Aluminium Feeds for Reflector for NadirSAR

With the long term aim of developing a NadirSAR quadrotor UAV system specialized for monitoring broad acre grain fields, a large aperture load bearing antenna to use as the main structural element was sort. Here initial design work is presented on a candidate short f/D parabolic reflector antenna. An optimized splash plate feed and a dual mode coaxial horn were designed for the 10 to 10.5GHz experimenter’s band and were fed by aluminum waveguide. Both feeds gave better than 30% aperture efficiency on a low cost 11.6l0 diameter reflector that had a focal length of f/D=0.27

Empirical Analysis of Chirp and Multitones Performances with a UWB Software Defined Radar: Range, Distance and Doppler

In this study, a protocol for an unbiased analysis of radar signals' performance. Using a novel UWB software-defined radar, range profile, Doppler profile and detection range are evaluated for both Linear Frequency Modulated pulse and Multitones. The radar was prototyped and is comparable in overall performance to software defined radar test-beds found in the literature. The measured performance was in agreement with the simulations

Mathematics and science in South Africa :an international achievement study at junior secondary level

The Third International Mathematics and Science Study is the largest international study of its type undertaken. Over 500 000 students in Grades 7 and 8 (Standards 5 and 6) from forty-two countries participated in the programme. The South African sample involved 9 88 7 students. The ranking order shows that South Africa was placed last out of the forty-two countries ranked. This included only three other developing nations: Colombia, Iran and Thailand. South Africa was the only African country that participated in TIMSS; and this study was designed to investigate and evaluate South Africa's achievements in Mathematics and Science at the Junior Secondary level through the TIMSS testing instruments. Chapter 1 suggests reasons for and the likely benefits from participation in international studies of this nature. Chapter Z outlines relevant theories of learning and the opportunities to apply them to South African Mathematics and Science education and so provides a background for examining the test findings. Chapter 3 considers the contexts within which the South African study took place and describes the educational 'climate' in which the testing programme occurred. The fact that TIMSS - South Africa took place amidst all the uncertainties of restructuring eighteen different education departments into nine provincial departments is highlighted. The technical design, data processing and methodology of TIMSS are set out in Chapter 4. Chapter 5 comprises a comparative analysis of South African performance in specific groups of Mathematics and Science questions with those of the other participating developing nations and selected developed nations in order to provide as broad a perspective as possible. Important findings are that the South African students displayed poor competency in concept formation and thinking skills in Mathematics and Science and were weak in fundamental processes and awareness of number sense, particularly in Mathematics. In the Natural Sciences there a corresponding lack of problem solving abilities was displayed. Although the South African Science curriculum was shown to be appreciably 'out of step' both with the curricula of other participating countries this had little impact on the eventual achievement levels. Chapter 6 examines the profile of participating South African students in terms of their home and school milieux, attitudes towards Mathematics and Science learning and teaching and language of instruction. It is significant that with the exception of Colombia, South Africa had the oldest participating group; and South African students are allocated a minimum of scheduled time for these subjects compared to most other nations. The concluding chapter reviews the aims, objectives and premises of this study and makes recommendations summarises identified problems. In particular, a synopsis of the impact of second language instruction on learning and the 'time on task' problem in Mathematics and Science is given. The findings are particularly relevant since they present a 'first ever' national picture and international comparison of Mathematics and Science achievement in South Africa at Junior Secondary level.Thesis (PhD (Didactics))--University of Pretoria, 1997.Humanities EducationPhD (Didactics)Unrestricte

On purity relative to an hereditary torsion theory.

Thesis (Ph.D.)-University of Natal, 1992.The thesis is mainly concerned with properties of the concept "σ-purity" introduced by J. Lambek in "Torsion Theories, Additive Semantics and Rings of Quotients", (Springer-Verlag, 1971). In particular we are interested in modul es M for which every exact sequence of the form O→M→K→L→O (or O→K→M→L→O or O→K→L→M→O) is σ-pure exact. Modules of the first type turn out to be precisely the σ- injective modules of O. Goldman (J. Algebra 13, (1969), 10-47). This characterization allows us to study σ- injectivity from the perspective of purity. Similarly the demand that every short exact sequence of modules of the form O→K→M→L→O or O→K→L→M→O be σ-pure exact leads to concepts which generalize regularity and flatness respectively. The questions of which properties of regularity and flatness extend to these more general concepts of σ- regularity and σ-flatness are investigated. For various classes of rings R and torsion radicals σ on R-mod, certain conditions equivalent to the σ-regularity and the σ-injectivity of R are found. We also introduce some new dimensions and study semi-σ-flat and semi-σ-injective modules (defined by suitably restricting conditions on σ-flat and σ-injective modules). We further characterize those rings R for which every R-module is semi- σ-flat. The related concepts of a projective cover and a perfect ring (introduced by H. Bass in Trans. Amer. Math. Soc. 95, (1960), 466-488) are extended in a 'natural way and, inter alia , we obtain a generalization of a famous theorem of Bass. Lastly, we develop a relativized version of the Jacobson Radical which is shown to have properties analogous to both the classical Jacobson Radical and a radical due to J.S. Golan

Development of an ISO8729 Compliant Passive RCS Enhancer, Part 1.

An aplanatic lens backed by an offset conductive bowl was found to satisfy the ISO8729 passive RCS enhancer requirements in a 12GHz scaled model across ±15°. Here the effects of permittivity on 4λ0 radius lens weight, focal arc angular spread and position were studied in simulation at 9.41GHz for f/D=0.9. Increasing permittivity decreased lens weight. Cutting a circular lens to a square reduced the focal arc and angular spread. A novel lens consisting of a dielectric rod with 2 concentric toroids increased the focal peak from 6V/m to 6.6V/m and decreased the plastic mass from 1.7kg to 1.2kg, but will require an aerogel or foam support

Qualification of Ripple in Medium Gain Horns

A conventional rectangular mouth 25dBi pyramidal horn and an equivalent circular mouth spline horn were fully qualified by simulation in commercially available software across 54% relative bandwidth for sensing application in and around the ESA vacuum chamber at the University of Glasgow. Both antenna types showed small-scale 0.2dB ripple in directivity, 3dB beamwidth and first sidelobe level caused by internal standing waves. This represents about 0.5% of the power passing through the antennas. Performance differences from feeding by either conventional rectangular waveguide proportions of 2:1 or 2:0.88 were investigated, as was the behaviour dependence of the waveguide to spline horn junction

Passive RCS Enhancer Field of View Study

Passive radar cross section enhancers are used to increase the return from small targets like fishing boats, as well as as standards for radar systems’ calibration. Alignment of small enhancers is difficult at high mm-wave due to the small physical size. To better understand the scan loss of a commonly used trihedral reflector, it was studied using a commercially available antenna simulator. It gave 7dBm2 or better across a ±12° arc with 2dB variation. An equivalent area disk gave 13dBm2 on axis only, while a spherical lens reflector gave the same RCS across a ±25° arc with 0.4dB variation

Development of an ISO8729 Compliant Passive RCS Enhancer, Part 2.

An aplanatic lens backed by an offset conductive bowl was found to satisfy the ISO8729 passive RCS enhancer recommendation in a 12GHz scaled model across ±25°. Four wavelength radius, negative refractive index lenses composed of air or foam filled hexagonal waveguide were investigated as potential low mass and low cost alternatives to the natural plastic aplanatic lenses used in the past. The focal arc angular spread and position were studied in simulation at 9.41GHz for f/D=0.3 to f/D=1, and were found to be equivalent to the focusing ability of the prior natural plastic lenses. The maximum lens thickness was less than 1.50