# HERAS: A Modular Matlab Tool Using Physical Optics for the Analysis of Reflector Antennas
## 4 Applications of the Tool
### Efficient Estimation of Antenna System Performance for VHTS Applications in a SFPB Scenario
HERAS can be used for a convergence analysis to identify the optimum mesh in terms of aforementioned trade-off. It is noted that HERAS implements parallel computing in order to simultaneously calculate multiple beams using the different cores available in a microprocessor. For this purpose, the Matlab instruction _parfor_ has been used [51]. This allows an acceleration factor directly proportional to the number of cores. A schematic representation of the general working operation of the tool embedding HERAS for the evaluation of reflector antenna systems is shown in Figure 7. The system receives inputs which define the reflector and feeding system, the coverage definition, and the acceleration techniques to be used. Far-field patterns in two orthogonal polarisations are provided by the tool, which are used to compute the \(C/I\) values for every point of the coverage. While SFPB configurations commonly employ several reflectors to avoid overlapping of the feeds, the simulation only defines one of them and the feeds are placed in the relative position to their corresponding reflector. This approach simplifies the implementation without affecting the numerical results. A combination of all these techniques demonstrated a total acceleration factor of 80 in the scenario proposed in [56], which can reduce the computational time from hours to a few minutes with an acceptable accuracy. The antenna design used for this VHTS scenario with a SFPB configuration is also described. Several coverage characteristics can be estimated with the far-field patterns obtained with HERAS. These include \(C/I\), aggregate gain, total throughput, payload efficiency, etc. As an example, \(C/I\) and aggregate gain for the SFPB scenario presented in [56] are reported in Figure 8. In addition, Figure 9 shows the evaluated error in a SFPB configuration in terms of \(C/I\) over the full Earth coverage when applying the acceleration techniques previously described with reference to the \(C/I\) computed using GRASP for all feeds. This error was intended to remain below a certain acceptable level (marked by the red line) enabling a good statistical estimation of the system performance adequate for trade-off analyses driven by worst case values. Far-field points with lower \(C/I\) need to be more accurately estimated than those with higher values. The definition of this acceptable error is described in [56]. Figure 7: System representation of the Matlab code used to efficiently obtain an estimation of coverage characteristics for a global GEO satellite mission. Taking advantage of the flexibility provided by this approach, a system study may start with a broader parametric evaluation tolerating a slightly higher error, and gradually increase the accuracy as the antenna geometry becomes consolidated. A more refined analysis and fine-tuning of the design may then be conducted at a sub-system level using dedicated tools, such as GRASP, to further improve the performance using a more realistic feed model or introducing reflector surface shaping, for example. It is also noted that the aforementioned acceleration techniques may be implemented using commercial software packages. This is the case for the beam interpolation, for example, which can be directly applied using commercial solvers; the threshold technique is more readily implemented directly in the code and thus benefits from the access to the source code.