Research And Design Of Multi-frequency Combiner Based On Common Cavity

Multi-frequency combiner is passive microwave device whichcomposed of two or more filter units, widely used in most mobilecommunication system, to synthesize from different radio frequency channelsignals (from antenna or the transmitter). In recent years, with the constantemergence of large number of large stores，hotels and subways, the mobilecommunication indoor coverage become the key of construction, the currentmajor domestic carriers have taken much system, much network sharing mode,this pair of multi-frequency combiner various channel isolation put forwardhigher requirements, therefore research and design of the multi-frequencycombiner is very necessary.This paper first introduces the design basis of combiner, introduces the basictheory of microwave filter simply, analyses the synthesis the theory of GeneralizedChebyshev filter, consist of matrix synthesis and coupling matrix simplification,especially, using MATLAB programming to complete the coupling matrix extraction.Secondly, research on the synthesis method of the combiner based oncommon cavity, the method based on the scattering function of combiner,figures out the combiner characteristic polynomial, then the combiner areintegrated, finally we get the design parameters of combiner through antinormalization, which contains each resonant cavity resonant frequency ofeach channel filter, coupling coefficient between cavities and external Qvalue.Finally, according to the filter design theory and synthesis designmethod of combiner based on common cavity, a four frequency coaxial cavitycombiners which work at GSM/TD-SCDMA/TD-LTE/WLAN band. Weoptimize the common port of combiner through the method of road simulationand field imitation, and introduce the design steps of combiner in detail, thedesigned combiner is fabricated and further measured by the use of Agilentnetwork analyzer, and the measurement results meets quite well with the desired indexes, in addition, the combiner is tested under high and lowtemperature, the test results show that the combiner can work at-70-20℃environment.