| 摘要 |
A surface wave filter including at least one pair of transducers with a predetermined spacing (X). The filter comprises 2N+1 pairs of parallel transducers (T11, T21...T1'2N+1' T2'2N+1') where N is an integer other than zero. The transducers have a non-zero short-circuit reflection coefficient in the pass-band of the filter and, for the transducers in row n where n is an integer </= 2N, the distance Ln between transducers has the value: Ln = X + kn lambda + n lambda /2N+1, where lambda is the nominal wavelength of the filter and kn is any integer or zero. The phase coherence of the 2N+1 filter signals is obtained only for multiple paths (2k+1) (2N+1), whereby a foldover-extended pulse response, and therefore a narrower band, are achieved.
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