Ceramic-based Microwave Bandpass Filter Design And Production

With the rapid development of the communication technology, frequency spectrum resource becomes more and more crowded. In communication system, whether commercial or military communication systems, specifications for filters have tended to become much more severe, which are commonly met only by those filters with smaller size, stringent frenquency-selectivity, and lower insertion-loss in passband. Filters which are fabricated on ceramic substrate have advantages such as low-insertion, small size and high reliability. This filter play an increasing important role in the communication systerm, especially in military communications, where is growing concern about these filters.In this thesis, the selection of ceramic substrate materials, substrate preparation to filter design, simulation and testing of the filter are making a systematic study. At first, the thesis introduces the development of microwave ceramic materials and the research significance of microstrip filter.Then, the relevent theory of microwave filter was presented. In order to select proper microwave ceramic material for filter substrate,experiments of modifing MgTiO3 microwave dielectric performences are put forward,which include the dielectric properties, Q×f,τf,εr and get the best mirowave dielectric properties, Q×f=52000GHz,τf = 9 ppm /oC,εr= 18.2when CaTiO₃ addtion achived 3wt%.And then a hairpin bandpass filter was designed by microstrip theory, in combination with the Advanced Design System version 2008 (ADS2008) and Ansoft High Frequency Structure Simulation version11(HFSS11), the microstrip hairpin bandpass filter was designed and optimized. Based on the simulation results, from the perspective of substrate material, the influnces of substrate dielectric constant and thickness on filters'performances were investigated which include insertion-loss, return-loss, voltage standing wave ratio, group-delay etc.Finally, the fabrication and testing of the hair-pin filter was presented. The influnces of microstrip thickness, processing, and surface roughness on filter performances were researched. The adhensive force between ceramic and nickel cadmium metal layer was studied based on tensile experiments in order to ensure the reliability of the filter. The 50 ohm SMA connectors were weeded with the input and out put of the filter. The test results showed on Agilent E8463A indicate that the fabricated filter has excellent port scattering characteristics, central frequency (f0) = 3.5GHz and a bandwith 400MHz, insertion-loss 2dB. The filter fabricated on ceramic substrate with a size of 14mm×10mm×8mm.The size is one fifth of the filter which has the same performances fabricated on Rogers materials. The hair-pin filter realizes the goal of miniaturization, low insertion.