Research On Balun/power Division Filter Based On Microstrip-slotline Hybrid Transmission Structure

With the rapid development of wireless communication technology,the design requirements of low-cost,multi-function and miniaturization have gradually become the important consideration for microwave devices design.At the same time,it has led to the highly integrated multi-functional passive devices that are becoming hot research directions at home and abroad nowadays,such as the research on passive three-port devices about filters with the functions of balun and power divider.Based on the above background,this paper focuses on the research about filters with the functions of balun and power divider.The design scheme of two kinds of high-performance balun filters and one filtering power divider are mainly proposed,then the correctness and feasibility of the scheme are verified through the actual measurement of the model.In short,the specific content of this article is as follows:First of all,review the research background,industry development direction and the status quo at home and abroad of the miniaturized design of filters with the functions of balun and power divider and microstrip-slotline hybrid transmission structure.Then,this paper introduces the theoretical basis of this paper in detail,including three-port network analysis,analysis of the operating characteristics of the filters with the functions of balun and power divider,equivalent circuit analysis of the microstrip-slotline hybrid transmission structure and the two commonly used microwave transmission line.This will provide a more direct theoretical basis for the design of the balun filter and filtering power divider.Secondly,the design method of high performance balun filter based on microstrip-slotline.This article mainly presents two different balun filter design.The first one is based on the microstrip-slotline transition structure and the E-shape dual-mode resonator with high selectivity.First of all,the inherent field distribution of the slotline and two types of transitional structures are analyzed in-depth,and the characteristics of balun is realized in advance.Followed by the use of dual-mode resonators to achieve bandpass response,and finally cleverly introduce four different working mechanisms of the out-band transmission zeros to improve selectivity.The second one is a wideband balun filter which is based on the stub-loaded slotline resonators.First of all,the resonance characteristics of the stub-loaded slotline resonators under weak coupling are analyzed in order to get a comprehensive understanding of their resonance characteristics.Secondly,the wideband filter responses are realized by mutual coupling between the two resonators,and the relative bandwidth is up to 50%.On this basis,the design of wideband balun filter is realized by using the special feeding structure of microstrip-slotline transition.Finally,a microstrip-slotline structure based filtering power divider is proposed in this paper.A new type of T-junction and dual-mode resonator with vertical feeding of microstrip to slotline was designed for the primary power divider structure.Afterwards,the resistance is cleverly placed between the two microstrip-slotline transitions structures for better isolation,up to 22dB.Finally,on the basis of this structure,four transmission zeros are introduced to improve the selectivity and out-of-band suppression of the device by using terminals short-circuited stub and source-load coupling.