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Title:Synthesis process using characteristic modes for multiple in situ antennas for system radiation requirements
Author(s):Bohannon, Nicole L
Director of Research:Bernhard, Jennifer T.
Doctoral Committee Chair(s):Bernhard, Jennifer T.
Doctoral Committee Member(s):Franke, Steven J.; Jin, Jianming; Buxton, Carey G
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
characteristic mode theory
radiation pattern
platform radiation
Abstract:Current methods for installing multiple antennas on a platform rely on trial and error or are primarily focused on isolation. Antenna designers create elements, place them on the platform, and then evaluate the results. This method is slow and does not utilize the platform geometry to achieve better performance. The goal of this research is to develop a synthesis method to design multiple antennas on a platform with a focus on radiation pattern performance. Characteristic mode theory is commonly used to determine how structures will radiate. Solving for the modes on a structure gives the antenna designer an idea of which modes are easily excited on a structure. Each mode is associated with a modal far field. Because this research focuses on the impact of platform geometry on radiation pattern, characteristic mode theory is a natural fit. This dissertation first examines how to excite higher order modes on structures. It compares the surface currents for each mode and determines a feed region. The element is then designed based on the feed location and the required direction of the surface current. When the desired pattern is not associated with a modal far field, this dissertation develops a novel method for solving for the radiation pattern closest to the goal radiation pattern hat is achievable on the structure. The radiation pattern solution corresponds to a specific surface current that must be excited by an element to create the optimized pattern. There are two optimization techniques provided. The first method requires the designer to specify power and polarization for the goal pattern while the second only requires specifying power. These methods are novel as they do not require the modal weighting coefficients to be equiphase. These methods for determining surface current are combined to make a synthesis method for designing antenna elements at multiple frequencies to be installed on one platform based on goal radiation patterns. The synthesis method begins with calculating the optimal surface currents for each frequency. Starting at the lowest frequency, antenna elements are designed based on the surface current. To demonstrate the new method, three antennas were designed and installed on a CubeSat chassis for operation at 400 MHz, 435 MHz, and 915 MHz. The platform was then constructed and the antenna performance was compared to the simulated performance. Last, the modal far fields for the CubeSat were compared when there were slight changes to the simulated platform to account for changes between the simulated and constructed platform. Using a slightly altered platform, the optimized patterns were found for the identical scenario as the previous example. The resulting patterns and surface currents are compared to show the impact of model fidelity on the success of the developed synthesis method.
Issue Date:2016-11-11
Rights Information:Copyright 2016 Nicole L. Bohannon
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12

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