Stellenbosch, South Africa
Stellenbosch, South Africa

Time filter

Source Type

De Villiers D.I.L.,Stellenbosch University | Lehmensiek R.,EMSS Antennas Pty Ltd
Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012 | Year: 2012

This paper describes a simple and low cost method to improve the noise performance of low-noise offset Gregorian antenna systems using a low-side sub-reflector mount configuration. A low-side mount has some logistical and maintenance advantages over the high-side counterpart, since the feed can be accessed without the need for a crane. A simple extension to the bottom of the sub-reflector is proposed which is shown to improve the antenna noise performance over that of the standard high-side mount configuration. © 2012 IEEE.


Lehmensiek R.,EMSS Antennas Pty Ltd | De Villiers D.I.L.,Stellenbosch University
Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012 | Year: 2012

This paper outlines the design of a wide flare angle axially corrugated conical horn for a classical offset dual-reflector antenna system. The design minimizes the input reflection coefficient of the horn and maximizes the antenna efficiency of the antenna system by simultaneously limiting the sidelobe and cross-polarization levels to the system specifications. The effects of the number of corrugations in the horn and the number of parameters used in the optimization are also investigated. © 2012 IEEE.


De Villiers D.I.L.,Stellenbosch University | Lehmensiek R.,EMSS Antennas Pty Ltd.
2013 7th European Conference on Antennas and Propagation, EuCAP 2013 | Year: 2013

A comparative study of different models to calculate the radiometric noise in an offset Gregorian antenna system is presented. Some convergence studies on the radiometric noise integral are performed, and the required radiation pattern grid densities are deduced. A simplified brightness temperature model is suggested and evaluated, and the model is shown to produce accurate results at the lower microwave frequencies. The accuracy of a simplified physical reflector model which offers a significant calculation time advantage is also investigated over a wide range of parameters, and it is shown to perform well even for relatively small systems. © 2013 EurAAP.


De Villiers D.I.L.,Stellenbosch University | Lehmensiek R.,EMSS Antennas Pty Ltd.
IEEE Transactions on Antennas and Propagation | Year: 2015

Antenna noise temperature calculations of reflector systems is often a slow process and makes direct optimization of the sensitivity of these systems a difficult and time-consuming task. This paper presents an improvement to a recently proposed method to speed up these calculations by several orders of magnitude for large dish systems. The accuracy of the improved method is tested for several types of offset Gregorian systems, and errors are shown to be in the order of a few percent. Comparisons of several layers of simplification to a standard brightness temperature model are also presented to aid the designer in the choice of model complexity to use. © 1963-2012 IEEE.


De Villiers D.I.L.,Stellenbosch University | Lehmensiek R.,EMSS Antennas Pty Ltd
Proceedings - 2014 International Conference on Electromagnetics in Advanced Applications, ICEAA 2014 | Year: 2014

Dual offset Gregorian reflector shaping can provide improved sensitivity performance by reducing radiometric noise and improving aperture efficiency. Optimizing the shaped system for optimum sensitivity performance is slow due to the full radiation pattern integration required to calculate the radiometric noise temperature. This paper shows that, in certain situations for a feed-down sub-reflector mount, the optimum aperture efficiency result, which is fast to calculate, guarantees a near optimum sensitivity system. © 2014 IEEE.


Theron I.P.,EMSS Antennas Pty Ltd. | Lehmensiek R.,EMSS Antennas Pty Ltd. | De Villiers D.I.L.,Stellenbosch University
Proceedings of the 2012 International Conference on Electromagnetics in Advanced Applications, ICEAA'12 | Year: 2012

This paper highlights some of the trade-offs as well as the implications of the selected options during the design of the MeerKAT radio telescope antenna optics. The purpose is to achieve the best possible performance for the physical system at given cost. © 2012 IEEE.


De Villiers D.I.L.,Stellenbosch University | Lehmensiek R.,EMSS Antennas Pty Ltd.
Proceedings - 2011 International Conference on Electromagnetics in Advanced Applications, ICEAA'11 | Year: 2011

This paper provides a simple analytical formulation to predict the effect of sub-reflector diffraction on the efficiency performance of shaped offset dual-reflector antenna systems, without the need to design and simulate the shaped surfaces. It is shown, through simple analytical approximations, that for strong edge illumination of the sub-reflector the increased efficiency obtained by shaping can be lost and even degraded due to the diffraction from the sub-reflector edge. Results compare favorably to physical optics simulations of the structures. © 2011 IEEE.


Lehmensiek R.,EMSS Antennas Pty Ltd. | De Villiers D.I.L.,Stellenbosch University
Proceedings of the 2015 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications, IEEE APWC 2015 | Year: 2015

Calculation of the antenna noise temperature for an offset Gregorian reflector system is computationally intensive. The main reflector masking technique, where the main reflector is removed from the calculation domain, considerably reduces the computation cost. This technique, however, is less accurate for electrically smaller systems. Recently an improvement to the technique was proposed by introducing a diffraction compensated correction factor. In this case the error on receiving sensitivity can be in the order of a few percent. This paper further improves on the technique by introducing a power dependence to the inverse frequency diffraction compensation. The technique reduces the error of the receiving sensitivity to well below a percent. © 2015 IEEE.


Lehmensiek R.,EMSS Antennas Pty Ltd. | Theron I.P.,EMSS Antennas Pty Ltd.
Proceedings of the 2012 International Conference on Electromagnetics in Advanced Applications, ICEAA'12 | Year: 2012

The design methodology of the MeerKAT L-band feed which consists of a wide flare angle axially corrugated conical horn, a horn matching section and a compact orthomode transducer (OMT) is presented. The dish is a classical Gregorian offset dual-reflector antenna system. The predicted results show stable radiation patterns over the frequency band with an ideal antenna efficiency above 73 %. The feed has losses below 0.05 dB resulting in very good system sensitivity. © 2012 IEEE.


Lehmensiek R.,EMSS Antennas Pty Ltd.
2016 10th European Conference on Antennas and Propagation, EuCAP 2016 | Year: 2016

A methodology for fast design of a compact wideband orthogonal mode transducer (OMT) matched to a wide flare angle axially corrugated conical horn for the Band 2 feed of the Square Kilometer Array (SKA) is presented. The design takes into account, through full-wave electromagnetic analyses, interactions that occur in the feed over the entire frequency band. To lower the computational cost and make the model suitable for optimization, problem decomposition together with a combination of high fidelity and physics-based models are employed. The reflection coefficients of the feed are designed to be less than -20 dB. © 2016 European Association of Antennas and Propagation.

Loading EMSS Antennas Pty Ltd collaborators
Loading EMSS Antennas Pty Ltd collaborators