![]() Traveling-waves are the “real” waves in the sense that they are linked directly to Maxwell’s equations and can be measured. All of these definitions give the same results for real-values characteristic impedances. When it is necessary to work with a complex reference impedance there are 3 types of waves: traveling-waves, pseudo-waves, and power-waves. Matching problems directed at maximum power transferĬan also use scattering parameters referenced to complex impedances. However for other cases, such as lossy lines, microstrip and coplanar waveguides, \(Z_0\) can be complex. Most of the time, using a real reference impedance is also OK even for low-loss lines such as coaxial lines. In lossless transmission line, \(Z_0\) is real and positive. Thus, \(Z_0\) depends of the characteristics of the material and can be determined from the transmission line distributed circuit parameters (R, L, C, G). ![]() ![]() For completeness, sometime the ratio of the electric field to the magnetic field is called the intrinsic impedance (like in free space). For transmission line supporting other modes than TEM, the definition of voltage and current may evenīe not unique (like for rectangular waveguides). Thus, voltage and current depends of the transmission line geometry and materials and in general their ratio may not be equal to the ratio of \(E/H\). Voltage and current are derived quantities from the fundamental electric \(E\) and magnetic fields \(H\) (by mean of line integrals of those fields in the transverse section of a transmission line for given set of boundary conditions). Impedance which can be measured using a DC Ohmmeter. It thus characterizes the property of the line to oppose a change in voltage for a change of current or vice-versa. SWR=1, meaning no reflection from a load and thus no backward voltage and current). The characteristic impedance \(Z_0\) associated to a transmission line (or any continuous media supporting the propagation of electromagnetic waves) is defined as the ratio of the (forward) voltage and current when the transmission line is infinite (i.e. However, pay attention that the power-waves definition may lead to uncorrect results/interpretations when using complex characteristic impedances, for example for lossy transmission lines. Unless having complex-valued characteristic impedances, this s-parameter definition should not affect your results. TL DR: scikit-rf use power-waves definition by default. This section considers the propagation of electromagnetic waves on a transmission line with a possibly complex characteristic impedance. Working with Complex Characteristic Impedance ¶
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