Research On The Extreme-narrow-band Saw Filter For Satellite Communication

There are a lot of high requirements for narrowband SAW filters in modern satellite communications,with clear requirementssuch as bandwidth,insertion loss?stopband rejection,and temperature stability.The conventionally designed narrow-band surface acoustic wave filter can no longer meet the requirements of use.It is necessary to carry out technical research on design methods and key processes to form a stable design,process and test platform,in order to develop a very narrow-band saw filter that meets the requirements of the whole machine.The main research contents of this thesis include high-precision acoustic simulation design technology of transversely coupling structure and high-order parasitic mode suppression and temperature stability technology of transversely coupling structure.The Transversely Coupled Resonator Filter structure uses a two-dimensional acoustic waveguide structure that utilizes the coupling between two acoustic channels to excite multiple waveguide modes,including low-order modes and several high-order modes.It is usually requiring the use of two lowest-order modes,in which the other parasitic modes are suppressed by the structural design,and finally a very narrow pass band is obtained.By using the COM model,the admittance of symmetric mode and antisymmetric mode can be calculate,and the FEM/BEM theory is used to extract the coupling-of-mode(COM)parameters.Then the acoustic simulation of the filter is obtained by the equivalent circuit model,and the full-wave simulation method of acoustic and electric cooperationwill be used to realizethe accurate simulation includingall of the elements such as electrically inter-connected silicon aluminum wire and package of HTCC ceramic.For the TCRF,the longitudinal acoustic mode excited and propagated on the input transducer is coupled to the other resonant channel and propagates in the channel,in addition,outputting the electrical signal.The strength of the transverselycoupling is closely related to the relative film thickness,the width of the intermediate coupling bus bar,the ratio of the reflection grating to the transducer period,and the transducer aperture.It is necessary to focus on the effects of these parameters on the attenuation of the transversely coupled resonator filter parasitic clutter relative to the main passband.Since the bandwidth of the laterally coupled resonator filter is extremely narrow and only 0.1%,so a piezoelectric material having a good temperature stability must be selected as the substrate.The relationship between the cut shape of quartz crystal and various structural parameters and the inflection point of the temperature drift coefficient is well studied,so that the inflection point can be around 25 °C.The TCRF structure was used to optimize the design through modeling simulation and high-order parasitic mode suppression.Finally,the filter transducer structure was established and the layout was formed by the acoustic surface planar semiconductor process,and the 160 MHz narrow-band surface acoustic wave filter is produced that the frequency of 160 MHz is always in the passband from-55 ° C to 85 ° C.