11 - Microwave Active Circuits and Integrated Antennas

Abstract

This chapter discusses a variety of topics concerning communication systems at microwave and millimeter-wave frequencies. Device technology and concepts are focused and it begins with a discussion on noise at these frequencies. Because wireless applications are the primary drive for development of these frequency bands, understanding the basic concepts of noise at these frequencies becomes of fundamental importance in understanding the sensitivity of high-frequency components, such as low-noise amplifiers and mixers. Further, this chapter discusses issues relevant to the design of the most common types of active microwave circuits. It presents the design of microwave amplifiers using an S-parameter approach and outlines microwave oscillator design. The stability conditions for both one-and two-port microwave oscillators are presented. A unique and practical class of antennas for application at microwave and milli-meter-wave frequencies is also presented. These antennas, often referred to as printed antennas, are completely compatible with many types of high-frequency transmission lines and can be constructed directly on a printed circuit board. A brief discussion on active integrated antennas (AIAs) is also provided in the chapter. In this approach, the compatibility of planar antennas with popular microwave frequency transmission lines and active devices is exploited by directly integrating the active circuitry with the antenna platform. This results in a compact and highly functional system with many interesting characteristics.