| Recent years have seen a rapid growth in the development of ultra-wideband antennas and arrays, primarily driven by the increasing requirements of modern radar, electronic warfare, wireless communication, and radio telescope systems that require very wide bandwidth. As the main part of a research project, this dissertation is mainly concerned with the design and implementation of various ultra-wideband tapered slot antennas (TSAs) and arrays. The author's major contributions are outlined as follows:1. Three low-loss ultra-wideband baluns are studied. Firstly, the improved version of a wideband microstrip-to-slotline transition is presented, in which an extremely large angle slot radial stub is used for reducing the radiation loss and a large angle microstrip radial stub for achieving the wideband impedance matching. Secondly, a extremely wideband CPW-to-slotline transition is proposed, in which a double-Y junction, a CPW impedance taper and several air-bridges are used to achieve the desired low loss and wideband operation. Finally, a compact and wideband stripline-to-slotline transition is realized.2. Several high-gain ultra-wideband TSAs are studied. Based on the design principles of surface-wave antennas, the effective radiation regions of TSAs are discussed. Some key problems of TSAs, including the design of the tapered slot shapes and the corrugated edges at the outer edges, are investigated. The wideband impedance matching and antenna gain are improved by introducing a novel logarithmically tapered slot. Finally, prototypes of the microstrip-fed and CPW-fed TSAs for ultra-wideband applications are constructed to validate the efficiency of the design method.3. The ultra-wideband infinite TSA arrays are studied. According to the effect of mutual coupling between the array elements of the TSA arrays on the performance, the design method for this kind of ultra-wideband TSA arrays is addressed. A full-wave analysis model is developed to predict the mutual coupling between elements with different dimensions in the TSA array and the strong coupling between TSA elements is identified as being essential for the operation of arrays over wide bandwidth. Finally, a stripline-fed TSA element for the wideband and wide-scan array is developed.4. The low-loss ultra-wideband feed networks used in finite arrays are studied. By eliminating unnecessary design requirements, a flexible topology is used to obtain a greater design freedom. In addition, all power dividers in the feed network are optimized as a whole. The proposed feed network not only achieves ultra-wideband impedance matching, but also exhibits good low-loss characteristics.5. The ultra-wideband finite TSA arrays are designed and implemented. Based on the analysis results of mutual coupling between the elements in the finite TSA arrays, the truncation effects of different size TSA arrays on their performance are analyzed. A solution to efficiently reduce the truncation effects in the finite TSA arrays is also proposed. Finally, an ultra-wideband TSA array prototype is constructed to validate the feasibility and efficiency of the design method.
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