Analysis And Design Of Microstrip Duplexer For WCDMA System

With the rapid development of information technology,mobile communications have now entered the era of 3G.At present the International Telecommunication Union (ITU) has identified three major mobile communication standards for 3G technologies, namely the United States' cdma2000,Europe and Japan's WCDMA,and China's TD-SCDMA standard.Like the second generation mobile communications such as GSM,transmitting and receiving of 3G base stations system also share one antenna, which will involve duplex technology,that is,how to make the transceiver system work without the impact of each other at the same time.Among the three major standards of 3G technology,cdma2000 and WCDMA standards have adopted the frequency division duplex(FDD) technology,and China's TD-SCDMA has adopted the time division duplex(TDD) technology.For the time division duplex technology,as long as the transmitting and receiving are arranged in different time slots,duplex problem can be solved.For the frequency division duplex,special devices are required to enable electromagnetic waves of different frequencies through one antenna without causing interference,and that is exactly the problem duplexer is designed to solve.Against such a background,according to the project of 3G mobile communications from Dandong HuaXun Electronics Ltd.,three structure types of microwave duplexer are designed in this paper,which meet the requirements of WCDMA system.For WCDMA,the center frequencies of uplink and downlink channels are 1950MHz and 2140MHz respectively,and two-channel relative bandwidth are 3%and 2.8% respectively.Against the narrow-band channel requests,in accordance with these narrow-band filter design methods,completed the design of three microwave duplexers of different structures,which were parallel coupled line structure,step impedance resonator(SIR) structure and open loop structure duplexer.Theories of microstrip and coupled microstrip are first introduced in this paper, after the microwave filter design principle and the process are studied.On this basis, design principle and achieve method of the duplexer are discussed and then simulated by ADS.Optimizations of the duplexer design are also performed,followed by a real testing task on a fabricated SIR duplexer with HP8753D vector network analyser.The final test results show that the duplexer met the pass band insertion loss less than 3 dB, stop band attenuation close to -40 dB,reflecting loss more than -20 dB performance requirements,can better meet the requirements of WCDMA system,with some practical applications.