| 摘要 |
PURPOSE:To improve the side lobe characteristic by providing a surface wave element having a grounding electrode and a group type one-way interdigital electrode on a piezoelectric substrate and a 4-terminal coupler made of conductor lines formed on a dielectric substrate, terminating one terminal of the conductor line with a resistor, constituting a 90 deg. phase shifter between other two terminals and connecting the two terminals to the grounding electrode. CONSTITUTION:A surface acoustic filter element 18 provided with input and output transducers 2, 3 is provided on a piezoelectric substrate 1. The transducers have respectively a common electrode 4 and and electrode 5 forming two groups of interdigital electrodes 7, 8. A metallic layer 21 is coated on the entire rear face of the dielectric substrate 20, a 4-terminal coupler made of the conductor line, that is, branch couplers 10, 10' are formed on the surface, the terminal a2 is connected to the metallic layer 21 via a resistor 17, and the 90 deg. phase shifter is constituted between terminals a3 and a4. The terminals a3, a4 of the coupler 10 are connected to the electrodes 5, 6 of the transducer 2 via a thin metallic wire 22 so that the phase of the signal given to the electrode 5 is led by 90 deg. than that of the electrode 6 and they are connected to the transducer 3 so that the phase is lagged by 90 deg..
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