Coaxial Microwave Dielectric Filter Study

In recent years,along with the exploitation and application of the high frequency radio wave, the rapid development of the microwave mobile communication, as well as the improvement of microwave dielectric materials, the microwave dielectric filters are widely used in electronic warfare, navigation communication, warning radar, home satellite broadcast TV receiver and mobile telephone with small size, low insertion loss, low temperature coefficient and high stability. However, research on the relationship between the filter structure and its electronic technical specifications needs solving the complex electromagnetic field equations. In order to extract the filter structure parameters, designers have to spend a lot of time and work for drawing the filter structure, which restricts the development of microwave dielectric filter greatly.In this thesis, the microwave dielectric filters have been analyzed. Then a series of microwave dielectric ceramic materials and structures of microwave dielectric filter were explored and investigated. Then a high stability and monolithic microwave dielectric filter structure was present. It's key preparation technics were also explored and investigated. Finally, calculation of the structure parameters via experience formula is conducted. Upbuilt the filter model then simulated and optimized it by Ansoft-HFSS. The correct structure parameters of the filter were extracted finally. The filter samples were fabricated by conventional electronic ceramic process. The measured results confirm the feasibility and validity of this design, which can meet the requirement of the filters.The main results are as follows:1. A high stability and monolithic microwave dielectric filter structure was present, then the feasibility and stability beforehand design of the filter were analyzed, which is expected to meet the high stability requirement of military product. Furthermore, circuit equivalent model of the filter structure is analyzed, and microwave realization was educed from circuit equivalent model to coaxial line structure.2. According to the technical specifications of the project, the design scheme was presented appropriately. And calculate the structure parameter via experience formula. Upbuilt dielectric filter model then simulated and optimized it by Ansoft-HFSS. The structure parameters of the filter were extracted correctly. The rules were also summarized that structure parameters affect the technics specifications of the filter.3. The key preparation technics were investigated, which resolved the difficult problem of dielectric resonance and printing silver paste, explored the test methods of microwave dielectric filter, and innovational designed the Teflon ports.4. The microwave dielectric ceramic (Zr ,Sn) TiO4 was selected to prepare the filter by a solid-state reaction method, whichε ris 36, Q·f = 25000 GHz,τ_f = 5×10-6 /℃. The microwave filters of LJ1616M and LJ2492M were prepared successfully, which measured results as follows:a) f₀ = 1616.6 MHz, IL is 1.48 dB, BW_{3 dB} is 23.3 MHz, ripple in passband is less than 0.1 dB, attenuation exceed 30 dB at f₀-50 MHz, exceed 40 dB at f₀ +50 MHz, exceed 50 dB at f₀ -125 MHz, exceed 70 dB at f₀ +125 MHz respectively, VSWR is less than 1.2.b) f₀ = 2493.0 MHz, IL is 1.539 dB, BW_{3 dB} is 30.2 MHz,ripple in passband is less than 0.1 dB,attenuation exceed 25 dB at f₀-50 MHz, exceed 30 dB at f₀ +50 MHz, exceed 45 dB at f₀ -125 MHz, exceed dB at f₀ +125 MHz respectively, VSWR is less than 1.2.