Aurora FEST3D 2018 FEST3D is able to efficiently analyse different kind of passive RF structures in waveguide technology. Basically, FEST3D is based on an integral equation technique efficiently solved by the Method of Moments. Additionally, the Boundary Integral-Resonant Mode Expansion (BI-RME) method is employed for extracting the modal chart of complex waveguides with arbitrary cross-section. The successful combination of such methods ensures a high degree of accuracy, as well as reduced computational resources (in terms of CPU time and memory). On this basis, FEST3D is able to simulate complex passive devices in extremely short times (of the order of seconds or few minutes), whereas general purpose software (based on segmentation techniques such as finite elements or finite differences) can spend hours for the same calculations. Moreover, unlike mode-matching techniques, the electromagnetic algorithms employed in FEST3D minimize the problems of relative convergence leading to more confident results. Furthermore, the integral equation technique extracts part of the frequency dependent computations, thus allowing a faster computational time per frequency point when compared to standard mode-matching techniques. This benefit is more evident when many modes are required for an accurate analysis of the component.