| 摘要 |
PURPOSE:To prevent the degradation of an out-band attenuation quantity without putting restrictions on the structure of a filter itself, by arranging a reed screen-type electrode for exciting unnecessary waves on a propagation line except a main propagation line of surface waves and connecting this electrode to a reed screen-type electrode for input and output. CONSTITUTION:Two reed screen-type electrodes 34 and 36 for transmission are arranged on both sides of a central reed screen-type electrode 35 for reception formed on a piezoelectric substrate 30. The electrode 35 and a reed screen-type electrode 37 for exciting unnecessary waves are connected in parallel, and they are so arranged that the surface wave propagation path of the electrode 37 exists in a place different from main propagation paths of surfaces waves of electrodes 34, 35, and 36. Electrodes 34 and 36 are connected to a high frequency power source 12 having an internal impedance 11 to constitute one input converter, and the electrode 35 is connected to a load impedance 13 to constitute an output converter, thus constituting the filter. Intervals of electrode fingers of the electrode 37 are made different from those of electrodes 34, 35, and 36. |
