Research On Ultra Wideband Spatial Power Combining Technology

With the rapid development of communication technology,the demand for high power and broadband devices is becoming more and more urgent in microwave systems.In view of the high power requirement,when the power amplifier chip is hard to achieve enough power,and the application of traveling wave tube is limited,power combining technology arises at the historic moment.The most common power combiner is planar power combiner,it is difficult to achieve large-scale combining due to the limition of the insertion loss and area.The spatial power combiner can effectively solve this problem for its low loss.In order to meet the requirement of broadband,it is an effective method to adopt broadband impedance matching technology and broadband transmission structure.The commonly used broadband impedance matching technology includes stepped impedance converter and tapered impedance transmission line.It is simple to design a stepped impedance converter,but in practical application,tapered transmission line is a better choice,considering the factors of size and processing cost.For broadband transmission lines,compared with the rectangular waveguide with cut-off frequency and the microstrip line with high insertion loss,the advantage of coaxial structure with no cut-off frequency and high quality factor is obvious.The extended coaxial spatial power combiner has the advantages of both high power and ultra wideband,which can be used to realize the ultra wideband spatial power combiner.The design of this combiner is divided into two parts:the extended coaxial design and the polar finline design.The design basis of both parts is the theory of wideband impedance matching.Extended coaxial spatial power combiner working in 6-18GHz with cosine square tapered impedance transmission line is designed and fabricated firstly.Considerating the complex structure of spatial power combining technology,sixteen tray structures,two cylindrical covers,two irregular cones and external heat dissipation structures are assembled to realize the mechanical structure of the extended coaxial spatial power combiner.The influence of the substrate deformation,and metal slit,and device misplacement are analyzed,which provide experience for the design of the second edition.The second edition is mainly improved from two aspects in size and structure.The minimum reflection theory is an optimal tapered impedance matching theory.It can calculate the best tapered characteristic impedance,but it can not be directly used to design tapered transmission line.Based on the minimum reflection theory,combined with the simulation software HFSS and programming software Matlab,a fast fitting method is proposed for the optimal size of the finline in this paper.Compared with the first edition,the overall size is reduced by about 30%.In terms of structure,in order to reduce the dislocation between different parts,the slot and boss design is added to the device connection.The slot design can improve the concentricity of each arc device and reduce the influence of mechanical error.Based on the above research,a 6-18GHz and a 2-18GHz extended coaxial spatial power combiner are designed.The two combiner have better simulation results.The 6-18GHz spatial power combiner is tested.The test results show that the return parameters in the whole working bandwidth is better than-8dB,and the insertion loss is better than 5dB,and the insertion loss in most bands is better than 3dB,which basically meets the design requirements.In this paper,the results of the test are analyzed,and the improvement method is put forward.