Miniaturized Phase-Shifters for Ka-Band Phased Array Antennas
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Realizing robust and stable two-way links between the mobile users and the satellite is an extremely challenging RF/Microwave engineering problem. Low cost and low profile phased array is considered as the best solution for this problem. High performance low cost and miniaturized variable phase shifter is a key enabling technology for such complex smart phased array antenna system. This thesis aims at the investigation of the existing solutions to realize miniaturized, low-cost and at the same time integrable phase shifters for commercial phased array antenna systems. Among few existing approaches, analog phase shifting devices based on voltage-tunable materials offers a promising solution. Liquid Crystal (LC) and Barium Strontium Titanate (BST) are the two voltage tunable materials, which, beside their own primary applications, have found their way into Microwave and mm-Wave tunable device technologies. In this study the utilization of LC and BST in analog phase shifters has been rigorously investigated, the advantages and drawbacks of each when applied in different realizations have been discussed and further development and improvements in designs have been suggested. To achieve more compact designs for Ka-band phase shifters, a comprehensive design methodology for tunable filter-type phase shifter is proposed in this dissertation. The most commonly used phase shifting architectures for the phased array antennas are RF, LO, IF and base-band phase shifting. It should be mentioned that LO, IF and base-band phase shifting are not suitable for phased arrays with large number of elements due to the formidable cost and complexity, particularly for Tx phased array systems which require one phase shifter per antenna element to meet the radiation mask. Therefore, this thesis is concentrated on RF (Microwave/mm-Wave) phase shifting, which is the most common for large phased array antenna systems. Since one of the most important requirement in the design of Ka-Band phase shifters for phased array systems is the high level of miniaturization, dictated by antenna element spacing constraint, the thesis also addresses the highly compact structure of such phase shifters. In particular, a novel phase shifting concept based on very high dielectric constant materials has been explored. It is shown that by using this new concept, a highly miniaturized variable phase shifter with more than 360 degrees phase tuning range is attainable.