Reserch And Design Of Miniaturized Microstrip Filter

With the rapid development of information industry, wireless communication has become one of the most popular technologies in the 21 st century. The microwave filter as an important element of microwave transceiver system which plays a very important role in the radio frequency engineering and microwave circuit. Due to the wide applications in radio communications and the different requirement of other communication standards, the filter has become a great demand of components in communication systems. In order to reduce the volume of microwave systems, enhance the performance of the whole system and to suppress harmonic wave interference, the design of a high performance, miniaturization, low cost and sample structure filter has become the focus of academic research.This paper first introduces the history and research status of the microwave filters, Beside, the developing trends and research significance of high performance filter is also analyzed. Some new structures and new technologies for the design of miniaturized microwave filter are introduced. Secondly, the basic theory for filter design which include the design parameters of the filter are presented. Furthemore, the frequency conversion theory of filter design from the low-pass filter prototype to bandpass filtes, microwave network theory and the basic principle of coupled resonator for bandpass filter design are given.Then the resonate characteristics of slow wave structure, which can realized by conventional split ring resonators, the loading of high-low impedance load and alternated stepped impedance, the size of filter can be reduced. Based on the periodic slow-wave structure, a novel fourth-order cross coupling filter is designed. Finally, based on the transition circuits between microstrip and coplanar waveguide, a novel UWB filter is proposed in this work. By introducing four stub load capacitor on coplanar waveguide, the out of band rejection of this filter is improved while the size of this filter remains unchanged. Due to the high-performance of this filter, it can satisfy the requirements of ultra-wideband filter circuits in hybrid integration systems.In this work, a fourth-order cross coupling filter is designed, fabricated and measured.The measured results agree well with the simulation results. The size of the proposed filter has decreased by 60% compared to traditional split ring resonator filter combining with a good out-of-band suppression characteristic which meet the requirements of the miniaturization in filter design. A microstrip-to-coplanar waveguide transition circuit conjunction with slot capacitance is adopted firstly in the design of ultra-wideband filter.The out of band rejection of the filter has enhanced while keeping the size constant compared to conventional filters.