The Research Of High-performance Suspended Stripline Demultiplexer/Multiplexer

With the rapid development of mobile communication systems today,the multiplexer is widely used in a variety of communication systems?base stations and indoor coverage projects such as subway,stadium and so on.multiplexer is the device that synthesized the multi-channel signal.In order to ensure the quality of communication system,the researches of low insertion loss?broadband?high isolation of the combiner have a great significance.The multiplexer proposed in this paper is based on suspended stripline.The main work will be showed in two parts as follows:1.Filter is the basic unit of multiplexer.Two different structure filters are proposed.One is based on Double-mode short-stub loaded resonators.Strong coupling coefficients can be achieved by putting the couple elements on different substrate side.At the same time,the bandwidth and the location of the transmission zero can be controlled by changing the length of resonators' stub.The other one is based on quarter wavelength stepped-impedance resonator(SIR)with controllable mixed electric and magnetic coupling.The location of transmission zero can be adjusted by changing the spacing of coupling gap and the position of the conducting pin.The validity of the filters are verified by measurement.As the multiplexer should be designed to have high power capacity,the corresponding test has been done to evaluate the filters and the improvement of the filter is maked according the result of test.2.Based on the characteristics of suspended stripline,the circuit is placed on the two side of the substrate to maximize heat dissipation.T-junction is utilized to connect two filters with the common port.As the traditional T-junction is not suitable for the wideband multiplexer,two-section transmission lines are used to form T-junction to achieve good impedance matching.The multiplexer has been confirmed to operate in 1710-2170 MHz and 2300-2700 MHz.At the same time,a compact multiplexer using suspended transmission line has been fabricated and the validity of it is verified by measurement.The proposed multiplexer has the advantages of low insertion loss? wideband and high power capacity.