SAW Resonator filters with improved temperature stability

摘要

Improvement in the temperature stability of a pair of resonator filters (70 and 71) disposed on an acoustic medium (39), which resonators are coupled by a first coupler means (500), is achieved by providing a second coupler means (501) for coupling between the resonator filters. The second coupler means is chosen so that acoustic interferences between waves propagating in the first and second coupling means compensates for the temperature variation in the propagation velocities of surface waves in different directions on the acoustic medium. The phase provided between second coupler means must be in near quadrature to the phase provided by the first coupler means. In an embodiment constructed according to the present invention which utilizes parallel electromechanical (600) and folded acoustical intercavity couplers (72) to provide the necessary pair of different temperature coefficient paths, the restriction that the phases be in near quadrature provides nearly flat phase versus temperature characteristics over several tens of degrees centigrade.