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

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

Regular sparse array direction of arrival estimation in one dimension

Traditionally regularly spaced antenna arrays follow the spatial Nyquist criterion to guarantee an unambiguous analysis. We present a novel technique that makes use of two sparse non-Nyquist regularly spaced antenna arrays, where one of the arrays is just a shifted version of the other. The method offers several advantages over the use of traditional dense Nyquist spaced arrays, while maintaining a comparable algorithmic complexity for the analysis. Among the advantages we mention: an improved resolution for the same number of receivers and reduced mutual coupling effects between the receivers, both due to the increased separation between the antennas. Because of a shared structured linear system of equations between the two arrays, as a consequence of the shift between the two, the analysis of both is automatically paired, thereby avoiding a computationally expensive matching step as is required in the use of so-called co-prime arrays. In addition, an easy validation step allows to automatically detect the precise number of incoming signals, which is usually considered a difficult issue. At the same time, the validation step improves the accuracy of the retrieved results and eliminates unreliable results in the case of noisy data. The performance of the proposed method is illustrated with respect to the influence of noise as well to the effect of mutual coupling

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

Expert consensus document: Clinical and molecular diagnosis, screening and management of Beckwith-Wiedemann syndrome: an international consensus statement.

Beckwith-Wiedemann syndrome (BWS), a human genomic imprinting disorder, is characterized by phenotypic variability that might include overgrowth, macroglossia, abdominal wall defects, neonatal hypoglycaemia, lateralized overgrowth and predisposition to embryonal tumours. Delineation of the molecular defects within the imprinted 11p15.5 region can predict familial recurrence risks and the risk (and type) of embryonal tumour. Despite recent advances in knowledge, there is marked heterogeneity in clinical diagnostic criteria and care. As detailed in this Consensus Statement, an international consensus group agreed upon 72 recommendations for the clinical and molecular diagnosis and management of BWS, including comprehensive protocols for the molecular investigation, care and treatment of patients from the prenatal period to adulthood. The consensus recommendations apply to patients with Beckwith-Wiedemann spectrum (BWSp), covering classical BWS without a molecular diagnosis and BWS-related phenotypes with an 11p15.5 molecular anomaly. Although the consensus group recommends a tumour surveillance programme targeted by molecular subgroups, surveillance might differ according to the local health-care system (for example, in the United States), and the results of targeted and universal surveillance should be evaluated prospectively. International collaboration, including a prospective audit of the results of implementing these consensus recommendations, is required to expand the evidence base for the design of optimum care pathways

Fast parametric modeling of radio astronomy reflector antenna noise temperature

CITATION: De Villiers, D. I. L. 2016. Fast parametric modeling of radio astronomy reflector antenna noise temperature. EEE Transactions on Antennas and Propagation, 64(6):2522-2526, doi:10.1109/TAP.2016.2543801.The original publication is available at http://ieeexplore.ieee.orgThis communication presents an approximate method to rapidly estimate the antenna noise temperature of a reflector antenna system as a function of the geometric parameters describing the reflector dishes. The initial estimate is established by neglecting the main reflector from the calculation domain, thus speeding up the calculations significantly. The accuracy may be improved by aligning the estimated results with those from full model simulations, performed at a limited set of points scattered through the parameter space, by a linear regression correction on the residuals. Results of applications on a variety of reflector configurations for some commonly used parameter sets confirm the accuracy of the method to be better than 1%, with speed-ups of more than an order of magnitude typical.Post prin

Prediction of aperture efficiency ripple in clear aperture offset Gregorian antennas

CITATION: De Villiers, D. I. L. 2013. Prediction of aperture efficiency ripple in clear aperture offset Gregorian antennas. IEEE Transactions on Antennas and Propagation, 61(5):2457-2465, doi: 10.1109/TAP.2013.2239953.The original publication is available at http://ieeexplore.ieee.orgENGLISH ABSTRACT: Electrically small clear aperture dual offset reflector systems often exhibit a directivity ripple over frequency due to the interference of the diffracted field from the sub-reflector with the main beam field. This paper investigates the cause of the ripple, and presents a technique to predict the expected system directivity, including the ripple, using the feed radiation pattern augmented by an efficient simulation strategy in a clear aperture offset Gregorian system. The method allows for accurate prediction of the directivity ripple using a severely under-sampled set of simulation results. Predicted results are compared to several simulations, and agreement to better than 0.5 % is found for the majority of configurations using both analytical and full wave simulated feed patterns.AFRIKAANSE OPSOMMING: Geen opsomming beskikbaarhttp://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6410347&tag=1Post print versio