Electromechanical band-pass filter - uses flexural resonators in cascade coupled by longitudinal vibrating half-wave resonators using direct synthesis design

摘要

The electro mechanical band pass filter consists of cascaded elements, each consisting of two resonators undergoing flexural vibrations and coupled by a half wave resonator which undergoes longitudinal vibrations. The design allows lower bandpass ripple than other known methods and over a 20% bandwidth it is similar to that of the low pass prototype. The flexural vibrating rods are parallel and consist of elinvar. The filter is coupled electrically by piezoelectric ceramic plates as input and output transducers. The resonators of each element are dimensioned so that one of the relative frequency limits is related by a mathematical formula to the frequency cut off of the corresp. low pass filter. The coupling of each stage is related by a mathematical formula to the upper or lower relative frequency of the stage. A 5 stage filter using the Chebyshev approximation with a 20% bandwidth at 50kHz and 0.04dB passband ripple has been produced with the technique.