A SW-tool has been developed which allows the user to optimise the RF performance of smooth or corrugated conical horns for communications and tracking purposes. A horn has been designed, manufactured and tested.
Corrugated conical horns play a key role in telecommunications systems, whether on the spacecraft as part of the dedicated telecom payload and the telemetry system, or in a ground terminal as the primary source of the reflector optics. In addition to the pure telecommunications service, these horns are often also required to carry a tracking function.
Tracking capabilities are thoroughly implemented in ground terminals. With the new broadband telecommunications services, the satellites will generate very narrow, multiple spot beams, with stringent requirements imposed on the pointing accuracy. Therefore it is necessary also to provide tracking capabilities on the telecom antenna itself, which creates a need for efficient telecommunications horns with integrated tracking capabilities.
This in turn requires availability of an efficient design tool which allows simultaneous optimisation of the antenna performances for both the fundamental mode and higher order mode excitation.
The project objectives are:
- Development of a software tool to be used for optimising RF/mechanical performance of multi-mode conical horn for communication and tracking purposes.
- Design of an optimised horn to demonstrate the capabilities of the software tool.
- Manufacturing and RF-testing the horn to validate the software calculations.
It was a requirement to develop a fast and accurate SW-tool. This was achieved by re-using the well-proven CHAMP horn-analysis SW as well as the MinMax optimisation engine of the POS SW.
The definition of an optimisation procedure is always a major point for horn designers, who need to have certain knowledge of the state of art and a feeling during the optimisation process, depending of their goals and performances priority. Therefore, the key issue was to develop an intuitive and user-friendly definition of the optimisation problem as well as a clear monitoring of the optimisation procedure.
The new software tool is targeted for the advanced horn designer who designs efficient telecommunication horns with integrated tracking capabilities. The software offers high accuracy and an easy-to-manage performance driven design procedure, with the main benefit to speed up the design process.
Even though the software development has focused on horns with tracking capabilities, the software is an equally strong design tool for any smooth or corrugated conical horn.
As an example, the new tool has been used to optimise an existing well-designed horn. It has been possible to increase the directivity in all parts of the frequency bands considered, leading to an enhancement of the aperture efficiency from ~65% to ~70%, and even more than 80% in some part of the bands.
The high flexibility for designing the horn is obtained with a very general and modular overall horn modelling together with a very general and modular formulation of the optimisation scenario. It enables an easy-to-manage performance driven design procedure where more and more refined designs are produced in a sequence of optimisations.
The selection of the geometrical parameters to be used as optimisation variables has been made in an overly general way. Each design parameter given as a real value (i.e. non-integer value) may be selected as optimisation variable simply by assigning a name to the parameter in the GUI. Also functional expressions may be used to link other design parameters to the optimisation variable.
The user specifies the required RF-performance in terms of a number of so-called optimisation goals. Several goal types are available, e.g., goals to the return loss, to the maximum level of the cross polarisation, etc. The selection of goals and the individual weighting of these are of utmost importance for the success of the horn synthesis. The software offers a toolbox of goal types, but it is emphasized that a strong user-interaction is required to monitor and change the goals during the optimisation.
The horn may be divided in several sections, and in each section, the horn profile may be modelled by a pre-defined profile function, with the advantage that the overall horn geometry is described in terms of a few parameters only. During the optimisation procedure, the geometry may be refined, using spline functions and/or a detailed description corrugation-by-corrugation allowing an intelligent iterative optimisation.
The analysis kernel of the program is an efficient, mode-matching solution for the horn interior combined with a Method of Moments analysis of the horn exterior. Also, the influence of a circularly symmetric subreflector may be included in the analysis.
Phase 1: Software requirements specifications
Phase 2: Synthesis tool design
Phase 3: Synthesis tool implementation
Phase 4: Design of multi-mode horn
Phase 5: Manufacturing and testing of multi-mode horn
Phase 6: Software validation
All project tasks have been completed, i.e. the SW has been designed and implemented, and the multi-mode horn has been designed, manufactured and tested. The horn has significantly improved performance compared to the initial, well-designed horn. The RF-testing demonstrated very close agreement between calculations and measurements. The results have been presented at a final presentation held at ESTEC.