The Research And Miniaturized Modeling Of Foure-port Balun And Balance Filter

With the rapid development of wireless communication industry, theminiaturization of RF system and devices is one of the most significant trends. Thispaper focus on the research of four-port balun and low pass balance filter which arebased on LTCC technics and then design some circuits and make the circuits into3-dimension modeling, which realize the miniature of devices.According to the design desire of four-port balun and balance filter, the technicalparameters are specified. This paper introduces a method which designs the filter, balunand coupler respectively, then puts them together to make a second optimization. Afterthe investigation of matched filter, a low pass match filter is designed with a1.6GHzcentral frequency and400MHz bandwidth. Then the work condition of balun isanalyzed, the S parameters matrix is discussed. In conformity to the work condition andS matrix, a Marchand Balun with1.6GHz central frequency and400MHz bandwidth isimplemented. After that, a semi-lumped balun is advanced, which has four extra portcapacitances. Because of the capacitances, the size of the balun decrease and thefrequency excursion caused by LTCC technics is restrained.The matched filter, balun and coupler are assembled to simulated and optimized. Inthe end, a low pass balance filter with1.6GHz central frequency,350Mhz bandwidthand a four-port balun with1.6GHz central frequency,400MHz band width are designed.The suppression out of the pass band of balance filter is less than-20dB, magnitudeunbalanced is less than1dB; the suppression of the band of the four-port balun is lessthan-20dB, the loss of four ports are bigger than-6.9dB. The results of the devices meetthe design desire completely.