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

Radiowave propagation through various complex environments is a field of active research due to the impact it has on various communication systems. One aspect of radiowave propagation in the marine atmospheric boundary layer (MABL) is the ducting propagation mechanism. Duct formation is highly dependent on atmospheric conditions and hence, research on ducting propagation involves propagation measurements with atmospheric characterization. These measurements eventually lead to improved modeling of such a propagation mechanism. Another aspect of electromagnetic (EM) signal propagation in the atmosphere is the presence of small scale fluctuations of the refractive index leading to the variation of the amplitude and the phase of the received signal. This signal fluctuation is known as scintillation. Scintillation is one of the reasons for signal enhancement or fading in any air-ground or ground-ground communication link. Apart from the atmospheric conditions, factors like rough seas, mountainous terrain or vegetation affect signal propagation. The goal of this dissertation is to develop a comprehensive simulation model using the parabolic wave equation (PWE) to predict the signal propagation effects in all the aforementioned atmospheric and surface conditions. Various experimental campaigns were conducted to measure the propagation loss which can be used to validate the different simulation cases. In all the experiments, a transceiver system, operating from 2 GHz - 40 GHz, was used to measure the propagation loss in different ground/air-ground communication links. In the 2017 CASPER West campaign in southern California, a link was established between the research platform, R/P Flip, stationed around 46.7 km from the shore to measure the propagation loss with time. These fixed ground-ground measurements were made such that the scintillation prediction made in the turbulent MABL by the PWE can be validated. In another campaign, PIMTER 2019, the transceiver system, (open full item for complete abstract)

Committee: Caglar Yardim (Advisor); Robert Burkholder (Committee Member); Joel Johnson (Committee Member) Subjects: Electrical Engineering; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

An important application of air-sea interaction research is in characterizing marine atmospheric boundary layer (MABL) properties, electromagnetic ducting in particular, in order to predict radar and radio communication conditions in the maritime environment. Ducting propagation is highly dependent on atmospheric conditions; experiments that combine propagation measurements with detailed atmospheric characterization can offer opportunities for improving modeling of the MABL effects on propagation. While refractive conditions can be directly measured or calculated using numerous methods, inversion methods using electromagnetic measurements can directly determine the impact of the atmosphere on radio frequency systems. A new X-band vertical array system is developed for measuring and characterizing electromagnetic (EM) propagation in the MABL. In particular, the evaporation duct that commonly forms over water is investigated as part of the CASPER (Coupled Air-Sea Processes and Electromagnetic ducting Research) at-sea experimental campaign conducted off the coast of Duck, NC, during October-November of 2015. Monte Carlo simulations are first used to develop an optimal array of four vertically spaced receiving antennas. In the experiment, the antennas are mounted on the stern A-frame of a research vessel and measure EM signals transmitted from beacons mounted on another research vessel and on the pier at the Army Field Research Facility. While the propagation loss vs. range provides a dataset similar to previous work, the vertical array can provide sampling of modes in the leaky waveguide formed in the duct. Combining both range and height sampling results in a robust inversion method for evaporation duct estimation. In this dissertation the efficacy of the 4-element array is demonstrated by estimation of the evaporation duct height through comparison with a library of precomputed propagation curves generated using the parabolic wave equation (PWE). Low model error gi (open full item for complete abstract)

Committee: Robert Burkholder (Advisor) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering

Variations in the refractive properties of the marine atmospheric boundary layer (MABL) can lead to non-standard propagation of radiowaves. An ability to quickly assess the influence of the atmosphere on shipboard surveillance and communication systems is required to avoid unwanted extended signal transmissions as well as poor functionality of these systems. While refractive conditions can be determined in numerous ways, methods utilizing radio frequency propagation measurements can directly determine the impact of the atmosphere on these systems. A novel transmit-receive array system called the X-band Beacon-Receiver array (XBBR) was developed with the purpose of determining MABL evaporation duct height (EDH) values. An experiment campaign was conducted to deploy the multichannel array system and corresponding beacon transmitters to investigate their ability to characterize MABL refractivity utilizing both the amplitude and phase of recorded signals. The method proposed compares propagation loss and phase values given by the Variable Terrain Radio Parabolic Equation (VTRPE, Ryan, 1991) modeling software for various propagation environments with measurements obtained by the XBBR array. Meteorological data was also recorded to act as input to the Navy Atmospheric Vertical Surface Layer Model (NAVSLaM); this allows for determination of the evaporation duct height from in-situ meteorological data to serve as the ground truth for comparison with our evaporation duct height estimation. Furthermore, this dissertation investigates the temporal and spatial fluctuations of radio frequency transmissions in a turbulent atmosphere. The multiple receive channels of the XBBR allow for the covariance of signals measured at each receiver to be compared with a model and atmospheric turbulence parameters to be extracted. This model is then used to simulate possible transmit and receive array configurations in an attempt to optimize system performance and minimize ambiguities (open full item for complete abstract)

Committee: Joel Johnson (Advisor); Fernando Teixeira (Committee Member); Robert Burkholder (Committee Member) Subjects: Electrical Engineering