Millimeter Wave Imaging and Phased Array Antennas for 5G and Aerospace Applications
Abstract: Phased array antennas are cornerstones in many proposed antenna solutions concerning the next generation of both airborne radar systems and wireless communication systems (5G). Additionally, millimeter wave (mm-wave) frequencies are expected to play an integral role in 5G, and are deemed well-suited for inspecting structural components used in the aerospace industry.This dissertation consists of a general introduction (Part I) and six scientific papers (Part II) - of which four have been published and two are under review in peer-reviewed international journals. The introduction comprises the background, the motivation and the subject-specific technical foundation on which the research presented in the included papers is based on. Fundamental theory on antenna arrays, mm-wave imaging systems and computational electromagnetics are presented together with the specific performance metrics, experimental setups, and computational acceleration algorithms that are of interest for the contained research work. The included papers can be divided into three tracks with two distinct applicational overlaps. Papers I and II concern electrically large phased arrays for airborne systems, and the numerical techniques that alleviate time-efficient and accurate simulations of such antennas. Paper I investigates the performance of two different approaches to the macro basis function (MBF) method for interconnected subdomains under the harsh electromagnetic conditions that endfire operation implies. Paper II presents a synthesis technique for endfire operation of large scale arrays that utilizes convex optimization to improve the impedance matching performance. Papers III and IV concern phased arrays for 5G applications. In Paper III, various array configurations of two microstrip antenna designs are evaluated with respect to two radiation performance metrics introduced specifically for evaluating the beam steering capabilities of phased array systems in the UE. A novel near field measurement technique for running electromagnetic field (EMF) exposure compliance tests of mm-wave phased arrays for future 5G devices is presented in Paper IV. Papers V and VI deal with mm-wave imaging systems developed for non-destructive testing (NDT) of composite materials used in the aerospace industry. A transmission-based bistatic imaging system is presented in Paper V, whereas Paper VI presents a further development of this system in a reflection-based measurement scenario. Data is retrieved using a planar scan, and the image retrieval algorithms comprise a numerical technique to separate the sources that contribute to the measured data, and an L1-minimization formulation to exploit potential sparsity of the sought-after solution.
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