TABLE OF CONTENTS Active microwave devices are the workhorses of microwave systems. They perform a variety of key functions, including the transformation of DC current to RF current (oscillation), the conversion of a signal at one frequency to another (multiplication, mixing), the redirection of a signal (switching), and the intensification and replication of a signal (amplification). Of the large variety of active microwave devices in use, we focus on the two most common, the solid-state diode and field effect transistor. We review the operational characteristics of these two devices and then explain the importance of grounding in circuits where they are used. With the aid of a number of examples, we show that the performance of a circuit can be optimized when the active device s ground path impedance is minimized and modeled accurately. We also describe techniques for grounding active devices. The chapter concludes with a discussion of grounding for multidevice modules and circuit boards.
The previous two chapters focused on transmission lines and related passive cir cuits whose predominant function is to transport RF and microwave signals from one point to another with as little loss as possible. The sources of the signals in such circuits are active microwave devices. The transfer characteristic of an active device is a function of its DC operating point, its frequency band, and the power level of its input signal. An active microwave device usually is embedded in a passive matching circuit, which optimizes its performance and provides the device s grounding path.
