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Introduction:

For the first time in recent history, a technology is emerging that promises to enable both new paradigms in RF circuits and systems topologies and architectures as well as unprecedented levels of performance and economy. RF MEMS is widely believed to be such a technology [1?3]. There are at least two fundamental approaches for exploiting RF MEMS, namely, bottoms-up and top-down.

In the bottoms-up approach, the program to be followed would involve the direct replacement of conventional circuit elements by their superior RF MEMS counterparts, with minimum or no change in circuit topology and system architecture. In the top-down approach, the designer would begin with the proverbial clean sheet of paper, unprejudiced by the limitations and constraints imposed by conventional RF technologies, and devise circuits and systems that exploit, in the fullest possible fashion, the flexibility and power of RF MEMS. In this chapter, we present a sample of novel RF MEMS?enabled functions, which are the first fruits of both approaches. The key words describing these functions are reconfigurable and programmable (i.e., these elements, endowed by RF MEMS with the ability to be actuated, embody not just a single value, but a range of commandable values). These properties, in turn, will be exhibited by the circuits and systems of which they are a part.

Since most of these visionary ideas and techniques have, understandably, anticipated RF MEMS technology maturation, the presentation will be largely of a descriptive and qualitative nature. Nevertheless, it is expected that the ideas we have chosen to present will form the pillars upon which the paradigm of ubiquitous connectivity will be built. In order to emphasize the various ideas, the chapter is organized into three main sections dealing with circuit elements (devices), circuits, and systems.