Research And Optimization Design Of Multi-frequency Coaxial Combiner

Combiner,one of the microwave passive components, which isdesigned on the basis of the theory of filter with multi-frequency coverage, iswidely used in indoor distribution system. In recent years, The continuousdevelopment of mobile communication technology led to the coexistencesituation of the old and new communication system network occurringtogether, that means the communication channel should have thecharacteristics both of multi-network and multi-system, so will it meet theneeds of communication. Due to the progress of modern manufacturingtechnology, the structure of the traditional combiner has been unable to meetthe requirement on index such as miniaturization, high isolation, highattenuation, low passive inter-modulation, therefore, study of traditionalcombiner and optimize design have become one of the hot topics in the studyof the microwave devices.In this paper common cavity structure was applied to make aimprovement in view of low efficiency on comprehensive implementationand large size. Compared with the traditional design scheme, thecomprehensive method was much more efficient, save the cavity number, andmake the device much more miniaturization. On the other hand, in view of thepoor inter-modulation distortion problem, this paper put forward coupling tapplate to replace tap line structure to make a improvement on theinter-modulation distortion.First of all, this paper introduces the basic theory of filter design,analyzes the polynomial comprehensive of Chebyshev filter and theextraction method of coupling matrix. Secondly, this paper studiescomprehensive design method both of he traditional non-common cavitycombiner and common cavity structure integrated design method of the combiner using polynomial synthesis method. Using polynomial synthesismethod, the design index was contacted with the circuit parameters(resonance frequency, the coupling coefficient and the outside world Q values.And then after simulation and physical contrast, it can be concluded thatcommon cavity structure compared with traditional directly connectedstructure improves the design efficiency, more device miniaturization.Thirdly, this paper makes a research in the resonator intermodulationdistortion based on the circuit model, according to the simulation analysisresult, it is concluded that the coupling tap plate structure will improveintermodulation distortion.Finally, according to the optimization design of modified method, usingpublic cavity structure and tap coupling plate structure, a four frequencylowpass and bandpass coaxial cavity combiners which work at GSM/WCDMA/LTE/WLAN band based on the filter design theory. Roadsimulation and field simulation are employed to calculate dimensions oflowpass and bandpass filter. After that the designed combiner ismanufactured with silver plating and further measured, measured results meetwell with design index. The passive intermodulation distortion test is made,the test results show that the intermodulation distortion of each channel isbelow-150dBc, which means the research achieves the optimal designpurpose.