Complex multiple antenna systems are emerging today as market pressures to improve link capacity and reliability on complex integrated platforms. Complexity is therefore inherent in both the analysis and design of such systems. Modal analysis of various types has been used in a variety of fields to manage this inherent complexity. For single antenna systems, the Theory of Characteristic Modes (CM) has been used to great success in designing single antennas. In this dissertation, four interconnected topics are discussed, which are crucial to the proper extension of Characteristic Modes to complex antenna systems, especially multiple antenna systems.
First, existing characteristic mode systems are reviewed and their common properties examined. A software architecture is then discussed which enables the computation of characteristic modes in general, requiring only that the particular system definition satisfies those common properties. The software is used to perform all computations, analyses, and designs in this dissertation.
Second, a general, high-performance, wideband mode tracking system is proposed. It is shown to be efficient and robust through several challenging examples. It is the first robust tracker proposed in connection with Characteristic Modes.
Third, a procedure is proposed to compute the number, location, and even voltages of ports on a given antenna or antennas using a CM description of the problem. Its mathematical construction is inspired by results from the emerging field of Compressed Sensing. Its generality is demonstrated through a number of simulated designs.
Lastly, two new modal systems related to CM are proposed. One modal system, Subsystem Classical Characteristic Modes, produces modes which successively optimize the ratio of stored power to radiated power for an antenna embedded in a multistructure system. The other modal system, Target Coupling Characteristic Modes, produces modes which successively optimize the ratio of induced current intensity on a target structure to the current intensity on a source antenna. The modal systems are related through a projection matrix, which demonstrates the tradeoff between mutual coupling and radiation properties for a given multiple antenna system. The two modal systems are applied to several examples to validate their properties. Then, they are used in a new design procedure to systematically reduce the mutual coupling between two parallel dipoles. It is found that through loading an intermediate structure suggested by the proposed modal systems, the mutual coupling may be reduced, also predicted by the modal coupling analysis. The resulting designs generally improve upon designs available in the literature.
The dissertation concludes with a summary and discussion of future work. The appendices discusses various definitions, including a novel derivation of Classical Characteristic Modes from the starting point of orthogonal eigenpatterns.