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Feliciano, WalberDesign and Implementation of a Radiometer and Rain Data Collection System for a Ka-band LEO Ground Station
Master of Science, University of Akron, 2009, Electrical Engineering
The design and performance of broadband Ka-band satellite communication systems depends mostly on the radio propagation characteristics of the earth-to-space path. The goal of this project was to develop and deploy a low earth orbit (LEO) ground station terminal capable of collecting radiometric and beacon data at Ka-band frequencies; which ranges approximately from 20 to 30 GHz. LEO satellites will employ high data rates to transfer very large amounts of data. High data rates require large channel bandwidth; a motivation to utilized Ka-band frequencies. Many radio frequency (RF) propagation effects are more severe at Ka-band frequencies than at lower frequencies. Collected data can be statistically analyzed and used to study the Earth’s atmosphere RF propagation effects at Ka-band, applicable to LEO links; thus improving the system availability models currently used. Collection of propagation data and its analysis is important for the development of satellite link analysis and communication component design, capability and requirements. Currently no LEO attenuation prediction models are available at Ka-band. This project provides a starting point to understand the dynamic effects of the Earth’s atmosphere on rapidly changing Ka-band transmission from a LEO spacecraft. A LEO propagation model will enable communication system designers to improve their systems availability.

Committee:

Nathan Ida, PhD (Advisor)

Subjects:

Electrical Engineering

Keywords:

LEO;Ka-band;Propagation;Ground Station;Radiometer

Zemba, Michael JSite Characterization of Phase Instability via Interferometer Measurement
Master of Science in Engineering, University of Akron, 2013, Electrical Engineering
Single-dish reflector antennas are often used for their ability to produce a highly directive (narrow beam) radiation pattern which increases in directivity as the diameter of the reflector increases. However, as reflectors grow larger in the pursuit of more directivity, they become more expensive and unwieldy to construct, maintain, and operate. A more practical solution is to employ an array of elements which are smaller individually, but which can yield similar or better gains when arrayed together. However, one trade-off associated with this approach is that antenna arrays are subject to losses introduced by atmospheric turbulence. Inhomogeneous cells of water vapor in the troposphere change the refractivity of the air along the path of the propagating wave, distorting the wavefront and introducing a phase error between the elements of the array. These losses are stochastic and site-dependent. Techniques have been developed over the past several decades to compensate for such losses on the receiving end, but uplink arraying remains challenging as it requires prediction of atmospheric conditions to effectively compensate the signal before transmitting. This is especially true at higher frequencies such as Ka-band given that atmospheric phase noise increases with frequency. Thus, a critical first step in system planning is to determine the losses a particular array configuration will experience based on the phase statistics of a given site. To this end, NASA Glenn Research Center has deployed site test interferometers to three ground-station sites with the intent to characterize their phase instability ahead of upgrades to Ka-Band operation. The sites to be studied are Goldstone, California; White Sands, New Mexico; and the island of Guam. Using three years of data collected from these campaigns, the primary goal of this thesis is to develop a thorough characterization of the phase statistics of each site which may then be used to determine the sites’ suitability for uplink arraying. In addition, a secondary goal is the development of the data analysis software suite that was used to process the data, which it is hoped will facilitate easy analysis of future sites for system designers.

Committee:

Nathan Ida, Dr. (Advisor); Igor Tsukerman, Dr. (Committee Member); Subramaniya Hariharan, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Electrical Engineering; Electromagnetics; Electromagnetism; Engineering

Keywords:

Antenna Arrays; Phase Noise; Atmospheric Phase Instability; Propagation Measurements; Interferometry; NASA; Ka-Band; Radio Frequency; Electrical Engineering; Electromagnetics; Antennas; Propagation; Site Test Interferometer

Richard, Mark AdrianAn experimental investigation of high temperature superconducting microstrip antennas at K- and Ka-band frequencies
Doctor of Philosophy, Case Western Reserve University, 1993, Electrical Engineering
The recent discovery of high temperature superconductors (HTS) has generated a substantial amount of interest in microstrip antenna applications. However, the high permittivity of substrates compatible with HTS results in narrow bandwidths and high patch edge impedances of such antennas. To investigate the performance of superconducting microstrip antennas, three antenna architectures at K and Ka-band frequencies are examined. Super-conducting microstrip antennas that are directly coupled, gap coupled, and electromagnetically coupled to a microstrip transmission line have been designed and fabricated on lanthanum aluminate substrates using YBa2Cu3O7 super-conducting thin films. For each architecture, a single patch antenna and a four element array were fabricated. Measurements from these antennas, including input impedance, bandwidth, patterns, efficiency, and gain are presented. The measured results show useable antennas can be constructed using any of the architectures. All architectures show excellent gain characteristics, with less than 2 dB of total loss in the four element arrays. Although the direct and gap coupled antennas are the simplest antennas to design and fabricate, they suffer from narrow bandwidths. The electromagnetically coupled antenna, on the ot her hand, allows the flexibility of using a low permittivity substrate for the patch radiator while using HTS for the feed network, thus increasing the bandwidth while effectively utilizing the low loss properties of HTS. Each antenna investigated in this research is the first of its kind reported.

Committee:

Paul Claspy (Advisor)

Keywords:

experimental investigation high temperature superconducting microstrip antennas K- and Ka-band frequencies

Nessel, James AaronEstimation of Atmospheric Phase Scintillation Via Decorrelation of Water Vapor Radiometer Signals
Doctor of Philosophy, University of Akron, 2015, Electrical Engineering
The coherent arraying of antenna elements by widely distributed ground-based antenna systems has proven to be a valuable technological approach for high precision astrometric measurements and imaging via Very Long Baseline Interferometry (VLBI) and has been performed with considerable success by radio astronomers for several decades. The fundamental factor limiting the precision in which these measurements can be conducted, however, is due to the turbulence-induced refractivity changes of the atmospheric medium (troposphere) through which the propagating waves must traverse. For radio science applications, this problem can be significantly reduced via three well-demonstrated means: (1) proper choice of ground site location (i.e., dry, high altitude climates), (2) conducting observations during non-turbulent times (i.e., nights vs. days, winter vs. summer), and (3) employing relatively long integration time (on the order of minutes) compensation through the use of water vapor radiometers in data post-processing. For communications applications, however, this may not necessarily be the case, and a means to accurately estimate the water vapor variability of the troposphere at short time scales will be required to efficiently combine signals from ground-based antenna elements in an array environment, particularly for transmit arraying. It is thus the goal of this research effort to identify and validate a means in which phase fluctuations induced by the atmosphere can be accurately measured which could be employed to ultimately improve the coherent combining of several spatially separated signals transmitted from ground to space without the use of an active source (i.e., receive signal). The method in which this will be accomplished is through the use of a passive radiometric technique capable of accurately determining phase fluctuations on the necessary time scales to provide real-time phase compensation to realize transmit arraying at Ka-band frequencies and higher. To improve the accuracy over the state of the art in radiometric water vapor retrieval techniques, a novel blind source separation technique has been developed and demonstrated. Utilizing experimental data using a water vapor radiometer and a two-element interferometer, it is statistically shown that the approach described herein improves water vapor retrieval accuracy, particularly during cloudy conditions, over the state of the art.

Committee:

Nathan Ida, Dr. (Advisor); Igor Tsukerman, Dr. (Committee Member); Arjuna Madanayake, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member); Ernian Pan, Dr. (Committee Member)

Subjects:

Communication; Electrical Engineering; Electromagnetics

Keywords:

propagation; atmosphere; microwave; antenna array; Ka-band; water vapor radiometer; phase scintillation; interferometer; blind source separation