propellant per day, as needed by the architecture. To provide power to processing equipment inside Shackleton Crater, optimal locations are determined on the crater rim, from which several reflecting TransFormers (TFs) would redirect sunlight, achieving a combined period of illumination of approx. 99% of the year. A single 40-m diameter reflector could provide up to 1 MW solar power. Inflatable rigidizable tower support structures raise reflectors above ground for better solar exposure. There are trade-offs: e.g., two reflectors at ground level would provide the same combined total illumination as a single tower approx. 100-m tall. Such a TF based on a 100-m tower made with inflatable 2-m beams and 40-m diameter reflectors would be of similar dimensions as an MSL-class rover (approx. 1000 kg, 10 m(exp 3)). A TF-prospector rover combo could be designed and deployed in a Discovery-class mission searching for water. The TransFormers would be nodes of a Lunar Utilities Infrastructure that provides solar power year-round in the proximity of the pole, as well as local data transmission andintermittent direct to earth communications. This infrastructure would be instrumental infacilitating the development of a lunar economy