A Study On Microwave Star-junction Multiplexers

Combiner,also known as multiplexer,is microwave passive devices composed of multiple filters.In a communication system,the function of the multiplexer is to divide a wideband signal into a number of narrowband signals.And due to the reciprocity of the filter network,the multiplexer can also integrate several narrowband signals into one broadband Signal function,and transmit the signal through the antenna finally.Multiplexers are widely used in satellite communications,wireless communication systems and electronic warfare systems and other different occasions,its performance have a great impact on the quality of communication systems.In this paper,firsty,we study the generalized Chebyshev coupling matrix,and deduce the relationship between the characteristic polynomial and the coupling matrix of the filter.Then we introduce several common implementation structures of the coupling matrix and introduce how to use the efficient microwave physics to extracted the coupling coefficient,the resonant frequency and the external quality factor,and the step-by-step debugging method of the coupled resonant filter is introduced.Then the design theory of the multiplexer with the common cavity is introduced.Different from the traditional design which directly connected a number of channel filters,the various channels will be taken into account the impact between each other at the beginning of the design.Firstly,the characteristic polynomials of each channel filter are calculated individually according to the design index,and then the characteristic polynomial of the multiplexer is obtained.Secondtly,the characteristic polynomial of each channel filter is obtained by an iterative process,then the coupling matrix and the external quality factor of each channel filter is obtained,as well as the resonant frequency and the external quality factor of the common caivity.In this paper,this method is compared with the traditional multi-processor design method which is directly connected with each channel through the common,and the advantages of this method in designing the narrow-band and the multi-multiplexers with different channels are discussed.And points out the potential defects of this method.Finally,based on the cavity filter design theory and the design method of the multiplexer with the common cavity,a diplexer with a common cavity is designed.The center frequency of the channel is 5550MHz and 5640MHz respectively.The diplexer is fabricated and further measured by the use of Keysight network analyzer,and results meet the requirements of the indicators.