5.1: Introduction

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Previous chapters discussed the low-frequency operation of transmission lines. This chapter describes the origins of frequency-dependent behavior. Figure 5.2.1 shows the typical frequency dependence of a line’s \(RLGC\) parameters, and, except with semiconductor substrates, \(G\) is usually negligible. This is called dispersion and a typical example is the spreading out of a pulse, see Figure 5.2.2.

The major limitation on the dimensions and maximum operating frequency of a transmission line is determined by the origination of higher-order modes (i.e., orientations of the fields). Different modes on a transmission line travel at different velocities. Thus the problem is that if a signal is split between two modes, then information sent from one end of the line will reach the other end in two packets arriving at different times. Multimoding must always be avoided.