8.1 Introduction

Microwave switches are essential elements for a number of widely varying applications, ranging from highly sophisticated space communications systems to more common applications simply requiring the switching of an RF signal from one path to another (e.g. for the purpose of providing redundancy or antenna diversity). Although the specific requirements for each application have to be tailored to individual needs, the essential characteristics of the switches remain the same. There is a continuing need for high performance, small and versatile microwave switches for use in a range of RF commercial systems such as cellular GSM, UMTS, cable modems, direct broadcast and other point-to-point and point-to-multi-point broadcast systems and applications. With the increasingly complex nature of information transmission the demand for bandwidth rises, and so also the need to accommodate these functions in smaller outlines and ever decreasing power consumption requirements. They allow routing of microwave signals through desired paths in the system and sub-system, and enable the realisation of different schemes for signal combinations necessary for system implementation.

Today there are phased-array antennas, smart antennas (capable of providing shaping and electronic control of the main beam) and modern communications systems that require amplitude control and gain equalisation in different paths. This means that there are increasing requirements for gain setting and control circuits. These circuits are generally of digital architecture and provide binary weighted attenuation control to achieve the required performance objectives, or they can be analogue in nature.

In this chapter, we will first...