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So far in this chapter we have addressed techniques for the reconfigurability of more or less discrete circuit elements. Another vein in the area of reconfigurability?namely, the MEMS microswitch array [14]?addresses the reconfigurability of distributed microwave components (i.e., of the very metal traces, or patterns, that would otherwise define the interconnection transmission lines and tuning stubs of microstrip-based microwave circuits). The fundamental enabler of this paradigm, the microswitch, is shown in Figure 4.9. The microswitch is a cantilever beam?type structure that can be arrayed in two dimensions with an interelement pitch of 100 mm. For implementation on a fused silica substrate (er = 3.8), this size corresponds to 1/20th the wavelength at 100 GHz or 1/200th the wavelength at 10 GHz, so that no issues of line-length quantization are elicited [14].

By addressing the two-dimensional array, where each microswitch may be thought of as a pixel, any given metal pattern image can be defined on the substrate, particularly as it is appropriate to a matching or tuning network. For example, Figure 4.10 shows the microswitch array-based tuning for a reconfigurable power amplifier, in which both the input and output matching networks are reconfigured to retune the optimum frequency of the amplifier.

Reconfigurable Circuits:

Impedance matching is one of the fundamental steps in the design and production of an RF/microwave circuit [15, 16]. In low-noise amplifiers (LNAs) and power amplifiers, properly tuned input/output matching networks are crucial to meeting required noise figure and power efficiency requirements.

In the production of low-volume MICs, or hybrid (discrete) circuits, it is the rule to manually tune the circuits until the desired performance levels are met; but this activity becomes too time consuming and expensive at millimeter-wave frequencies, not to mention impractical for high-volume applications and even impossible for MMICs. Thus, there is a strong incentive to exploit the power of RF MEMS to implement classic impedance matching schemes in an automated, reconfigurable fashion.