Geometric modeling and analysis of large latticed surfaces

The application of geometrical schemes, similar to geodesic domes, to large spherical antenna reflectors was investigated. The shape and size of flat segmented latticed surfaces which approximate general shells of revolution, and in particular spherical and paraboloidal reflective surfaces, were determined. The extensive mathematical and computational geometric analyses of the reflector resulted in the development of a general purpose computer program capable of generating the complete design parameters of the dish. The program also includes a graphical self contained subroutine for graphic display of the required design

2-D Ray-Tracing Model for Multilayer Dielectric Dome Arrays With Inner Reflections

The application of lenses combined with array antennas (also known as dome arrays or dome antennas) to the next generation of terrestrial and satellite communication systems brings a wide range of advantages in terms of improved radiation performance, reconfigurability in the use case, and reduction in power consumption. To facilitate the industrial implementation of dome antennas, highly efficient simulation tools are required. In this paper, we present a streamlined implementation of ray tracing for fast and efficient numerical analysis of the far-field radiation performance of 2D multilayer dielectric lenses combined with phased arrays. Unlike commercial physical-optical methods, our proposed ray-tracing method is capable of computing the effects of internal reflections in the dome in a multilayer configuration. In addition, the method estimates the absorption losses as a result of the Joule effect. To demonstrate the effectiveness of the proposed approach, we provide comparisons of the simulated radiation patterns using our proposed ray tracing with the results obtained from commercial full-wave simulation tools

The Four-Minute Warning Drawing Machine: revealing the assemblages of nuclear deterrence

Ph. D. ThesisThis research sets out to use art practice as a critical method to make the social and cultural production of nuclear weapon systems visible in everyday life experience. The research draws upon a critical framework based on new materialist philosophies that see reality as composed of interacting “machinic” assemblages of affects and more-than-human relationships (DeLanda 2015). These philosophies position active processes, such as artmaking, as tacit ways of making visible “the concrete yet complex materiality of bodies immersed in social relationships of power” (Braidotti 2015), which are otherwise invisible to fixed representational ontology. The artworks that have emerged establish entwined relationships between nuclear weapon manufacture and artmaking by making commonalities between workshop configuration, administrative processes and transportation. Insight has also been drawn from immersive work within the Cold War archives at RAF Fylingdales as the station’s – and the RAF’s – first artist in residence. Unprecedented access was given to the site, which reveals the ballistic missile early warning station’s interconnectivity beyond its barbed wire perimeter. These relationships have been conceptualised as the four-minute warning drawing assemblage comprising interactive social parts that include drawing practices and instruments of deterrence, constantly producing new techno–social worlds and novel arrangements of life beyond normative perception. In doing so, the research makes a contribution to new and urgent debates about nuclear weapons and the emerging risk of nuclear war by providing different and innovative ways of thinking about society and our relationships to the bomb

Unique Two-Way Field Probe Concept Utilizing a Geodesic Sphere and Quad-Rotor

Surveying the test volume of a radar range normally involves utilizing an antenna field probe to measure the electromagnetic field in that volume of space. Today, field probes vary in size and shape and can be difficult and time consuming to setup. They also have a limited range of motion due to their support structure and translational mechanism, which also has scattering mechanisms that can perturb the field they are measuring. Field probes are useful, but because of these shortcomings they can provide limited characterization of the field illuminating the measurement area. Leveraging quad-rotor technology, coupled with a two-way probe concept, will provide the flexibility and maneuverability to easily transverse the test volume without the interfering supporting structures. The two-way probe concept characterizes the illuminated field indirectly, by utilizing a geodesic sphere to encompass a quad-rotor and shield its many scatterers, which in-turn provides a much simpler scattering mechanism whose scattering statistics can provide an accurate measure of the illuminated field at the position of the quad-rotor. This new two-way flying field probe concept will provide valuable magnitude and phase information to the radar engineer

Ultra-low cross polarization antenna architectures for multi-function planar phased arrays

For over thirty years, single-beam mechanically steered radars have dominated the field of atmospheric observations, and since then, newer improved technologies have emerged that could provide a replacement for aging radars. Phased array radar technology offers meteorologists and scientists a unique opportunity to enhance weather forecasting through rapid electronic adaptive scans. Multiple array geometries exist for phased array radars (i.e., spherical, cylindrical, and planar); however, this work concentrates on enhancing the performance of planar antenna architectures. Planar phased array radar antennas have been under scrutiny due to the challenges posed when trying to satisfy all polarimetric weather requirements met by conventional parabolic dish reflectors (e.g., co-polarized beam mismatch under 0.1 dB, input isolation higher than 40 dB, cross-polarized radiation under -40 dB). This dissertation takes a fresh look into the electromagnetic characteristics of traditional antennas used in planar phased array geometries and provides mathematical insight to prove their performance, limitations, and advantages. The metrics used to evaluate essential performance characteristics were bandwidth, scanning range, polarization, co-polarized beam match, cross-polarization, isolation, and intrinsic cross-polarization (IXR). The antennas presented in this work (i.e., Horus, Polarimetric Atmospheric Imaging Radar (PAIR), and Horus-ONR) were validated by comparing the results of predictive simulating tools against physical antenna measurements. The Horus antenna was made using aperture coupling feeding technique with stacked microstrip patches. It achieved a fractional bandwidth of 15.4%, a co-polarized beam mismatch of 0.08 dB, and scanned cross-polarization levels of -29 dB, based on Ludwig’s third definition of polarization for θ = ± 45°. The PAIR antenna was made using balanced probe-fed stacked microstrip patches and it totaled fractional bandwidths of 7.7%, co-polarized beam mismatch of 0.21 dB, and -40 dB cross-polarization within the required imaging field of view. Lastly, the Horus-ONR antenna. Its design follows Horus guidelines for manufacturing but improves bandwidths up to 24.8% by trading the scanned co-polarized beam mismatch and cross-polarization required for weather missions. Other antenna architectures proposed for future phased array radar developments are the ultra-low cross-polarization microstrip patch (ULCP-MPA) and a dielectric covered slot antenna (ULCP-DCSA). The ULCP-MPA and the ULCP-DCSA can achieve cross-polarization levels of -40 dB for θ = ± 45°. The antenna designs presented in this dissertation show the lowest scanned cross-polarizations with highly calibratable polarization and might be the best planar radiating elements present in literature so far, despite not achieving all polarimetric weather requirements for multi-function phased array radars. Microstrip patch antennas offer a scalable, low profile solution with excellent polarization diversity and reasonable scanned bandwidths for multi-function, planar phased array radar platforms of the future

