Research On The Optimization And Design Of Cavity Combiners

Combiner is microwave devices which synthesizes multiple signalto one and output, widely used in modern communication systems. With theadvent of4G communications, limited bandwidth resources and narrowerisolation band between channels makes the situation of multi-systemcommunications networks become more complex, so it takes more demand onthe multi-band combiner which can achieve the integration of more kinds ofnetworks. Cavity combiner is widely used in communications networks withhigh Q value and high power. Therefore, it is necessary to have research oncavity combiner.This paper mainly studied the optimization design of cavity combiner,Taking optimization design research of cavity combiner is based on the filteras combiner is composed of the filter unit.Therefore we firstly study thedesign theory of microwave filters, introduce the basis of transfer function offilter, low-pass prototype filter, frequency conversion and impedance,admittance transform in detail, and then the generalized Chebyshev filterswith arbitrary transmission zeros is done in-depth research, including thegeneralized Chebyshev polynomial and its comprehensive, cross couplingfilter circuit model analysis and coupling matrix synthesis.In the third part,this paper proposes a cavity band-stop filter unit whosefrequency band can be adjusted flexibly to meet the modern communicationsystem requirements in breaker band flexible adjustment, easy processing andeasy to implement.First a study on the structure and properties of band-stopfilter is given, and it can be applied to different frequencies and with certainflexibility since its adjustable structure. At the same time adjusting devicecan index deterioration caused by the machining error compensation, reducethe demand for machining accuracy, improve the realizability. In addition,SIR (step impedance) structure is applied to make improvement on resonator. The position of spurious stopband can be precisely controlled by calculatingthe impedance ratio of the SIR structure, which extend the LSB width.Finally experiment of three cavity tunable cavity band-stop filter is designed,the simulation results show great meet with index.In the fourth part,this paper proposes a semi-lumped coaxial cavityband-pass filter to meet the requirements of low insertion loss and smallvolume.Firstly, this part studies the basic theory of semi lumped parameter.Secondly, analyzes the structure and features of semi-lumped coaxial cavitybandpass filter. The adoption of semi lumped parameters can meet lowinsertion loss and can be bent arbitrarily, that means it is easy to be applied tothe combiner structure to achieve miniaturization. Finally a six order semi-lumped parameter coaxial cavity band-pass filter is designed, the simulationresults shows great meet the requirement of low insertion loss and miniaturi-zation.Finally, a dual band-pass band-stop combiner is designed based on thenew type of adjustable cavity band-stop filter unit presented in the third part.The optimized bandstop filter expresses better characteristics on LSB width,band rejection,spurious stopband, and compact structure makes it easy to beminiaturized. Band-pass filter is realized with high Q value, high-powecoaxial cavity structure, combiner design method is given in this part. Finally,the combiner is manufactured and tested. The results show a great meet withthe design index. High and low temperature test results indicate that thedevice can work in-25℃~65℃environment.