Electronically Steerable Antenna Array using PCB-based MEMS Phase Shifters

Abstract

In this thesis, a novel approach for cost effective fabrication and assembly of MEMS based Electronically steerable antenna (ESA) arrays’ using flexible printed circuit processing techniques has been developed. The critical component of the MEMS ESA is a 3-bit phase shifter that is implemented using MEMS varactors, where each phase shifter consists of two MEMS varactors. The important feature of this approach is the use of flexible circuit film, kapton E polyimide film, as the movable membrane in the MEMS varactors used in the phase shifters that are used for the beam steering of the antenna. The important features of this approach are: a) The characteristic size is in the millimeter range and therefore the required dimensional tolerance and alignment accuracy can be achieved using conventional printed circuit processing techniques.

b) Batch fabrication of such antennas can be accomplished using existing roll-to-roll flexible printed circuit technology.

c) Beam steering angles of more than 10° can be easily attained. The ESA consists of three layers – polyimide film, spacer, and substrate. The Polyimide film, which is capable of withstanding millions of mechanical flexing cycles, is used as the movable phase shifter membrane layer. Phase shifter top electrode is defined on the polyimide film that forms the movable membrane. Coplanar waveguide (CPW) defined on the metallization layer of the substrate is used as the phase shifter bottom electrode. The spacer layer provides the required spacing between the substrate layer and the polyimide film layer. A dielectric layer spin-coated on CPW metallization is used to provide a capacitive contact in the phase shifter down position. Pull-down voltages for the MEMS varactors used in the phase shifters are in the range of 100 - 200 Volts. Design, modeling, and characterization of analog phase shifters, digital phase shifters and a folded slot antenna array are discussed. Beam steering performances of more than 10° for a two element MEMS ESA have been presented.