Date

2017

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Electrical Engineering

First Adviser

Hwang, James C.

Abstract

Low-dispersion phase shifters are key components for electrically large phased-array radar and communication systems. Unlike true-time-delay phase shifters with linear dispersion, low-dispersion phase shifters can be designed by switching between right-handed (low-pass) and left-handed (high-pass) states to achieve a constant phase shift over a wide bandwidth. However, the implementation of low-dispersion phase shifters with MEMS switches has been challenging. The designs to date suffer from either high insertion loss or high dispersion. Most important, they all occupy a large area and use a large number of MEMS switches, which negatively impact the yield and reliability, especially in view of the relatively immature RF MEMS technology.This dissertation studies design, implementation, characterization and modeling of novel metamaterial-based low-dispersion multi-bit phase shifters that use single-pole-single-throw MEMS capacitive switches to switch between right-handed and left-handed states for a specified phase shift. Three-dimensional finite-element electromagnetic simulation was used to design the basic unit cells. Each phase shifter unit cell is based on a coplanar slow-wave structure with defected ground and uses two MEMS switches in series and parallel configurations. In this dissertation, for the first time, we enhanced the maximum achievable phase shift of metamaterial-based MEMS phase shifter unit cell from 45° to 180°.Thanks to our novel 180° unit cell design, for the first time, the number of required MEMS switches for multi-bit phase shifter was reduced to two times of bits count such that a 3-bit phase shifter requires only six MEMS switches. For 2-bit and 3-bit phase shifters fabricated on a 600-µm-thick sapphire substrate, a relatively flat phase shift was obtained across the band of 21.5‒24.5 GHz with a root-mean-square phase error of less than 14°. Across the same frequency band, presented 2-bit and 3-bit phase shifters have less than 2.7 dB and 3.4 dB insertion loss, respectively.Accurate modeling and electromagnetic simulations were performed to characterize the insertion loss of the presented phase shifters. The loss is mainly due to replacing gold for copper during fabrication as well as having lossy substrate. Furthermore, there is extra mismatch loss associated with the non-flat membrane as well as radiation loss. This can be further reduced by optimizing the MEMS switch and the coplanar waveguide. The present design principle appears to be sound and can lead to phase shifters with high performance, yield and reliability with low cost for electrically large phased-array antennas.

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