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Stellenbosch, South Africa

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. Source


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. Source


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. Source


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. Source


Lehmensiek R.,EMSS Antennas Pty Ltd | De Villiers D.I.L.,Stellenbosch University
IEEE Transactions on Antennas and Propagation | Year: 2014

Given the correct terminal voltages on each element of a log-periodic dipole array constant radiation characteristics can be achieved for an omni-directional radiation pattern. In this communication it is shown that this can only be achieved through optimization, correcting a previously reported oversimplification which resulted in an analytical approach being tractable. This oversimplification assumed that vanishing terminal currents on a dipole's terminal/feed element implies no radiation from that dipole. This is clearly non-physical because, zeroing the terminal current on a dipole's feed element is the same as disconnecting its two arms, while having no radiation from that dipole implies that in effect both arms be entirely removed. We show that the effect of currents induced in the disconnected arms of a dipole cannot in general be ignored. © 2014 IEEE. Source

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