Feasibility Study of a Satellite Solar Power Station

A feasibility study of a satellite solar power station (SSPS) was conducted to: (1) explore how an SSPS could be flown and controlled in orbit; (2) determine the techniques needed to avoid radio frequency interference (RFI); and (3) determine the key environmental, technological, and economic issues involved. Structural and dynamic analyses of the SSPS structure were performed, and deflections and internal member loads were determined. Desirable material characteristics were assessed and technology developments identified. Flight control performance of the SSPS baseline design was evaluated and parametric sizing studies were performed. The study of RFI avoidance techniques covered (1) optimization of the microwave transmission system; (2) device design and expected RFI; and (3) SSPS RFI effects. The identification of key issues involved (1) microwave generation, transmissions, and rectification and solar energy conversion; (2) environmental-ecological impact and biological effects; and (3) economic issues, i.e., costs and benefits associated with the SSPS. The feasibility of the SSPS based on the parameters of the study was established

International Laser Ranging Service (ILRS) 2003-2004 Annual Report

The International Laser Ranging Service (ILRS) organizes and coordinates Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) to support programs in geodetic, geophysical, and lunar research activities and provides the International Earth Rotation and Reference Systems Service (IERS) with products important to the maintenance of an accurate International Terrestrial Reference Frame (ITRF). This reference frame provides the stability through which systematic measurements of the Earth can be made over thousands of kilometers, decades of time, and evolution of measurement technology. This 2003-2004 ILRS annual report is comprised of individual contributions from ILRS components within the international geodetic community for the years 2003-2004. The report documents changes and progress of the ILRS and is also available on the ILRS Web site at http://ilrs.gsfc.nasa.gov/reports/ilrs_reports/ilrsar_2003.html

3D conformal antennas for radar applications

Embedded below the radome of a missile, existing RF-seekers use a mechanical rotating antenna to steer the radiating beam in the direction of a target. Latest research is looking at replacing the mechanical antenna components of the RF seeker with a novel 3D conformal antenna array that can steer the beam electronically. 3D antennas may oer signicant advantages, such as faster beamsteering and better coverage but, at the same time, introduce new challenges resulting from a much more complex radiation pattern than that of 2D antennas. Thanks to the mechanical system removal, the new RF-seeker has a wider available space for the design of a new 3D conformal antenna. To take best benets of this space, dierent array shapes are studied, hence the impact of the position, orientation and conformation of the elements is assessed on the antenna performance in terms of directivity, ellipticity and polarisation. To facilitate this study of 3D conformal arrays, a Matlab program has been developed to compute the polarisation pattern of a given array in all directions. One of the task of the RF-seeker consists in estimating the position of a given target to correct the missile trajectory accordingly. Thus, the impact of the array shape on the error between the measured direction of arrival of the target echo and its true value is addressed. The Cramer-Rao lower bound is used to evaluate the theoretical minimum error. The model assumes that each element receives independently and allows therefore to analyse the potential of active 3D conformal arrays. Finally, the phase monopulse estimator is studied for 3D conformal arrays whose quadrants do not have the same characteristics. A new estimator more adapted to non-identical quadrants is also proposed

Comparison of sea-ice freeboard distributions from aircraft data and cryosat-2

The only remote sensing technique capable of obtain- ing sea-ice thickness on basin-scale are satellite altime- ter missions, such as the 2010 launched CryoSat-2. It is equipped with a Ku-Band radar altimeter, which mea- sures the height of the ice surface above the sea level. This method requires highly accurate range measure- ments. During the CryoSat Validation Experiment (Cry- oVEx) 2011 in the Lincoln Sea, Cryosat-2 underpasses were accomplished with two aircraft, which carried an airborne laser-scanner, a radar altimeter and an electro- magnetic induction device for direct sea-ice thickness re- trieval. Both aircraft flew in close formation at the same time of a CryoSat-2 overpass. This is a study about the comparison of the sea-ice freeboard and thickness dis- tribution of airborne validation and CryoSat-2 measure- ments within the multi-year sea-ice region of the Lincoln Sea in spring, with respect to the penetration of the Ku- Band signal into the snow