Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

With an increasing demand for high-speed wireless communication, current wire- less infrastructure cannot provide the bandwidth required for high-speed data transfer for multiple users. The next generation of millimeter-wave (mmW) communication systems operate in the frequency range of 30–300 GHz and can provide orders of magnitude greater bandwidth. In addition, these systems rely on adaptive strategies to achieve high data-rate communication which requires reconfigurable elements. In our research, we introduce a new class of reconfigurable radio frequency (RF) microsystems using paraffin phase-change material (PCM) that enables low-loss recon- figuration for mmW components. Paraffin (alkane) is a low-loss nonpolar dielectric that undergoes a 15% reversible volume change through its solid to liquid phase transition. Using this unique combination of loss characteristics and mechanical properties, we have developed continuously variable capacitors. These electro-thermally actuated variable capacitors are low loss with series resistance of less than 0.7 Ω at the mmW band and can be monolithically integrated with antennas and RF components to introduce reconfiguration. In this work, we present a frequency reconfigurable slot antenna which covers the 94 GHz–102 GHz band. In order to achieve reconfiguration, the slot antenna is loaded with two paraffin PCM capacitors. The capacitors are actuated using joule heaters and with the increase in temperature, paraffin goes through a solid to liquid transition. As the volume of the paraffin increases, the capacitance decreases continuously by approximately 15%, which results in increasing the resonance frequency. The realized gain of the antenna at 100 GHz is 3 dBi and it is approximately constant over the reconfiguration range. The Efficiency of the antenna is >72% for the entire reconfiguration range thanks to the low dielectric loss of the paraffin. To evaluate the performance gains of the reconfigurable antennas, new p (open full item for complete abstract)

Committee: Nima Ghalichechian Professor (Advisor); Khalil Waleed Professor (Committee Member); Kubilay Sertel Professor (Committee Member); Kisha Radliff Professor (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering

Semiconductor materials biased with a static magnetic field are used here to design and analyze several nonreciprocal devices that can operate above 30 GHz and into the terahertz range. These devices overcome some limitations of biased ferrites in terms of frequency, bandwidth, compatibility with the monolithic-microwave-integrated-circuits technology, and the required magnetic bias magnitude. In this dissertation, simulated results will be provided for several practical bulk and planar devices operating at room and liquid-nitrogen temperatures. The main structures that are being used are based on a longitudinally-biased coaxial waveguide, and a transversely-biased slotline waveguide. These two types of waveguiding structures were extensively studied under the influence of changing frequency, static bias, and device parameters. A long list of features accompanied the design of these devices, which, to the best knowledge of the author, are reported here for the first time and would facilitate the adoption of magnetoplasma-based devices to a variety of applications. The semiconductor materials are carefully modeled and introduced into Maxwell's equations by means of Drude's model. The loss mechanism in the magnetized plasma was taken into account due to its huge impact on the devices efficiency and overall performance. Based on a modified commercial finite element method code, two-dimensional eigenmode simulations as well as three-dimensional models are used as primary tools to illustrate the phenomena, analyze and optimize the devices, and demonstrate their operation. This dissertation concludes with a detailed study of surface plasmons and their relation to the well-known volumetric waveguide modes through a generalized microscale model of metals that is valid from DC to optical frequencies.

Committee: Roberto Rojas PhD (Advisor); Joel Johnson PhD (Committee Member); Siddharth Rajan PhD (Committee Member); Michael Ibba PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Master of Science, The Ohio State University, 2010, Electrical and Computer Engineering

Existing electronic upper frequency is being constantly challenged to cater for new and state-of-the-art wireless applications. The conventional voltage controlled oscillator (VCO) designs are not sufficient to meet the trend. This calls for innovative and novel architectures. Utilizing the concept of distributed-loaded phase shifters we delve on the idea of implementing a tunable wideband VCO in W and V band. By periodically loading a coplanar waveguide transmission line with varactors, we can vary the phase velocity of the signal travelling through the line and thus creating a true time delay element. Through proper feedback, this system becomes analogous to a ring oscillator which is tunable by an analog control voltage. Based on these concepts, a distributed-loaded phase shifter was designed in 90nm CMOS technology with center frequency of 100 GHz (W-band) and 60 GHz (V-band). A bandwidth of ~27% and ~30% were achieved respectively. The worst case insertion loss and worst case return loss were kept less than 10dB for both the bands. The performance is limited by the limited tuning range of CMOS varactors and deteriorating quality factor with increasing frequency.

Committee: Waleed Khalil (Advisor); Mohammed Ismail (Committee Member) Subjects: Electrical Engineering