Browsing by Subject "Antennas"

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    Characterizing Phase-Center Motion of GNSS Antennas Used in High-Accuracy Positioning
    (Center for Transportation Studies, University of Minnesota, 2019-06) Dave, Aditya; Saborio, Ricardo; Sun, Kerry; Sainati, Robert; Gebre-Egziaher, Demoz; Franklin, Rhonda
    Emerging transportation applications require positioning solutions with accuracy of a few centimeters. Current Global Navigation Satellite Systems (GNSS), such as GPS, GLONASS, and Galileo are, in some instances, capable of providing this level of accuracy. Real-Time Kinematic (RTK) techniques can generate solutions accurate to a few centimeters in a given locale. Precise Point Positioning (PPP) techniques promise to deliver RTK-level performance on a global scale. Even though low-cost, RTK-capable GNSS receivers are available today, antennas are a key component affecting quality of the positioning solution. Unless coupled with a high-quality (thus, more expensive) antenna, a low-cost receiver may not provide the centimeter-level accuracy needed for a safety-critical transportation application (e.g., autonomous vehicle, driver assist systems, etc.). Stability of the antenna phase-center is dependent on the antenna quality and can potentially move on the order of tens of mm if not centimeters. The purpose of the work reported here was to characterize the nature of this motion as a function of antenna quality. Anechoic chamber tests were performed using one high-cost and another low-cost GNSS antenna. The selected antennas represented “book ends” on the cost spectrum. These experiments showed that phase-center motion on the low-cost antenna can be a factor of four times larger than on high-quality antennas. Since anechoic chamber tests are not practical for each antenna installation in transportation applications, methods for antenna-specific, in-situ, phase-center motion calibration (modelling) methods have been suggested. Preliminary results suggested efficacy of these in-situ methods.
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    Development of High Efficiency Metamaterial Antenna Structures for Near-Field and Far-Field Applications
    (2022-08) Dave, Aditya
    With the advent of mmwave 5G, and future G technologies, there is a path paved for multitude of applications in the cellular, augmented and virtual reality (AR/VR), internet-of-things (IoT) etc. domains. There is a need for compact, highly directional and low-loss antennas for reduced size, greater coverage, low power consumption. Partially reflective surfaces as superstrates are well known for enhancing antenna radiation. However, in the past, electrically large surfaces were used with little regards to the size and aperture efficiency of the antennas. In this dissertation, compact source antennas are used with smaller 2D metamaterial superstrates acting as partially reflective surfaces (PRS) to form metamaterial antenna (MMA) block. The dissertation is divided into three segments. After going over the theoretical framework for infinite periodic surfaces and development of equivalent circuits in chapter 2, finite PRS surfaces with source antennas are analyzed in chapters 3 and 4. Different types of PRS surfaces and source antennas are changed one at a time to explain the design methodology and arrive at highly aperture efficient MMA blocks. In chapter 5, single MMA block is used to create virtual arrays using beam-splitting PRS designs and analyze its performance with conventional arrays. The single MMA blocks are also showcased in array element reduction applications to reduce feedline complexities associated with conventional arrays. Chapter 6 focuses on formation of passive phased arrays using near field phase manipulation properties of the PRS. This property is used to create dual beam antennas. Next, designs that focus on creating polarization splitters using yet another variation of PRS, called beam and polarization splitting PRS (BPS-PRS) are proposed. The dual beam antennas and polarization splitters can be applied to emerging multiple-input multiple-output (MIMO) communication applications. MMAs are also useful as GNSS positional sensors as seen by their low phase center variation properties which are also showcased. Finally, chapter 7 focuses on near-field applications of the MMA by proposing free space vertical interconnects and power dividers that are useful for high frequency printed circuit board (PCB) integrated chip-to-chip intra-connects and interconnects. Additional loss reduction technologies that are useful for on-chip silicon implementations are also demonstrated by using Copper nanowires on coplanar waveguide transmission lines for frequency ranges up to 180 GHz. Chapter 8 concludes the work and gives directions for the future work.