Graduation Year

2016

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Gokhan Mumcu, Ph.D.

Committee Member

Thomas Weller, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Nathan Crane, Ph.D.

Committee Member

Paul Herzig, B.S.E.E.

Keywords

High-power, Microstrip, Resonator, Tunable, X-Band

Abstract

Radio Frequency (RF) filters are among the key components of today’s multifunctional devices and test equipment. However, the multifuctionality need significantly drives the required filter number and causes large areas to be allocated for filters. To alleviate this issue, over the recent years, reconfigurable filters have been proposed as an attractive alternative. Nevertheless, existing reconfigurable filter technologies demonstrate degraded performances in terms of loss, frequency tunability bandwidth, and power handling capability. This work investigates, for the first time, microfluidic based reconfiguration techniques for implementation of RF bandpass filters. Specifically, microfluidics is shown to provide mechanisms for achieving compact RF bandpass filters that can exhibit low loss, high power handling, and high frequency tunability. First, we present the utilization of liquid metals for realization of a frequency-agile microstrip bandpass filters consisting of broadside coupled split ring resonator (BC-SRR). In this design approach, one of the loops of the BC-SRR is realized from liquid metal to be able to microfluidically change the resonator shape and associated resonance frequency. The filter exhibits a 29% frequency tunable range from 870 MHz to 650 MHz, with insertion loss <3 dB, over the entire frequency tuning range, for a fractional bandwidth (FBW) of 5%. To the best of our knowledge, this filter design is the first in available literature that shows a continuously frequency reconfigurable microfluidic RF band-pass filter. To overcome the oxidization and lower conductivity issues associated with liquid metals and enhance the frequency tuning range further, subsequently, we introduce a filter design technique in which microfluidically repositionable metallized plates are utilized within microfluidic channels with ultra-thin insulator walls. Specifically, this technique is employed to design a two pole microstrip bandpass filter where microfluidically repositionable metalized plates are used to capacitively load printed open loop resonators. To operate the filter (and control movement of multiple metalized plates) with a single bi-directional micropump unit, a strategically designed meandered microfluidic channel is implemented. The filter exhibits a 50% tuning range (from 1.5 GHz to 0.9 GHz), with an insertion loss <1.7 dB for a fractional bandwidth (FBW) of ~5%. Following this success, the concept of microfluidic based reconfigurability is generalized to the implementation of higher order filters, for the first time in available literature, by designing two different fourth order bandpass filters. These filters exhibit linear and diagonal layout arrangements to demonstrate that microfluidic based reconfigurable RF filters can meet different footprint requirements as well. Selectively metallized plates are also employed for the first time to alleviate synchronized movement issues. The filters operate with 60% frequency tuning range, 5% (+/- 1%) FBW, and <4.5 dB of insertion loss. Finally, we demonstrate that microfluidically repositionable selectively metalized plates can also be used to dynamically redefine the lengths of the microstrip line half wavelength resonators when resorted to ultra-thin microfluidic channel walls. By using this approach, a microstrip line combline filter is designed to realize a low loss and highly tunable (~2.7:1) RF bandpass filter that can also operate with near constant insertion loss performance. The fabricated prototype exhibits a 90% (2.7:1, 4 GHz to 1.5 GHz) frequency tuning range with 5% (+/- 1%) FBW and insertion loss below 3 dB. Since microfluidics presents an opportunity for high power RF applications, power handling capabilities of these novel combline filters are computationally and experimentally demonstrated. The filters can handle above >15 W input power without the need of thick ground planes and/or heat sinks.

Share

COinS