| 摘要 |
PURPOSE:To obtain a small-sized filter with high performance by selecting a specific value to an elastic surface wave propagating distance between interdigital electrodes for transmission and reception when an elastic surface wave velocity and a subcarrier frequency on a substrate are given. CONSTITUTION:The interdigital electrode 4 for transmission and the interdigital electrode 5 for reception are provided on the substrate having the piezoelectricity made of a crystal or piezoelectric porcelain or the like with an elastic surface wave propagating distance (d), and input terminals 1a, 1b and output terminals 2a, 2b are connected respectively to the electrodes 4 and 5. A ripple period DELTAf due to a directly propagated wave depends definitely upon the distance (d) between the electrodes 4 and 5. Then, the relation of 0.9X(V/fsc)Xn< d<1.1X(V/fsc)Xn is obtained in order to decrease the differentiating gain and differentiating phase in taking the ripple period DELTAf as one fraction of an integral number of the carrier frequency fsc with the allowance of error of + or -10%, where V is an elastic surface wave velocity and n is a natural number. |
