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1 Introduction

As operational frequency increases, parameters of lines, circuits, and traces on PCB will play a critical role, because geometrical sizes become comparable with wavelength. Geometrical sizes help users determine their physical sizes (length and width). As an example, waves lengths from 433 MHz to 5.5 GHz (Table 1-1).

Table 1-1 Frequency and Corresponding Length

Frequency, MHz	Wave length, λ, cm	Wave length, λ/4, cm
433	69.23	17.30
868	34.53	8.63
2440	12.29	3.07
5500	5.45	1.36

Lines and traces change their operational behavior while operational frequency increases and have not only an active resistance. Depending on frequency, inductive or capacitive reactance can be dominant and their values varies. For high frequencies, use the impedance or “Z” (meaning active with reactive resistances). Resistance (R) doesn’t change with the frequency, but reactance (±jX) does change. This means the impedance (Z) varies by frequency.

Figure 1-1 Graphical Representation of Impedance (Z)