| With the rapid development of communication systems,users have ever-growing demands on communication rates.In the urban area with numerous lofty buildings,low directional antennas are difficult to provide sufficient signal intensity to ensure high-quality voice calls and data transmissions.The multibeam array antennas,which can realize accurate beam-steering and cover a specific area,greatly enhance the signal intensity of mobile terminals in this area,thus effectively improving the quality of communication and data transfer rate.A multibeam array antenna is usually composed of a feeding network and an antenna array.In recent years,Butler matrices,as the most commonly used feeding network,have become a research hotspot.However,in the recently published literature,Butler matrices with new topology are rare,which limits the range of output signal phase differences.It is found that most multibeam array antennas cannot produce the broadside beam.Because of this,to obtain more types of scanning beams,there is a further study about passive feeding networks.Millimeter-wave communication is consistent with the development trend of future mobile communication,and the multibeam technique will play an important role in the mobile communication system.All the prototypes in this dissertation operate around 28 GHz.Nowadays,millimeter-wave multibeam array antennas are usually realized by substrate integrated waveguide(SIW)technology.This technology can lower the profile of the feeding network and provide a relatively lower transmission insertion loss.Based on the above literature research and analysis,several Butler matrices with new topologies are designed and applied in multibeam array antennas to realize the broadside beam in this dissertation.(Ⅰ)A millimeter-wave multibeam array antenna based on the 5 × 8 Butler matrix is designed in this dissertation.The 5 × 8 Butler matrix is extended from two 3 × 4 Butler matrices by adding two couplers and one power divider,providing an equal amplitude signal distribution with five phase differences(0°,±45°,±135°)between the adjacent output ports.In order to reduce the number of crossover and complexity of the matrix structure,a dual-layer and symmetrical SIW structure is used to design the proposed BM.To verify the concept,a multibeam antenna array prototype is designed and fabricated,achieving a broadside beam and four tilted beams in the frequency range of 27.8-30.8 GHz.(Ⅱ)A millimeter-wave multibeam array antenna based on the 7 × 8 Butler matrix is designed in this dissertation.By using in-phase and out-of-phase power combination properties of the couplers,the matrix can provide equal power distribution output signals with 0°,±45°,±90°,and ±135° phase differences.An experimental 7 × 8 Butler matrix is designed and fabricated as the feeding network of an eight-element slot antenna array,achieving a broadside beam and six tilted beams in the frequency range of 26.5-29.5 GHz.In addition,these beams can achieve continuous scanning in the range of-55° to 55°.(Ⅲ)Generally,a 1-D scanning multibeam array can only obtain the scanning beam in one direction,which limits the user demands on some specific occasions.In contrast,the 2-D scanning multibeam array antenna can provide better scanning coverage,which is a good solution for this problem.A millimeter-wave 2-D scanning multibeam array antenna based on the 9 × 16 Butler matrix is designed in this dissertation.The 9 × 16 Butler matrix is devised based on the design concept of the 2-D Butler matrix.It can provide output signals with equal power distributions and 0° and ±90° phase differences between adjacent output ports in each direction.A 4 × 4 planar slot array is cascaded with the Butler matrix to construct a 2-D scanning multibeam array antenna.The 2-D multibeam array antenna operates in the millimeter-wave band of 26.5-29.5 GHz,achieving a broadside beam and eight tilted beams. |
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