Diffraction and Pattern Perturbation Effects in Offset Gregorian Reflector Antennas with Wideband Feeds

The offset Gregorian reflector system of the Square Kilometer Array radio telescope is required to operate with wideband feed (WBF) antennas down to very low frequencies, where reflectors become (electrically) relatively small. The considered WBF technologies are the log-periodic (Eleven) antenna and the quadruple-ridged flared horn. This paper investigates some of the performance degradation effects that are specific for the low frequencies and typical for these WBFs, including the feed pattern perturbations and diffraction. Several performance metrics, such as the antenna receiving sensitivity and side lobe levels are considered

Analysis and design of conical transmission line power combiners

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2007.This dissertation presents a technique for the design of N-way conical line power combiners, which offers significant advantages over existing axially symmetric combining techniques. A full analytical study of conical transmission lines is done, and evaluated results are presented. These include a proof of the cutoff frequency equation, and plots of the field patterns, of higher order modes which are unavailable in literature. A coaxial fed conical line combiner for 10 inputs is proposed, designed and evaluated. The design technique relies on the uniform transmission line characteristics of the conical lines to eliminate the need for complex full wave optimisation, typically needed in the design of the more commonly used radial line combiners. Circuit models are instead employed to achieve a wide matched bandwidth by using optimised stepped impedance coaxial lines to feed the combining structure. The prototype developed at X-band displays more than an octave bandwidth with a return loss of better than -14.5 dB. Using tapered line matching sections increases the power handling capability of the combiner by eliminating sharp edges, and allows for tolerance insensitive manufacture of the structure by widening conductor spacings. Such a 10-way prototype is developed at X-band which displays a -18.7 dB return loss bandwidth of 47% with very low losses. A study is done to determine the limitations on the design of general N-way combiners, and the results are incorporated into the design technique. The full process is demonstrated by the design and simulation of a 30-way combiner at Ku-band which displays a simulated -20 dB return loss bandwidth of 34%. The design technique is simple to execute and requires very little full wave analysis. Results obtained with the manufactured combiners are better than those of any previously published axially symmetric combiners

The effects of the antenna power pattern uncertainty within a global 21 cm experiment

Experimental 21 cm cosmology aims to detect the formation of the first stars during the cosmic dawn and the subsequent epoch of reionization by utilizing the 21 cm hydrogen line transition. While several experiments have published results that begin to constrain the shape of this signal, a definitive detection has yet to be achieved. In this paper, we investigate the influence of uncertain antenna-sky interactions on the possibility of detecting the signal. This paper aims to define the level of accuracy to which a simulated antenna beam pattern is required to agree with the actual observing beam pattern of the antenna to allow for a confident detection of the global 21 cm signal. By utilising singular value decomposition, we construct a set of antenna power patterns that incorporate minor, physically motivated variations. We take the absolute mean averaged difference between the original beam and the perturbed beam averaged over frequency ($\Delta D$) to quantifying this difference, identifying the correlation between $\Delta D$ and antenna temperature. To analyse the impact of $\Delta D$ on making a confident detection, we utilize the REACH Bayesian analysis pipeline and compare the Bayesian evidence $\log \mathcal{Z}$ and root-mean-square error for antenna beams of different $\Delta D$ values. Our calculations suggest that achieving an agreement between the original and perturbed antenna power pattern with $\Delta D$ better than -35 dB is necessary for confident detection of the global 21 cm signal. Furthermore, we discuss potential methods to achieve the required high level of accuracy within a global 21~cm experiment

Antenna position estimation through sub-sampled exponential analysis of harmonically related input signals

Accurate placement of elements in large antenna arrays is a difficult and costly process. We explore the use of the validated exponential analysis (VEXPA) technique that was previously formulated to solve a direction-of-arrival (DOA) estimation problem, to find the antenna element positions in an array after the installation phase, so that cost-savings can be realised during placement of the antenna elements. Measurements are taken from harmonically related input signals transmitted from an Unmanned Aerial Vehicle (UAV) for which the position in the sky is known. It is shown how the UAV's zenith angle can be manipulated to generate parameters required for VEXPA's de-aliasing step. A simple simulation illustrates the functioning of the proposed method

Ecodomy - Life in its fullness

This book provides a coherent and conceptual portrayal of aspects of the theological research theme, entitled Ecodomy (literally meaning to ‘build a house’). In its figurative meaning the term Ecodomy addresses the theme, ‘life in its fullness’. This fullness of life entails a polarity which is inherently part of life, namely its brokenness and its wholeness. From various theological disciplines, namely Old Testament Studies, New Testament Studies, Systematic Theology, Church History and Practical Theology, both the brokenness and wholeness are addressed theologically. Every chapter focuses on a specific theological discipline, while the combination of theological disciplines, addresses the brokenness and wholeness of life as coherent concept. One pole does not exclude the other. Brokenness is visible in current or recent very relevant societal challenges, such as racism and xenophobia, apartheid, foreignness and exclusivism, leadership crises and violence. In contrast, wholeness is embedded in themes such as the African concept of ubuntu, a life of faith and wisdom, reconciling leadership, or transforming space and community. Ultimately, a Greek term ἀναίδεια (persistence) is connected to the meaning of Ecodomy and ‘life in its fullness’. Several methodologies have been used in the different contributions of the book. Every theological discipline applies a different methodology for the purpose of exposing a specific topic or research theme. In general, the contributions in this book follow a combination of a literature study with the further application of diachronic and synchronic exegetical methods. In addition, single contributions follow an own hermeneutical approach. Not one single contribution, but a combination of different theological disciplines, which form the concepts of brokenness and wholeness (life in its fullness), which expose the polarity of life, are included in this book. In its exposed interdisciplinary interwovenness, the book provides a tapestry of how different theological disciplines are combined into a single theme and how they contribute together by means of theological analyses and attempted building blocks to build the broken ‘houses’ of societal structures or human life. The book contributes to selected aspects of broken life in society and the healing experiences of human life. Several themes touch on recent and relevant challenges which have contributed to the brokenness of life. Not only in South Africa, but globally these are currently relevant themes. They include realities of racism and xenophobia, apartheid, foreignness and exclusivism, leadership crises and violence. With the focus on wholeness, specific attention is given to the African concept of ubuntu, a life of faith and wisdom, reconciling leadership, and transforming space and society. A Greek term ἀναίδεια (insolence as ‘in keeping on asking’ – Lk 11:8) illuminates the theme of Ecodomy from the perspective of a parable. The target audience of the book is academic scholars and theologians, who specialise in the different fields of Theology, the Humanities and other Social Sciences. Furthermore, the book is also accessible to scholars of other academic disciplines outside these disciplines. The book contains original research and contributions have not been plagiarised from publications elsewhere

