Design Of Multi-frequency Cavity Combiner

In recent years,with the constant emergence of large number of largestores,hotels and subways, indoor distribution system presents new features.In orderto improve the construction speed of communication network and reduce the cost ofrepetitive construction, The signals distribution systerm which is commonly used byseveral operating agencies and kinds of communication systerms has been widelyused nowadays.As a key combining devices of the indoor distribution systerm, themultiplexers’ performance directly affect the quality of the whole communicationsysterm. As a result of increasing crowded communication frequency resource recentyears,indoor coverage distribution systerm put forward higher performance requeststo combiner. High isolation, low loss, low PIM and high power become the keytechnical indexes.This paper first introduces the design principle of microwave filters,due to thatmicrowave filter is the basic unit of multiplexer. Then matrix synthesis ofgeneralized chebyshev filter and reduction of coupling matrix has been spaciallyanalysed.And taking the folded topology structure as an example, this paper usesimilar transformation and matrix rotation to reduce the coupling matrix. Secondlycross coupling structure(CT&CQ)which is usually used in multiplexers is introduced.Besides, phase analysis are maked to the two kinds of structure and theircombination ones.Secondly, This paper introduces comprehensive design method ofmultiplexer,and lay more emphasis on analysis of star-junction multiplexers. Thismethod, based on the design principle of coupling resonator bandpass filter andaccording to the scattering function of bandpass filter, figures out the multiplexercharacteristic polynomials.Eventually,the design parameters is figured out withmultiplexer characteristic polynomials,which contains resonant frequency,couplingcoefficient and external Qe.Finally, A dual-layer multi-frequency structure with public ports is designed and implemented according to the principle of bandpass filter and design method ofmultiplexer. Each layer has a two-frequency star-junction multiplexers.Besides,eachport uses double deck shareing port,which means each port is a combining one.Sothat three ports are able to achieve four channel filters.According to the measuredresults, its performance fully comply with requirements,and the isolationg is evenbetter.