A high fidelity feed with an operating bandwidth of more than an octave remains an unsolved problem in radio telescope design. Several feeds have recently been developed around the world with wide operating bandwidths (Eleven Feed, Quad-Ridged Horns, etc), but with inferior performance to the so-called octave band horns that are used in the MeerKAT system.
Given the wide range of science goals of the SKA, however, some trade-offs between different performance metrics of wide-band feeds must be considered. This is, however, normally a difficult task since much of the information might not be available in detail beforehand.
A solution to this issue is to perform formal multi-objective optimization of the feeds, so that the system engineer has access to the exact trade-off levels encountered for each antenna technology. Traditional methods of performing such optimizations are computationally prohibitively expensive, due to the long simulation times of full wave solvers, and the very large number of evaluations required to properly explore the (often high dimensional) design space. Surrogate based optimization (SBO) is a technique well suited to solve such problems. Here a coarse model is sought, which is very fast to evaluate, but still relatively accurate and based on the physical fine simulation model. A surrogate model is constructed by aligning the coarse and fine models in sub-regions of the design space – normally close to the desired optimum (or Pareto front in multi objective optimization problems).
The goal of this project is thus to develop coarse and surrogate models, for use in multi-objective SBO, for all the antennas to be considered for the wide band single pixel receivers. Once these models are available the full trade off space, or so called Pareto front, for all the performance metrics of the feeds may be calculated. The Pareto fronts will provide quantitative information on the performance limitations of current feed technologies. When the design methods are in place, new technologies can be rapidly designed, in a multi-objective sense, for possible use as a wide band single pixel feed in the SKA. One such technology option is a sinuous antenna currently under development as a Masters project at Stellenbosch University, showing great promise.
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