Antenna Position Estimation Through Subsampled Exponential Analysis of Signals in the Near Field

In a previous article we explored the use of a subsampled exponential analysis algorithm to find the antenna-element positions in a large irregular planar array after the installation phase. The application requires an unmanned aerial vehicle to be flown over the antenna array while transmitting several odd harmonic signals. The received signal samples at a chosen reference antenna element are then compared to those at every other element in the array in order to find its position. Previously, the far-field approximation was used to calculate the time delay between received signals. In this article the method is reconsidered for the more realistic case of when the source is in the near field of the array. A number of problems that arise are addressed, and results from a controlled simulation are presented to illustrate that the computational method works

Reassessing Mg/Ca temperature calibrations of <em>Neogloboquadrina pachyderma</em> (sinistral) using paired δ^44/40 and Mg/Ca measurements

The Mg/Ca temperature calibration of the polar to subpolar planktonic foraminifera Neogloboquadrina pachyderma (sinistral) (sinistral indicates left coiling) was refined by a multiproxy approach combining hydrographic temperature and salinity data with Mg/Ca, delta Ca-44/40, and delta O-18 values from Holocene Nordic seas core top samples. Reliable Mg/Ca-based temperature estimates are limited to foraminiferal tests that calcified in water masses with temperatures above similar to 3 degrees C at habitat depth. In these samples, Mg/Ca and delta Ca-44/40 values are positively correlated (Mg/Ca (mmol/mol) = 0.77 (+/- 0.22) x delta Ca-44/40 (parts per thousand SRM 915a) + 0.52 (+/- 0.12); n = 20, R-2 = 0.76). Both Mg/Ca- and delta Ca-44/40-derived temperatures projected onto their corresponding depth intervals reveal that the &quot;apparent'' calcification depth of N. pachyderma (sinistral) averaging the specimens' whole life cycle is bound to an isopycnal layer defined by water densities (sigma(t)) between 27.7 and 27.8. This implies that N. pachyderma (sinistral) prefers gradually deeper habitats with increasing sea surface temperatures, thus counterbalancing absolute temperature variations. Consequently, the total temperature range recorded in this foraminiferal species is restricted and only partly reflects environmental changes. On the basis of the new Mg/Ca, delta Ca-44/40, and delta O-18 multiproxy data set, we propose a linear Mg/Ca temperature relation for high-latitude N. pachyderma (sinistral): Mg/Ca (mmol/mol) = 0.13 (+/- 0.037) T (degrees C) + 0.35 (+/- 0.17); T &gt; 3 degrees C. In core top samples from polar waters with peak summer temperatures below similar to 3 degrees C, the temperature response in the Mg/Ca and delta Ca-44/40 proxy signal is inversed and poorly correlated. Both Mg/Ca- and delta Ca-44/40-derived temperature estimates pretend significantly higher calcification temperatures than maximum summer sea surface temperatures of these water masses

Risk factors for Coronavirus disease 2019 (Covid-19) death in a population cohort study from the Western Cape province, South Africa

Risk factors for coronavirus disease 2019 (COVID-19) death in sub-Saharan Africa and the effects of human immunodeficiency virus (HIV) and tuberculosis on COVID-19 outcomes are unknown. We conducted a population cohort study using linked data from adults attending public-sector health facilities in the Western Cape, South Africa. We used Cox proportional hazards models, adjusted for age, sex, location, and comorbidities, to examine the associations between HIV, tuberculosis, and COVID-19 death from 1 March to 9 June 2020 among (1) public-sector “active patients” (≥1 visit in the 3 years before March 2020); (2) laboratory-diagnosed COVID-19 cases; and (3) hospitalized COVID-19 cases. We calculated the standardized mortality ratio (SMR) for COVID-19, comparing adults living with and without HIV using modeled population estimates.Among 3 460 932 patients (16% living with HIV), 22 308 were diagnosed with COVID-19, of whom 625 died. COVID19 death was associated with male sex, increasing age, diabetes, hypertension, and chronic kidney disease. HIV was associated with COVID-19 mortality (adjusted hazard ratio [aHR], 2.14; 95% confidence interval [CI], 1.70–2.70), with similar risks across strata of viral loads and immunosuppression. Current and previous diagnoses of tuberculosis were associated with COVID-19 death (aHR, 2.70 [95% CI, 1.81–4.04] and 1.51 [95% CI, 1.18–1.93], respectively). The SMR for COVID-19 death associated with HIV was 2.39 (95% CI, 1.96–2.86); population attributable fraction 8.5% (95% CI, 6.1–11.1)