Tunable Patch Antennas Using Microelectromechanical Systems

Abstract

Abstract : Patch antennas are enablers in wireless applications due to their manufacturability, conformability, low cost, and low weight. However, they have narrow bandwidths and fixed operating frequencies that limit their utility when frequency agility is critical. The solution is a tunable patch antenna that retains the desirable features of its fixed frequency counterparts. Patch antennas can be tuned without changes in geometry through loading with variable capacitors or inductors. These components must be small, compatible with antenna and integrated electronics processing, and electrically controlled. Microelectromechanical systems (MEMS) variable components have these characteristics and have been applied in reconfigurable patch antennas. Loading with MEMS capacitors is a more mature technology while the use of MEMS inductors is in its infancy. Antennas tuned with both MEMS variable inductors and capacitors in combination have not been reported. This research presents tunable patch antennas using MEMS variable inductors and capacitors co-fabricated in the same process. To prove the tuning concept, patch antennas were loaded with discrete inductors and capacitors and tested. The results demonstrated frequency shifts as wide as 1.71 GHz with little impact on antenna radiation patterns. MEMS capacitors and inductors were designed and manufactured using the MetalMUMPS process. The capacitor uses electrostatic control to vary the distance between parallel plates, altering device capacitance. The inductor features pre-deformed beams that buckle under thermally-actuated mechanical force. Change in loop area formed by the beams alters device inductance. The MEMS were tested over an input voltage range from 0-100V. A 5 GHz patch antenna incorporating the MEMS inductor as a variable load was designed and tested. Results were compared to those of the unloaded antenna and demonstrated an operating frequency shift of 810 MHz, a tunable range of 40 MHz for input voltages from 0-30V.