Research On X-Band Planar Filter Based On Microwave Dielectric Ceramics

In recent years, the Ultra-wideband technology is widely used in military and civilian fields. Planar filter is widely used in the field of communications system equipment because of its’ small volume, short production cycle, easy integration with pcb-level circuit. However, with the rapid development of information technology, more stringent requirements for planar filter are proposed. In the Ultra-wideband technology, planar filter only requires a small volume, easy to integrate, and need to have a small insertion loss. Filters composed of the traditional microstrip, stripline structure are unable to meet those requirements. In this paper, a comprehensive study was presented, focusing on the goals about the planar filter miniaturization and its high performance, based on the two aspects of filter substrate material and its structure. In order to realize a kind of planar filter which is compact, high performance, easy to integrate.In the part of filter substrate material experiments, the dielectric properties and sintering properties of B₂T₉（Ba2Ti9O20） microwave dielectric material were prepared by the solid-phase reaction. Firstly, I determined material formula of（B₂T₉） microwave dielectric material based on the previous results of research group. Then sintering characteristics, dielectric properties and microstructures of samples were studied with BBSZ（Bi-B-Si-Zn） glass, Al₂O₃ nanometer powder, LBSA（Li-B-Si-Al） glass addition, respectively. Results show that, 1) the dielectric constant of samples which doped BBSZ glass is the largest, but its’ Q*f values are the lowest in three kinds. The dielectric constant and Q*f values of samples which doped Al₂O₃ nanometer powder are relatively modest. Samples which doped LBSA glass have the minimal dielectric constant, but those Q*f values are maximum. 2) the dielectric properties of samples which particle size is relatively uniform and has few holes are excellent.In the part of filter structure, an UWB suspended stripline filter which was 11 orders using microwave dielectric material called B₂T₉ as filter substrate was designed. The size of the filter is 23.34 mm*10.65 mm*10 mm. There is differences between the measured results and simulation results. Finally, its testing bandwidth was 5.38¹3.27 GHz. The feasibility and convenience of simulation software to design filter was verified. Then, using the same dielectric substrate two types of planar filters were designed. Those filters were 9 orders and their bandwidth were designed for 8.55-11.7 GHz. Their size is respectively 10.92 mm*16.04 mm*10 mm and 41.62 mm*10.65 mm*14 mm. Compared with them, results showed that, 1)using microwave dielectric material called B₂T₉ as substrate can effectively reduce the size of filters. 2)microstrip filters have a small volume but its frequency is susceptible to deviate. 3)while the size of suspended stripline filter was large, its’ insertion loss and band rejection are better than microstrip filter.