Optimization of AT berlinite and quartz thickness shear devices for VHF filter applications

Systematic investigations concerning the design of VHF berlinite and quartz resonators were made to find the best designs for the elements of filters for the intermediate frequency of the future pan-European digital radiotelephone of the GSM system. An investigation of the influence of the parameters of the plane fundamental resonators using the AT cut of berlinite and quartz on the elements of the equivalent scheme and on the anharmonic spectrum was made. This was done using a numerical model based on the theory of the essentially thickness modes. Several families of designs were found to lead to nearly satisfactory sensitivities and values of the equivalent scheme, but when a constraint was put on the impedance level and on the sensitivities to the variations of several parameters that are difficult or costly to totally control in an industrial process, one family of designs, using elliptical electrodes with an axis ratio respecting the lateral anisotropy, was found to be much better