2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/149676The beam coupling impedances of small axisymmetric obstacles having a semi-elliptical cross section along the beam in the vacuum chamber of an accelerator are calculated at frequencies for which the wavelength is large compared to a typical size of the obstacle. Analytical results are obtained for both the irises and the cavities with such a shape which allow simple estimates of their broad-band impedances.6 pages, LaTeX, style revtex, 2 figures (eps). Submitted to Phys. Rev. EAccelerator Physicstext