Impedances: measurements and calculations for nonsymmetric structures

Coupling impedances are most often calculated for beam enclosures of circular cross section, and resulting formulae are used to interpret beam measurements, sometimes even in the case of flat chambers. This leads to misunderstanding and inaccurate evaluations. Rigorous analytic formulae exist for smooth, resistive chambers of elliptical or rectangular cross section, while computer programs allow one to evaluate more complicated, noncircular-symmetric geometries. At low frequencies the impedance of thin resistive walls departs from classical formulae. (14 refs)