Saw filter with specified electrode dimensions

Abstract

A surface acoustic wave filter has pairs of interdigital transducers and reflectors formed on a 36° Y-X LiTaO 3 substrate, the reflectors sandwiching the interdigital transducers in between. The film thickness h of the electrode fingers of the interdigital transducers and the reflectors is such that 0.06≦h/λ≦0.01 0.10 where λ is the wavelength of the surface acoustic wave adapted to be generated by the filter. The width-to-pitch ratio M/P of these electrode fingers for the interdigital transducers and the reflectors is such that M/P≧0.6 in order to improve the shape factor of the filter.

What is claimed is:  
     
       1. A surface acoustic wave filter comprising: 
       a 36° Y-X LiTaO 3  substrate;  
       a plurality of interdigital transducers formed on said substrate; and  
       reflectors formed on said substrate and sandwiching said interdigital transducers therebetween, said interdigital transducers and said reflectors comprising elongated electrode fingers, thickness h of said fingers being such that 0.06≦h/λ≦0.10 where λ is the wavelength of surface acoustic wave adapted to be generated by said filter, the fingers of said interdigital transducers having width M and being arranged at a constant pitch of P, M/P being a constant equal to or greater than 0.6, the ratio of passband width to center frequency of said filter being greater than 0.03.  
     
     
       2. The surface acoustic wave filter of claim  1  wherein the fingers of said reflectors are arranged at a constant pitch and have a constant width-to-pitch ratio. 
     
     
       3. A surface acoustic wave filter comprising: 
       a 36° Y-X LiTaO 3  substrate; and  
       a plurality of filter sections formed parallel and cascaded to one another on said substrate, each of said filter sections comprising a plurality of interdigital transducers formed on said substrate and reflectors which are formed on said substrate and sandwich said interdigital transducers therebetween, said interdigital transducers and said reflectors comprising elongated electrode fingers, thickness h of said fingers being such that 0.06≦h/λ≦0.10 where λ is the wavelength of surface acoustic wave adapted to be generated by said filter, the fingers of said interdigital transducers having width M and being arranged at a constant pitch of P, M/P being a constant equal to or greater than 0.6, the ratio of passband width to center frequency of said filter being greater than 0.03.  
     
     
       4. The surface acoustic wave filter of claim  3  wherein the fingers of said reflectors are arranged at a constant pitch and have a constant width-to-pitch ratio. 
     
     
       5. A surface acoustic wave filter comprising: 
       
         a piezoelectric substrate;  
       
       
         a plurality of interdigital transducers formed on said substrate; and  
       
       
         reflectors formed on said substrate and sandwiching said interdigital transducers therebetween, said interdigital transducers and said reflectors comprising elongated electrode fingers, a thickness h of said fingers being such that  0 . 06 ≦h/λ≦ 0 . 10  where λ is the wavelength of surface acoustic wave adapted to be generated by said filter, the fingers of said interdigital transducers having width M and being arranged at a constant pitch of P, M/P being a constant equal to or greater than about  0 . 6 , the ratio of passband width to center frequency of said filter being greater than about  0 . 03 . 
       
     
     
       6. The surface acoustic wave filter of claim  5 , wherein the fingers of said reflectors are arranged at a constant pitch and have a constant width- to - pitch ratio.   
     
     
       7. The surface acoustic wave filter of claim  5 , wherein the substrate is a LiTaO 3    substrate.   
     
     
       8. The surface acoustic wave filter of claim  5 , wherein the substrate is a  36 ° Y- X substrate.   
     
     
       9. The surface acoustic wave filter of claim  5 , wherein the substrate is a  36 ° Y- X LiTaO   3    substrate.   
     
     
       10. A surface acoustic wave filter comprising: 
       
         a piezoelectric substrate; and  
       
       
         a plurality of filter sections formed parallel and cascaded to one another on said substrate, each of said filter sections comprising a plurality of interdigital transducers formed on said substrate and reflectors which are formed on said substrate and reflectors which are formed on said substrate and sandwich said interdigital transducers therebetween, said interdigital transducers and said reflectors comprising elongated electrode fingers, thickness h of said fingers being such that  0 . 06 ≦h/λ≦ 0 . 10  where λ is the wavelength of surface acoustic wave adapted to be generated by said filter, the fingers of said interdigital transducers having width M and being arranged at a constant pitch of P, M/P being a constant equal to or greater than about  0 . 6 , the ratio of passband width to center frequency of said filter being greater than about  0 . 03 . 
       
     
     
       11. The surface acoustic wave filter of claim  10 , wherein the fingers of said reflectors are arranged at a constant pitch and have a constant width- to - pitch ratio.   
     
     
       12. The surface acoustic wave filter of claim  10 , wherein the substrate is a LiTaO 3    substrate.   
     
     
       13. The surface acoustic wave filter of claim  10 , wherein the substrate is a  36 ° Y- X substrate.   
     
     
       14. The surface acoustic wave filter of claim  10 , wherein the substrate is a  36 ° Y- X LiTaO   3    substrate.   
     
     
       15. A surface acoustic wave filter comprising: 
       
         a LiTaO 
         3  
         substrate;  
       
       
         a plurality of interdigital transducers formed on said substrate; and  
       
       
         reflectors formed on said substrate and sandwiching said interdigital transducers therebetween, said interdigital transducers and said reflectors comprising elongated electrode fingers, a thickness h of said fingers being such that  0 . 06 ≦h/λ≦ 0 . 10  where λ is the wavelength of surface acoustic wave adapted to be generated by said filter, the fingers of said interdigital transducers having width M and being arranged at a constant pitch of P, M/P being a constant equal to or greater than about  0 . 6 , the ratio of passband width to center frequency of said filter being greater than about  0 . 03 . 
       
     
     
       16. The surface acoustic wave filter of claim  15 , wherein the fingers of said reflectors are arranged at a constant pitch and have a constant width- to - pitch ratio.   
     
     
       17. The surface acoustic wave filter of claim  15 , wherein the substrate is a  36 ° Y- X substrate.   
     
     
       18. A surface acoustic wave filter comprising: 
       
         a LiTaO 
         3  
         substrate;  
       
       
         a plurality of filter sections formed parallel and cascaded to one another on said substrate, each of said filter sections comprising a plurality of interdigital transducers formed on said substrate and reflectors which are formed on said substrate and reflectors which are formed on said substrate and sandwich said interdigital transducers therebetween, said interdigital transducers and said reflectors comprising elongated electrode fingers, thickness h of said fingers being such that  0 . 06 ≦h/λ≦ 0 . 10  where λ is the wavelength of surface acoustic wave adapted to be generated by said filter, the fingers of said interdigital transducers having width M and being arranged at a constant pitch of P, M/P being a constant equal to or greater than about  0 . 6 , the ratio of passband width to center frequency of said filter being greater than about  0 . 03 . 
       
     
     
       19. The surface acoustic wave filter of claim  18 , wherein the fingers of said reflectors are arranged at a constant pitch and have a constant width- to - pitch ratio.   
     
     
       20. The surface acoustic wave filter of claim  19 , wherein the substrate is a  36 ° Y- X substrate.