Author: Chad Slick

Publisher:

Published: 2007

Total Pages: 452

ISBN-13:

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Abstract: The current state-of-the-art adaptive antennas for Global Positioning System (GPS) receivers are planar antenna arrays. Due to the planar nature of these antenna arrays, the resolution with respect to the elevation plane is limited if the antenna is mounted in a horizontal plane. The nulls formed by the adaptive antenna in response to low elevation radio frequency interference (RFI) signals extend significantly into the elevation plane resulting in performance degradation. One solution to combat this problem is to use non-planar adaptive antennas with GPS receivers. The non-planar adaptive antenna can exploit its geometry to provide RFI suppression against low elevation interfering signals while maintaining reception of low angle signals of interest (SOI) to yield highly accurate Position, Velocity, and Time (PVT) solutions. It will be shown that convex non-planar antenna arrays perform significantly better than planar antenna arrays as well as concave non-planar antenna arrays in the presence of low elevation RFI signals. Also, an increase in the curvature of the antenna array will result in AJ performance improvement. All antenna arrays studied in this thesis have similar projected area (looking from the top) relative to the current state-of- the-art planar adaptive antenna (GAS-1 CRPA). Moreover, the convex non-planar antenna arrays contains more surface area allowing the addition of more antenna elements resulting in further performance improvement. The antenna element used in this study is a dual stacked microstrip patch antenna designed to operate at the L1(1575.42 MHz) and L2(1227.6 MHz) GPS frequencies. Rigorous electromagnetic (EM) modeling, which takes into account mutual coupling of antenna elements and array structure, of the various antenna arrays is performed to obtain the in situ volumetric patterns of the individual antenna elements. This thesis also focuses on determining the optimum number of elements as well as their distributions based upon antenna array performance for a fixed aperture size of a six inch high and two inch high convex non-planar adaptive antenna. The antenna arrays investigated have a single constraint to have the reference element distributed at the top of the convex surface to provide upper hemispherical coverage. The adaptive antenna performance is evaluated with respect to the adaptive algorithms of simple power minimization and beam forming / null steering. The performance metrics are the output Signal-to-Interference plus Noise Ratio (SINR) and the average available region over the upper hemisphere for which the output SINR exceeds a selected value in the presence of multiple interfering signals, where the average value is obtained by performing Monte Carlo simulations. It will be shown that for the six inch high surface, it is better to distribute the antenna elements along two rings, with the inner ring at an angle of 450 from the centroid (a height of 4.24"), and the other ring along the bottom outer edge of the hemisphere. However, if less surface area is available, as is the case with the two inch high surface, it is best to distribute the remaining elements on the periphery of the antenna array. Furthermore, it will be shown that when adaptive antenna is operating in the beam forming / null steering mode the addition of more elements always leads to improved performance; however, this does not hold true when the adaptive antenna is operating in the simple power minimization mode.

Download or read book Non-planar Adaptive Antennas for GPS Receivers written by Chad Slick and published by . This book was released on 2007 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The current state-of-the-art adaptive antennas for Global Positioning System (GPS) receivers are planar antenna arrays. Due to the planar nature of these antenna arrays, the resolution with respect to the elevation plane is limited if the antenna is mounted in a horizontal plane. The nulls formed by the adaptive antenna in response to low elevation radio frequency interference (RFI) signals extend significantly into the elevation plane resulting in performance degradation. One solution to combat this problem is to use non-planar adaptive antennas with GPS receivers. The non-planar adaptive antenna can exploit its geometry to provide RFI suppression against low elevation interfering signals while maintaining reception of low angle signals of interest (SOI) to yield highly accurate Position, Velocity, and Time (PVT) solutions. It will be shown that convex non-planar antenna arrays perform significantly better than planar antenna arrays as well as concave non-planar antenna arrays in the presence of low elevation RFI signals. Also, an increase in the curvature of the antenna array will result in AJ performance improvement. All antenna arrays studied in this thesis have similar projected area (looking from the top) relative to the current state-of- the-art planar adaptive antenna (GAS-1 CRPA). Moreover, the convex non-planar antenna arrays contains more surface area allowing the addition of more antenna elements resulting in further performance improvement. The antenna element used in this study is a dual stacked microstrip patch antenna designed to operate at the L1(1575.42 MHz) and L2(1227.6 MHz) GPS frequencies. Rigorous electromagnetic (EM) modeling, which takes into account mutual coupling of antenna elements and array structure, of the various antenna arrays is performed to obtain the in situ volumetric patterns of the individual antenna elements. This thesis also focuses on determining the optimum number of elements as well as their distributions based upon antenna array performance for a fixed aperture size of a six inch high and two inch high convex non-planar adaptive antenna. The antenna arrays investigated have a single constraint to have the reference element distributed at the top of the convex surface to provide upper hemispherical coverage. The adaptive antenna performance is evaluated with respect to the adaptive algorithms of simple power minimization and beam forming / null steering. The performance metrics are the output Signal-to-Interference plus Noise Ratio (SINR) and the average available region over the upper hemisphere for which the output SINR exceeds a selected value in the presence of multiple interfering signals, where the average value is obtained by performing Monte Carlo simulations. It will be shown that for the six inch high surface, it is better to distribute the antenna elements along two rings, with the inner ring at an angle of 450 from the centroid (a height of 4.24"), and the other ring along the bottom outer edge of the hemisphere. However, if less surface area is available, as is the case with the two inch high surface, it is best to distribute the remaining elements on the periphery of the antenna array. Furthermore, it will be shown that when adaptive antenna is operating in the beam forming / null steering mode the addition of more elements always leads to improved performance; however, this does not hold true when the adaptive antenna is operating in the simple power minimization mode.