TABLE OF CONTENTS At microwave frequencies, a conducting wire is a poor purveyor of electrical energy. Instead we use a transmission line or waveguide to transfer electromagnetic waves between a generator and load. In contrast to wires, the conductors of a transmission line are configured in a specific geometrical relationship to make this energy transfer as efficient as possible. In this chapter, we review transmission line and waveguide theory and examine the characteristics of multiwire, planar, coaxial, and waveguide guided structures. We then describe how discontinuities and impedance in the ground path of transmission lines hinder the flow of current and cause loss of power and unwanted radiation. We also compare DC and RF short circuits for terminating transmission lines and other passive circuits. The chapter concludes with an extensive discussion of techniques for grounding multilayer, mixed signal RF printed circuit boards and passive surface mount components.
There are two ways to transfer electromagnetic energy between an electrical source and a load that are separated in space. As shown in Figure 3.1, we can use either antennas or a transmission line. In the first method, we use the source to drive an antenna, which focuses the peak intensity of the radiated electromagnetic field in the direction of the load. We receive the signal on another antenna as currents induced to flow by the transmitting antenna s electromagnetic field. These currents flow to the load. For example, a high power transmitter drives a radio station s vertical monopole antenna, which broadcasts radio...
