Theory of Dipoles, Array Factors, and Multi-Element Antennas with Physics-Based Propagation for Mobile Communications

摘要

Bandwidth, volume and energy are the basic resources for communications, and current signal processing techniques use these in many different ways. The bandwidth is limited by the antenna size, and maximizing the bandwidth of the elements and the design of multielement antennas (MEAs) require new research. This two-part thesis addresses antenna theoretic bandwidth and MEA evaluation. The limiting bandwidth of the most fundamental antenna element - the dipole - remains elusive despite its long research history. This motivates Part I, in which the bandwidth of the electric dipole is developed from theoretical and numerical methods, and recent measurements. The resulting antenna-theoretic bandwidth of the dipole with a feed gap offers new benchmark results for compact elements. The lossless, thin dipole with finite gap has a much wider bandwidth than was previously known, and the non-radiating feed is identified as the challenge to realize the available bandwidth. Using multiple-input multiple-output (MIMO) and other diversity techniques with large dimensions (many elements) is the key technology for high spectral efficiency. But large dimension MIMO is not yet used commercially, and the design methodology and evaluation of MEAs is undeveloped. There is no standard for evaluating MEAs used for MIMO communications, and currently, the physical evaluation of a MIMO terminal comprises coarse throughput tests in an idealized environment. The real-world performance of the terminal, and especially the antenna performance, remains unclear from such tests. This motivates Part II, which explores MEA evaluation using physical antenna parameters together with site-specific, ray-traced models for the spatial channel. Ray-tracing calculation is well established, but its application with MEAs is in its infancy. Using third-party ray-tracing files, an approach for evaluating MEAs for urban channels is presented. The advantage is that it maintains the full control of being computer-driven, thereby avoiding expensive,hard-to-repeat physical measurements, while incorporating the ground-truth of empirical antenna parameters.