Design And Fabrication Of 28GHz LTCC Band-pass Filter

As an important component of communication system,microwave and millimeter wave filters with high quality factor,high frequency selectivity and low insertion loss performances are the focus of research.Substrate integrated waveguide(SIW)filters make up for the shortcomings of planar waveguide and three-dimensional waveguide,so they with these structures can easily achieve the purpose of high quality factor,high power capacity and low loss.Low Temperature Co-fired Ceramic(LTCC)technology is an useful manufacturing process on microwave ceraimics substrate for high-density packaging technology,due to the realization of three-dimensional circuit by printing.And it is considered as a integration technology,which is suitable for the miniaturization,high frequency,planarization and integration of components.Therefore,if we combine the SIW structure design and LTCC process,the miniaturization of high-performance SIW filter can be obtained possible.According to the working principle of the filter and the requirements of LTCC process,four physical structure models of 28 GHz bandpass filters with small volume are proposed in this paper based on the theory and design technology of SIW resonator.The related samples are successfully fabricated by LTCC process.The specific work is as follows:Firstly,according to the effective conversion method of reference filter from low-pass prototype to target filter,and the equivalence between SIW and traditional waveguide,four novel 28 GHz band-pass filters with multilayer structure are established from the resonant characteristics of SIW filter,transition structure of signal transmission,coupling mode between cavities and miniaturization of substrate integrated waveguide structure.The physical structure and simulation parameters of SIW bandpass filter with28 GHz center frequency are obtained by modeling in HFSS software.The simulation results show that its bandwidth is 3GHz,return loss is better than 29.5d B and insertion loss is better than 1.5d B.For further research,three kinds of 28 GHz band-pass filters with smaller size are designed and simulated,which are named as HMSIW,QMSIW and EMSIW band-pass filters.Then,several factors that affect the quality of the microwave ceramic thich film are analyzed.The relationship between additives and viscosity of casting slurry was obtained by experimental analysis with additions of solvents,plasticizers,dispersants and adhesives,the proper proportion of slurry was carefully selected,and the good quality green ceramic sheet was obtained by ball milling and tape casting.The four filters were successfully fabricated by LTCC technology,and the key controlling process were discussed in details.Finally,the S-parameters of the samples are measured by the vector network analyzer.The testing results show that the S parameters of samples are basically consistent with the designed and simulated results,which confirms that the SIW,HMSIW,QMSIW and EMSIW bandpass filters with multi-layer structure possesst smaller size,better performances and higher integration.And it is indeed an effective miniaturization method for high-performances filter.