Study On X-Band RF MEMS Switched-Line Phase Shifter

Microwave phase shifters have been widely used in many fields such as instrumentation, metrology, power combining and linear amplifiers. In particular, the most prevalent use of phase shifters is in scanning phased-array antennas. Even though the utility of phased-array antennas continues to be occupied by military radar and tracking platforms, many commercial applications have emerged in the past decade or so. For example, it can be employed in low-Earth-orbit (LEO) communications satellite constellations and collision warning radar, or in an aspect of the Intelligent Vehicle Highway System or Automated Highway System. Military phased-array radar has been facilitated with high cost ferrite phase shifters, which hold a portion of 40 percent of the overall antenna cost. Besides ferrite phase shifters, PIN diode or FET based phase shifters have been well developed in the past ten years. Microwave phase shifters with MEMS switches have merits over solid-state devices such as the high cut-off frequency, low loss, small volume,etc.The application of MEMS technology in radio frequency field annouced the advent of a new research branch-RF MEMS. RF MEMS devices are not only much smaller in size and easier to be integrated than conventional ones, but the performances have also been enhanced. Compared with conventional radio frequency components, RF MEMS devices have advantages of small size, low consumption, light weight, low cost, etc. It has good compatibility with standard integrated circuit processing, which makes monolithic integration possible. MEMS technology has provided an effective solution for wireless communication system to be miniaturized, low consumption and low loss. The fundamental theory of MEMS-based microwave phase shifters has been introduced, and also the mechanism of various MEMS phase shifters has been discussed. A meandered CPW configuration has been proposed as transmission line of phase shifters to overcome the deficiency of conventional switched-line phase shifters with large chip area. The elastic coefficient and actuated voltage have decreased by adding auxiliary driven electrodes and bend structures with suspending beam. It is shown that the simulated 45°, 90°and 180°RF MEMS phase shifters with switches driven by electrostatic power have low driven voltage, low return loss, low insertion loss and effectively reduced on-chip size of phase shifters by introducing meandered CPW.0/45°, 0/90°and 0/180°MEMS phase shifts have been designed, simulated and finally fabricated through UV-LIGA process. The area of the proposed phase shifter has achieved about 60% reduction of the conventional one's on silicon wafer. Fabricated phase shifters showed low insertion losses of 2.25dB at 10GHz and return losses of less than -21.1dB in X-band. The offsets of phase differences in all fabricated devices were below 7.6% at 10GHz. The measured results are better than simulated ones.