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Many communications systems demand the ability to receive narrowband signals that can occur anywhere, in any one of a number of channels, within a wide frequency band. Since the equipment receiving these signals must operate in coexistence with high-power transmitters [22] and because it is imperative to avoid interference, it is required that excellent filters with narrow instantaneous bandwidth, high out-of-band rejection, wide tunability, and low insertion loss be utilized. As these requirements are only met by unrealizable filters, the usual approach to the problem involves the parallelization of the receiver into independent channels, each one containing a filter of realizable characteristics (Figure 4.18) [22].

The key to this massively parallel receiver scheme, however, is to utilize, for signal routing and reconfiguration purposes, RF/microwave switches with virtually ideal performance (particularly low insertion loss) because they directly impact the noise figure, high linearity (because in some case they must route high-power signals), and low power consumption (because of the large number of them that are required). This is precisely one of the quintessential opportunities that may be enabled by RF MEMS switches [22]. Brown [22] pointed out that traditional implementations of this architecture, based on conventional switch technology (i.e., pin diode switches), are very massive, power-consuming, and expensive. For example [22], if the pin diode switches utilized in the front-end of the ARC-210?perhaps the premier radio for military airborne communications in the VHF and UHF bands between 30 and 400 MHz?

were to be replaced by MEM switches, the front-end noise figure would improve by 0.5 dB (from 4.5 to 4 dB), the transmitter-to-receiver isolation due to MEM switches in combination would improve by 20 dB (from 60 to more than 80 dB), and the total power consumption would be reduced from approximately 100 mW to less than 1 mW. Clearly, these projections could apply to the multiband/multistandard wireless transceivers that will enable the ubiquitous communications vision.