Theoretical modeling of longitudinal variations of electric field and line impedance in TEM cells

Longitudinal variations of the electric field inside a TEM cell have been observed in an in-depth experimental investigation and reported by M.L. Crawford et al. (see IEEE Trans. Instrum. Meas., vol.26, pp.225-230, Sept. 1977). Here, the authors present a theoretical approach to modeling these variations using standard transmission-line techniques, since only the dominant mode, TEM mode, is considered in this analysis. In addition, longitudinal variations of line impedance in the TEM cell are modeled. Their relations with voltage standing wave ratio (VSWR), losses, cell dimensions, and terminal load impedance are reflected in the expressions derived. Numerical results agree well with the reported experimental data at some frequencies. Concepts concerning longitudinal nonuniformity of both the field and the line impedance are proposed