Research On Broadband Beamforming Network Based On Microstrip Butler Matrix

Beamforming network is an important part of multi-beam antenna systems.When the Butler matrix is combined with the antenna,not only the gain of the antenna array can be obtained,but also the Butler matrix is lossless,so it is widely used in the multi-beam antenna.Among various types of Butler matrices,the one based on the microstrip structure is widely used in the design of multi-beam antennas due to its simple structure,low cost and easy integration.However,the Butler matrix based on the microstrip structure has the disadvantage of narrowband.To solve this problem,the broadband Butler matrix is studied in this thesis.The main contents are as follows:Firstly,the background and significance of the wideband Butler matrix based on microstrip structure are summarized,and the existing methods for extending its bandwidth are introduced.Secondly,started form the principle,several of 4×4 Butler matrices are given according to the different scenarios,and a simplified scheme for 8×8 Butler matrix is introduced.Based on the transmission line theory,the bandwidth extension methods for coupler,crossover and shifter are introduced,respectively.By increasing the number of branches of coupler to broaden its bandwidth,the resulting coupler not only has good output inconsistency in the required frequency band but also has a stable phase output relationship.The symmetrical crossover is designed by using microstrip ring structure,and the bandwidth is further broadened by increasing the number of micro-belts of the crossover.The obtained crossover not only has wideband characteristics,but also has the advantages of low insertion loss and easy processing.A wideband phase shifter with simple structure is obtained by using the method of short circuit microstrip loading.The corresponding broadband schemes are obtained by theoretical calculation and simulation,which lays a foundation for the design of broadband Butler matrix.Then,based on the proposed wideband sub-components,the solution that satisfies the bandwidth requirement is obtained by the ADS schematic analysis of the 4×4 Butler matrix.The last Butler matrix covers 1.710~2.690 GHz with 48.3% relative bandwidth form the simulation and measurement.Therefore it can meet the requirements of broadband application of multi-beam antenna feed network,due to its stable phase output relationship and uniform transmission coefficient.Finally,conclusions and future work are given.