The millimeter wave (mmW) band, commonly referred to as the frequency band between 30 GHz and 300 GHz, is seen as a possible candidate to increase achievable rates for mobile applications due to the existence of free spectrum. However, the high path loss necessitates the use of highly directional antennas. Furthermore, impairments and power constraints make it difficult to provide full digital beamforming systems. In this thesis, we approach this problem by proposing effective beam alignment and beam tracking algorithms for low-complex analog beamforming (ABF) systems, showing their applicability by experimental demonstration. After taking a closer look at particular features of the mmW channel properties and introducing the beamforming as a spatial filter, we begin our investigations with the application of detection theory for the non-convex beam alignment problem. Based on an M-ary hypothesis test, we derive algorithms for defining the length of the training signal efficiently. Using the concept of black-box optimization algorithms, which allow optimization of non-convex algorithms, we propose a beam alignment algorithm for codebook-based ABF based systems, which is shown to reduce the training overhead significantly. As a low-complex alternative, we propose a two-staged gradient-based beam alignment algorithm that uses convex optimization strategies after finding a subregion of the beam alignment function in which the function can be regarded convex. This algorithm is implemented in a real-time prototype system and shows its superiority over the exhaustive search approach in simulations and experiments. Finally, we propose a beam tracking algorithm for supporting mobility. Experiments and comparisons with a ray-tracing channel model show that it can be used efficiently in line of sight (LoS) and non line of sight (NLoS) scenarios for walking-speed movements.

The growing demand for high data rates, reliable connections, low latency, and increased user density has driven the operating frequency of modern wireless communication systems towards the millimeter-wave (mmWave) band. Large-scale antenna arrays capable of supporting simultaneous multi-beamforming are crucial for these mmWave systems. Passive beamforming networks, particularly Butler matrices (BM), offer several advantages for mmWave applications due to their low complexity, high energy efficiency, zero DC power consumption, and ability to generate multiple orthogonal beams. However, existing BM designs are often limited to low-order matrices, supporting a restricted number of radiating elements and featuring bulky cubic structures unsuitable for the microwave range. The contributions of this work include extensions in the Butler matrix order to support a massive antenna array, simplification of the Butler matrix topology to reduce the insertion loss, and layout optimization for straightforward antenna array integration. The novel multi-beam antenna systems for the one- and two-dimensional beamforming at mmWave band are designed and experimentally validated. First of all, a theoretical analysis of the Butler matrix topology is conducted to find effective solutions for matrix order extension, simplification, and loss reduction. Then, a multi-beam system consisting of a compact 8×8 one-dimension BM and an antenna array is implemented. To further extend the number of multi-beams, a 28 GHz multi-beam array system based on high-dimension 16 × 16 one-dimension BM and 1 × 16 linear antenna array is proposed. Additionally, a 28 GHz multi-beam array system fed by a planar 16 × 16 twodimensional Butler matrix is examined. Utilizing the proposed concept for the planarization of the cubic-formed two-dimensional Butler matrix, a system implemented with the multi-layer lamination in a dramatically reduced size provides 16 spatial orthogonal beams over a conical space. Furthermore, two new concepts for the planar and uni-planar 32 × 32 two-dimensional Butler matrix are developed not only for more beams but also to reduce the required signal layers.