Design Of Miniaturized Combiners Based On Substrate Integrated Waveguides

Combiners having the function of selecting frequency are usually used in radio frequency system to combine signals from different frequency bands in mobile communication field,with the purpose of using a set of antenna and feed system.In order to maximize the use of resources and reduce the cost,the current major domestic carriers have taken much system sharing mode to construct the mobile communication network.This puts forward higher requirements for the combiner in the multi-network convergence,so it is necessary to research and design the multi frequency combiner.On the other hand,with the development of miniaturization of amplifier,oscillator and other active circuits,the miniaturization of the passive circuits such as filter,combiner and antenna for RF and microwave front-end is becoming more and more important.Therefore,the miniaturization and high performance microwave combiner has attracted more and more attention in recent years.First,this thesis reviews the development of microwave filters and combiners,and briefly summarizes the application of substrate integrated waveguide technology in microwave passive circuit.In the aspect of basic theory,this thesis not only states some basic concepts involved in the design of microwave filters,but also presents the space mapping algorithm briefly which can be used to rapid the design of microwave filters.Finally,this thesis designs the following two different forms of combiner:1?From the point of view of the miniaturization of the combiner,the simulation and design of a miniature combiner with two channels is completed by using SIW structure.The combiner operates at C-band,and the relative bandwidth of the two filters is about 7%.In addition,the relative size of the combiner machining by the PCB is only0.66?₀×0.66?₀×0.02?₀.The miniaturization of combiner is mainly due to the using of microstrip T shaped structure and the one-third-mode triangular substrate integrated waveguide resonator loading DGS structure.In order to improve the simulation efficiency of SIW structure,the aggressive space mapping algorithm is used to realize the fast and accurate design of SIW filter.2?In view of engineering,a coaxial cavity combiner used in mobile communication is designed in this thesis.The combiner has four ports,including a common port and three input ports.The three working bands are GSM900,FDD-LTE 2.1G and DCS1800.In the design of the GSM900 band,five resonant cavities are used to ensure that the return loss is greater than 20dB,the insertion loss is less than 1dB,and the out of band rejection at880MHz is greater than 60dB.At the same time,four resonant cavities is used to complete the design of FDD-LTE 2.1G,and the return loss is better than 20dB.The insertion loss in passband is less than 0.5dB,and the out of band rejection at 1880MHz and 2320MHz is greater than 70dB and 60dB respectively.In the DCS1800 band,a topology structure with nine resonant resonators and one cross coupled structure is used to design the filter to achieve a out of band rejection greater than 80d B at the 1860MHz.Finally,in order to combine these signals,a common cavity is used to obtain a good impedance matching at high frequency bands,while the filter is directly connected to the common port in the low frequency.