RF MEMS phase shifters: design and applications

Recent results obtained with MEMS phase shifters demonstrate that their performance is much better than GaAs phase shifters using either standard (switched-line, reflect-line) or distributed designs. The reliability of MEMS phase shifters is worse than of single switches since they employ 8-16 MEMS switches and do not tolerate a failure in any of the switches. On the other hand, a large phased array will still function properly, albeit with a slightly decreased efficiency and higher sidelobes if 3-4% of the phase shifters fail. Currently, the failure mechanisms of MEMS switches are being investigated and will greatly benefit the reliability of MEMS phase shifters. Also, the hermetic packaging of MEMS phase shifters is not straightforward, due to their relatively large size. It is for these reasons that the authors believe that MEMS phase shifters will be mostly used in satellite and defense applications in the next five years.

The Case for RF MEMS Phase Shifters

MEMS switches result in lower loss phase shifters at any frequency, especially from 8–120 GHz. The average loss of state-of-the-art 3-b MEMS phase shifters is −0.9 dB at 10–14 GHz, which is a 3–4 dB improvement over comparable on-wafer designs using FET switches. This translates to a 6–8 dB improvement in a radar or two-way telecommunication system. The improvement is quite high for Ka-band (35 GHz), V-band (60 GHz), or W-band (77 GHz, 94 GHz) systems (see Table 1). This means that one can eliminate an amplifier stage (or two) in the transmit/receive (T/R) chain, thereby resulting in a dc power reduction of 20–100 mW per element at X-to