Impedance Determination from Bench Measurements

The concept of the coaxial wire technique as a bench method for beam coupling impedance measurements is presented. Starting with the lumped element impedance model formulae are given for impedance evaluation from measured scattering parameters, both for the longitudinal and transverse case and also for the loss-factor. Followed by a section on distributed impedances many hints, precautions and practical aspects for the proper use of the measuring instrument are mentioned. The paper concludes with a brief discussion on special methods in particular for simulation of slow beams, measurements beyond waveguide cutoff and resonator techniques for evaluation of very small impedances.