文档介绍：Source: Complete Wireless Design
Chapter
1
Wireless Essentials
A firm understanding of how passive and ponents function at high
frequencies, as well as a strong grasp of the fundamental concepts of lumped
and distributed transmission lines, S-parameters, and radio-frequency (RF)
propagation, is essential to essful circuit design.
ponents at RF
Introduction
At radio frequencies, lumped (physical) resistors, capacitors, and inductors are
not the “pure” components they are assumed to be at lower frequencies. As
shown in Fig. , their true nature at higher frequencies has undesirable
resistances, capacitances, and inductances—which must be taken into account
during design, simulation, and layout of any wireless circuit.
At microwave frequencies the lengths of ponent leads have to be min-
imized in order to decrease losses due to lead inductance, while even the board
traces that connect these ponents must be converted to transmis-
sion line structures. Surface mount devices (SMDs) are perfect for decreasing
this lead length, and thus the series inductance, of ponent (Fig. ),
while the mon transmission line structure is microstrip, which main-
tains a 50-ohm constant impedance throughout its length—and without
adding inductance or capacitance.
As the frequency of operation of any wireless circuit begins to increase,
so does the requirement that the actual physical structure of all of the
ponents themselves be as small as possible, since the part’s
effective frequency of operation increases as it shrinks in size: the smaller
package lowers the harmful distributed reactances and series or parallel
resonances.
1
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Wireless Essentials
2 Chapter One
Figure ponent’s real-life behavior at high frequencies (HF) and low