Acoustic surface wave multiplexing filter

An acoustic surface wave multiplexing filter for receiving an electric signal at one of first and second input ports and for developing a filtered electrical signal at an output port, comprising:

• a substantially rectangular substrate having a plurality of boundaries;
• a first frequency sensitive, electro-acoustic transducer responsive to a signal at the first input port and situated on the substrate so as to launch acoustic surface waves in a direction which is oblique to the substrate boundaries;
• a first multistrip coupler disposed on the substrate adjacent said first transducer, said coupler having a first track, a second track and lines in the first and second tracks which are oblique to the substrate boundaries for receiving, in the first track, acoustic waves launched by said transducer and for shifting the energy associated with its received waves to the second track for launching corresponding acoustic waves;
• a first uniform transducer disposed on the substrate adjacent said coupler, having a bonding pad coupled to the output port, and having fingers which are substantially parallel to the lines in said multistrip coupler for receiving the acoustic waves launched by the second track of the first multistrip coupler and for converting the received waves to an electric output at the bonding pad;
• a second frequency sensitive electro-acoustic transducer responsive to a signal at the second input port and situated on the substrate so as to launch acoustic surface waves in a direction which is oblique to the substrate boundaries;
• a second multistrip coupler disposed on the substrate adjacent said second transducer, said second coupler having a first track, a second track, and lines in the first and second tracks which are oblique to the substrate boundaries for receiving, in its first track, acoustic waves launched by said first transducer and for shifting the energy associated with its received waves to its second track for launching corresponding surface waves;
• a second uniform transducer disposed on the substrate adjacent the second multistrip coupler, having a bonding pad coupled to the output port, and having fingers which are substantially parallel to the lines in the second coupler for receiving acoustic waves launched by the second track of the second multistrip coupler and for converting the received waves to an electrical output at its bonding pad,
• whereby an electrical signal applied to one of the input ports is converted to a filtered signal at the output port, and acoustic waves reflected by the substrate's boundaries are rendered less easily detectable by the transducers.

An acoustic surface wave multiplexing filter for receiving an electrical signal at one of first and second input ports and for developing a filtered electrical signal at an output port, comprising:

• a substantially rectangular, four cornered substrate;
• first and second frequency sensitive electro-acoustic transducers situated on the substrate in diagonally opposite corners, the first transducer being responsive to a signal at the first input port for launching an acoustic surface wave at an angle of about forty-five degrees with respect to the immediately opposite substrate boundary, and said second transducer being responsive to a signal at the second input port for launching an acoustic surface wave in a direction opposite the direction in which the first transducer launches its waves, each of said transducers having buss bars between which a plurality of fingers extend;
• a first multistrip coupler having a first track, a second track and lines in the first and second tracks which run parallel to the fingers in the first electro-acoustic transducer, the lines of the first track being adjacent and co-extensive with the fingers in the first electro-acoustic transducer for receiving waves launched by the first transducer and for shifting the energy associated with the received waves to the second track for launching corresponding acoustic waves;
• a second multistrip coupler having a first track, a second track and lines in the first and second tracks which run parallel to the fingers in the second electro-acoustic transducer, the lines of its first track being adjacent and co-extensive with the fingers in the second electro-acoustic transducer for receiving acoustic waves launched by the second transducer and for shifting the energy associated with the received waves to the second track for launching corresponding acoustic waves;
• first and second uniform transducers situated near the center of the substrate, connected acoustically in parallel with each other by means of connecting lines, and each connected to the output port by means of a bonding pad, the fingers of the first uniform transducer being adjacent, parallel to, and co-extensive with the lines in the second half of the first multistrip coupler for receiving acoustic waves launched therefrom and for converting the latter waves to an electrical signal at the output port, the fingers of the second uniform transducer being adjacent, parallel to, and co-extensive with the lines in the second half of the second multistrip coupler for receiving acoustic waves launched therefrom and for converting the latter waves to an electrical signal at the output port.