Moreno et al. Figure 20. Figure 23. 1.81-GHz gain objective results using NSGA-II. 1.81-GHz cross-polar objective results using SPEA-2. Figure 21. Figure 24. 2.55-GHz cross-polar objective results using NSGA-II. 1.81-GHz gain objective results using SPEA-2. Figure 22. Figure 25. 2.55-GHz gain objective results using NSGA-II. 2.55-GHz cross-polar objective results using SPEA-2. CONCLUSIONS AND FUTURE WORK In this paper, we presented a simulation-optimization approach to the design of helical antennas. This is a very complex problem with several restrictions that must be met in two frequencies and, additionally, compacting the antenna dimensions as possible. To address the problem, we used two well-known multiobjective algorithms and still state-of-the-art algorithms, NSGA-II and SPEA-2, that were capable of improving the time and effort needed to find JULY 2019 valid solutions (antenna shape and dimensions) when compared with finding solutions using the GD as a searching technique together a simulator tool. The use of multiobjective algorithms reduced the time cost of algorithm execution when compared with a previous approach using the GD. Also, the simulation-optimization approach allow us to obtain multiple correct solutions that provide some flexibility and can help us to choose the final design of the antenna. Having more solutions, with different dimensions but all optimal from the radiation point of view, offers more IEEE A&E SYSTEMS MAGAZINE 29