Novel lateral RF MEMS switch and its application to multi-band microstrip antenna.

摘要

To meet the requirements for modern RF (Radio Frequency) systems such as small size and multi-band operation, the widespread development of MEMS (Micro-ElectroMechanical System) technologies gives one possibility for the development of a new class of RFICs (Radio Frequency Integrated Circuits). RF MEMS components promise a new era in RF systems in terms of reconfigurable or programmable microwave systems. This research is focussed on two areas, one is a multi-band microstrip antenna loaded with a varactor, and the other is a laterally-actuated RF MEMS switch. Extensive research has been focussed on the development of antennas that radiate and collect signals efficiently across a broad range of frequencies. Microstrip antennas are the most suitable configuration for a miniaturized RF portable system due to their smaller size, light weight, low cost and ease of fabrication and integration with RF devices. A common technique for the multi-band operation of microstrip antennas is reactive loading. The resonant frequency variation of microstrip antennas by a varactor is studied theoretically using full-wave Finite Difference Time Domain (FDTD) methods and experimentally using a GaAs FET diode. A tuning range of 46% around a center frequency of 2.75 GHz was achieved in the fabricated four-corner-varactor loaded microstrip antenna. It is well known that the MEMS varactor or MEMS switched-capacitor is superior to a conventional solid-state varactor. A MEMS varactor or MEMS switched-capacitor will overcome the tuning limits of conventional solid-state varactor, and increase the efficiency of loaded microstrip antenna due to high Q-factor, and avoid DC bias problem.; The electrostatically actuated RF MEMS switch is the most attractive configuration, and a natural choice for low power applications due to its ideally zero dc power dissipation. To achieve both good RF performance and low actuation voltage, a novel laterally-actuated RF MEMS switch is proposed and demonstrated in this research. It moves laterally, and inherently has a push-pull configuration, which significantly reduces the actuation voltage and the switching speed. In addition, this lateral RF MEMS switch can easily adopt new mechanisms to reduce the actuation voltage, such as narrow-gap techniques and mechanical amplification. A new narrow gap technique is proposed, applicable to gold electroplating. The simple fringing capacitance model is also revised to explain the mechanical characteristics of laterally-actuated RF MEMS switches using parallel-beam actuators. Switching operation up to 20 GHz is demonstrated in a lateral RF MEMS shunt switch, with the actuation voltage of 34 V. An insertion loss of 0.13 dB and the isolation of 26 dB at 1 GHz are achieved. The lateral shunt switch with bypass inductor is shown through HFSS (High Frequency Structure Simulator) simulation to improve the isolation, as much as 20 dB up to 20 GHz. The lateral RF MEMS shunt switch with bypass inductor is an example of optimizing the RF performance and mechanical characteristics separately by avoiding trade-off relationships in designing the RF and mechanical structures.